All Free Biology MCQs with Answers

831. The enzyme that unwinds DNA during replication is

• A. DNA polymerase
• B. Helicase
• C. Ligase
• D. Primase

Explanation: Helicase breaks hydrogen bonds between base pairs, unwinding the DNA double helix.

832. Okazaki fragments are formed on the

• A. Leading strand
• B. Lagging strand
• C. Both strands equally
• D. Neither strand

Explanation: The lagging strand is synthesized discontinuously as Okazaki fragments because DNA polymerase only works 5'→3'.

833. Transcription produces

• A. A DNA copy of DNA
• B. An RNA copy of DNA
• C. A protein from DNA
• D. A DNA copy of RNA

Explanation: Transcription is the synthesis of RNA using DNA as a template, catalyzed by RNA polymerase.

834. The start codon is

• A. UAA
• B. AUG
• C. UAG
• D. UGA

Explanation: AUG codes for methionine and serves as the start codon, initiating protein synthesis.

835. Introns are

• A. Coding sequences
• B. Non-coding sequences removed during splicing
• C. Found only in prokaryotes
• D. Essential for translation

Explanation: Introns are non-coding intervening sequences removed during RNA splicing; exons are joined together.

836. Which is a stop codon?

• A. AUG
• B. UAA
• C. UUU
• D. GGC

Explanation: UAA, UAG, and UGA are stop codons (nonsense codons) that terminate translation.

837. The genetic code is

• A. Overlapping
• B. Non-overlapping and degenerate
• C. Ambiguous
• D. Different for each organism

Explanation: The genetic code is non-overlapping, degenerate (multiple codons for one amino acid), and universal.

838. Reverse transcriptase is found in

• A. All bacteria
• B. Retroviruses
• C. All eukaryotes
• D. Plants only

Explanation: Reverse transcriptase synthesizes DNA from an RNA template, found in retroviruses like HIV.

839. Restriction enzymes cut DNA at

• A. Random sites
• B. Specific recognition sequences
• C. Only ends
• D. Only bacterial DNA

Explanation: Restriction endonucleases recognize and cut at specific palindromic DNA sequences.

840. PCR is used to

• A. Cut DNA
• B. Amplify DNA
• C. Sequence DNA
• D. Translate DNA

Explanation: Polymerase Chain Reaction (PCR) amplifies specific DNA sequences exponentially.