Tag: enzymes

Questions Related to enzymes

Cyanide causes irreversible inhibition of cytochrome oxidase. This is because it

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

  1. Combines with iron.

  2. Destroys tertiary structure.

  3. Attaches to copper.

  4. All the above.

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Correct Option: A
Explanation:
Cyanide inhibits cytochrome oxidase by combining with Iron within the enzyme which results in the prevention of transport of electrons from cytochrome oxidase to oxygen. So, the correct answer is A.

Which statement regarding enzyme inhibition is correct?

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

  1. Competitive inhibition occurs when a substrate competes with enzyme for binding to inhibitor protein

  2. Competitive inhibition occurs when the substrate and the inhibitor compete for active site on the enzyme

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

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

Show answer
Correct Option: B
Explanation:
A molecule similar to substrate competes with the substrate for active site. Such molecules are known as inhibitor. The presence of the inhibitor decreases availability of the active site for the substrate and further decreases the rate of reaction. This inhibition is known as competitive inhibition.
For example, malonate acts as a inhibitor which  competes with the succinate and prevents its attachment to the enzyme succinate dehydrogenase.
So, the correct answer is option B.

An enzyme brings about

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

  1. Decrease in reaction time

  2. Increase in reaction time

  3. Increase in activation energy

  4. Reduction in activation energy

Show answer
Correct Option: D
Explanation:

Enzymes are proteins which accelerate the rate of the reaction. The substrate and product have different energy state. The energy gap between the substrate and the product is known as activation energy which is the minimum energy required to initiate a reaction. The enzymes lower the activation energy and lead to the faster conversion of substrate to the product.

So, the correct answer is option D.

Nerve gas (DFP) inhibits neurotransmission as it reacts with

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

  1. Serine of acetylcholine-esterase.

  2. Choline of acetylcholine-esterase.

  3. Acetylcholine.

  4. Noradrenaline.

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Correct Option: A
Explanation:
Nerve gas attacks the nervous system of the human body. All such gases function in the same way, it inhibits the enzyme acetylcholine esterase by reacting with the active site of serine, and is responsible for the breakdown of the acetylcholine in the synapse.
So, the correct answer is A.

An enzyme promotes a chemical reaction by

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

  1. lowering the energy of activation

  2. changing the free energy difference between substrate and product

  3. increasing molecular motion

  4. all of these.

Show answer
Correct Option: A
Explanation:
There are so many reactions occurring inside the living body that the activation energy of all these reactions cannot be supplied. So, enzymes decrease the activation energy of the reaction and thus increase the speed of the reaction.
So, the correct option is 'lowering the energy of activation'

Modulators

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

  1. Inhibit enzyme activity

  2. Stimulate enzyme activity

  3. Function as coenzymes

  4. Both A and B

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Correct Option: D
Explanation:

A modulator is a type of molecule which either stimulates or inhibits enzyme activity. Those which stimulate enzyme activity are known as inducers while those which inhibit enzyme activity are known as inhibitors. The inhibitors can be competitive, non-competitive or allosteric inhibitors. 

Thus, the correct answer is option D. 

Which of the following inactivates the enzyme by changing its shape?

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

  1. Competitive inhibitor

  2. Allosteric inhibitor

  3. Coenzyme

  4. All of the above

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Correct Option: B
Explanation:

Allosteric means in a different steric conformation or occurrence of more than one shapes. Allosteric modulators bind to a site different from the active site and bring changes in the shape or conformation of the enzyme molecule. The change in shape can activate the enzyme or inhibit the activity of enzyme. An allosteric inhibitor will bind to allosteric site and bring in the conformational changes to reduce the enzyme activity.

Identify the correct statement regarding enzyme inhibition.

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

  1. Non-competitive inhibition of an enzyme can be overcomed 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:

Competitive inhibition is the inhibition of an enzyme by an inhibitor which has structural similarity to the active site and thus competes with the substrate for binding with the active site. Competitive inhibition is a reversible inhibition and depends on the relative concentration of substrate and inhibitor.

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$.