Vidaara.orgClass 12 · Chemistry
CodeVID-C12-14-T3-01
Assignment — Vitamins & Nucleic Acids
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Beri-beri is caused by deficiency of vitamin:
- A.A
- B.B1
- C.C
- D.D
2.
The sugar present in DNA is:
- A.ribose
- B.2-deoxyribose
- C.glucose
- D.fructose
3.
Guanine in DNA pairs with:
- A.adenine
- B.thymine
- C.cytosine
- D.uracil
4.
Which is a fat-soluble vitamin?
- A.Vitamin C
- B.Vitamin B12
- C.Vitamin K
- D.Vitamin B1
5.
The RNA that carries the genetic message to the ribosome is:
- A.tRNA
- B.rRNA
- C.mRNA
- D.dsRNA
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Why must water-soluble vitamins be supplied in the diet regularly?
7.
What is a nucleotide?
8.
Name the two purine and two pyrimidine bases found in DNA.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
List three structural differences between DNA and RNA.
10.
Outline the roles of mRNA, tRNA and rRNA in protein synthesis.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the Watson–Crick double-helix model of DNA and explain how its base pairing allows accurate replication.
Answer Key
Section A — Multiple Choice Questions
- (B) B1
- (B) 2-deoxyribose
- (C) cytosine
- (C) Vitamin K
- (C) mRNA
Section B — Short Answer (2 marks)
- They are not stored in the body (excess is excreted in urine), so a continuous dietary supply is needed to prevent deficiency.
- A unit made of a nitrogenous base, a pentose sugar and a phosphate group; it is the repeating building block of nucleic acids.
- Purines: adenine and guanine; pyrimidines: cytosine and thymine.
Section C — Short Answer (3 marks)
- DNA has 2-deoxyribose, RNA has ribose; DNA has thymine, RNA has uracil; DNA is double-stranded (helix) while RNA is generally single-stranded.
- mRNA carries the coded message transcribed from DNA to the ribosome; rRNA forms the ribosome where assembly occurs; tRNA reads each codon and delivers the matching amino acid to build the polypeptide.
Section D — Long Answer (5 marks)
- DNA is a right-handed double helix of two antiparallel polynucleotide strands with a sugar–phosphate backbone outside and bases inside. The strands are held by complementary H-bonding: adenine with thymine (two H-bonds) and guanine with cytosine (three H-bonds), so the amount of A equals T and G equals C (Chargaff's rule). Because each base pairs with only one partner, the two strands are complementary. During replication the helix unwinds and each strand acts as a template; free nucleotides pair with the exposed bases (A with T, G with C), producing two identical daughter helices, each keeping one parent strand. This semi-conservative copying transmits the genetic information faithfully to daughter cells.
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