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Genetics > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

Replication has to be extremely accurate.

A

– Human zygote – contains 6.4 billion bp of DNA
– One error/million bp leads to 6400 mistakes every
time a cell divides, which would be catastrophic.

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2
Q

Replication also takes place at high speed.

A

– E. coli replicates its DNA at a rate of 1000
nucleotides/second.
– Human DNA - 50 nucleotides/second

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3
Q

Conservative replication model

A

Entirely new template

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4
Q

Dispersive replication model

A

Little pieces both broke down into fragments

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5
Q

Semiconservative replication model

A

Strands separate and new strand Synthesis

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6
Q

semiconservative replication depends on

A

Circular vs. linear DNA

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7
Q

replicon

A

A segment of DNA that undergoes replication

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8
Q

Origin of replication

A

What each replicon has

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9
Q

Bacteria VS. Eukaryote origin of replication

A

Bacteria: 1
Eukaryotes-many

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10
Q

Theta replication

A

common mode of replication in circular DNA

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11
Q

Rolling-circle replication

A

takes place in some viruses and in the F factor of E. Coli

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12
Q

conclusion of rolling-circle

A

multiple circular DNA molecules

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13
Q

Linear Eukaryotic Replication

A

Slower than bacteria
Too much DNA for single origin

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14
Q

Linear eukaryotic replication requirements

A

A template strand consisting of single stranded DNA

Raw material: Nucleotides

Enzymes and other proteins that read the template and assemble the substrate into A DNA molecule

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15
Q

Direction of replication

A

DNA polymerase adds nucleotides only to 3’ end of growing strand

Anti parallel nature of the double stranded DNA means
- one template is exposed in the 5’ to 3’ direction
vise versa

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16
Q

Continuous replication

A

occurring on the leading strand

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17
Q

Dissentious replication

A

Occurs on lagging strand

Synthesis is proceeding in the direction of the unwinding

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18
Q

Discontinuous replication is a result of Which property of DNA?

A

Anti Parallel nucleotide Strands

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19
Q

Replication taxes place in four stages

A
  1. Initiation
  2. unwinding
    3.Elongation
  3. Termination
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20
Q

Bacterial DNA Replication: Initiation

A

single origin of replication
(oriC)

  • Initiator proteins bind and
    cause short section of DNA to
    unwind, allowing other single-strand-binding proteins to
    attach to the polynucleotide
    strand
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21
Q

Bacterial DNA Replication: Unwinding

A

The cell relies on several proteins and enzymes for unwinding

DNA helicase

Single-strand-binding proteins (SSBs)

DNA gyrase

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22
Q

Single-strand-binding proteins (SSBs)

A
  • – attach to the exposed
    single-stranded DNA after helicase unwinds DNA and prevent unnecessary binding and hairpins
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23
Q

DNA helicase

A

– breaks hydrogen bonds between strands, taking between nucleotides and breaking them

24
Q

DNA gyrase

A

– a type II topoisomerase that reduces strain
ahead of the replication fork by making double-strand breaks
and then resealing the broken ends of DNA

