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109-399: There are many industries where moisture control is critical. Moisture sensitive foods and pharmaceuticals are put in packaging with controlled MVTR to achieve the required quality , safety , and shelf life . In clothing , MVTR as a measure of breathability has contributed to greater comfort for wearers of clothing for outdoor activity. The building materials industry also manages

218-466: A futile cycle . Although fat is a common way of storing energy, in vertebrates such as humans the fatty acids in these stores cannot be converted to glucose through gluconeogenesis as these organisms cannot convert acetyl-CoA into pyruvate ; plants do, but animals do not, have the necessary enzymatic machinery. As a result, after long-term starvation, vertebrates need to produce ketone bodies from fatty acids to replace glucose in tissues such as

327-440: A DNA template from its viral RNA genome. RNA in ribozymes such as spliceosomes and ribosomes is similar to enzymes as it can catalyze chemical reactions. Individual nucleosides are made by attaching a nucleobase to a ribose sugar. These bases are heterocyclic rings containing nitrogen, classified as purines or pyrimidines . Nucleotides also act as coenzymes in metabolic-group-transfer reactions. Metabolism involves

436-423: A constant set of conditions within cells, a condition called homeostasis . Metabolic regulation also allows organisms to respond to signals and interact actively with their environments. Two closely linked concepts are important for understanding how metabolic pathways are controlled. Firstly, the regulation of an enzyme in a pathway is how its activity is increased and decreased in response to signals. Secondly,

545-429: A cycle of reactions that add the acyl group, reduce it to an alcohol, dehydrate it to an alkene group and then reduce it again to an alkane group. The enzymes of fatty acid biosynthesis are divided into two groups: in animals and fungi, all these fatty acid synthase reactions are carried out by a single multifunctional type I protein, while in plant plastids and bacteria separate type II enzymes perform each step in

654-743: A diverse range of species from annelids to elephants, chimpanzees and many birds. About 182 fish consume seeds or fruit. Animals (domesticated and wild) use as many types of grasses that have adapted to different locations as their main source of nutrients. Humans eat thousands of plant species; there may be as many as 75,000 edible species of angiosperms , of which perhaps 7,000 are often eaten. Plants can be processed into breads, pasta, cereals, juices and jams or raw ingredients such as sugar, herbs, spices and oils can be extracted. Oilseeds are pressed to produce rich oils – ⁣ sunflower , flaxseed , rapeseed (including canola oil ) and sesame . Many plants and animals have coevolved in such

763-583: A high protein, fibre, vitamin E and B content. Seeds are a good source of food for animals because they are abundant and contain fibre and healthful fats, such as omega-3 fats . Complicated chemical interactions can enhance or depress bioavailability of certain nutrients. Phytates can prevent the release of some sugars and vitamins. Animals that only eat plants are called herbivores , with those that mostly just eat fruits known as frugivores , leaves, while shoot eaters are folivores (pandas) and wood eaters termed xylophages (termites). Frugivores include

872-458: A hydrogen acceptor. Hundreds of separate types of dehydrogenases remove electrons from their substrates and reduce NAD into NADH. This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to transfer hydrogen atoms to their substrates. Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. The NAD /NADH form is more important in catabolic reactions, while NADP /NADPH

981-558: A large group of compounds that contain fatty acids and glycerol ; a glycerol molecule attached to three fatty acids by ester linkages is called a triacylglyceride . Several variations of the basic structure exist, including backbones such as sphingosine in sphingomyelin , and hydrophilic groups such as phosphate in phospholipids . Steroids such as sterol are another major class of lipids. Carbohydrates are aldehydes or ketones , with many hydroxyl groups attached, that can exist as straight chains or rings. Carbohydrates are

1090-404: A larger increase in the entropy of their environments. The metabolism of a cell achieves this by coupling the spontaneous processes of catabolism to the non-spontaneous processes of anabolism. In thermodynamic terms, metabolism maintains order by creating disorder. As the environments of most organisms are constantly changing, the reactions of metabolism must be finely regulated to maintain

1199-472: A membrane. Pumping protons out of the mitochondria creates a proton concentration difference across the membrane and generates an electrochemical gradient . This force drives protons back into the mitochondrion through the base of an enzyme called ATP synthase . The flow of protons makes the stalk subunit rotate, causing the active site of the synthase domain to change shape and phosphorylate adenosine diphosphate —turning it into ATP. Chemolithotrophy

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1308-678: A million. Herbivores generally have more than carnivores as they need to tell which plants may be poisonous. Not all mammals share the same tastes: some rodents can taste starch , cats cannot taste sweetness, and several carnivores (including hyenas , dolphins, and sea lions) have lost the ability to sense up to four of the five taste modalities found in humans. Food is broken into nutrient components through digestive process. Proper digestion consists of mechanical processes ( chewing , peristalsis ) and chemical processes ( digestive enzymes and microorganisms ). The digestive systems of herbivores and carnivores are very different as plant matter

1417-591: A set of xenobiotic-metabolizing enzymes. In humans, these include cytochrome P450 oxidases , UDP-glucuronosyltransferases , and glutathione S -transferases . This system of enzymes acts in three stages to firstly oxidize the xenobiotic (phase I) and then conjugate water-soluble groups onto the molecule (phase II). The modified water-soluble xenobiotic can then be pumped out of cells and in multicellular organisms may be further metabolized before being excreted (phase III). In ecology , these reactions are particularly important in microbial biodegradation of pollutants and

