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Cell and molecular biology > Week 8 : DNA replicatio > Flashcards

Week 8 : DNA replicatio Flashcards

1
Q

cell spends most of its life in what phase ?

A

S phase of interphase

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2
Q

DNA replication is semi-conservative . what does that mean?

A

it means that each strand of DNA will be used as a template during replication

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3
Q

what are the steps of DNA replication ?

A
  1. ) identification of origin of replication
  2. )unwinding of double stranded DNA to provide a single stranded template
  3. )formation of replication fork
  4. )initiation of DNA synthesis and elongation
  5. )primer removal and ligation of the newly synthesized DNA segments
  6. )reconstruction of chromatin structure
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4
Q

what is the origin of replication ?

A

specific sequence ( rich in A-T) in a genome at which specific protein called initiator proteins bind and replication is initiated

there are multiple origins of replication in eukaryotic cells but only 1 origin in prokaryotic cells

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5
Q

why is the origin of replication rich in A-T ?

A

because adenine and thymine have 2 hydrogen bonds , meaning they will sperate more readily to give the replication mechanism the space to move in and start working

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6
Q

how is the replication fork formed ?

A

interaction of initiator protein and origin of replication provides short region of single stranded DNA . helicase then allows for the unwinding of DNA.

Single stranded DNA binding proteins prevent the strands from coming back together and stabilizes the replication fork complex.

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7
Q

DNA replication consists of 3 stages , what are they?

A

initiation :activation of origin of replication in order to create 2 replication forks
. it begins at the origin of replication when initiator proteins bind to them . helicase then promotes unwinding and single stranded DNA binding proteins stabilize the structure

is preparing for elongation by formation of primers which are short sequences of RNA to bind with DNA( formed by RNA primase

elongation :

termination

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8
Q

what direction does DNA polymerase synthesize DNA?

A

5’ TO 3 Direction (new strand starts from 5 to 3) because the DNA strands are antiparallel , the polymerase functions asymmetrically

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9
Q

how is DNA synthesis different in the leading strand when compared with the lagging strand ?

A

on the leading strand it is synthesized continuously while on the lagging strand it is synthesized in short segments called Okazaki fragments

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10
Q

What are primers removed by ?

A

DNA polymerase I by replacing ribonucleotides with deoxyribonucleotides

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11
Q

what are nicks sealed by?

A

ligase

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12
Q

how many primers are on the leading and lagging strands ?

A

the leading strand only has 1 primer while the lagging strand has many

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13
Q

what is the last portion of the lagging strand ?

A

telomere section that consists of repeating non coded sequence of bases

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14
Q

What structure is responsible for proofreading and correction

A

DNA polymerase 1 in eukaryotes

DNA polymerase 1 , 2 , and 3 in prokaryotes

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15
Q

what is the main function of DNA polymerase?

A

adds deoxynucleotide polymerization

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16
Q

what is the main function of helicase?

A

unwinding of DNA

17
Q

what is the main function of topoisomerase ?

A

relieves torsional strain that results from helicase unwinding

18
Q

what is the main function of RNA primase ?

A

initiates synthesis of RNA primers

19
Q

what structure is responsible for prevention of reannealing of ds DNA ?

A

Single stranded binding proteins

20
Q

what is the function of DNA ligase ?

A

seals the single strand nick between the nascent chain and Okazaki fragments on lagging strand

21
Q

what are the features of DNA replication ?

A

it is semi-conservative : when DNA unwinds , each stand acts as a template for new DNA . meaning each new strand has 1 strand from the parental DNA

it is bidirectional :when the DNA is opened at the origin of replication , 2 replication forks moving in opposite directions are formed .

and it is semi continuous: daughter strands are synthesized different because DNA is always synthesized from 5 end to 3 end , this creates leading and lagging strand

Cell and molecular biology (8 decks)

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