Malonate inhibits succinic dehydrogenase because it

resembles succinate in structure and competes for the active site

resembles fumarate and oxidises the enzyme's haem group

denatures the enzyme by breaking its tertiary structure

binds far from the active site and changes the enzyme's shape

Given below are two statements: Statement I: Arachidonic acid has 16 carbon atoms, including the carboxyl carbon. Statement II: Lecithin is a phospholipid. Choose the correct answer.

Statement I is incorrect but Statement II is correct

Both Statement I and Statement II are incorrect

Statement I is correct but Statement II is incorrect

Both Statement I and Statement II are correct

Biomolecules

21 NEET-UG practice questions on Biomolecules, part of Zoology. The first 21 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Malonate inhibits succinic dehydrogenase because it
1. Aresembles fumarate and oxidises the enzyme's haem group
2. Bdenatures the enzyme by breaking its tertiary structure
3. Cresembles succinate in structure and competes for the active site
4. Dbinds far from the active site and changes the enzyme's shape
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Answer: C · resembles succinate in structure and competes for the active site
Malonate closely resembles the substrate succinate, so it competes for the active site and blocks binding. This is competitive inhibition.
- A: Malonate resembles the substrate, not the product.
- B: Malonate does not denature the protein.
- D: Malonate acts at the substrate-binding site.
Remember this
A competitive inhibitor resembles the substrate; such inhibitors are used in controlling bacterial pathogens.
Question 2 · Medium
Without any enzyme, about 200 molecules of H₂CO₃ form in an hour. With carbonic anhydrase, about 600,000 molecules form every second. By roughly how many times does the enzyme speed up the reaction?
1. AAbout 2 × 10⁹ times
2. BAbout 1.8 × 10⁵ times
3. CAbout 3000 times
4. DAbout 10⁷ times
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Answer: D · About 10⁷ times
Per hour, the enzyme gives 600,000 × 3600 ≈ 2.16 × 10⁹ molecules, and 2.16 × 10⁹ ÷ 200 ≈ 1.08 × 10⁷. Per second, the uncatalysed rate is 200 ÷ 3600 = 1/18, and 600,000 × 18 gives the same value.
- A: This forgets to divide by the uncatalysed 200.
- B: This converts seconds only to minutes.
- C: This ignores the difference between hour and second.
Remember this
Carbonic anhydrase speeds this reaction about 10 million times.
Question 3 · Medium
Given below are two statements: Statement I: Arachidonic acid has 16 carbon atoms, including the carboxyl carbon. Statement II: Lecithin is a phospholipid. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BBoth Statement I and Statement II are incorrect
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are correct
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Answer: A · Statement I is incorrect but Statement II is correct
Palmitic acid has 16 carbons; arachidonic acid has 20, including the carboxyl carbon, so Statement I is wrong. Lecithin is a phospholipid found in cell membranes.
- B: Statement II is true of lecithin.
- C: Statement I is the false one, not Statement II.
- D: Statement I gives the carbon count of palmitic acid.
Remember this
Palmitic acid has 16 carbons; arachidonic acid has 20; both counts include the carboxyl carbon.
Question 4 · Hard
Consider these statements on enzyme cofactors: A. The protein part of a holoenzyme is the apoenzyme. B. A coenzyme associates with the apoenzyme only during catalysis. C. The coenzymes NAD and NADP contain the vitamin niacin. D. Zinc is a cofactor of carboxypeptidase. Choose the correct answer.
1. AB, C and D only
2. BA and C only
3. CA, B, C and D
4. DA, C and D only
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Answer: C · A, B, C and D
All four match NCERT. Also, removing a cofactor destroys catalytic activity, which shows that it is essential.
- A: A is also true, since the protein part is the apoenzyme.
- B: B and D are also true.
- D: B is also true, since a coenzyme's binding is transient.
Remember this
Holoenzyme equals apoenzyme plus cofactor; cofactors are prosthetic groups, coenzymes or metal ions.
Question 5 · Medium
Match List-I with List-II. List-I (secondary metabolite) A. Concanavalin A B. Abrin C. Vinblastin D. Morphine List-II (group) I. Drug II. Lectin III. Alkaloid IV. Toxin
1. AA-I, B-IV, C-II, D-III
2. BA-II, B-IV, C-I, D-III
3. CA-IV, B-II, C-I, D-III
4. DA-II, B-IV, C-III, D-I
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Answer: B · A-II, B-IV, C-I, D-III
Concanavalin A is a lectin and abrin a toxin, while vinblastin is a drug and morphine an alkaloid.
- A: This swaps lectin and drug.
- C: This swaps lectin and toxin.
- D: This swaps drug and alkaloid.
Remember this
Abrin and ricin are toxins; morphine and codeine are alkaloids; vinblastin and curcumin are drugs.
Question 6 · Hard
Match List-I with List-II. List-I (enzyme class) A. Oxidoreductases B. Transferases C. Lyases D. Ligases List-II (reaction catalysed) I. Removal of groups by means other than hydrolysis, leaving double bonds II. Linking two compounds, as in forming C-O or C-N bonds III. Transfer of a group other than hydrogen between a pair of substrates IV. Oxidation of one substrate with reduction of another
