Codons & Genetic code

Codons and genetic codes

Q. 1

A codon in the genetic code consists of:

 A

One molecule of charged-tRNA

 B

A Shine-Dalgarno sequence

 C

Three consecutive nucleotides

 D

Two complementary base pairs

Q. 1

A codon in the genetic code consists of:

 A

One molecule of charged-tRNA

 B

A Shine-Dalgarno sequence

 C

Three consecutive nucleotides

 D

Two complementary base pairs

Ans. C

Explanation:

A codon is a triplet sequence of bases. The tRNA molecule contains an anticodon.

The Shine-Dalgarno sequence is found in the 23S prokaryotic ribosomal RNA. A codon is on the same strand of DNA or mRNA.


Q. 2

Which of the following is the CORRECT explanation for ‘degeneracy of codon’?

 A

More than one codon for a single amino acid

 B

More than one amino acid for a single codon

 C

No punctuation in codons

 D

Termination of protein synthesis

Q. 2

Which of the following is the CORRECT explanation for ‘degeneracy of codon’?

 A

More than one codon for a single amino acid

 B

More than one amino acid for a single codon

 C

No punctuation in codons

 D

Termination of protein synthesis

Ans. A

Explanation:

Three of the 64 possible codons do not code for specific amino acids; these have been termed nonsense codons. These nonsense codons are utilized in the cell as termination signals; they specify where the polymerization of amino acids into a protein molecule is to stop. The remaining 61 codons code for the 20 naturally occurring amino acids. Thus, there is “degeneracy” in the genetic code—that is, multiple codons decode the same amino acid.

 
Ref: Weil P. (2011). Chapter 37. Protein Synthesis & the Genetic Code. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Q. 3

Amino acids not coded by triplet codon:

 A

Lysine

 B

Hydroxyproline

 C

Selenocysteine

 D

Pyrrolysine

Q. 3

Amino acids not coded by triplet codon:

 A

Lysine

 B

Hydroxyproline

 C

Selenocysteine

 D

Pyrrolysine

Ans. B

Explanation:

B i.e. Hydroxyproline

Quiz In Between


Q. 4

Stop codons are:

 A

UAA

 B

UAG

 C

UGA

 D

All

Q. 4

Stop codons are:

 A

UAA

 B

UAG

 C

UGA

 D

All

Ans. D

Explanation:

A, B, C i.e. UAA, UAG, UGA


Q. 5

If there are 4 nucleotides instead of 3 in codon, how many amino acids may be formed?

 A

16

 B

21

 C

256

 D

64

Q. 5

If there are 4 nucleotides instead of 3 in codon, how many amino acids may be formed?

 A

16

 B

21

 C

256

 D

64

Ans. C

Explanation:

C i.e. 256


Q. 6

Stop codon:

 A

UAG

 B

UCA

 C

UAC

 D

AUG

Q. 6

Stop codon:

 A

UAG

 B

UCA

 C

UAC

 D

AUG

Ans. A

Explanation:

A i.e. UAG

Quiz In Between


Q. 7

A codon consists of –

 A

One molecule of amono acyl-t RNA

 B

Two complementary base pairs

 C

3 consecutive nucleotide units

 D

4 individual nucleotides

Q. 7

A codon consists of –

 A

One molecule of amono acyl-t RNA

 B

Two complementary base pairs

 C

3 consecutive nucleotide units

 D

4 individual nucleotides

Ans. C

Explanation:

C i.e. 3 consecutive nucleotide units


Q. 8

Nonsense codons bring about-

 A

Elongation of polypeptide chain

 B

Pre-translational modificastion of protein

 C

Initiation of protein synthesis

 D

Termination of protein synthesis

Q. 8

Nonsense codons bring about-

 A

Elongation of polypeptide chain

 B

Pre-translational modificastion of protein

 C

Initiation of protein synthesis

 D

Termination of protein synthesis

Ans. D

Explanation:

D i.e. Termination of protein synthesis


Q. 9

Same aminoacid is coded by multiple codons d/t following :

 A

Degeneracy

 B

Frame-shift mutation

 C

Transcription

 D

Mutation

Q. 9

Same aminoacid is coded by multiple codons d/t following :

 A

Degeneracy

 B

Frame-shift mutation

 C

Transcription

 D

Mutation

Ans. A

Explanation:

A i.e. Degeneracy

Quiz In Between


Q. 10

The anticodon region is an important part of the

 A

r-RNA

 B

m-RNa

 C

t-RNa

 D

hn-RNa

Q. 10

The anticodon region is an important part of the

 A

r-RNA

 B

m-RNa

 C

t-RNa

 D

hn-RNa

Ans. C

Explanation:

C i.e. t – RNA


Q. 11

In transcription anticodon is seen in ‑

 A

t-RNA

 B

m-RNA

 C

r-RNA

 D

None

Q. 11

In transcription anticodon is seen in ‑

 A

t-RNA

 B

m-RNA

 C

r-RNA

 D

None

Ans. A

Explanation:

 A i.e. t – RNA


Q. 12

Amber codon refers to

 A

Mutant codon

 B

Stop codon

 C

Initiating codon

 D

Codon for more than one amino acids

Q. 12

Amber codon refers to

 A

Mutant codon

 B

Stop codon

 C

Initiating codon

 D

Codon for more than one amino acids

Ans. B

Explanation:

