BIOL-UA 21 Lecture Notes - Lecture 6: Dna Ligase, Homologous Recombination, Okazaki Fragments

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copperclam97

18 Mar 2016

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(1) separation of strand of dna via helicase. Dna polymerase continuously synthesizes in direction of 3" 5" synthesizing a strand of dna that is 5" 3". Lagging strand: (in opposite direction of replication fork) Because dna can only be synthesized in 3" to 5" direction lagging strand is in the wrong direction, so polymerase has to synthesize in opposite direction. (1) enzyme primase has to synthesize a primer a short rna sequence in which dna is extended of of that (because dna can only synthesize at an existing 3" nucleotide but rna polymerase can synthesize) (2) discontinuous synthesis of dna via the primer creates okazaki fragments that are then fused together by the enzyme ligase. Dna ligase catalyzes formation of phosphodiester bond between. Other important enzymes: adjacent free 5" and 3" ends. Topoisomerase = relieves torsional stress from the helicase. Ribonuclease h & fen i = removes rna primers which are then replaced by polymerase beta.

Related Questions

Why does each replication fork require both leading and lagging strand synthesis?
Select the 2 reasons below.

A) Because DNA synthesis is semi-conservative.
B) Because DNA polymerases must synthesize DNA 3' to 5'.
C) Because the DNA templates are antiparellel.
D) Because DNA polymerase only synthesizes DNA in one direction.

I chose A and C but got it wrong.
Can anyone explain this?

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

During DNA replication, which of the following would you expectto be true?
True or False: and why.

1. More ligase would be associated with the lagging strand thanwith the leading strand.
2. More primase would be associated with the lagging strand thanwith the leading strand.
3. More helicase would be associated with the lagging strand thanwith the leading strand.
4. DNA ligase links the 3' end of one Okazaki fragment to the 5'end of another Okazaki fragment in the lagging strand.
5. In the lagging strand, the enzyme DNA polymerase III thatproduces the next Okazaki fragment also removes the short segmentof primer RNA on the previous Okazaki fragment.

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BIOL-UA 21 Lecture Notes - Lecture 6: Dna Ligase, Homologous Recombination, Okazaki Fragments

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