relieves the tension

25
Bacterial DNA Replication: Elongation
Single-stranded DNA is used as a template for the synthesis of DNA! DNA Polymerase Primase
26
DNA Polymerase
– enzymes which elongate the new polynucleotide strand. All DNA polymerases require a nucleotide with a 3’-OH group in order to add the new nucleotides. So, it needs primase to synthesize short stretches of RNA nucleotides (primers).
27
Primase
– enzyme responsible for synthesizing short stretches (~10-12) of RNA nucleotides (termed primers) which provide the needed 3’-OH group for DNA polymerase to attach DNA nucleotide!
28
DNA Polymerase III
duplication of the chromosomal DNA
29
DNA Polymerase I
DNA polymerase I functions to fill DNA gaps that arise during DNA replication, repair, and recombination
30
5' to 3' polymerase activity
each polymerase can do the following P1: Removes and replaces primers P2:DNA repair; restarts replication DNA halts synthesis P3:Elongates DNA P4:DNA repair P5:DNA repair; translesion DNA synthesi
31
3' to 5' exonuclease activity
remove in 3' to 5' direction P1: Removes and replaces primers P2:DNA repair; restarts replication DNA halts synthesis P3:Elongates DNA
32
5' to 3' exonuclease activity
P1: Removes and replaces primers
33
DNA ligase
Connecting nicks after RNA primers are removed DNA ligase seals the nicks with a phosphodiester bond!
34
Elongation at replication fork requires:
1.Helicase to unwind DNA 2.SSB to protect single nucleotide strands and prevent secondary structures. 3.DNA gyrase to remove strain 4. Primase to synthesize primers with a 3’-OH group 5. DNA polymerase to synthesize the nucleotide strands.
35
Bacterial DNA Replication: Termination
In some DNA molecules, termination occurs whenever two replication forks meet. In others, specific termination sequences (Ter sites) block further replication.
36
Replication at the Ends of Chromosomes
single-celled eukaryotes and early embryonic cells –chromosomes do not shorten! ends of linear chromosome replicated by telomerase
37
Nucleosomes assembly
Nucleosomes reassemble quickly following replication.
38
* Creation of nucleosomes requires:
‒ Disruption of original nucleosomes on the parental DNA ‒ Redistribution of preexisting histones on the new DNA ‒ The addition of newly synthesized histones to complete the formation of new nucleosomes
39
Initiator protein
Binds to origin and separates strands of DNA to initiate replication
40
DNA helicase
Unwinds DNA at replication fork
41
Single-strand-binding proteins
Attach to single-stranded DNA and prevent secondary structures from forming
42
DNA gyrase
Moves ahead of the replication fork, making and resealing breaks in the double-helical DNA to release the torque that builds up as a result of unwinding at the replication fork
43
DNA primase
Synthesizes a short RNA primer to provide a 3'-OH group for the attachment of DNA nucleotides
44
DNA polymerase III
Elongates a new nucleotide strand from the 3'
45
DNA polymerase I
Removes RNA primers and replaces them with DNA
46
DNA ligase
Joins Okazaki fragments by sealing breaks in the sugar– phosphate backbone of newly synthesized DNA
47
The Fidelity of DNA replication
Most of the errors that do arise are corrected in a proofreading process. – DNA polymerase I: 3" to 5' exonuclease activity removes the incorrectly paired nucleotide
48
Mismatch repair:
corrects errors after replication is complete (will discuss more in Ch. 18).
49
Eukaryotic DNA Replication Differs in Several Aspects
1. Larger size of eukaryotic genomes requires that replication be initiated at multiple origins 2. Eukaryotic chromosomes are linear 3. DNA template is associated with histone proteins in the form of nucleosomes, and nucleosome assembly must immediately follow DNA replication
50
Eukaryotic Origins of Replication
Origins of replication vary greatly in sequence Research suggests origins in eukaryotes are defined by modifications to the chromatin structure
51
Origin-recognition complex (ORC);
a multiprotein complex, serves as initiator Initiator ORC recruits and loads the helicase right to the double-stranded DNA at the origin!
52
In eukaryotic cells – replication is
coordinated with the cell cycle. G1/S checkpoint holds cell in G1 until the DNA is ready to be replicated! Cell then enters S phase and DNA is replicated. -This system ensures that the DNA is not replicated again until the cell passes through mitosis.
53
The licensing of DNA Replication
Thousands of origins of replication allows entire eukaryotic genome to be replicated in a timely manner.
53
The precise replication is accomplished by separation of the initiation of replication into two distinct steps
1. Origins are first licensed – approved for replication This takes place early in the cell cycle, when replication licensing factors attach to each origin. 2. Replication machinery initiates replication at each licensed origin.
54
Eukaryotic Unwinding
Helicases that separate double-stranded DNA have been isolated from eukaryotic cells. Enzymes and proteins are assumed to function in unwinding of eukaryotic DNA in a similar manner as their bacterial counterparts! Eukaryotic cells contain many more different DNA polymerases than bacteria.
55
Three DNA polymerases carry out most of the nuclear DNA synthesis during replication
alpha, delta, and epsilon

Genetics (19 decks)

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