Test: Enzymes (May 28) - NEET MCQ

NAD is known as nicotinamide adenine dinucleotide. It is a dinucleotide which has two dinucleotides joined by the phosphodiester bond. It is a coenzyme found in all living cell. NAD+ acts an electron acceptor in metabolic reaction. During glycolysis, it accepts the electron and changes to NADH which is further changed to ATP. One NADH produces three ATP. 
Nicotinamide adenine dinucleotide phosphate is known as NADP. It acts as an electron acceptor. The reduced form of the NADP is known as NADPH.
Purines are double ring while pyrimidines are single ring structure. Adenine and guanine are purines while thymine and cytosine are pyrimidines. A purine is attached to pyrimidine by hydrogen bond. Adenine is attached to thymine by two hydrogen bonds while three hydrogen bond is present between guanine and cytosine.
So, the correct answer is option A.

A lysosome is a membrane-bound organelle found in nearly all animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules.

Desmolase catalyzes the formation or destruction of carbon-carbon bonds within a molecule. It is involved in the transfer of electrons.

Hydrolase is the enzyme which catalyzes the splitting of compounds by addition of water.

Dehydrogenase is an enzyme which participates in the oxidoreductase reaction by using an electron acceptor.

Transaminase catalyzes aminotransferase reaction between an amino acid and a α-keto acid.

Feedback inhibition is the process by where the end product terminates the reaction. The accumulation of the end product interferes with the enzymatic activity by changing the shape of its active site. On changing the shape of the active site, the substrate does not attach to the active site and thus the reaction terminates. During glycolysis, the glucose changes to glucose 6 phosphates in presence of hexokinase. When the amount of glucose 6 phosphate exceeds it deactivate hexokinase.

So, the correct answer is option B.

Every enzyme posses an optimum pH value where it is most effective. Most enzymes show maximum activity in a pH rang of about 6.0 to 7.5 i.e, near neutra pH. Some digestive enzymes have their optimum pH in the acidic or alkaline range. E.g., pepsin of gastic juice has its optimum at pH 2 (acidic) whereas typsin of pancreatic juice shows maximum activity at pH 8.8 (alkaline). A rise and fall in pH reduces enzyme activity by changing the degree of ionisation of its side chain.

Low temperature preserves the enzymes in their inactive state. Therefore it is used in preservation of foods inside cold storage. Low temperature present inside cold storage prevents spoilage of food.

High temperature destroys enzymes by causing their denaturation, This occurs at 50^oC or so. In between the minimum and maximum temperature the reaction velocity doubles for every 10^oC in temperature (general rule of thumb).

In non-competitve inhibition, the inhibitor binds at a site other than the active site ob the enzyme surface. This binding impairs the enzyme function. The inhibitor has no structural resemblance with the sunstrate. It does not interfere with the enzyme-substrate binding but the catalysis is prevented, possibly due to a distortion in the enzyme conformation. Non-competitive inhibition is usually irreversible because it cannot be overcome by increasing the substrate concentration. The inhibitor (l) generally binds with the enzyme as well as the ES complex. The overall relation in non.competitve inhibition is represented as :

Isomerases catalyse the change of a substrate into a related isomeric form by rearrangement of molecules.

Enzymes work precisely at certain narrowly optimum conditions, such as appropriate temperature, pH, and ion concentration. Deviation from the optimal conditions adversely affects enzyme activity. Most enzymes have an optimal temperature, at which the rate of reaction is fastest. For human enzymes, the temperature optima are near the human body temperature (35-40°C). Enzymatic reactions occur slowly or not at all at low temperatures. As the temperature increases, molecular motion increases, resulting in more molecular collisions. The rates of most enzyme-controlled reactions, therefore, increase as the temperature increases, within limits. High temperatures rapidly denature most enzymes. The molecular conformation (3-D shape) of the protein becomes altered as the hydrogen bonds responsible for its secondary, tertiary, and quaternary structures are broken. Because this inactivation is usually not reversible, activity is not regained when the enzyme is cooled.