Part 6: Genetic Code & Translation (25 MCQs)
Part 6: Genetic Code & Translation (25 MCQs)
Q126. The term “genetic code” refers to:
a) Rules by which DNA replicates
b) Rules by which nucleotide sequence codes for amino acids
c) Rules of transcription
d) Ribosome binding sites
Answer: b
- b) Correct: Genetic code = triplet of nucleotides specifying amino acids.
- a, c, d) Not complete definition.
Q127. Genetic code is written in terms of:
a) DNA triplets
b) RNA codons
c) Amino acids
d) tRNA
Answer: b
- b) Correct: Genetic code is expressed in mRNA codons.
Q128. The genetic code is:
a) Non-overlapping and comma-less
b) Overlapping and comma-full
c) Ambiguous
d) Random
Answer: a
- a) Correct: Code is non-overlapping, comma-less, unambiguous.
Q129. How many codons exist in total?
a) 16
b) 20
c) 64
d) 128
Answer: c
- c) Correct: 4³ = 64 possible codons.
Q130. Out of 64 codons, how many code for amino acids?
a) 20
b) 61
c) 64
d) 3
Answer: b
- b) Correct: 61 codons code for amino acids, 3 are stop codons.
Q131. The codon AUG functions as:
a) Stop codon
b) Start codon and methionine codon
c) Lysine codon
d) Leucine codon
Answer: b
- b) Correct: AUG = initiation codon + codes methionine.
Q132. The stop codons are:
a) UAA, UAG, UGA
b) AUG, UAA, UGA
c) UAG, UGG, UAA
d) UAA, AAA, UUU
Answer: a
- a) Correct: Stop codons = UAA, UAG, UGA.
Q133. Which codon is called amber stop codon?
a) UAG
b) UAA
c) UGA
d) AUG
Answer: a
- a) Correct: UAG = amber stop codon.
- b) UAA = ochre.
- c) UGA = opal.
Q134. The degeneracy of genetic code means:
a) Each codon codes multiple amino acids
b) Multiple codons can code for same amino acid
c) Stop codons overlap
d) RNA is unstable
Answer: b
- b) Correct: Degenerate code → redundancy (e.g., Leucine has 6 codons).
Q135. Wobble hypothesis explains:
a) Accuracy of DNA replication
b) Multiple codons coding same amino acid
c) Flexibility in pairing of 3rd codon base
d) Codon overlap
Answer: c
- c) Correct: Wobble hypothesis → flexibility at 3′ codon (3rd base) allows degeneracy.
Q136. The genetic code is universal, except in:
a) Humans
b) Mitochondria and some protozoa
c) Bacteria
d) Plants
Answer: b
- b) Correct: Minor variations exist in mitochondria & protozoa.
Q137. Which amino acid is coded by UUU?
a) Leucine
b) Phenylalanine
c) Lysine
d) Proline
Answer: b
- b) Correct: UUU = phenylalanine.
Q138. Which amino acid is coded by UGG?
a) Tryptophan
b) Glycine
c) Tyrosine
d) Serine
Answer: a
- a) Correct: UGG = tryptophan (unique single codon).
Q139. The adaptor molecule in translation is:
a) mRNA
b) rRNA
c) tRNA
d) snRNA
Answer: c
- c) Correct: tRNA (discovered by Francis Crick as adaptor molecule).
Q140. The anticodon loop is present in:
a) mRNA
b) tRNA
c) rRNA
d) hnRNA
Answer: b
- b) Correct: Anticodon loop in tRNA pairs with mRNA codon.
Q141. The 3′ end of tRNA carries:
a) Anticodon
b) Amino acid attachment site (CCA)
c) Ribosome binding site
d) Promoter
Answer: b
- b) Correct: tRNA 3′ end has CCA sequence → amino acid attachment site.
Q142. The ribosome has two main subunits made of:
a) DNA and RNA
b) Proteins and rRNA
c) DNA and proteins
d) RNA only
Answer: b
- b) Correct: Ribosome = rRNA + proteins.
Q143. In prokaryotes, ribosome size is:
a) 70S (50S + 30S)
b) 80S (60S + 40S)
c) 60S only
d) 30S only
Answer: a
- a) Correct: Prokaryotic ribosome = 70S (50S large, 30S small).
Q144. In eukaryotes, ribosome size is:
a) 70S
b) 80S (60S + 40S)
c) 90S
d) 100S
Answer: b
- b) Correct: Eukaryotic ribosome = 80S (60S + 40S).
Q145. Which site of ribosome accepts incoming tRNA with amino acid?
a) P-site
b) A-site
c) E-site
d) None
Answer: b
- b) Correct: A-site (aminoacyl site) accepts new tRNA.
Q146. The site where growing polypeptide chain is formed is:
a) P-site
b) A-site
c) E-site
d) All sites
Answer: a
- a) Correct: P-site (peptidyl site) holds growing chain.
Q147. The exit site of ribosome for tRNA is:
a) A-site
b) P-site
c) E-site
d) G-site
Answer: c
- c) Correct: E-site = exit site for tRNA.
Q148. Peptidyl transferase enzyme is a function of:
a) Ribosomal protein
b) rRNA in large subunit
c) mRNA
d) DNA
Answer: b
- b) Correct: Peptidyl transferase is catalytic rRNA (ribozyme) in ribosome.
Q149. Translation ends when ribosome encounters:
a) Start codon
b) Stop codon
c) Promoter
d) Enhancer
Answer: b
- b) Correct: Stop codons (UAA, UAG, UGA) end translation.
Q150. Which statement is true for translation?
a) It occurs in the nucleus only
b) It occurs on ribosomes in cytoplasm
c) DNA is directly translated
d) tRNA carries codons
Answer: b
- b) Correct: Translation = cytoplasmic ribosomes synthesize proteins.
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