Question

b.cancer cells invade surrounding tissues -...posis 18. What is the function of DNA primase in DNA replication in prokaryotes? A.make the RNA part of the chromosome B.maintain DNA in a single stranded state before replication C.synthesize a free 3' OH for DNA polymerase to use D. break the hydrogen bonds between complementary strands E.alleviate supercoiling ahead of the replication fork 19. If crossing over occurs between the short arms of the X and Y chromosomes, inserting the SRY gene into the X chromosome, the result is a) XX males c) Both XX males and XY females d)XX females and XY males with fertility issues b) XY females 20. A researcher is attempting to replicate DNA in vitro. He adds all of the components to the tube except Mg2+. What kind of result can he expect to observe? A. The DNA will replicate at a normal rate B. The DNA will replicate but at a much slower rate 2 C. The DNA will not replicate because DNA polymerase will not be active D.The DNA will not replicate because DNA polymerase was not added

Answer 1

18) Option C is the right answer i.e synthesize a free 3^'OH for DNA polymerase to use because DNA primase help in the formation of RNA primer. RNA primer is a small strand of RNA which is synthesized at the 5^' end of new DNA strand. Formation of RNA primer constitute the initiation phase of DNA synthesis because without the presense of RNA primer ,DNA polymerase cannot add nucleotides .

19) If SRY gene is inserted in to the X chromosome then both XX males and XYfemales can be produced (i.e OPTION C) because in XX male syndrome , the person has female chromosomes but male physical features.the majority of persons with male XX syndrome have Y chromosome gene SRY attached to one of their x chromosomes. Moreover these people inherit one normal X chromosome from mother and one defective X chromosome from father.

• any type of mutations in the SRY gene give rise to XY females with gonadal dysgenesis who appears to be normal females at birth,but at puberty do not develop secondary sexual characteristics.

20) In the absense of Mg2+ ions ,DNA will replicate but at much slower rate because Mg2+ increases the fidelity of DNA replication means it helps in recognizing the right nucleotide from the nucleotide pool. It also makes the DNA more active.