Tag: metabolism

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

The enzymes ribulose biphosphate carboxylase-oxygenase and phosphoenol pyruvate carboxylase are activated by

  1. Mg

  2. Zn

  3. Mo

  4. Mn
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Both RUBISCO and PEP carboxylase are important enzymes of dark reaction of photosynthesis. RUBISCO catalyzes carboxylation in C3 plants. In the presence of magnesium activated RUBISCO, carbon dioxide combines with ribulose bis phosphate to form phosphoglyceric acid. In C4 plants, mesophyll cells fix carbon dioxide with the help of phospho enol pyruvate in the presence of magnesium activated phospho-enol pyruvate carboxylase.

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

Haemoglobin is composed of four subunits. When one subunit binds to oxygen, it increases the chances that the other three subunits will also bind to oxygen. What is this type of activity called?

  1. Inhibition

  2. Cooperativity

  3. Enzyme substrate complex

  4. Catalysis

  5. Activation
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
A. When the binding of chemical shuts off the enzymatic activity, the process is called inhibition.
B. When binding of a molecule to the enzyme increase its affinity for more molecules, it is called cooperativity.
C. Binding of the substrate to the active site of enzyme produces a highly reactive short lived complex called Enzyme substrate complex which breaks into chemical products and unchanged enzyme.
D. Catalysis is the increase in rate of reaction by a catalyst.
E. Activation is the start of reaction by an enzyme.
Hence, the increase in affinity of haemoglobin for oxygen by binding of one oxygen molecule, is cooperativity.
So, the correct answer is 'Cooperativity'.
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

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

  1. Combines with iron.

  2. Destroys tertiary structure.

  3. Attaches to copper.

  4. All the above.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Which statement regarding enzyme inhibition is correct?

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

An enzyme brings about

  1. Decrease in reaction time

  2. Increase in reaction time

  3. Increase in activation energy

  4. Reduction in activation energy
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Nerve gas (DFP) inhibits neurotransmission as it reacts with

  1. Serine of acetylcholine-esterase.

  2. Choline of acetylcholine-esterase.

  3. Acetylcholine.

  4. Noradrenaline.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

An enzyme promotes a chemical reaction by

  1. lowering the energy of activation

  2. changing the free energy difference between substrate and product

  3. increasing molecular motion

  4. all of these.
Reveal answer Fill a bubble to check yourself
A Correct answer
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'
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Modulators

  1. Inhibit enzyme activity

  2. Stimulate enzyme activity

  3. Function as coenzymes

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
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. 

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

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

  1. Competitive inhibitor

  2. Allosteric inhibitor

  3. Coenzyme

  4. All of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Identify the correct statement regarding enzyme inhibition.

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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.