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 antiparallel, or line up in opposite directions (Fig. 4). On one strand the phosphate group is on one end of the DNA backbone while the deoxyribose is at the opposite end. In the second strand, phosphate is on the end in which the deoxyribose of the first strand is located, while the deoxyribose end of the second strand is adjacent to the first strand’s phosphate end. The phosphate end of a DNA strand is called the 5’ end of the DNA backbone, while the deoxyribose end is the 3’ end. KEY Cytosine - SSBP Adenine - Helicase Guanine - DNA Polymerase I Thymine - DNA Polymerase II Uracil - DNA Polymerase III Deoxyribose - Primase Ribose - Ligase Phosphate - Telomerase Fig. 4. DNA prior to replication. 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. Identify the function of helicase. Fig. 5. Initiation of replication, part 1.

          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 antiparallel, or line up in opposite directions (Fig. 4). On one strand the phosphate group is on one end of the DNA backbone while the deoxyribose is at the opposite end. In the second strand, phosphate is on the end in which the deoxyribose of the first strand is located, while the deoxyribose end of the second strand is adjacent to the first strand’s phosphate end. The phosphate end of a DNA strand is called the 5’ end of the DNA backbone, while the deoxyribose end is the 3’ end.
KEY
Cytosine - SSBP
Adenine - Helicase
Guanine - DNA Polymerase I
Thymine - DNA Polymerase II
Uracil - DNA Polymerase III
Deoxyribose - Primase
Ribose - Ligase
Phosphate - Telomerase
Fig. 4. DNA prior to replication.
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.
Identify the function of helicase.
Fig. 5. Initiation of replication, part 1.

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 antiparallel, or line up in opposite directions (Fig. 4). On one strand the phosphate group is on one end of the DNA backbone while the deoxyribose is at the opposite end. In the second strand, phosphate is on the end in which the deoxyribose of the first strand is located, while the deoxyribose end of the second strand is adjacent to the first strand’s phosphate end. The phosphate end of a DNA strand is called the 5’ end of the DNA backbone, while the deoxyribose end is the 3’ end.
KEY
Cytosine - SSBP
Adenine - Helicase
Guanine - DNA Polymerase I
Thymine - DNA Polymerase II
Uracil - DNA Polymerase III
Deoxyribose - Primase
Ribose - Ligase
Phosphate - Telomerase
Fig. 4. DNA prior to replication.
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.
Identify the function of helicase.
Fig. 5. Initiation of replication, part 1.

Added by Charles M.

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