1526-459: A short ancestral pathway, the duplication and then divergence of entire pathways as well as the recruitment of pre-existing enzymes and their assembly into a novel reaction pathway. The relative importance of these mechanisms is unclear, but genomic studies have shown that enzymes in a pathway are likely to have a shared ancestry, suggesting that many pathways have evolved in a step-by-step fashion with novel functions created from pre-existing steps in

1635-530: A source of energy, while switching between carbon fixation and the fermentation of organic compounds. In many organisms, the capture of solar energy is similar in principle to oxidative phosphorylation, as it involves the storage of energy as a proton concentration gradient. This proton motive force then drives ATP synthesis. The electrons needed to drive this electron transport chain come from light-gathering proteins called photosynthetic reaction centres . Reaction centers are classified into two types depending on

1744-546: A source of food for protozoa, who in turn provide a source of food for other organisms such as small invertebrates. Other organisms that feed on bacteria include nematodes, fan worms, shellfish and a species of snail. In the marine environment, plankton (which includes bacteria , archaea , algae , protozoa and microscopic fungi ) provide a crucial source of food to many small and large aquatic organisms. Without bacteria, life would scarcely exist because bacteria convert atmospheric nitrogen into nutritious ammonia . Ammonia

1853-425: A system with nineteen food classifications: cereals, roots, pulses and nuts, milk, eggs, fish and shellfish, meat, insects, vegetables, fruits, fats and oils, sweets and sugars, spices and condiments, beverages, foods for nutritional uses, food additives, composite dishes and savoury snacks. In a given ecosystem, food forms a web of interlocking chains with primary producers at the bottom and apex predators at

1962-413: A vast array of chemical reactions, but most fall under a few basic types of reactions that involve the transfer of functional groups of atoms and their bonds within molecules. This common chemistry allows cells to use a small set of metabolic intermediates to carry chemical groups between different reactions. These group-transfer intermediates are called coenzymes . Each class of group-transfer reactions

2071-456: A way that the fruit is a good source of nutrition to the animal who then excretes the seeds some distance away, allowing greater dispersal. Even seed predation can be mutually beneficial, as some seeds can survive the digestion process. Insects are major eaters of seeds, with ants being the only real seed dispersers. Birds, although being major dispersers, only rarely eat seeds as a source of food and can be identified by their thick beak that

2180-646: A wide range of other social and political issues, including sustainability , biological diversity , economics , population growth , water supply , and food security . Food safety and security are monitored by international agencies like the International Association for Food Protection , the World Resources Institute , the World Food Programme , the Food and Agriculture Organization , and

2289-515: Is ingested by an organism and assimilated by the organism's cells to provide energy, maintain life, or stimulate growth. Different species of animals have different feeding behaviours that satisfy the needs of their metabolisms and have evolved to fill a specific ecological niche within specific geographical contexts. Omnivorous humans are highly adaptable and have adapted to obtain food in many different ecosystems. Humans generally use cooking to prepare food for consumption. The majority of

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2398-419: Is oxidative stress . Here, processes including oxidative phosphorylation and the formation of disulfide bonds during protein folding produce reactive oxygen species such as hydrogen peroxide . These damaging oxidants are removed by antioxidant metabolites such as glutathione and enzymes such as catalases and peroxidases . Living organisms must obey the laws of thermodynamics , which describe

2507-447: Is a fruit if the part eaten is derived from the reproductive tissue , so seeds, nuts and grains are technically fruit. From a culinary perspective, fruits are generally considered the remains of botanically described fruits after grains, nuts, seeds and fruits used as vegetables are removed. Grains can be defined as seeds that humans eat or harvest, with cereal grains (oats, wheat, rice, corn, barley, rye, sorghum and millet) belonging to

2616-696: Is a sensation considered unpleasant characterised by having a sharp, pungent taste. Unsweetened dark chocolate, caffeine , lemon rind, and some types of fruit are known to be bitter. Umami, commonly described as savory, is a marker of proteins and characteristic of broths and cooked meats. Foods that have a strong umami flavor include cheese, meat and mushrooms. While most animals taste buds are located in their mouth, some insects taste receptors are located on their legs and some fish have taste buds along their entire body. Dogs, cats and birds have relatively few taste buds (chickens have about 30), adult humans have between 2000 and 4000, while catfish can have more than

2725-571: Is a type of metabolism found in prokaryotes where energy is obtained from the oxidation of inorganic compounds . These organisms can use hydrogen , reduced sulfur compounds (such as sulfide , hydrogen sulfide and thiosulfate ), ferrous iron (Fe(II)) or ammonia as sources of reducing power and they gain energy from the oxidation of these compounds. These microbial processes are important in global biogeochemical cycles such as acetogenesis , nitrification and denitrification and are critical for soil fertility . The energy in sunlight

2834-401: Is an organic compound needed in small quantities that cannot be made in cells. In human nutrition , most vitamins function as coenzymes after modification; for example, all water-soluble vitamins are phosphorylated or are coupled to nucleotides when they are used in cells. Nicotinamide adenine dinucleotide (NAD ), a derivative of vitamin B 3 ( niacin ), is an important coenzyme that acts as

2943-446: Is called gluconeogenesis . Gluconeogenesis converts pyruvate to glucose-6-phosphate through a series of intermediates, many of which are shared with glycolysis . However, this pathway is not simply glycolysis run in reverse, as several steps are catalyzed by non-glycolytic enzymes. This is important as it allows the formation and breakdown of glucose to be regulated separately, and prevents both pathways from running simultaneously in

