Subjective & Short Questions of Molecular Genetics

SUBJECTIVE QUESTIONS

1-Describe process of DNA replication.

  1. Discuss nature of gene.
  2. Write note on genetic code.
  3. Describe transcription.
  1. Describe process of protein synthesis.
  2. Describe regulation of gene expression in prokaryotes. Or discuss lac operon.
  3. Discuss control of gene expression in eukaryotes.

SHORT  QUESTIONS

  1. Name different enzymes involved in replication of DNA.
    Ans:
    DNA polymerase I, DNA polymerase II, Primase and DNA I igase.
  2. Why is RNA primer synthesized?

Ans: The DNA polymerase III can add nucleotides only to a chain of nucleotides that is already paired with the parent strands. Hence DNA polymerase cannot itself initiate synthesis of DNA. Thus another enzyme, primase synthesize an RNA primer.

  1. Differentiate between leading strand and lagging strands.

Ans:   Leading strand elongates toward the replication fork. In this

case, the nucleotides are added continuously to its growing 3′ end. Lagging strand elongates away from the replication fork.

  1. What are Okazaki fragments? Why are they formed?

Ans: Lagging strand is synthesized discontinuously. A series of short segments are synthesized. These segments are connected later on. These segments are called Okazaki fragments.

  1. What is gene expression?

Ans: The central dogma is composed of transcription and translation. These two steps of central dogma are also collectively called gene expression.

  1. What is translation?

Ans: The synthesis of mRNA from the DNA is called transcription.

  1. What is promoter?

Ans: Transcription starts at the promoter on the DNA template strand. Promoter is the RNA polymerase binding site.

  1. What is rRNA?

Ans: It is found in ribosome. The rRNA provide

  1. What is the function of tFtNA?

Ans: Transfer RNA molecules read massage (code) on the mRNA and transport the amino acids to the ribosomes.

10-Differentiate between codes and anticodes.

Ans: Codes are present on mRNA and anticodes are present on tRNA.

11-What is the function of mRNA?

Ans: The mRNA is long strands of RNA. It is transcribed from DNA and it travels to the ribosomes and direct precisely which amino acids are assembled into polypeptide.

12-Differentiate between translation and transcription.

Ans: The synthesis of mRNA from DNA is called transcription. The synthesis of protein from mRNA is called translation.

13-Differentiate between template strand or the antisense strand and coding strand or the sense strand.

Ans: Template is the strand which is transcribed during transcription. The opposite strand is called coding or sense strand.

14-What is transcription bulb?


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Ans: The DNA strands open tip at the place where enzyme is attached with the template strand. It forms transcription bubble.

15-What is cap and tail of mRNA?

Ans: Cap is in the form of 7 methyl GTP. It is linked to 5′ end with the first nucleotide of mRNA. Tail is in the form of poly A tail. It is linked to 3′ end of the RNA.

16-What is genetic code?

Ans: Genetic code is a combination of 3 nucleotides, which specify a particular amino acid.

17-Why are three nucleotides taken as most appropriate Mr genetic codes?

Ans: Three Nucleotides can form 43 or 64 different combinations. It is more than enough to code for the 20 amino acids. Thus genetic code is a triplet code and the reading occurs continuously.

18-What are terminations or nonsense codes?

Ans: These are three codons UAA, UAG and UGA. They do not code for any amino acid. So they are known as nonsense codon.

19-What is initiation codon?

Ans:        It is present at the start of every gene. This initiation codon
AUG. It encodes the amino acid methionine.

20-Are genetic codes universal?

Ans:     No, genetic codes are not universal. The study of genetic

code of mitochondrial DNA showed that genetic codes are not so universal. For example, UGA codon is normally a stop codon but in mitochondria it codes for tryptophan amino acid.

21-What is translation?

Ans: The synthesis of protein from mRNA is called translation.

22-What is anticodon?

Ans: The tRNA molecules possess complementary three nucleotide sequence. It is called anticodon.

23-What is the function of P site (peptidyl site) of ribosome?

Ans: It is the site of the ribosome where peptide bonds are formed.

24-What is the function of A site (aminoacyl site)?

Ans:     This site contains successive (next) amino acid with its

25-What is initiation factor?

Ans:     A proteins initiation factor control the attachment of the

tRNA on the ribosomal surface at the P site.

26-What is translocation?

Ans: During Translocation, the ribosome now moves (translocates) to next code along the mRNA molecule in the

5′       3′ direction.

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