BIOSC 0160 Lecture Notes - Lecture 3: Dna Clamp, Okazaki Fragments, Dna Mismatch Repair

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5 Apr 2018

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Enzyme dna helicase uses e from atp hydrolysis to unwind and separate the strands and single-strand binding proteins bind to the unwound strands to keep them from reassociating into a double helix. Two template strands available for complementary base pairing. The two dna strands grow differently at the replication fork. The dna at the replication for opens up like a zipper in one direction. The 3" end template strand(leading strand) is able to have a 5" strand synthesized continuously. The 5" template strand (lagging strand) end synthesizes backwards, but the new strand can only synthesize to the point where the zipper closes again so it forms in okazaki fragments. Synthesis of the lagging strand requires the synthesis of relatively small, discontinuous stretches of dna (100-200 nucleotides in eukaryotes, 1000-2000 nucleotides in prokaryotes. Leading strand only needs one primer, but each okazaki fragment requires its own primer to be synthesized by the primase.

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1. During DNA replication, proteins unwind the DNA duplex, and separate the DNA strands. Those proteins include:

a.) DNA polymerase and ligase

b.) Single-stranded DNA binding and protein primase

c.) Helicase and DNA polymerase

d.) Helicase and single-stranded DNA binding protein

2. What determines the nucleotide sequence of the newly synthesized strand during DNA replication?

a.) The particular DNA polymerase catalyzing the reaction

b.) The relative amounts of the four nucleotide triphosphates (ATP, GTP, CTP, and TTP) in the cell

c.) The nucleotide sequence of the template strand

d.) The primase used in the reaction

e.) Both A and D

3. The leading and the lagging strands differ in that

a.) The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

b.) The leading strand is synthesized by adding nucleotides to the 3â hydroxyl (OH) end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5â phosphate (PO4) end.

c.) The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short fragments that are ultimately stitched together.

d.) Both A and B

e.) Both A and C

1) What is the difference between the leading strand and the lagging strand in DNA replication? Place the following steps of DNA replication in right chronological order.

1. Primase adds an ribonucleotide primer
2. Initiator proteins bind the origin of replication and helicase breaks hydrogen bonds between complementary bases of double stranded template DNA
3. DNA polymerase III extends by complementary base pairing deoxyribonucleotides to the template strands
4. Ligase phosphodiester bonds the nucleotides to connect okazaki fragments nad connect fragments at the origin and where the "crotches or forks" collide
5. DNA polymerase I removes RNA primer and replaces with Deoxyribonucleotides

2) Given the template DNA and primer sequences below, what bases will be added to the primer as DNA replication proceeds? (The bases should appear in the order that they will be added)

5'-GTCGTCTCCCTTTTTAAAAACCCCCCC-3'
5'-UUUUUAAAAAGGG-3'

3) Given the DNA sequence below, what could be a primer sequence used in its replication?
5'-CGTACGGCCCCAAAATTGCTACTCTGCTG-3'

raspberryleopard304

Order the following steps of the DNA replication process fromfirst to last. (From 1 to 8)

DNA ligase joins Okazaki fragmments together

Elongation of leading strands occurs continuosly and elongationof lagging strands occurs via generation of Okazaki fragments. Bothare synthesized in 5' to 3' direction.

DNA polymerase I removes the RNA primers and replaces them withDNA nucleotides

DNA polymerase III starts adding DNA nucleotides to the 3' endof the existing RNA chain.

Helicase untwists the double helix at the replication fork

Single-stranded binding proteins bind the unpaired DNA strands,keeping them from re-pairing.

Topoisomerase helps releive the strain caused by DNA untwisting.It breaks, swivels and rejoins DNA strands.

Primase starts a complementary RNA chain using parental DNAstrand as a template

lilacgoose192

BIOSC 0160 Lecture Notes - Lecture 3: Dna Clamp, Okazaki Fragments, Dna Mismatch Repair

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