3052-409: Is captured by plants , cyanobacteria , purple bacteria , green sulfur bacteria and some protists . This process is often coupled to the conversion of carbon dioxide into organic compounds, as part of photosynthesis, which is discussed below. The energy capture and carbon fixation systems can, however, operate separately in prokaryotes, as purple bacteria and green sulfur bacteria can use sunlight as

3161-405: Is carried out by a particular coenzyme, which is the substrate for a set of enzymes that produce it, and a set of enzymes that consume it. These coenzymes are therefore continuously made, consumed and then recycled. One central coenzyme is adenosine triphosphate (ATP), the energy currency of cells. This nucleotide is used to transfer chemical energy between different chemical reactions. There

3270-638: Is carried out by the enzyme RuBisCO as part of the Calvin–Benson cycle . Three types of photosynthesis occur in plants, C3 carbon fixation , C4 carbon fixation and CAM photosynthesis . These differ by the route that carbon dioxide takes to the Calvin cycle, with C3 plants fixing CO 2 directly, while C4 and CAM photosynthesis incorporate the CO 2 into other compounds first, as adaptations to deal with intense sunlight and dry conditions. In photosynthetic prokaryotes

3379-402: Is caused by acids , such as vinegar in alcoholic beverages. Sour foods include citrus, specifically lemons and limes . Sour is evolutionarily significant as it can signal a food that may have gone rancid due to bacteria. Saltiness is the taste of alkali metal ions such as sodium and potassium. It is found in almost every food in low to moderate proportions to enhance flavor. Bitter taste

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3488-485: Is composed of a phosphate attached to a ribose or deoxyribose sugar group which is attached to a nitrogenous base . Nucleic acids are critical for the storage and use of genetic information, and its interpretation through the processes of transcription and protein biosynthesis . This information is protected by DNA repair mechanisms and propagated through DNA replication . Many viruses have an RNA genome , such as HIV , which uses reverse transcription to create

3597-731: Is drunk or processed into dairy products (cheese, butter, etc.). Eggs laid by birds and other animals are eaten and bees produce honey , a reduced nectar from flowers that is used as a popular sweetener in many cultures. Some cultures consume blood , such as in blood sausage , as a thickener for sauces, or in a cured , salted form for times of food scarcity, and others use blood in stews such as jugged hare . Animals, specifically humans, typically have five different types of tastes: sweet , sour , salty , bitter , and umami . The differing tastes are important for distinguishing between foods that are nutritionally beneficial and those which may contain harmful toxins. As animals have evolved ,

3706-874: Is found in many foods and has been defined as a food by itself. Water and fiber have low energy densities, or calories , while fat is the most energy-dense component. Some inorganic (non-food) elements are also essential for plant and animal functioning. Human food can be classified in various ways, either by related content or by how it is processed. The number and composition of food groups can vary. Most systems include four basic groups that describe their origin and relative nutritional function: Vegetables and Fruit, Cereals and Bread, Dairy, and Meat. Studies that look into diet quality group food into whole grains/cereals, refined grains/cereals, vegetables, fruits, nuts, legumes, eggs, dairy products, fish, red meat, processed meat, and sugar-sweetened beverages. The Food and Agriculture Organization and World Health Organization use

3815-491: Is harder to digest. Carnivores mouths are designed for tearing and biting compared to the grinding action found in herbivores. Herbivores however have comparatively longer digestive tracts and larger stomachs to aid in digesting the cellulose in plants. According to the World Health Organization (WHO), about 600 million people worldwide get sick and 420,000 die each year from eating contaminated food. Diarrhea

3924-477: Is its primary structure . Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a huge variety of proteins. Proteins are made from amino acids that have been activated by attachment to a transfer RNA molecule through an ester bond. This aminoacyl-tRNA precursor is produced in an ATP -dependent reaction carried out by an aminoacyl tRNA synthetase . This aminoacyl-tRNA

4033-635: Is likely due to their efficacy . In various diseases, such as type II diabetes , metabolic syndrome , and cancer , normal metabolism is disrupted. The metabolism of cancer cells is also different from the metabolism of normal cells, and these differences can be used to find targets for therapeutic intervention in cancer. Most of the structures that make up animals, plants and microbes are made from four basic classes of molecules : amino acids , carbohydrates , nucleic acid and lipids (often called fats ). As these molecules are vital for life, metabolic reactions either focus on making these molecules during

4142-559: Is needed, or back to glucose in the Cori cycle . An alternative route for glucose breakdown is the pentose phosphate pathway , which produces less energy but supports anabolism (biomolecule synthesis). This pathway reduces the coenzyme NADP to NADPH and produces pentose compounds such as ribose 5-phosphate for synthesis of many biomolecules such as nucleotides and aromatic amino acids . Fats are catabolized by hydrolysis to free fatty acids and glycerol. The glycerol enters glycolysis and

4251-475: Is only a small amount of ATP in cells, but as it is continuously regenerated, the human body can use about its own weight in ATP per day. ATP acts as a bridge between catabolism and anabolism . Catabolism breaks down molecules, and anabolism puts them together. Catabolic reactions generate ATP, and anabolic reactions consume it. It also serves as a carrier of phosphate groups in phosphorylation reactions. A vitamin

4360-411: Is produced in response to rises in blood glucose levels . Binding of the hormone to insulin receptors on cells then activates a cascade of protein kinases that cause the cells to take up glucose and convert it into storage molecules such as fatty acids and glycogen . The metabolism of glycogen is controlled by activity of phosphorylase , the enzyme that breaks down glycogen, and glycogen synthase ,