1. AA-IV, B-I, C-III, D-II
2. BA-III, B-IV, C-I, D-II
3. CA-IV, B-III, C-II, D-I
4. DA-IV, B-III, C-I, D-II
Answer and explanation in LearnFree account
Question 7 · Easy
Compared with the Earth's crust, which element is far more abundant, by weight, in the human body?
1. ASilicon
2. BCarbon
3. CMagnesium
4. DSodium
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Question 8 · Medium
An experimenter keeps one sample of a human enzyme at 4 °C and another at 90 °C for an hour, then tests both at 37 °C. Which result is expected?
1. ANeither sample shows any activity at 37 °C
2. BBoth samples show full activity at 37 °C
3. CThe cold sample shows activity, but the heated sample does not
4. DThe heated sample shows activity, but the cold sample does not
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Question 9 · Hard
Given below are two statements: Statement I: As a polypeptide is conventionally written, the left-end amino acid is N-terminal and the right-end amino acid is C-terminal. Statement II: Adult human haemoglobin has two alpha and two beta subunits, which is a quaternary structure. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is incorrect but Statement II is correct
3. CBoth Statement I and Statement II are incorrect
4. DStatement I is correct but Statement II is incorrect
Answer and explanation in LearnFree account
Question 10 · Medium
Which statements on polysaccharides are correct? A. Cellulose is a homopolymer of glucose. B. Inulin is a polymer of fructose. C. The arthropod exoskeleton has chitin, a complex polysaccharide. D. Glycogen is a heteropolymer of glucose and fructose.
1. AA, B and C only
2. BB, C and D only
3. CA and B only
4. DA, C and D only
Answer and explanation in LearnFree account
Question 11 · Medium
In peroxidase and catalase, which break down hydrogen peroxide, haem acts as a
1. Acoenzyme
2. Bapoenzyme
3. Cprosthetic group
4. Dmetal ion cofactor
Answer and explanation in LearnFree account
Question 12 · Medium
Consider these statements on amino acids: A. Tyrosine, phenylalanine and tryptophan are aromatic. B. Lysine is an acidic amino acid. C. Glutamic acid is an acidic amino acid. D. Valine is a basic amino acid. Choose the correct answer.
1. AA and D only
2. BB and D only
3. CA and C only
4. DA, B and C only
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Question 13 · Easy
When iodine solution is added to a starch sample, a blue colour appears. This is because
1. AI₂ binds at the reducing end of the chain
2. BI₂ oxidises each glucose unit in the chain
3. CI₂ is held in the helical parts of starch
4. DI₂ breaks starch down into glucose
Answer and explanation in LearnFree account
Question 14 · Hard
Arrange the steps of an enzyme's catalytic action in the correct order. A. An enzyme-product complex is formed B. The substrate binds to the active site C. The enzyme alters its shape and fits more tightly around the substrate D. The active site breaks the chemical bonds of the substrate
1. AC, B, D, A
2. BB, C, D, A
3. CB, C, A, D
4. DB, D, C, A
Answer and explanation in LearnFree account
Question 15 · Easy
The R group of an amino acid is a hydroxymethyl group in
1. Aserine
2. Balanine
3. Cvaline
4. Dglycine
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Question 16 · Medium
Match List-I with List-II. List-I (protein) A. Collagen B. GLUT-4 C. Insulin D. Antibody List-II (function) I. Hormone II. Fights infectious agents III. Intercellular ground substance IV. Enables glucose transport into cells
1. AA-III, B-I, C-IV, D-II
2. BA-IV, B-III, C-I, D-II
3. CA-III, B-IV, C-I, D-II
4. DA-III, B-IV, C-II, D-I
Answer and explanation in LearnFree account
Question 17 · Medium
Lipids have molecular weights that do not exceed about 800 Da, yet they appear in the acid-insoluble fraction of a tissue extract. This is because
1. Aacid treatment raises the molecular weight of lipids
2. Blipids polymerise into chains in the acid
3. Clipids bond covalently to proteins during grinding
4. Dmembranes broken on grinding form water-insoluble vesicles
Answer and explanation in LearnFree account
Question 18 · Easy
A ribozyme is
1. Aa polysaccharide that stores ribose
2. Ba lipid that speeds up a reaction
3. Ca nucleic acid that behaves like an enzyme
4. Da protein that binds to the ribosome
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Question 19 · Medium
Two separate, unbranched polypeptide chains have 40 and 25 amino acids. How many peptide bonds do they have in total?
1. A63
2. B62
3. C64
4. D65
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Question 20 · Medium
Assertion A: An enzyme speeds up a reaction by lowering its activation energy. Reason R: An enzyme is used up in the reaction it catalyses. Choose the correct answer.
1. AA is correct but R is not correct
2. BBoth A and R are correct but R is not the correct explanation of A
3. CBoth A and R are correct and R is the correct explanation of A
4. DA is not correct but R is correct
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Question 21 · Easy
Adenosine consists of
1. Aadenine joined to a pentose sugar
2. Badenine, a pentose sugar and a phosphate
3. Cadenine alone, without any sugar
4. Dadenine joined to a phosphate
Answer and explanation in LearnFree account

