৪৯তম বিসিএস ⎯ প্রাণ রসায়ন [৬০১]

Answer: B) Semi-conservative
Explanation:
Each daughter DNA molecule contains one original parental strand and one newly synthesized strand, as proven by the Meselson-Stahl experiment.

Answer: B) Primase
Explanation:
Primase, a type of RNA polymerase, synthesizes short RNA primers to initiate DNA replication.

Answer: A) 3’ → 5’ exonuclease activity of DNA polymerase
Explanation:
DNA polymerase removes incorrectly paired nucleotides using its 3’ → 5’ exonuclease activity.

Answer: B) 7-methylguanosine cap
Explanation:
The 5’ cap protects mRNA from degradation and aids ribosome binding.

Answer: B) Sense strand
Explanation:
The sense strand has the same sequence as the mRNA (except for thymine replaced by uracil).

Answer: B) Transcription initiation
Explanation:
Sigma factors help RNA polymerase recognize promoter sequences.

Answer: B) Amino acid
Explanation:
The 3’ end of tRNA has a CCA sequence where an amino acid attaches.

Answer: A) Peptidyl transfer
Explanation:
The P site holds the tRNA carrying the growing polypeptide chain.

Answer: B) Peptidyl transferase
Explanation:
Peptidyl transferase, part of the large ribosomal subunit, catalyzes peptide bond formation.

Answer: B) Prokaryotic mRNA
Explanation:
It helps align the ribosome with the start codon in prokaryotes.

Answer: B) 5’ cap
Explanation:
The 5’ cap guides the ribosome to the start site.

Answer: B) Flexibility in codon-anticodon pairing
Explanation:
The wobble position allows one tRNA to recognize multiple codons.

Answer: C) Change in one amino acid
Explanation:
Missense mutations alter a single amino acid, possibly affecting protein function.

Answer: B) DNA
Explanation:
Southern blot is for detecting specific DNA sequences.

Answer: C) Proteins
Explanation:
Western blot uses antibodies to identify specific proteins.

Answer: C) Antibodies
Explanation:
Specific antibodies bind proteins, allowing detection.

Answer: C) Denaturation
Explanation:
High temperature separates DNA strands for amplification.

Answer: C) Nonsense mutation
Explanation:
It introduces a premature stop codon, truncating the protein.

Answer: B) Size and charge
Explanation:
Smaller molecules migrate faster through the gel matrix.

Answer: D) All of the above
Explanation:
All listed factors can cause mutations.

Answer: B) Exponential
Explanation:
Each cycle doubles the DNA, leading to exponential growth.

Answer: B) Transferring nucleic acids or proteins
Explanation:
Nitrocellulose acts as a solid support in blotting techniques.

Answer: A) DNA staining in gels
Explanation:
Ethidium bromide binds DNA and fluoresces under UV light.

Answer: B) Type of molecule analyzed
Explanation:
Southern = DNA, Northern = RNA.

Answer: B) Size standard for comparison
Explanation:
It helps determine the size of unknown fragments.

Answer: B) Do not change the amino acid sequence
Explanation:
Due to code redundancy, a different codon may specify the same amino acid.

Answer: B) dideoxynucleotides
Explanation:
Dideoxynucleotides terminate chain elongation for sequencing.

Answer: B) Stop codons
Explanation:
These are termination signals in translation.

Answer: C) rRNA and proteins
Explanation:
Ribosomes consist of rRNA and protein subunits.

Answer: B) DNA denaturation
Explanation:
The template DNA must be single-stranded before sequencing.

Answer: B) 70S with 50S and 30S subunits
Explanation:
Prokaryotic ribosomes are 70S, composed of 50S and 30S.

Answer: C) AUG
Explanation:
AUG codes for methionine and signals translation initiation.

Answer: C) tRNA
Explanation:
tRNA carries specific amino acids to the ribosome.

Answer: B) RNA analysis
Explanation:

Northern blot detects and studies RNA molecules.

Answer: C) Taq polymerase
Explanation:
Taq polymerase is heat-resistant, ideal for repeated heating cycles in PCR.

Answer: D) Far-Western blot
Explanation:
Far-Western blot is specifically designed to study protein-protein interactions.

Answer: B) Promoter region
Explanation:
The TATA box is a promoter sequence where transcription factors and RNA polymerase bind.

Answer: B) Terminator
Explanation:
The terminator sequence halts transcription.

Answer: B) Nucleus in eukaryotes, cytoplasm in prokaryotes
Explanation:
In eukaryotes, transcription happens in the nucleus, while prokaryotes lack nuclei.

Answer: B) 3’ end of mRNA
Explanation:
The poly-A tail increases mRNA stability and facilitates export from the nucleus.

Answer: C) Helicase
Explanation:
Helicase unwinds DNA by breaking hydrogen bonds, creating a replication fork.

Answer: B) Seal nicks between Okazaki fragments
Explanation:
DNA ligase forms phosphodiester bonds, joining discontinuous DNA fragments.

Answer: C) S phase
Explanation:
DNA replication occurs during the S (synthesis) phase of the cell cycle.

Answer: C) Single-strand binding proteins (SSB)
Explanation:
SSB proteins prevent re-annealing of DNA during replication.

Answer: A) DNA polymerase I
Explanation:
DNA polymerase I has 5’ → 3’ exonuclease activity that removes RNA primers and replaces them with DNA.

Answer: B) Topoisomerases
Explanation:
DNA gyrase, a topoisomerase, relieves supercoiling during replication.

Answer: C) DNA polymerase III
Explanation:
DNA polymerase III performs the bulk of DNA chain elongation in prokaryotes.

Answer: B) Lagging strand
Explanation:
The lagging strand is synthesized discontinuously, forming Okazaki fragments that are later joined by ligase.

Answer: B) Cloverleaf
Explanation:
tRNA has a cloverleaf structure with acceptor, anticodon, and D and TΨC loops.

Answer: B) Nucleolus
Explanation:
rRNA synthesis occurs in the nucleolus of eukaryotic cells.