4469-546: Is scarce, or when cells undergo metabolic stress. Lipids are the most diverse group of biochemicals. Their main structural uses are as part of internal and external biological membranes , such as the cell membrane . Their chemical energy can also be used. Lipids contain a long, non-polar hydrocarbon chain with a small polar region containing oxygen. Lipids are usually defined as hydrophobic or amphipathic biological molecules but will dissolve in organic solvents such as ethanol , benzene or chloroform . The fats are

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4578-617: Is the measure of the amount of energy consumed by all of these chemical reactions. A striking feature of metabolism is the similarity of the basic metabolic pathways among vastly different species. For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all known organisms, being found in species as diverse as the unicellular bacterium Escherichia coli and huge multicellular organisms like elephants . These similarities in metabolic pathways are likely due to their early appearance in evolutionary history , and their retention

4687-497: Is the most common illness caused by consuming contaminated food, with about 550 million cases and 230,000 deaths from diarrhea each year. Children under five years of age account for 40% of the burden of foodborne illness, with 125,000 deaths each year. A 2003 World Health Organization (WHO) report concluded that about 30% of reported food poisoning outbreaks in the WHO European Region occur in private homes. According to

4796-556: Is the precursor to proteins, nucleic acids, and most vitamins. Since the advent of industrial process for nitrogen fixation, the Haber-Bosch Process , the majority of ammonia in the world is human-made. Plants as a food source are divided into seeds, fruits, vegetables, legumes, grains and nuts. Where plants fall within these categories can vary, with botanically described fruits such as the tomato, squash, pepper and eggplant or seeds like peas commonly considered vegetables. Food

4905-529: Is the set of life -sustaining chemical reactions in organisms . The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the conversion of food to building blocks of proteins , lipids , nucleic acids , and some carbohydrates ; and the elimination of metabolic wastes . These enzyme -catalyzed reactions allow organisms to grow and reproduce, maintain their structures , and respond to their environments. The word metabolism can also refer to

5014-422: Is the synthesis of carbohydrates from sunlight and carbon dioxide (CO 2 ). In plants, cyanobacteria and algae, oxygenic photosynthesis splits water, with oxygen produced as a waste product. This process uses the ATP and NADPH produced by the photosynthetic reaction centres , as described above, to convert CO 2 into glycerate 3-phosphate , which can then be converted into glucose. This carbon-fixation reaction

5123-495: Is then a substrate for the ribosome , which joins the amino acid onto the elongating protein chain, using the sequence information in a messenger RNA . Nucleotides are made from amino acids, carbon dioxide and formic acid in pathways that require large amounts of metabolic energy. Consequently, most organisms have efficient systems to salvage preformed nucleotides. Purines are synthesized as nucleosides (bases attached to ribose ). Both adenine and guanine are made from

5232-402: Is then released, and the glucose stored as an energy reserve. Photosynthetic plants, algae and certain bacteria often represent the lowest point of the food chains, making photosynthesis the primary source of energy and food for nearly all life on earth. Plants also absorb important nutrients and minerals from the air, natural waters, and soil. Carbon, oxygen and hydrogen are absorbed from

5341-423: Is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme . Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts —they allow a reaction to proceed more rapidly—and they also allow

5450-429: Is used in anabolic reactions. Inorganic elements play critical roles in metabolism; some are abundant (e.g. sodium and potassium ) while others function at minute concentrations. About 99% of a human's body weight is made up of the elements carbon , nitrogen , calcium , sodium , chlorine , potassium , hydrogen , phosphorus , oxygen and sulfur . Organic compounds (proteins, lipids and carbohydrates) contain

5559-406: Is used to crack open the seed coat. Mammals eat a more diverse range of seeds, as they are able to crush harder and larger seeds with their teeth. Animals are used as food either directly or indirectly. This includes meat, eggs, shellfish and dairy products like milk and cheese. They are an important source of protein and are considered complete proteins for human consumption as they contain all

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5668-605: The International Food Information Council . Food is any substance consumed to provide nutritional support and energy to an organism . It can be raw, processed, or formulated and is consumed orally by animals for growth, health, or pleasure. Food is mainly composed of water, lipids , proteins , and carbohydrates . Minerals (e.g., salts) and organic substances (e.g., vitamins ) can also be found in food. Plants, algae , and some microorganisms use photosynthesis to make some of their own nutrients. Water

5777-740: The Poaceae (grass) family and pulses coming from the Fabaceae (legume) family. Whole grains are foods that contain all the elements of the original seed (bran, germ, and endosperm ). Nuts are dry fruits, distinguishable by their woody shell. Fleshy fruits (distinguishable from dry fruits like grain, seeds and nuts) can be further classified as stone fruits (cherries and peaches), pome fruits (apples, pears), berries (blackberry, strawberry), citrus (oranges, lemon), melons (watermelon, cantaloupe), Mediterranean fruits (grapes, fig), tropical fruits (banana, pineapple). Vegetables refer to any other part of

5886-426: The bioremediation of contaminated land and oil spills. Many of these microbial reactions are shared with multicellular organisms, but due to the incredible diversity of types of microbes these organisms are able to deal with a far wider range of xenobiotics than multicellular organisms, and can degrade even persistent organic pollutants such as organochloride compounds. A related problem for aerobic organisms

