Question

Which of the following is an accurate statement regarding the relationship between primers and nucleic acid synthesis?

		During DNA replication, primers are used to initiate DNA synthesis, and these primers are incorporated into the final daughter strand products.
		During DNA replication, leading strands are synthesized by DNA polymerase III without utilizing a primer.
		During DNA replication, every Okazaki fragment synthesized by DNA polymerase III is elongated from a separate RNA primer.
		Primase catalyzes the de novo polymerization of DNA.

Which of the following best describes the TATA box?

		It is a sequence in the promoter region of genes that marks transcription start sites.
		It is a sequence in chromosomes that marks replication origins.
		It is a sequence in primary transcripts that marks cleavage and polyadenylation sites.
		It is a sequence in mRNAs that marks translation start sites.

Answer 1

Answer [Q-1]: During DNA replication, every Okazaki fragment synthesized by DNA polymerase III is elongated from a separate RNA primer.

Explanation: DNA replication is a process producing two daughter DNA from one parent DNA. There are two strands of DNA having opposite directionality and the DNA synthesis goes from 5' to 3' that is the leading strand.

- So Okazaki fragment is the one which are synthesized in the lagging strand (3' to 5'). When Okazaki fragments are synthesized by DNA poly III, they are elongated from the short separate RNA primers which are synthesized by enzyme primase.

- At the final product RNA primers are removed, DNA ligase ligates the rest sequence and forms a new DNA sequence from the lagging strand.

- This shows the accurate relationship between the two.

Incorrect Answer:

Option A: Though primers are used to indicate DNA synthesis but they are not present in the final daughter strand products. They are replaced by DNA nucleotides.

Option B: Leading strand is synthesized by DNA polymerase III with utilizing a whole long RNA primer.

Option D: Primase does perform de novo and provides a 3'-OH group for the DNA nucleotides to be added. But it does not show accurate relationship between primer and nucleic acid synthesis.

Answer [Q-2]: It is a sequence in the promoter region of genes that marks transcription start sites

Explanation: TATA box is a regulatory DNA sequence which is a part of the promoter sequence. It tells the transcription molecules from where the transcription begins by providing a signaling sequence (TATAAA).

Incorrect Answers:

Option B: Marking of replication origin is done by OriC. It is a region from where DNA replication starts.

Option C: Regulatory sequence that has polyadenylation signal sequence (AAUAAA) marks the cleavage site. This cleavage process is followed by addition of poly-A tail (AAAAAAA).

Option D: Start codon(AUG) is the one which marks the translation start sites.