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Methods in Plant Biochemistry Volume 1 - 1st Edition
You could not be signed in. Most rare elements on Earth are not needed by life exceptions being selenium and iodine , while a few common ones aluminum and titanium are not used. Most organisms share element needs, but there are a few differences between plants and animals. For example, ocean algae use bromine , but land plants and animals seem to need none. All animals require sodium , but some plants do not.
Methods in Plant Biochemistry Volume 1
Plants need boron and silicon , but animals may not or may need ultra-small amounts. In addition to the six major elements that compose most of the human body, humans require smaller amounts of possibly 18 more. The four main classes of molecules in biochemistry often called biomolecules are carbohydrates , lipids , proteins , and nucleic acids.
When monomers are linked together to synthesize a biological polymer , they undergo a process called dehydration synthesis. Different macromolecules can assemble in larger complexes, often needed for biological activity.
Two of the main functions of carbohydrates are energy storage and providing structure. Sugars are carbohydrates, but not all carbohydrates are sugars. There are more carbohydrates on Earth than any other known type of biomolecule; they are used to store energy and genetic information , as well as play important roles in cell to cell interactions and communications. The simplest type of carbohydrate is a monosaccharide , which among other properties contains carbon, hydrogen, and oxygen, mostly in a ratio of generalized formula C n H 2 n O n , where n is at least 3.
Glucose C 6 H 12 O 6 is one of the most important carbohydrates; others include fructose C 6 H 12 O 6 , the sugar commonly associated with the sweet taste of fruits ,  [a] and deoxyribose C 5 H 10 O 4 , a component of DNA. A monosaccharide can switch between acyclic open-chain form and a cyclic form. The open-chain form can be turned into a ring of carbon atoms bridged by an oxygen atom created from the carbonyl group of one end and the hydroxyl group of another.
The cyclic molecule has a hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose. In these cyclic forms, the ring usually has 5 or 6 atoms. These forms are called furanoses and pyranoses , respectively—by analogy with furan and pyran , the simplest compounds with the same carbon-oxygen ring although they lack the carbon-carbon double bonds of these two molecules.
For example, the aldohexose glucose may form a hemiacetal linkage between the hydroxyl on carbon 1 and the oxygen on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose.
The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called glucopyranose. Cyclic forms with a 7-atom ring called heptoses are rare. Two monosaccharides can be joined together by a glycosidic or ether bond into a disaccharide through a dehydration reaction during which a molecule of water is released.
The reverse reaction in which the glycosidic bond of a disaccharide is broken into two monosaccharides is termed hydrolysis. The best-known disaccharide is sucrose or ordinary sugar , which consists of a glucose molecule and a fructose molecule joined together. Another important disaccharide is lactose found in milk, consisting of a glucose molecule and a galactose molecule.
Lactose may be hydrolysed by lactase , and deficiency in this enzyme results in lactose intolerance. When a few around three to six monosaccharides are joined, it is called an oligosaccharide oligo- meaning "few". These molecules tend to be used as markers and signals , as well as having some other uses. They can be joined together in one long linear chain, or they may be branched. Two of the most common polysaccharides are cellulose and glycogen , both consisting of repeating glucose monomers. Cellulose is an important structural component of plant's cell walls and glycogen is used as a form of energy storage in animals.
Sugar can be characterized by having reducing or non-reducing ends. A reducing end of a carbohydrate is a carbon atom that can be in equilibrium with the open-chain aldehyde aldose or keto form ketose. If the joining of monomers takes place at such a carbon atom, the free hydroxy group of the pyranose or furanose form is exchanged with an OH-side-chain of another sugar, yielding a full acetal. This prevents opening of the chain to the aldehyde or keto form and renders the modified residue non-reducing.
Lactose contains a reducing end at its glucose moiety, whereas the galactose moiety forms a full acetal with the C4-OH group of glucose. Saccharose does not have a reducing end because of full acetal formation between the aldehyde carbon of glucose C1 and the keto carbon of fructose C2. Lipids comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including waxes , fatty acids , fatty-acid derived phospholipids , sphingolipids , glycolipids , and terpenoids e.
