Genetic Code, Human Genome Project & DNA Fingerprinting

1 Mark Questions

1. How is repetitive/satellite DNA separated from bulk genomic DNA for various genetic experiments. [Delhi 2014] Ans. Satellite DNA is separated from bulk genomic DNA by density-gradient centrifugation technique
2. Mention the role of the codons AUG and UGA during protein synthesis. [Delhi 2011,2010] Ans. AUG Acts as initiation codon and codes for amino acid methionine. UGA Acts as stop/termination codon that signals termination of polypeptide synthesis.
3. Mention the contribution of genetic maps in human genome project. [MI India 2011] Ans. Genetic maps are used as a starting point in the sequencing of whole genomes.

4.Mention any two ways in which Single Nucleotide Polymorphisms (SNPs) identified in human genome, can bring out revolutionary changes in biological and medical sciences?[MI India 2011 C] Ans.(i)By tracing human history.

1. By finding chromosomal locations for disease associated sequences.

5.State which human chromosome has [Foreign 2011] (i)the maximum number of genes and (ii)the one which has the least number of genes Ans.(i)Chromosome 1

1. Chromosome Y

1. Given below is a schematic representation of a lac operon in the absence of an inducer.

Identify 'A' and 'B' in it. [Foreign 2008]

p Z y а

Repressor mRNA

Ans.A- Repressor

1. Repressor bound to the operator region and prevent transcription of structural genes.

2 Marks Questions

1. How would lac operon operate in E.coli growing in a culture medium where lactose is present as source of sugar? [All India 2014C]

Ans. When lactose is present in a medium having E. coli, it will act as a substrate for enzyme beta-galactosidase and switches on the operon. Hence, it is also termed as an inducer.

1. Where does peptide bond formation occur in a bacterial ribosome and how? [Foreign 2014]

Ans. A peptide bond is formed between carboxyl group (-COOH) of amino acid at P-site and amino groun (-NH) of amino acid at A-site by the enzyme peptidyl transferase in a bacterial ribosome.

9.(i) Name the scientist who suggested that the genetic code should be made of a combination of three nucleotides.

1. Explain the basis on which he arrived at this conclusion. [Delhi 2014]

Ans.(i) George Gamow suggested that the genetic code should be made of a combination of three nucleotides.

1. This is because the code must be of three bases in order to code for 20 amino acids since

there, are only four bases (i.e. <math>4^3</math> or <math>4 \times 4 \times 4 = 64</math>) which code for 20 amino acids.

10.Explain aminoacylation of tRNA.[All India 2014 C]

Ans.Aminoacylation of the tRNA It is also, called as charging of tRNA. It is the first phase of translation where amino acids are activated in the presence of ATP and linked to their cognate tRNA.

Enzyme and AMP are released. tRNA complexed with amino acid is sometimes called charged fRNA. The amino acid is linked to 3'-OH end of tRNA through its -COOH group.

AA— AMP + t + tRNA-> AA—tRNA+ AMP+ E (aminoacyl adenylate enzyme

11. Why is charging of fRNA necessary during translation process? [All India 2014 C; Delhi 2008]

Ans. Process of Charging of fRNA

Amino acids are activated in the presence of ATP and linked to their cognate tRNA. This is called charging of tRNA (amino acylation).

The process is required as the formation of peptide bond between the amino acids is favoured energetically, when they are brought together. Activation of amino acids by ATP provides the energy for the formation of peptide bond.

1. One of the salient features of the genetic code is that it is nearly universal from bacteria

to humans. Mention two exceptions to this rule, Why are some codes said to be degenerated? [Foreign 2014]

Ans. Genetic code is nearly universal except in mitochondrial codons and in some protozoans. Some amino acids are coded by more than one codon, hence somes codes are said to be