5995-499: The chloroplast . These protons move back through the membrane as they drive the ATP synthase, as before. The electrons then flow through photosystem I and can then be used to reduce the coenzyme NADP . This coenzyme can enter the Calvin cycle or be recycled for further ATP generation. Anabolism is the set of constructive metabolic processes where the energy released by catabolism is used to synthesize complex molecules. In general,

6104-467: The control exerted by this enzyme is the effect that these changes in its activity have on the overall rate of the pathway (the flux through the pathway). For example, an enzyme may show large changes in activity (i.e. it is highly regulated) but if these changes have little effect on the flux of a metabolic pathway, then this enzyme is not involved in the control of the pathway. There are multiple levels of metabolic regulation. In intrinsic regulation,

6213-441: The cytoskeleton , a system of scaffolding that maintains the cell shape. Proteins are also important in cell signaling , immune responses , cell adhesion , active transport across membranes, and the cell cycle . Amino acids also contribute to cellular energy metabolism by providing a carbon source for entry into the citric acid cycle ( tricarboxylic acid cycle ), especially when a primary source of energy, such as glucose ,

6322-504: The food energy required is supplied by the industrial food industry , which produces food through intensive agriculture and distributes it through complex food processing and food distribution systems. This system of conventional agriculture relies heavily on fossil fuels , which means that the food and agricultural systems are one of the major contributors to climate change , accounting for as much as 37% of total greenhouse gas emissions . The food system has significant impacts on

6431-406: The last universal common ancestor . This universal ancestral cell was prokaryotic and probably a methanogen that had extensive amino acid, nucleotide, carbohydrate and lipid metabolism. The retention of these ancient pathways during later evolution may be the result of these reactions having been an optimal solution to their particular metabolic problems, with pathways such as glycolysis and

6540-550: The mevalonate pathway produces these compounds from acetyl-CoA, while in plants and bacteria the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates. One important reaction that uses these activated isoprene donors is sterol biosynthesis . Here, the isoprene units are joined to make squalene and then folded up and formed into a set of rings to make lanosterol . Lanosterol can then be converted into other sterols such as cholesterol and ergosterol . Organisms vary in their ability to synthesize

6649-426: The regulation of the rate of a metabolic reaction, for example in response to changes in the cell's environment or to signals from other cells. The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous . For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The basal metabolic rate of an organism

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6758-407: The stomach and pancreas , and in salivary glands . The amino acids or sugars released by these extracellular enzymes are then pumped into cells by active transport proteins. Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. Carbohydrates are usually taken into cells after they have been digested into monosaccharides such as glucose and fructose . Once inside,

6867-428: The 20 common amino acids. Most bacteria and plants can synthesize all twenty, but mammals can only synthesize eleven nonessential amino acids, so nine essential amino acids must be obtained from food. Some simple parasites , such as the bacteria Mycoplasma pneumoniae , lack all amino acid synthesis and take their amino acids directly from their hosts. All amino acids are synthesized from intermediates in glycolysis,

6976-559: The USA, g/100in/day is also in use, which is 0.064516 (approximately 1/15) of the value of g/m/day units. Typical rates in aluminium foil laminates may be as low as 0.001 g/m/day, whereas the rate in fabrics can measure up to several thousand g/m/day. Often, barrier testing is conducted on a sheet of material. Calculations based on that can be useful when designing completed structures, clothing, and packages. Seams, creases, access points, and heat seals are critical to end-use performance. For example,

7085-551: The WHO and CDC , in the USA alone, annually, there are 76 million cases of foodborne illness leading to 325,000 hospitalizations and 5,000 deaths. From 2011 to 2016, on average, there were 668,673 cases of foodborne illness and 21 deaths each year. In addition, during this period, 1,007 food poisoning outbreaks with 30,395 cases of food poisoning were reported. Metabolism Metabolism ( / m ə ˈ t æ b ə l ɪ z ə m / , from Greek : μεταβολή metabolē , "change")

7194-607: The air or water and are the basic nutrients needed for plant survival. The three main nutrients absorbed from the soil for plant growth are nitrogen, phosphorus and potassium, with other important nutrients including calcium, sulfur, magnesium, iron boron, chlorine, manganese, zinc, copper molybdenum and nickel. Bacteria and other microorganisms also form the lower rungs of the food chain. They obtain their energy from photosynthesis or by breaking down dead organisms, waste or chemical compounds. Some form symbiotic relationships with other organisms to obtain their nutrients. Bacteria provide

7303-440: The apex predators, the animals that have no known predators in its ecosystem. Humans are considered apex predators. Humans are omnivores, finding sustenance in vegetables, fruits, cooked meat, milk, eggs, mushrooms and seaweed. Cereal grain is a staple food that provides more food energy worldwide than any other type of crop. Corn (maize) , wheat, and rice account for 87% of all grain production worldwide. Just over half of

7412-431: The brain that cannot metabolize fatty acids. In other organisms such as plants and bacteria, this metabolic problem is solved using the glyoxylate cycle , which bypasses the decarboxylation step in the citric acid cycle and allows the transformation of acetyl-CoA to oxaloacetate , where it can be used for the production of glucose. Other than fat, glucose is stored in most tissues, as an energy resource available within

7521-439: The cell for energy. M. tuberculosis can also grow on the lipid cholesterol as a sole source of carbon, and genes involved in the cholesterol-use pathway(s) have been validated as important during various stages of the infection lifecycle of M. tuberculosis . Amino acids are either used to synthesize proteins and other biomolecules, or oxidized to urea and carbon dioxide to produce energy. The oxidation pathway starts with

