The primase enzyme synthesizes a short stretch of RNA complementary to a part of

Question

The primase enzyme synthesizes a short stretch of RNA complementary to a part of the template DNA strand. synthesizes a short stretch of DNA that is complementary to a part of the template strand of DNA. acts as the recognition site to which DNA polymerases bind to start the replication process. replaces the RNA primers used to initiate DNA replication with DNA polymerase. ligates the nicks formed by discontinuous replication along the lagging strand. During the replication of prokaryotic DNA, both strands are simultaneously synthesized in a continuous manner. one strand is synthesized in a continuous manner and the other is synthesized by reverse transcription. both stands are simultaneously synthesized in short pieces which are later joined by DNA ligase. one strand is synthesized continuously and the other is synthesized in short segments. both strands are synthesized continuously, but the lagging strand is synthesized only after the leading strand has been completely replicated. Recombination of DNA is important in many biochemical processes. Which of the following is NOT among these processes? generation of genetic diversity integration of viral DNA into a host cell repair of damaged DNA generation of genetic knockout animal models generation of antibody diversity
The primase enzyme synthesizes a short stretch of RNA complementary to a part of the template DNA strand. synthesizes a short stretch of DNA that is complementary to a part of the template strand of DNA. acts as the recognition site to which DNA polymerases bind to start the replication process. replaces the RNA primers used to initiate DNA replication with DNA polymerase. ligates the nicks formed by discontinuous replication along the lagging strand.

Explanation / Answer

Ans. #1. Correct option- a.

DNA primase or simply primase, (a DNA dependent RNA polymerase) bind to both single strands of separated dsDNA (both strands serve as template) and synthesizes a short length RNA oligonucleotide (RNA primer) onto each strand in 5’?3’ direction.

#2. Correct option- D. One strand is synthesized continuously and the other is synthesized in short fragment (Okazaki fragment).

Since the two parental strands run antiparallel, the direction of replication on the two strands run opposite to each other.

# The DNA pol III holoenzyme progresses in 3’-5’ direction (thus, DNA synthesis occurs in complementary 5’-3’ direction) of the parental template leading strand. The replication machinery adds several thousands of bases onto the elongating of the leading daughter stand every time it’s loaded onto the leading template strand. Thus, replication on the leading strand is said to be CONTINUOUS.

# The DNA pol III also shall progress on template lagging strands in 3’-5’ direction, however, since the lagging strand runs antiparallel to the leading strand, the direction of its replication seems to be away from the 3’-end of the template strand because of its looping back. The DNA synthesis on lagging strand occurs relatively in short stretches (Okazaki fragment), and the replication machinery need to be dislodged from the lagging template strand more frequently (thus stopping replication temporarily), and then to be reloaded (to resume replication). Therefore, the synthesis of lagging strand is said to be DIS-CONTINUOUS.

# Option- A. Incorrect. Continuous and discontinuous manner. See #D above.

# Option- B. Incorrect. Reverse transcription is the synthesis of DNA from an RNA template. During replication DNA is synthesized from a DNA template.

# Option- C. Incorrect. Continuous and discontinuous manner. See #D above.

# Option- E. Incorrect. Both strands are synthesized simultaneously – but one in continuous manner while the other in discontinuous manner.

#3. Recombination of DNA is insertion (RDT, transduction) or exchange of DNA segments (during crossing over in prophase I of meiosis).

#Option- A. True. Genetic recombination or Crossing-over during meiosis increases the genetic diversity.

Option B- True. Integration of viral genome (in full or part) into a host cell genome is called transduction. It is also a natural method of recombination between virus and cellular organisms.

# Option- C. True. Recombination also facilitates DNA repair.

# Option- E. True. Recombination increases antibody diversity by shuffling the stretches of DNA segments within the gene.

# Option- D. NOT true. Generation of knock out animal models involves REMOVAL of one or more specified genes from the animals. Removal/loss of genes from an organism’s genome is NOT a recombination process.

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