Chemistry: CUET Mock Test - 6 - CUET MCQ

Drugs that either prevent the enzyme from holding the substrate or prevent it from providing functional groups that attack the substrate, are called enzyme inhibitors. These inhibit the catalytic activity of enzymes.

When a drug binds to an enzyme from a site other than the active site, it is called an allosteric site. Binding to this site causes the change in shape of active site such that the substrate cannot recognise it.

Receptors are proteins that are embedded in the cell membrane with the binding site protruding outwards. They change the shape of the binding site to accommodate the incoming messenger and facilitate communication.

Agonists are drugs that replicate the behaviour and properties of the chemical messenger and activate the receptor. These are used when the actual messenger is not present in the body.

There are lots of different types of receptors in the body at different locations. They interact with different kinds of chemical messengers. Their selectivity for one messenger over the other is because of the difference in their binding sites, structure and composition of amino acids.

When there is a strong covalent bond between the enzyme and the drug, the enzyme is blocked permanently. This results in the degradation of the entire drug-enzyme complex and the synthesis of a new enzyme.

Non-competitive inhibitors are drugs that affect the catalytic activity of enzymes by changing the shape of the active site by binding to the enzyme at some other site. This prevents the substrate from binding to the enzyme.

The shape of the active site resembles a triangle, which means that the substrate should also have a similar shape. The drug that will inhibit the activity of this enzyme should closely resemble the substrate and block the active site. These are called competitive inhibitors.

Insulin consists of a chain of 51 amino acids and hence is a polypeptide. Estrogen and androgen are steroids, whereas epinephrine is an amine.

Amine hormones are water-soluble compounds which have amino groups and are structurally derived from amino acids. Oxytocin is a peptide hormone.

Epinephrine and norepinephrine are amine hormones that mediate response to external stimuli. Adrenaline plays an important role in fight or flight situations by increasing blood flow to muscles, blood sugar level and pulse rate.

Thyroxine is an iodinated derivative of tyrosine. Abnormally low levels of thyroxine leads to hypothyroidism, which causes enlargement of thyroid gland (goitre). Increases level of thyroxine causes hyperthyroidism.

Steroid hormones are produced by adrenal cortex and gonads. Hormones released by the adrenal cortex play a very important role in the functions of the bod.

If adrenal cortex does not function properly then one of the results may be Addison’s disease characterized by hypoglycaemia, weakness and increased susceptibility to stress. This may be fatal unless treated by glucocorticoids and mineralocorticoids.

Hormones are chemical substances produced by the endocrine glands in the human body. They are carried to different parts of the body through the blood stream. Because of the action of hormones as intercellular communicators, they are called chemical messengers.

Insulin is released in response to the rapid rise in blood glucose level. On the other hand, the hormone glucagon tends to increase the glucose level in blood. These two hormones together regulate the blood glucose level.

Oxytocin controls the contraction of the uterus during child birth and helps in the release of milk from mammary glands. Progesterone is responsible for the preparation of uterus for implantation of fertilised egg.

Low levels of iodine in the diet may lead to hypothyroidism and enlargement of the thyroid gland. This can be controlled by adding sodium iodide to table salt to form iodised salt.

Mineralocorticoids are steroid hormones which control the level of excretion of water and salt by the kidney, thus balancing the water and mineral levels as required.

Enzymes are biological catalysts produced by living cells. They differ from other catalysts in being highly selective and specific. Almost all enzymes are globular proteins. They are very specific for a particular reaction and a particular substrate.

Proteases are enzymes that helps in protein catabolism by hydrolysis of peptide bonds. Pepsin and trypsin are the most common proteases, found in the human stomach and pancreas respectively. Both of them are major digestive enzymes.

Enzymes are biological catalysts produced by living cells which catalyse the biochemical reactions in living organisms. Chemically, enzymes are naturally occurring simple or conjugate proteins.

The enzyme cellulase hydrolyses cellulose into glucose and thereby digests it. However, the human stomach does not produce any enzyme capable of digesting cellulose, and hence it cannot be digested.

Deficiency of tyrosinase results in insufficient production of melanin. This causes a condition of white skin and hair called albinism. It can be prevented by including the required supply of enzyme through diet.

Enzymes decrease the activation energy of a reaction. Extremely small quantities of enzymes can increase the rate of reaction by thousands. Enzyme action can be inhibited by compounds known as enzyme inhibitors.

Most active enzymes are associated with some non-protein components required for their activity. These are called prosthetic groups and they may be cofactors or coenzymes.

Almost all enzymes are globular proteins, which are nothing but very long chains of amino acids residues (>100) and higher molecular mass, or polypeptides.

Substrate specific enzymes are those which can act only on one particular compound to give a product(s). For example, maltase acts only on maltose to break the glycosidic linkage between the two glucose units.

Enzymes are generally name after the compound or class of compounds on which they work. For example, the catalyst that hydrolyses the reaction of starch (amylum) to glucose is called as amylase.

Secondary amines react slowly with nitrous acid at low temperatures to give yellow oily nitrosoamines. Diethylamine specifically produces N,N-diethylnitrosoamine.