7630-441: The citric acid cycle producing their end products highly efficiently and in a minimal number of steps. The first pathways of enzyme-based metabolism may have been parts of purine nucleotide metabolism, while previous metabolic pathways were a part of the ancient RNA world . Many models have been proposed to describe the mechanisms by which novel metabolic pathways evolve. These include the sequential addition of novel enzymes to

7739-416: The citric acid cycle, or the pentose phosphate pathway. Nitrogen is provided by glutamate and glutamine . Nonessensial amino acid synthesis depends on the formation of the appropriate alpha-keto acid, which is then transaminated to form an amino acid. Amino acids are made into proteins by being joined in a chain of peptide bonds . Each different protein has a unique sequence of amino acid residues: this

7848-637: The coenzyme nicotinamide adenine dinucleotide (NAD ) into NADH. Macromolecules cannot be directly processed by cells. Macromolecules must be broken into smaller units before they can be used in cell metabolism. Different classes of enzymes are used to digest these polymers. These digestive enzymes include proteases that digest proteins into amino acids, as well as glycoside hydrolases that digest polysaccharides into simple sugars known as monosaccharides . Microbes simply secrete digestive enzymes into their surroundings, while animals only secrete these enzymes from specialized cells in their guts , including

7957-534: The complex molecules that make up cellular structures are constructed step-by-step from smaller and simpler precursors. Anabolism involves three basic stages. First, the production of precursors such as amino acids , monosaccharides , isoprenoids and nucleotides , secondly, their activation into reactive forms using energy from ATP, and thirdly, the assembly of these precursors into complex molecules such as proteins , polysaccharides , lipids and nucleic acids . Anabolism in organisms can be different according to

8066-488: The construction of cells and tissues, or on breaking them down and using them to obtain energy, by their digestion. These biochemicals can be joined to make polymers such as DNA and proteins , essential macromolecules of life. Proteins are made of amino acids arranged in a linear chain joined by peptide bonds . Many proteins are enzymes that catalyze the chemical reactions in metabolism. Other proteins have structural or mechanical functions, such as those that form

8175-445: The electrons removed from organic molecules in areas such as the citric acid cycle are transferred to oxygen and the energy released is used to make ATP. This is done in eukaryotes by a series of proteins in the membranes of mitochondria called the electron transport chain . In prokaryotes , these proteins are found in the cell's inner membrane . These proteins use the energy from reduced molecules like NADH to pump protons across

8284-683: The end of the reaction catalyzed. Metal micronutrients are taken up into organisms by specific transporters and bind to storage proteins such as ferritin or metallothionein when not in use. Catabolism is the set of metabolic processes that break down large molecules. These include breaking down and oxidizing food molecules. The purpose of the catabolic reactions is to provide the energy and components needed by anabolic reactions which build molecules. The exact nature of these catabolic reactions differ from organism to organism, and organisms can be classified based on their sources of energy, hydrogen, and carbon (their primary nutritional groups ), as shown in

8393-469: The enzyme that makes it. These enzymes are regulated in a reciprocal fashion, with phosphorylation inhibiting glycogen synthase, but activating phosphorylase. Insulin causes glycogen synthesis by activating protein phosphatases and producing a decrease in the phosphorylation of these enzymes. The central pathways of metabolism described above, such as glycolysis and the citric acid cycle, are present in all three domains of living things and were present in

8502-567: The essential amino acids that the human body needs. One 4-ounce (110 g) steak, chicken breast or pork chop contains about 30 grams of protein. One large egg has 7 grams of protein. A 4-ounce (110 g) serving of cheese has about 15 grams of protein. And 1 cup of milk has about 8 grams of protein. Other nutrients found in animal products include calories, fat, essential vitamins (including B12) and minerals (including zinc, iron, calcium, magnesium). Food products produced by animals include milk produced by mammary glands , which in many cultures

8611-650: The exchange of electrolytes between the extracellular fluid and the cell's fluid, the cytosol . Electrolytes enter and leave cells through proteins in the cell membrane called ion channels . For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules . Transition metals are usually present as trace elements in organisms, with zinc and iron being most abundant of those. Metal cofactors are bound tightly to specific sites in proteins; although enzyme cofactors can be modified during catalysis, they always return to their original state by

8720-480: The exposure to water . For drugs sold in the United States, the U.S. Pharmacopeia (USP) defines standards for moisture transmission of drug packaging. Food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin and contains essential nutrients such as carbohydrates , fats , proteins , vitamins , or minerals . The substance

8829-414: The fatty acids are broken down by beta oxidation to release acetyl-CoA, which then is fed into the citric acid cycle. Fatty acids release more energy upon oxidation than carbohydrates. Steroids are also broken down by some bacteria in a process similar to beta oxidation, and this breakdown process involves the release of significant amounts of acetyl-CoA, propionyl-CoA, and pyruvate, which can all be used by

8938-484: The first stage, large organic molecules, such as proteins , polysaccharides or lipids , are digested into their smaller components outside cells. Next, these smaller molecules are taken up by cells and converted to smaller molecules, usually acetyl coenzyme A (acetyl-CoA), which releases some energy. Finally, the acetyl group on acetyl-CoA is oxidized to water and carbon dioxide in the citric acid cycle and electron transport chain , releasing more energy while reducing

