Given below are two statements: Statement I: Denaturation of a protein breaks its peptide bonds, so that its primary structure is lost. Statement II: In the α-helix, polypeptide chains are stretched out and laid side by side, held by hydrogen bonds between chains. Choose the correct answer.

Both Statement I and Statement II are incorrect

Both Statement I and Statement II are correct

Statement I is incorrect but Statement II is correct

Statement I is correct but Statement II is incorrect

Assertion A: α-D-Glucose and β-D-glucose differ in configuration at C-4. Reason R: In the cyclic form of glucose, C-1 becomes a chiral centre, which gives two anomers. Choose the correct answer.

A is not correct but R is correct

Both A and R are correct but R is not the correct explanation of A

A is correct but R is not correct

Both A and R are correct and R is the correct explanation of A

Biomolecules

9 NEET-UG practice questions on Biomolecules, part of Chemistry. The first 9 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
Given below are two statements: Statement I: Denaturation of a protein breaks its peptide bonds, so that its primary structure is lost. Statement II: In the α-helix, polypeptide chains are stretched out and laid side by side, held by hydrogen bonds between chains. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is incorrect but Statement II is correct
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are incorrect
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Answer: D · Both Statement I and Statement II are incorrect
Denaturation destroys secondary and tertiary structure, but the primary structure stays intact. The chain stretched side by side describes the β-pleated sheet. The α-helix is a right-handed coil of one chain, held by hydrogen bonds within it.
- A: Neither statement is right, as each one misdescribes the structure.
- B: Statement II is wrong, because it describes the β-pleated sheet.
- C: Statement I is wrong, because peptide bonds survive denaturation.
Remember this
Denaturation leaves primary structure unchanged; α-helix has hydrogen bonds within a chain, β-sheet between chains.
Question 2 · Hard
Assertion A: α-D-Glucose and β-D-glucose differ in configuration at C-4. Reason R: In the cyclic form of glucose, C-1 becomes a chiral centre, which gives two anomers. Choose the correct answer.
1. ABoth A and R are correct but R is not the correct explanation of A
2. BA is correct but R is not correct
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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Answer: D · A is not correct but R is correct
When the C5 hydroxyl adds to the C1 aldehyde, C1 becomes a new chiral centre, so R is right. The two forms, called anomers, differ only at C1 and not at C4, so A is wrong.
- A: A is wrong, since the difference is at C-1.
- B: R is correct and A is not, which is the reverse of this choice.
- C: A is wrong, so this pairing cannot hold.
Remember this
α- and β-D-glucose are anomers and differ only at C-1, the carbon that was the aldehyde carbon.
Question 3 · Easy
Exposure to sunlight serves as a source of which vitamin?
1. AVitamin D
2. BVitamin E
3. CVitamin C
4. DVitamin K
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Answer: A · Vitamin D
Sunlight, fish and egg yolk are the sources of vitamin D, whose deficiency causes rickets in children.
- B: This comes from vegetable oils such as wheat germ oil and sunflower oil.
- C: This comes from citrus fruits, amla and green leafy vegetables.
- D: This comes from green leafy vegetables.
Remember this
Sources worth remembering: vitamin D from sunlight, vitamin C from citrus fruits and amla, vitamin K from green leafy vegetables.
Question 4 · Hard
A linear tetrapeptide contains exactly two glycine units, one alanine and one valine. How many different amino acid sequences are possible?
1. A4
2. B24
3. C6
4. D12
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Answer: D · 12
Arranging four units with two alike gives 4!/2! = 12. Check: choose positions for glycine in C(4,2) = 6 ways, then place alanine and valine in 2 ways, so 6 × 2 = 12. Sequences differ even when they are reverses, because a chain has distinct N- and C-terminal ends.
- A: This counts only one position choice for each amino acid.
- B: This treats the two glycine units as different.
- C: This counts the glycine positions but not the alanine and valine order.
Remember this
Gly-Ala and Ala-Gly are different peptides, so sequence order counts, but identical units do not add arrangements.
Question 5 · Medium
Read these statements on nucleic acids. A. DNA contains ribose and thymine. B. RNA contains thymine in place of uracil. C. In DNA, guanine pairs with adenine. D. Nucleotides in a chain are joined by phosphodiester links between C5′ and C3′ of the pentose units. Which of these are correct?
1. AC and D only
2. BA and D only
3. CD only
4. DA, B and C only
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Answer: C · D only
DNA contains 2-deoxyribose, so A is wrong. RNA contains uracil in place of thymine, so B is wrong. In DNA adenine pairs with thymine and guanine with cytosine, so C is wrong. Only D correctly describes the chain.
- A: This includes C, but guanine pairs with cytosine.
- B: This includes A, but the sugar in DNA is 2-deoxyribose.
- D: This picks the three wrong statements and leaves out the only right one.
Remember this
DNA has deoxyribose and thymine; RNA has ribose and uracil; pairs are A-T and G-C.
Question 6 · Medium
Glycine (M = 75 g/mol) and alanine (M = 89 g/mol) form the tripeptide Gly-Ala-Gly. Calculate its molar mass.
1. A221 g/mol
2. B203 g/mol
3. C185 g/mol
4. D239 g/mol
Answer and explanation in LearnFree account
Question 7 · Easy
Which of these carbohydrates is non-reducing?
1. ALactose
2. BGlucose
3. CSucrose
4. DMaltose
Answer and explanation in LearnFree account
Question 8 · Medium
Name the dipeptide drawn in the figure.
Figure: MedExams
1. AAlanylalanine
2. BGlycylglycine
3. CGlycylalanine
4. DAlanylglycine
Answer and explanation in LearnFree account
Question 9 · Medium
X and Y in the figure are two nitrogenous bases of nucleic acids. Given below are two statements: Statement I: Y occurs in DNA but not in RNA. Statement II: X and Y are both pyrimidine bases. Choose the correct answer.
Figure: MedExams
1. AStatement I is correct but Statement II is incorrect
2. BBoth Statement I and Statement II are correct
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are incorrect
Answer and explanation in LearnFree account

Biomolecules

Given below are two statements: Statement I: Denaturation of a protein breaks its peptide bonds, so that its primary structure is lost. Statement II: In the α-helix, polypeptide chains are stretched out and laid side by side, held by hydrogen bonds between chains. Choose the correct answer.

Assertion A: α-D-Glucose and β-D-glucose differ in configuration at C-4. Reason R: In the cyclic form of glucose, C-1 becomes a chiral centre, which gives two anomers. Choose the correct answer.

Exposure to sunlight serves as a source of which vitamin?

A linear tetrapeptide contains exactly two glycine units, one alanine and one valine. How many different amino acid sequences are possible?

Read these statements on nucleic acids. A. DNA contains ribose and thymine. B. RNA contains thymine in place of uracil. C. In DNA, guanine pairs with adenine. D. Nucleotides in a chain are joined by phosphodiester links between C5′ and C3′ of the pentose units. Which of these are correct?

Glycine (M = 75 g/mol) and alanine (M = 89 g/mol) form the tripeptide Gly-Ala-Gly. Calculate its molar mass.

Which of these carbohydrates is non-reducing?

Name the dipeptide drawn in the figure.

X and Y in the figure are two nitrogenous bases of nucleic acids. Given below are two statements: Statement I: Y occurs in DNA but not in RNA. Statement II: X and Y are both pyrimidine bases. Choose the correct answer.