B i.e Stop Codon

Quiz In Between


Q. 13

A mutation in the codon which causes a change in the coded amino acid, is known as:

 A

Mitogenesis

 B

Somatic mutation

 C

Missense mutation

 D

Recombination

Q. 13

A mutation in the codon which causes a change in the coded amino acid, is known as:

 A

Mitogenesis

 B

Somatic mutation

 C

Missense mutation

 D

Recombination

Ans. C

Explanation:

C i.e. Missense mutation


Q. 14

A codon codes for a single amino acid. This characteristic is called ‑

 A

Non-overlapping

 B

Unambiguous

 C

Non-punctate

 D

Degeneracy

Q. 14

A codon codes for a single amino acid. This characteristic is called ‑

 A

Non-overlapping

 B

Unambiguous

 C

Non-punctate

 D

Degeneracy

Ans. B

Explanation:

Ans. is ‘b’ i.e., Unambiguous

Characteristics of genetic codes

Genetic codes have following characteristics ‑

1) Universal :- Each codon specifically codes for same amino acid in all species, e.g. UCA codes for serine and CCA codes for proline in all organisms. That means specificity of codon has been conserved from very early stages of evolution. Exception to the universality of genetic coder are found in human mitochondria, where the code :-

α UGA codes for tryptophan instead of serving as a stop codon.

AUA codes for methionine instead of isoleucine.

CUA codes for threonine instead of leucine.

LI AGA and AGG serve as stop codon instead of coding for arginine.

2) Unambiguous/Specific :- A particular codon always codes for the same amino acid. For example CCU always codes for proline and UGG always codes for tryptophan.

3)  Degeneracy/Redundancy :- A given amino acid may have more than one codon. For example, CCU, CCC, CCA and CCG all four codons code for proline. Therefore, there are 61 codons for 20 amino acids.

4) Stop or termination or nonsense codons:- Three of the 64 possible nucleotide triplets UAA (amber), UAG (Ochre) and UGA (opal) do not code for any amino acid. They are called nonsense codons that normally signal termination of polypeptide chains. Thus, though there are 64 possible triplet codons, only 61 codes for 20 amino acids (as remaining three are non-sense codons).

5) Non overlapping and nonpuntate (Comma less) :- During translation, the code is read sequentially, without spacer bases, from a fixed starting point, as a continuous sequence of bases, taken 3 at a time, e.g. AUGCUA GACUUU is read as AUG/CUA/GAC/UUU without “ponctation” (coma) between codons.


Q. 15

Multiple codons code for same amino acid ‑

 A

Ambiguity

 B

Wobble phenomenon

 C

Degeneracy

 D

Mutation

Q. 15

Multiple codons code for same amino acid ‑

 A

Ambiguity

 B

Wobble phenomenon

 C

Degeneracy

 D

Mutation

Ans. C

Explanation:

Quiz In Between


Q. 16

RNA which contains codon for speicific amino acid ‑

 A

tRNA

 B

rRNA

 C

mRNA

 D

None

Q. 16

RNA which contains codon for speicific amino acid ‑

 A

tRNA

 B

rRNA

 C

mRNA

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., m RNA

The m RNA carries genetic information in the form of codons.

  • Codons are a group of three adjacent nucleotides that code for the amino acids of protein.
  • Each mRNA molecule is a transcript of antisense or template strand of a particular gene.
  • Its nucleotide sequence is complementary to that of antisense or template strand of the gene, i.e. adenine for thyamine, guanine for cytosine, uracil for adenine (as RNA does not contain thymine) and cytosine for guanine.
  • For example, if antisense strand of DNA has a gene with sequence 5′-TTACGTAC-3′, its complementary RNA transcript will be 5 ‘-GUACGUAA-3’.

Q. 17

Total mubers of codons are ‑

 A

60

 B

61

 C

62

 D

64

Q. 17

Total mubers of codons are ‑

 A

60

 B

61

 C

62

 D

64

Ans. D

Explanation:

Ans. is ‘d’ i.e., 64 

  • The information needed to direct the synthesis of protein is contained in the mRNA in the form of a genetic code, which inturn is transcribed from template strand of DNA and is therefore complementary to it.
  • The genetic code is the system of nucleotide sequences of mRNA that determines the sequence of amino acids in protein.
  • Codon is a sequence of three adjacent bases that corresponds to one amino acid.
  • There are 64 possible codom sequences.
  • Because four nucleotide bases A,G, C and U are used to produce the three base codons, there are therefore 64(43) possible codon sequences.

Q. 18

Which is non-sense codon –

 A

UGG

 B

AUG

 C

UGA

 D

CCA

Q. 18

Which is non-sense codon –

 A

UGG

 B

AUG

 C

UGA

 D

CCA

Ans. C

Explanation:

Ans. is ‘c’ i.e., UGA 

Stop codons or nonsense codons or termination codons

  • Three of the 64 possible nucleotide triplets UAA (amber), UAG (Ochre) and UGA (opal) do not code for any amino acid.
  • They are called nonsense codons that normally signal termination of polypeptide chains.
  • Thus, though there are 64 possible triplet codons, only 61 codes for 20 amino acids (as remaining three are non­sense codons).

Quiz In Between



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