9047-550: The form of starch, fructose, glucose and other sugars. Most vitamins are found from plant sources, with exceptions of vitamin D and vitamin B 12 . Minerals can also be plentiful or not. Fruit can consist of up to 90% water, contain high levels of simple sugars that contribute to their sweet taste, and have a high vitamin C content. Compared to fleshy fruit (excepting Bananas) vegetables are high in starch, potassium , dietary fiber, folate and vitamins and low in fat and calories. Grains are more starch based and nuts have

9156-405: The form of water-soluble messengers such as hormones and growth factors and are detected by specific receptors on the cell surface. These signals are then transmitted inside the cell by second messenger systems that often involved the phosphorylation of proteins. A very well understood example of extrinsic control is the regulation of glucose metabolism by the hormone insulin . Insulin

9265-593: The gain or loss of moisture by mass, to highly sophisticated instrumental techniques that in some designs can measure extremely low transmission rates. Special care has to be taken in measuring porous substances such as fabrics, as some techniques are not appropriate. For very low levels, many techniques do not have adequate resolution. Numerous standard methods are described in ISO , ASTM , BS , DIN etc.—these are quite often industry-specific. Instrument manufacturers are often able to provide test methods developed to fully exploit

9374-411: The glass of a bottle may have an effective total barrier, but the screw cap closure and the closure liner might not. Performance verification and validation of complete containers, structures, or irregular objects is often recommended. For the special case of OLEDs , where the levels of allowed permeation are in the 10 g/m/day level , the methods preferred exploit an oxidation of a metal upon

9483-529: The major route of breakdown is glycolysis , in which glucose is converted into pyruvate . This process generates the energy-conveying molecule NADH from NAD , and generates ATP from ADP for use in powering many processes within the cell. Pyruvate is an intermediate in several metabolic pathways, but the majority is converted to acetyl-CoA and fed into the citric acid cycle , which enables more ATP production by means of oxidative phosphorylation . This oxidation consumes molecular oxygen and releases water and

9592-506: The majority of the carbon and nitrogen; most of the oxygen and hydrogen is present as water. The abundant inorganic elements act as electrolytes . The most important ions are sodium , potassium , calcium , magnesium , chloride , phosphate and the organic ion bicarbonate . The maintenance of precise ion gradients across cell membranes maintains osmotic pressure and pH . Ions are also critical for nerve and muscle function, as action potentials in these tissues are produced by

9701-680: The mechanisms of carbon fixation are more diverse. Here, carbon dioxide can be fixed by the Calvin–Benson cycle, a reversed citric acid cycle, or the carboxylation of acetyl-CoA. Prokaryotic chemoautotrophs also fix CO 2 through the Calvin–Benson cycle, but use energy from inorganic compounds to drive the reaction. In carbohydrate anabolism, simple organic acids can be converted into monosaccharides such as glucose and then used to assemble polysaccharides such as starch . The generation of glucose from compounds like pyruvate , lactate , glycerol , glycerate 3-phosphate and amino acids

9810-482: The metabolic pathway self-regulates to respond to changes in the levels of substrates or products; for example, a decrease in the amount of product can increase the flux through the pathway to compensate. This type of regulation often involves allosteric regulation of the activities of multiple enzymes in the pathway. Extrinsic control involves a cell in a multicellular organism changing its metabolism in response to signals from other cells. These signals are usually in

9919-541: The moisture barrier properties in architectural components to ensure the correct moisture levels in the internal spaces of buildings. Optoelectronic devices based on organic material, generally named OLEDs , need an encapsulation with low values of WVTR to guarantee the same performances over the lifetime of the device. MVTR generally decreases with increasing thickness of the film/barrier, and increases with increasing temperature. There are various techniques to measure MVTR, ranging from gravimetric techniques that measure

10028-512: The most abundant biological molecules, and fill numerous roles, such as the storage and transport of energy ( starch , glycogen ) and structural components ( cellulose in plants, chitin in animals). The basic carbohydrate units are called monosaccharides and include galactose , fructose , and most importantly glucose . Monosaccharides can be linked together to form polysaccharides in almost limitless ways. The two nucleic acids, DNA and RNA , are polymers of nucleotides . Each nucleotide

10137-420: The nature of photosynthetic pigment present, with most photosynthetic bacteria only having one type, while plants and cyanobacteria have two. In plants, algae, and cyanobacteria, photosystem II uses light energy to remove electrons from water, releasing oxygen as a waste product. The electrons then flow to the cytochrome b6f complex , which uses their energy to pump protons across the thylakoid membrane in

10246-412: The pathway. Terpenes and isoprenoids are a large class of lipids that include the carotenoids and form the largest class of plant natural products . These compounds are made by the assembly and modification of isoprene units donated from the reactive precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate . These precursors can be made in different ways. In animals and archaea,

10355-413: The plant that can be eaten, including roots, stems, leaves, flowers, bark or the entire plant itself. These include root vegetables (potatoes and carrots), bulbs (onion family), flowers (cauliflower and broccoli), leaf vegetables ( spinach and lettuce) and stem vegetables (celery and asparagus ). The carbohydrate, protein and lipid content of plants is highly variable. Carbohydrates are mainly in

10464-674: The precursor nucleoside inosine monophosphate, which is synthesized using atoms from the amino acids glycine , glutamine , and aspartic acid , as well as formate transferred from the coenzyme tetrahydrofolate . Pyrimidines , on the other hand, are synthesized from the base orotate , which is formed from glutamine and aspartate. All organisms are constantly exposed to compounds that they cannot use as foods and that would be harmful if they accumulated in cells, as they have no metabolic function. These potentially damaging compounds are called xenobiotics . Xenobiotics such as synthetic drugs , natural poisons and antibiotics are detoxified by