Some lipids are linear, open chain aliphatic molecules, while others have ring structures. Some are aromatic with a cyclic [ring] and planar [flat] structure while others are not. Some are flexible, while others are rigid. Lipids are usually made from one molecule of glycerol combined with other molecules.
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In triglycerides , the main group of bulk lipids, there is one molecule of glycerol and three fatty acids. Fatty acids are considered the monomer in that case, and may be saturated no double bonds in the carbon chain or unsaturated one or more double bonds in the carbon chain. Most lipids have some polar character in addition to being largely nonpolar. In general, the bulk of their structure is nonpolar or hydrophobic "water-fearing" , meaning that it does not interact well with polar solvents like water. Another part of their structure is polar or hydrophilic "water-loving" and will tend to associate with polar solvents like water.
This makes them amphiphilic molecules having both hydrophobic and hydrophilic portions. In the case of cholesterol , the polar group is a mere —OH hydroxyl or alcohol. In the case of phospholipids, the polar groups are considerably larger and more polar, as described below. Lipids are an integral part of our daily diet. Most oils and milk products that we use for cooking and eating like butter , cheese , ghee etc. Vegetable oils are rich in various polyunsaturated fatty acids PUFA. Lipid-containing foods undergo digestion within the body and are broken into fatty acids and glycerol, which are the final degradation products of fats and lipids.
Lipids, especially phospholipids , are also used in various pharmaceutical products , either as co-solubilisers e. Proteins are very large molecules—macro-biopolymers—made from monomers called amino acids. The side chain "R" is different for each amino acid of which there are 20 standard ones. It is this "R" group that made each amino acid different, and the properties of the side-chains greatly influence the overall three-dimensional conformation of a protein.
Some amino acids have functions by themselves or in a modified form; for instance, glutamate functions as an important neurotransmitter. Amino acids can be joined via a peptide bond. In this dehydration synthesis, a water molecule is removed and the peptide bond connects the nitrogen of one amino acid's amino group to the carbon of the other's carboxylic acid group.
The resulting molecule is called a dipeptide , and short stretches of amino acids usually, fewer than thirty are called peptides or polypeptides. Longer stretches merit the title proteins. As an example, the important blood serum protein albumin contains amino acid residues. For instance, movements of the proteins actin and myosin ultimately are responsible for the contraction of skeletal muscle.
One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be extremely selective in what they bind. Antibodies are an example of proteins that attach to one specific type of molecule.
Antibodies are composed of heavy and light chains. Two heavy chains would be linked to two light chains through disulfide linkages between their amino acids. Antibodies are specific through variation based on differences in the N-terminal domain. In fact, the enzyme-linked immunosorbent assay ELISA , which uses antibodies, is one of the most sensitive tests modern medicine uses to detect various biomolecules. Probably the most important proteins, however, are the enzymes.
Virtually every reaction in a living cell requires an enzyme to lower the activation energy of the reaction. These molecules recognize specific reactant molecules called substrates ; they then catalyze the reaction between them. By lowering the activation energy , the enzyme speeds up that reaction by a rate of 10 11 or more; a reaction that would normally take over 3, years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates.
Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole. The structure of proteins is traditionally described in a hierarchy of four levels. The primary structure of a protein consists of its linear sequence of amino acids; for instance, "alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-lysine-…".
Secondary structure is concerned with local morphology morphology being the study of structure. Tertiary structure is the entire three-dimensional shape of the protein. This shape is determined by the sequence of amino acids. In fact, a single change can change the entire structure. The alpha chain of hemoglobin contains amino acid residues; substitution of the glutamate residue at position 6 with a valine residue changes the behavior of hemoglobin so much that it results in sickle-cell disease.
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Finally, quaternary structure is concerned with the structure of a protein with multiple peptide subunits, like hemoglobin with its four subunits. Not all proteins have more than one subunit.
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Ingested proteins are usually broken up into single amino acids or dipeptides in the small intestine , and then absorbed.
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