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Molecular Basis of Inheritance · Question 143

AIPMT 2003MCQMedium📈 Topic in 25% papers+4−1
1

What would happen if in a gene encoding a polypeptide of 50 amino acids, 25th codon (UAU) is mutated to UAA?

  1. A polypeptide of 49 amino acids will be formed
  2. A polypeptide of 25 amino acids will be formed
  3. Two polypeptides of 24 and 25 amino acids will be formed
  4. A polypeptide of 24 amino acids will be formed

Answer

(4) A polypeptide of 24 amino acids will be formed

Solution

UAU codes for tyrosine, whereas UAA is a stop (nonsense) codon that codes for no amino acid.

⇒ Translation proceeds through codons 1 to 24 and terminates at the 25th codon (UAA).

∴ A polypeptide of only 24 amino acids is formed.

Answer: (4)

AIPMT 2003

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2

What does "lac" refer to in what we call the lac operon?

  1. The number 1,00,000
  2. Lac insect
  3. Lactase
  4. Lactose
AIPMT 2003
3

During translation initiation in prokaryotes, a GTP molecule is needed in:

  1. Association of 30S-mRNA with formyl-met-tRNA
  2. Formation of formyl-met-tRNA
  3. Association of 50S subunit of ribosome with initiation complex
  4. Binding of 30S subunit of ribosome with mRNA
AIPMT 2003
4

Which one of the following triplet codes, is correctly matched with its specificity for an amino acid in protein synthesis or as 'start' or 'stop' codon?

  1. UUU – Stop
  2. UAC – Tyrosine
  3. UGU – Leucine
  4. UCG – Start
AIPMT 2003
5

During transcription, the DNA site at which RNA polymerase binds is called:

  1. Receptor
  2. Regulator
  3. Enhancer
  4. Promoter
AIPMT 2003
6

Degeneracy of a genetic code is attributed to the:

  1. Second member of a codon
  2. Third member of a codon
  3. First member of a codon
  4. Entire codon
AIPMT 2003
7

In the genetic code dictionary, how many codons are used to code for all the 20 amino acids:

  1. 64
  2. 20
  3. 60
  4. 61
AIPMT 2003
8

In a DNA percentage of thymine is 20% then what is the percentage of guanine : -

  1. 40%
  2. 20%
  3. 30%
  4. 60%
AIPMT 2002
9

Transformation experiment was first performed on which bacterium : -

  1. Diplococcus pneumoniae
  2. Pasteurella pestis
  3. E. coli
  4. Salmonella
AIPMT 2002
10

Jacob and Monod studied lactose metabolism in E. coli and proposed operon concept. Operon concept is applicable for :

  1. All prokaryotes and all eukaryotes
  2. All prokaryotes and some protozoans
  3. All prokaryotes
  4. All prokaryotes and some eukaryotes
AIPMT 2002
11

In E. coli, during lactose metabolism repressor binds to : -

  1. Promoter gene
  2. Operator gene
  3. Structural gene
  4. Regulator gene
AIPMT 2002

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