10573-430: The removal of the amino group by a transaminase . The amino group is fed into the urea cycle , leaving a deaminated carbon skeleton in the form of a keto acid . Several of these keto acids are intermediates in the citric acid cycle, for example α- ketoglutarate formed by deamination of glutamate . The glucogenic amino acids can also be converted into glucose, through gluconeogenesis . In oxidative phosphorylation,

10682-450: The same. An MVTR result without specifying these conditions is almost meaningless. Certainly no two results should be compared unless the conditions are known. For example, the effect of temperature on the permeability can be as high as 10% per °C, making it possible that MVTR results achieved at 23°C and 37°C can differ by a factor 4. The most common international unit for the MVTR is g/m/day. In

10791-627: The source of constructed molecules in their cells. Autotrophs such as plants can construct the complex organic molecules in their cells such as polysaccharides and proteins from simple molecules like carbon dioxide and water. Heterotrophs , on the other hand, require a source of more complex substances, such as monosaccharides and amino acids, to produce these complex molecules. Organisms can be further classified by ultimate source of their energy: photoautotrophs and photoheterotrophs obtain energy from light, whereas chemoautotrophs and chemoheterotrophs obtain energy from oxidation reactions. Photosynthesis

10900-415: The specific design which they are selling. The search for the most appropriate instrument is a zealous task which is in itself part of the measurement. The conditions under which the measurement is made has a considerable influence on the result. Both the temperature and humidity gradients across the sample need to be measured, controlled and recorded with the result, and the thickness of the sample should be

11009-425: The substrate can be acceptors, the polysaccharides produced can have straight or branched structures. The polysaccharides produced can have structural or metabolic functions themselves, or be transferred to lipids and proteins by the enzymes oligosaccharyltransferases . Fatty acids are made by fatty acid synthases that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by

11118-729: The sum of all chemical reactions that occur in living organisms, including digestion and the transportation of substances into and between different cells, in which case the above described set of reactions within the cells is called intermediary (or intermediate) metabolism. Metabolic reactions may be categorized as catabolic —the breaking down of compounds (for example, of glucose to pyruvate by cellular respiration ); or anabolic —the building up ( synthesis ) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy, and anabolism consumes energy. The chemical reactions of metabolism are organized into metabolic pathways , in which one chemical

11227-826: The table below. Organic molecules are used as a source of hydrogen atoms or electrons by organotrophs , while lithotrophs use inorganic substrates. Whereas phototrophs convert sunlight to chemical energy , chemotrophs depend on redox reactions that involve the transfer of electrons from reduced donor molecules such as organic molecules , hydrogen , hydrogen sulfide or ferrous ions to oxygen , nitrate or sulfate . In animals, these reactions involve complex organic molecules that are broken down to simpler molecules, such as carbon dioxide and water. Photosynthetic organisms, such as plants and cyanobacteria , use similar electron-transfer reactions to store energy absorbed from sunlight. The most common set of catabolic reactions in animals can be separated into three main stages. In

11336-448: The tastes that provide the most energy are the most pleasant to eat while others are not enjoyable, although humans in particular can acquire a preference for some substances which are initially unenjoyable. Water, while important for survival, has no taste. Sweetness is almost always caused by a type of simple sugar such as glucose or fructose , or disaccharides such as sucrose , a molecule combining glucose and fructose. Sourness

11445-407: The tissue through glycogenesis which was usually being used to maintained glucose level in blood. Polysaccharides and glycans are made by the sequential addition of monosaccharides by glycosyltransferase from a reactive sugar-phosphate donor such as uridine diphosphate glucose (UDP-Glc) to an acceptor hydroxyl group on the growing polysaccharide. As any of the hydroxyl groups on the ring of

11554-523: The top. Other aspects of the web include detrovores (that eat detritis ) and decomposers (that break down dead organisms). Primary producers include algae, plants, bacteria and protists that acquire their energy from sunlight. Primary consumers are the herbivores that consume the plants, and secondary consumers are the carnivores that consume those herbivores. Some organisms, including most mammals and birds, diet consists of both animals and plants, and they are considered omnivores. The chain ends with

11663-480: The transfer of heat and work . The second law of thermodynamics states that in any isolated system , the amount of entropy (disorder) cannot decrease. Although living organisms' amazing complexity appears to contradict this law, life is possible as all organisms are open systems that exchange matter and energy with their surroundings. Living systems are not in equilibrium , but instead are dissipative systems that maintain their state of high complexity by causing

11772-465: The waste product carbon dioxide. When oxygen is lacking, or when pyruvate is temporarily produced faster than it can be consumed by the citric acid cycle (as in intense muscular exertion), pyruvate is converted to lactate by the enzyme lactate dehydrogenase , a process that also oxidizes NADH back to NAD for re-use in further glycolysis, allowing energy production to continue. The lactate is later converted back to pyruvate for ATP production where energy

11881-403: The world's crops are used to feed humans (55 percent), with 36 percent grown as animal feed and 9 percent for biofuels . Fungi and bacteria are also used in the preparation of fermented foods like bread , wine , cheese and yogurt . During photosynthesis , energy from the sun is absorbed and used to transform water and carbon dioxide in the air or soil into oxygen and glucose. The oxygen

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