NEET Biology Molecular Basis of Inheritance MCQs Set 28

Answer: (a) L-shaped

Explanation:
1. Cloverleaf is the two-dimensional shape of tRNA.
2. In three dimensions it folds into an L shape.
3. Hence option (a) is correct: L-shaped

Teacher's Note:
1. Remember clover leaf (2D) and L-shape (3D).

Answer: (d) tRNA

Explanation:
1. tRNA has a clover-leaf structure in two dimensions.
2. mRNA is linear and rRNA forms the ribosome.
3. Hence option (d) is correct: tRNA

Teacher's Note:
1. tRNA is the smallest RNA.
2. It has the anticodon and the amino acid attachment site.

Answer: (b) Reverse transcriptase

Explanation:
1. cDNA is made from mRNA by reverse transcriptase.
2. This enzyme is RNA-dependent DNA polymerase.
3. Hence option (b) is correct: Reverse transcriptase

Teacher's Note:
1. Reverse transcriptase is from retroviruses.
2. cDNA lacks introns.

Answer: (a) Transcription

Explanation:
1. The flow of information from DNA to RNA is transcription.
2. Translation then reads RNA to make protein.
3. Hence option (a) is correct: Transcription

Teacher's Note:
1. Central dogma: DNA to RNA to protein.

Answer: (d) tRNA

Explanation:
1. tRNA is also called soluble RNA (sRNA) because it dissolves in the cytoplasm.
2. hnRNA, rRNA and mRNA are not called soluble RNA.
3. Hence option (d) is correct: tRNA

Teacher's Note:
1. tRNA = adaptor RNA = soluble RNA.

Answer: (b) intron

Explanation:
1. An intron is a part of the gene that is transcribed but is removed from the mRNA and not translated.
2. Exons are translated.
3. Hence option (b) is correct: intron

Teacher's Note:
1. Introns are cut out during splicing.
2. Exons are expressed sequences.

Answer: (c) CAG. UCG. GAU

Explanation:
1. The non-template strand has the same sequence as the mRNA, with U in place of T.
2. CAG TCG GAT therefore gives CAG UCG GAU.
3. Hence option (c) is correct: CAG. UCG. GAU

Teacher's Note:
1. Coding strand = non-template strand.
2. mRNA is a copy of it with uracil.

Answer: (b) 7–methyl guanosine at 5' end and polyadenine bases at 3' end

Explanation:
1. Mature eukaryotic mRNA has a cap (methyl guanosine) at the 5' end and a poly-A tail at the 3' end.
2. Shine-Dalgarno sequence is found in prokaryotes.
3. Hence option (b) is correct: 7–methyl guanosine at 5' end and polyadenine bases at 3' end

Teacher's Note:
1. Capping and tailing are part of hnRNA processing.
2. Splicing removes the introns.

Answer: (b) DNA dependent RNA polymerase

Explanation:
1. Transcription is done by DNA-dependent RNA polymerase.
2. It makes RNA from a DNA template.
3. Hence option (b) is correct: DNA dependent RNA polymerase

Teacher's Note:
1. The enzyme reads DNA and builds RNA.
2. Primer is not needed.

Answer: (c) Splicing

Explanation:
1. Splicing removes introns and joins the exons together.
2. Capping and tailing add the 5' cap and the poly-A tail.
3. Hence option (c) is correct: Splicing

Teacher's Note:
1. Splicing happens in the nucleus.
2. The result is mature mRNA.

Answer: (a) 3-bases

Explanation:
1. A codon is a triplet of nucleotides, so it has 3 bases.
2. It codes for one amino acid.
3. Hence option (a) is correct: 3-bases

Teacher's Note:
1. Genetic code is triplet.
2. Gamow suggested this, and Crick proved it.

Answer: (d) M.W. Nirenberg

Explanation:
1. M. W. Nirenberg, with Khorana and others, deciphered the genetic code by using synthetic RNAs.
2. Watson and Crick gave the DNA model.
3. Hence option (d) is correct: M.W. Nirenberg

Teacher's Note:
1. Nirenberg used a cell-free system.
2. Khorana made RNA of known repeating sequences.

Answer: (c) Genetic code is triplet

Explanation:
1. There are 4 bases taken three at a time, so 4 x 4 x 4 = 64 codons.
2. This is because the code is a triplet.
3. Hence option (c) is correct: Genetic code is triplet

Teacher's Note:
1. Mathematically 4 cubed is 64.
2. Only 61 codons code for amino acids.

Answer: (a) AUG

Explanation:
1. AUG is the initiation codon.
2. UGA and UAG are stop codons.
3. Hence option (a) is correct: AUG

Teacher's Note:
1. AUG codes for methionine and starts translation.

Answer: (c) To terminate the message of a gene controlled protein synthesis-

Explanation:
1. Nonsense codons (UAA, UAG, UGA) do not code for any amino acid.
2. They stop the synthesis of a protein.
3. Hence option (c) is correct: To terminate the message of a gene controlled protein synthesis-

Teacher's Note:
1. Stop codons = termination codons.
2. No tRNA for them.

Answer: (d) Protein is formed fromRNA message

Explanation:
1. Translation is the synthesis of a protein (polypeptide) from the message of mRNA.
2. DNA to DNA is replication and DNA to RNA is transcription.
3. Hence option (d) is correct: Protein is formed fromRNA message

Teacher's Note:
1. Translation takes place on ribosomes.
2. tRNA brings the amino acids.

Answer: (c) A polypeptide of 24 amino acid is formed

Explanation:
1. A UAA codon at position 25 is a stop codon.
2. So the chain stops after the 24th amino acid, giving a polypeptide of 24 amino acids.
3. Hence option (c) is correct: A polypeptide of 24 amino acid is formed

Teacher's Note:
1. A stop codon in the middle makes a short protein.
2. This is a nonsense mutation.

Answer: (c) UUU

Explanation:
1. Nirenberg and Matthaei used poly-U in a cell-free system and got polyphenylalanine.
2. So the first codon deciphered was UUU.
3. Hence option (c) is correct: UUU

Teacher's Note:
1. UUU codes for phenylalanine.
2. Their work started the cracking of the code.

Answer: (a) Beadle and Tatum

Explanation:
1. Beadle and Tatum worked on Neurospora and proposed that one gene controls one enzyme.
2. Jacob and Monod worked on the lac operon.
3. Hence option (a) is correct: Beadle and Tatum

Teacher's Note:
1. Later it was changed to one gene - one polypeptide.

Answer: (c) UGU & GUG

Explanation:
1. Repeats UGU GUG UGU GUG gave alternate cysteine and valine.
2. The two codons are UGU for cysteine and GUG for valine.
3. Hence option (c) is correct: UGU & GUG

Teacher's Note:
1. Khorana used repeating copolymers.
2. Reading frame shows the alternate codons.

Answer: (b) Structural gene

Explanation:
1. A structural gene codes for a polypeptide.
2. The regulator, promoter and operator genes control it.
3. Hence option (b) is correct: Structural gene

Teacher's Note:
1. In the lac operon z, y and a are structural genes.