Tag: metabolism

Questions Related to metabolism

All of the following  statement about feedback inhibition of enzyme is true, with an exception of

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. It is exerted through allosteric effects.

  2. It is directed at the enzyme that catalyzes the first committed step in a branch of a pathway.

  3. It affects the rate of reaction, not the concentration of enzyme.

  4. It acts very slowly.

Show answer
Correct Option: D
Explanation:

Feedback inhibition is the inhibition mechanism in metabolic pathways where the end product of one reaction are the substrates for next reaction. Such feedback inhibition is usually directed at the first or first few reactions in the pathway to help conserve precious cellular resources, thus in case the end product is not required the metabolic pathway is blocked at the initial stages itself. The feed back regulation is mostly brought about by the allosteric modulators. Usually the first steps in metabolic pathways are catalysed by allosteric enzymes whose catalysis rate can be increased with the help of positive modulators and decreased with the help of negative modulators.

Which of the following is true?
Non-competitive inhibitor differs from a competitive inhibitor in that it

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. Reduces the affinity of substrate for enzymes

  2. Does not alter K$ _m$

  3. May attach it self to the enzyme at a site other than the active site

  4. Both B and C

Show answer
Correct Option: D
Explanation:

A non-competitive inhibitor is one that binds to a site distinct from the site which binds the substrate; inhibitor binding does not block substrate binding or vice versa. The enzyme is inactivated when inhibitor is bound, whether or not substrate is also present. The inhibitor effectively lowers the concentration of active enzyme and hence, lowers the apparent V$ _{max}$. There is often little or no effect on K$ _m$.

Which of the following statements regarding enzyme inhibition is correct?

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. Non-competitive inhibition of an enzyme can be overcome by adding large amount of substrate.

  2. Competitive inhibition is seen, when a substrate competes with an enzyme for binding to an inhibitor protein.

  3. Competitive inhibition is seen, when the substrate and the inhibitor compete for the active site on the enzyme.

  4. Non-competitive inhibitors often bind to the enzyme irreversibly.

Show answer
Correct Option: C
Explanation:

A competitive inhibitor is a reversible inhibition where the inhibitor competes with the substrate for the active site of an enzyme. While the inhibitor occupies the active site it prevents binding of the substrate to the enzyme. Many competitive inhibitors are compounds that resemble the substrate and combine with the enzyme to form an enzyme inhibitor complex, but without leading to catalysis. Even fleeting combinations of this type will reduce the efficiency of the enzyme. By taking into account the molecular geometry of inhibitors that resemble the substrate, we can reach conclusions about which parts of the normal substrate bind to the enzyme. Competitive inhibition can be analyzed quantitatively by steady-state kinetics.

Which of the following is an allosteric enzyme?

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. Hexokinase

  2. Phosphofructokinase

  3. Succinic dehydrogenase

  4. Cytochrome oxidase

Show answer
Correct Option: A
Explanation:
An allosteric enzyme is the one that changes its conformational ensemble upon binding of an effector, which results in an apparent change in the binding affinity at a different ligand binding site. Hexokinase is an example of such enzymes. It undergoes an induced-fit conformational change when it binds to glucose, which ultimately prevents the hydrolysis of ATP.

So, the correct answer is 'Hexokinase'.

Competitive inhibitors of enzymes compete with the active sites of enzyme.

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Competitive inhibitors of enzymes compete with the active site of enzyme making them unavailable for the originally desired substrate. 

So, the given statement is true.

An inhibitor is added to a cell culture so that succinate accumulates. The enzyme catalysing the formation of which substance has been blocked?

biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

  1. Citrate

  2. Oxaloacetate

  3. $\alpha$-ketoglutarate

  4. Fumarate

Show answer
Correct Option: A
Explanation:

Succinate was placed in one of the most important cyclic pathways in metabolism, a collecting pool of catabolic and a starting point of many anabolic processes. Succinate is a product of substrate-level phosphorylation materialized in the citric acid cycle. It is involved in a macrophage-specific metabolic pathway generating and is also a downstream product of the α-ketoglutarate dehydrogenase complex, a heavily regulated multi-subunit complex.

So the correct answer is 'Citrate'.