Biomolecules

Malonate inhibits succinic dehydrogenase because it

Without any enzyme, about 200 molecules of H₂CO₃ form in an hour. With carbonic anhydrase, about 600,000 molecules form every second. By roughly how many times does the enzyme speed up the reaction?

Given below are two statements: Statement I: Arachidonic acid has 16 carbon atoms, including the carboxyl carbon. Statement II: Lecithin is a phospholipid. Choose the correct answer.

Consider these statements on enzyme cofactors: A. The protein part of a holoenzyme is the apoenzyme. B. A coenzyme associates with the apoenzyme only during catalysis. C. The coenzymes NAD and NADP contain the vitamin niacin. D. Zinc is a cofactor of carboxypeptidase. Choose the correct answer.

Match List-I with List-II. List-I (secondary metabolite) A. Concanavalin A B. Abrin C. Vinblastin D. Morphine List-II (group) I. Drug II. Lectin III. Alkaloid IV. Toxin

Compared with the Earth's crust, which element is far more abundant, by weight, in the human body?

An experimenter keeps one sample of a human enzyme at 4 °C and another at 90 °C for an hour, then tests both at 37 °C. Which result is expected?

Which statements on polysaccharides are correct? A. Cellulose is a homopolymer of glucose. B. Inulin is a polymer of fructose. C. The arthropod exoskeleton has chitin, a complex polysaccharide. D. Glycogen is a heteropolymer of glucose and fructose.

In peroxidase and catalase, which break down hydrogen peroxide, haem acts as a

Consider these statements on amino acids: A. Tyrosine, phenylalanine and tryptophan are aromatic. B. Lysine is an acidic amino acid. C. Glutamic acid is an acidic amino acid. D. Valine is a basic amino acid. Choose the correct answer.

When iodine solution is added to a starch sample, a blue colour appears. This is because

Arrange the steps of an enzyme's catalytic action in the correct order. A. An enzyme-product complex is formed B. The substrate binds to the active site C. The enzyme alters its shape and fits more tightly around the substrate D. The active site breaks the chemical bonds of the substrate

The R group of an amino acid is a hydroxymethyl group in

Match List-I with List-II. List-I (protein) A. Collagen B. GLUT-4 C. Insulin D. Antibody List-II (function) I. Hormone II. Fights infectious agents III. Intercellular ground substance IV. Enables glucose transport into cells

Lipids have molecular weights that do not exceed about 800 Da, yet they appear in the acid-insoluble fraction of a tissue extract. This is because

A ribozyme is

Two separate, unbranched polypeptide chains have 40 and 25 amino acids. How many peptide bonds do they have in total?

Assertion A: An enzyme speeds up a reaction by lowering its activation energy. Reason R: An enzyme is used up in the reaction it catalyses. Choose the correct answer.

Adenosine consists of