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Biomolecules (Biology) · Question 53

AIPMT 2015 (Cancelled)MCQMedium📈 Topic in 38% papers+4−1
1

Which one of the following statements is incorrect?

  1. The competitive inhibitor does not affect the rate of breakdown of the enzyme-substrate complex.
  2. The presence of the competitive inhibitor decreases the Km of the enzyme for the substrate.
  3. A competitive inhibitor reacts reversibly with the enzyme to form an enzyme-inhibitor complex.
  4. In competitive inhibition, the inhibitor molecule is not chemically changed by the enzyme.

Answer

(2) The presence of the competitive inhibitor decreases the Km of the enzyme for the substrate.

Solution

As per NCERT, when the inhibitor closely resembles the substrate in its molecular structure, it competes with the substrate for the substrate-binding site of the enzyme, so the substrate cannot bind; this is competitive inhibition.

∵ The inhibitor binds reversibly and the substrate has to compete with it, a higher substrate concentration is needed to reach half of Vmax,

⇒ the apparent Km increases ( Vmax is unchanged).

∴ The statement that a competitive inhibitor decreases Km is incorrect.

Statements (1), (3) and (4) are correct: the inhibitor forms a reversible enzyme-inhibitor complex, is not changed by the enzyme, and does not alter the breakdown of the ES complex once it is formed.

Answer: (2)

AIPMT 2015 (Cancelled)

Keep practising — Biomolecules (Biology)

2

Select the option which is not correct with respect to enzyme action.

  1. Substrate binds with enzyme at its active site.
  2. Addition of a lot of succinate does not reverse the inhibition of succinic dehydrogenase by malonate.
  3. A non-competitive inhibitor binds the enzyme at a site distinct from that which binds the substrate.
  4. Malonate is a competitive inhibitor of succinic dehydrogenase.
AIPMT 2014
3

Which one of the following is a non-reducing carbohydrate?

  1. Maltose
  2. Sucrose
  3. Lactose
  4. Ribose 5-phosphate
AIPMT 2014
4

A phosphoglyceride is always made up of

  1. a saturated or unsaturated fatty acid esterified to glycerol molecule to which a phosphate group is also attached.
  2. a saturated or unsaturated fatty acid esterified to a phosphate group which is also attached to a glycerol molecule.
  3. only a saturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached.
  4. only an unsaturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached.
NEET 2013
5

Macromolecule chitin is

  1. sulphur containing polysaccharide
  2. simple polysaccharide
  3. nitrogen containing polysaccharide
  4. phosphorus containing polysaccharide.
NEET 2013
6

Transition state structure of the substrate formed during an enzymatic reaction is

  1. transient and unstable
  2. permanent and stable
  3. transient but stable
  4. permanent but unstable.
NEET 2013
7

The essential chemical components of many coenzymes are

  1. carbohydrates
  2. vitamins
  3. proteins
  4. nucleic acids.
NEET 2013
8

Which of the following statements about enzymes is wrong?

  1. Enzymes are denaturated at high temperatures.
  2. Enzymes are mostly proteins but some are lipids also.
  3. Enzymes are highly specific.
  4. Enzymes require optimum pH and temperature for maximum activity.
NEET 2013 (Karnataka)
9

Uridine, present only in RNA is a

  1. nucleoside
  2. nucleotide
  3. purine
  4. pyrimidine.
NEET 2013 (Karnataka)
10

The figure shows a hypothetical tetrapeptide portion of a protein with parts labelled A - D. Which one of the following options is correct? [figure]

  1. D is an acidic amino acid-glutamic acid.
  2. C is an aromatic amino acid-tryptophan.
  3. A is the C-terminal amino acid and D is N-terminal amino acid.
  4. A is a sulphur containing amino acid methionine.
NEET 2013 (Karnataka)
11

Which one of the following biomolecules is correctly characterized?

  1. Lecithin – a phosphorylated glyceride found in cell membrane.
  2. Palmitic acid – an unsaturated fatty acid with 18 carbon atoms.
  3. Adenylic acid – adenosine with a glucose phosphate molecule.
  4. Alanine amino acid – contains an amino group and an acidic group anywhere in the molecule.
AIPMT 2012 (Mains)

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