A DNA replication fork is shown above. Answer the following questions based on that.
(i) Why does DNA replication occur in such small forks?
(ii) What is a synthesis and b synthesis?
(iii) Mention the polarity at A and B.

A particular stage in the transcription of a bacterium is given above. Answer the following questions:
(a) Name the stage in the process.
(b) Identify A, B, C, D and E in the diagram.

A hypothetical mRNA with 12 codons is shown above.
(a) How many amino acids will be coded by this? Justify your answer.
(b) Mention the dual functions of the codon, AUG.

Read the following and answer any four questions from (i) to (v) given below:
In prokaryotes, DNA is circular and present in the cytoplasm but in eukaryotes, DNA is linear and mainly confined to the nucleus. DNA or deoxyribonucleic acid is a long polymer of nucleotides. In 1953, the first correct double helical structure of DNA was worked out by Watson and Crick. Based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin. It is composed of three components, i.e., A phosphate group, a deoxyribose sugar and a nitrogenous base. Different forms of DNA are B-DNA, Z-DNA, A-DNA, C-DNA and D-DNA.
(i) Name the linkage present between the nitrogen base and pentose sugar in DNA.

(ii) The double helix structure of DNA was proposed by

(iii) The double chain of B-DNA is coiled in a helical fashion. The spiral twisting of B-DNA duplex produces

(iv) Assertion: The two strands of DNA helix have uniform distance between them.
Reason: A large sized purine always paired opposite to a small sized pyrimidine.

 (v) Which of the following describes the structure of B-DNA?

Read the following and answer any four questions from (i) to (v) given below:
The process of translation requires transfer of genetic information from a polymer of nucleotides to synthesise a polymer of amino acids. The relationship between the sequence of amino acids in a polypeptide and nucleotide sequence of DNA or mRNA is called genetic code. George Gamow suggested that in order to code for all the 20 amino acids, code should be made up of three nucleotides.
(i) What is a codon?

(ii) Three consecutive bases in the DNA molecule provide the code for each amino acid in a protein molecule. What is the maximum number of different triplets that could occurs ?

(iii) Listed below are some amino acids and their corresponding mRNA triplets.

Which DNA sequence would be needed to produce the following polypeptide sequence? Alanine- Arginine- Lysine- Phenylalanine

(iv) Identify the non-sense codons among the following.

(v) A polypeptide is made using synthetic mRNA molecules as shown.

What are the DNA codes for the amino acids phenylalanine and lysine?