DNA Replication Exercise B: DNA Replication (con\'t) DNA prior to replication Pr
ID: 194428 • Letter: D
Question
DNA Replication Exercise B: DNA Replication (con't) DNA prior to replication Prior to replication, DNA is a double stranded helix with complementary base pairing. In order to achieve complementary base pairing, the two strands of DNA are antiparalWlel or line up in opposite directions (Fig 4). On one strand the phosphate group is on one end of Cytosine -5SBP Adenine -Helicase . Thymine DNA Polymerase ll . Deoayribose + Primase 1-Guanine.DNA Polymerase I the DNA backbone while the deoxyribose is at the opposite end. In the second strand, phosphate is on the Uracil end in which the deoxyribose of the first strand is -uracil .. DNA Polymerase lll located, while the deoxyribose end of the second strand -Ribose A-Ligase is adjacent to the first strand's phosphate end. The O- PhosphateTelomerase phosphate end of a DNA strand is called the S' end of the DNA backbone, while the deoxyribose end is the 3 end 9 Fig. 4. DNA prior to replication. 2 In Fig. 4, label the 3' and 5' ends of both DNA strands prior to DNA replication. Initiation of replication The replication bubble begins with the enzyme, helicase, breaking the hydrogen bonds between nitrogenous bases of the two parental DNA strands (Fig. 5). In order to prevent the hydrogen bonds from reforming, single-strand DNA-binding proteins (SsBPs) attach to the separated DNA strands (Fig. 6). The breaking of the parental DNA's hydrogen bonds causes the double helix to relax, creating tension further down the molecule. Another enzyme, topoisomerase, cuts the covalent bonds (phosphodiester linkages) of the double helix further downstream of the replication bubble and immediately reattaches them, relieving the tension /g Identify the function of helicase ($). Fig-5. Initiation of replication, part 1. www.thebiologyprimer.comExplanation / Answer
Q. 1 In a DNA molecule 5' end has phosphate group however 3' end is labelled with -OH group.
Therefore in the double helix shown (fig. 4) the top strand has 3' labelled at the left and 5' at the right. In the bottom strand 5' end is at the left and 3' is labelled at the right beause DNA is antiparallel.
Q.2 Function of helicase
Helicase enzyme breaks the hydrogen bonds between the two nitrogenous bases in a DNA strand and helps in opening up the double helix.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.