Enzymes breaking

The left end of each sequence is the 5 end and the right end is 3. Only one strand is shown for convenience, although the enzymes break duplex DNA. The arrow shows the position of the bonds broken. 

Pectin is a long chain of pectic acid and pectinic acid molecules. Because these acids are sugars, pectin is categorized as a polysaccharide. It is prepared from citrus peels and the remains of apples after they are squeezed for juice. In the plant, pectin is the material that joins the plant cells together. When fungus enzymes break down the pectin in fruit, the fruit gets soft and mushy. 

In the ground-breaking scientific paper that presented their work, Menten and Michaelis also derived an important mathematical formula. This formula describes the rate at which enzymes break down their substrates. It correlates the speed of the enzyme reaction with the concentrations of the enzyme and the substrate. Called the Michaelis-Menten equation, it remains fundamental to our understanding of how enzymes catalyze reactions. 

Wilson, E. (1998) Spinach enzymes break down explosives. Chem. Eng. News, 76, 40. 

Photorespiration results from the oxygenation reaction catalyzed by ribulose bisphosphate carboxylase/ oxygenase. 2-Phosphoglycolate generated by the reaction moves from the chloroplast to the cytosol, where other enzymes break it down to C02, H20, and Pj. The oxygenation reaction, like carboxylation, does not require light directly. It occurs mainly during illumination, however, because the formation of the substrate, ribulose-1,5-bisphosphate, requires ATP and NADPH (see fig. 15.25). 

Brevibacterium albidum cuts the sequence TGGCCA (Figure 7.4). There are over 400 different restriction enzymes purified from about 250 different microorganisms. The restriction enzymes break the double-stranded DNA molecules in two different ways as shown in Figure 7.4 ... 

Deoxyribonucleic acid (DNA) belongs to a group of chemicals called the nucleic acids (Figure 15.26) They are also biopolymers. DNA controls the prote synthesis within your cells. When you eat a food containing proteins, such as meat or cheese, your digestive enzymes break down the proteins present into individual amino acids. The DNA in your cells controls the order in which the amino acids are repolymerised to make the proteins you need ... 

Cellulase enzymes break down the surface of the denim, thus releasing the indigo dye. The desired abrasion effect can be obtained totally without the use of purnice stones. 

Papayas contain papain, an enzyme that is similar to the digestive juice pepsin. Because this enzyme breaks down protein, papain extract from papayas is marketed as a meat... 

G. Metabolic Difference. Micro-organisms attack wood by secreting enzymes into the immediate structure which in turn break down the wood components into small, soluble units that become nutrients for the organism. The main destructive enzyme system the wood-rotters contain is a class of proteins known as cellulases. These enzymes break down he polymeric cellulose, the strong backbone of wood, into digestible units. Humans do not possess this enzyme system consequently, we cannot degrade cellulose-containing materials. 

Question Some biochemicals are stable when in pure form on a shelf and yet in the presence of an enzyme break down rapidly. Why ... 

The principal locations for digestion of starch in humans are the mouth, the lumen of the small intestine, and the brush border of the epithelial cells of the intestinal mucosa. Food is masticated in the mouth, forming a bolus ready for swallowing, while the salivary a-amylase attacks the hydrated starch. The enzyme breaks the starch at random intervals, hydrolyzing internal a-1,4 bonds (and not the a-1,6 bonds constituting the branching points). The a-amylase will not break the bonds nearest the nonreducing... 

Hydrolysis is the reverse process of condensation as a water molecule and specific enzymes break all the glycosidic linkages in disaccharides and polysaccharides into their constituting monosaccharides. 

Many low molecular weight amines have very foul odors. Trimethylamine [(CH3)3N], formed when enzymes break down certain fish proteins, has the characteristic odor of rotting fish. Putrescine (NH2CH2CH2CH2CH2NH2) and cadaverine (NH2CH2CH2CH2CH2CH2NH2) are both poisonous diamines with putrid odors. They, too, are present in rotting fish, and are partly responsible for the odors of semen, urine, and bad breath. 

The monoamine oxidase enzyme breaks down presynaptic amines. 

The production of ethanol by fermentation of grains and sugars is one of the oldest known organic reactions, going back at least 2500 years. Fermentation is carried out by adding yeast to an aqueous sugar solution, where enzymes break down carbohydrates into ethanol and CO2 ... 

As noted in Chapter 3, stimulant drugs such as cocaine and the amphetamines are thought to affect the brain primarily through complex actions on monoamine neurotransmitters dopamine, norepinephrine, and serotonin. For example, both cocaine and the amphetamines block rcuptake of norepinephrine, serotonin, and particularly dopamine (Meyer 8c Quenzer, 2005). In addition, the amphetamines and methylphenidatc also increase the release of dopamine (Sulzer, Sonders, Poulsen, 8c Galli, 2005). Thus, the initial effect of stimulants is to produce a storm of activity in neural pathways that are sensitive to the monoamine transmitters. Because of this increased activity, however, and particularly because reuptake is blocked so that enzymes break down the neurotransmitters, the long-term effects of stimulant use involve depletion of monoamines. If you remember that low levels of monoamines are linked to clinical depression (see Chapter 3), tlien you have the basis for one theory of why the aftereffects of heavy cocaine use involve depression (Dackis 8c Gold, 1985). To explain this hypothesis, we must turn briefly to data from the animal laboratory. 

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