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Genetics > Chapter 12 > Flashcards

Chapter 12 Flashcards

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Biology 101 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
Q

Bacterial DNA Replication: Elongation

A

Single-stranded DNA is used as a template for the synthesis of DNA!

DNA Polymerase

Primase

26
Q

DNA Polymerase

A

– 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
Q

Primase

A

– 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
Q

DNA Polymerase III

A

duplication of the chromosomal DNA

29
Q

DNA Polymerase I

A

DNA polymerase I functions to fill DNA gaps that arise during DNA replication, repair, and recombination

30
Q

5’ to 3’ polymerase activity

A

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
Q

3’ to 5’ exonuclease activity

A

remove in 3’ to 5’ direction

P1: Removes and
replaces primers

P2:DNA repair; restarts
replication DNA
halts synthesis

P3:Elongates DNA

32
Q

5’ to 3’ exonuclease activity

A

P1: Removes and
replaces primers

33
Q

DNA ligase

A

Connecting nicks after RNA
primers are removed

DNA ligase seals the nicks
with a phosphodiester bond!

34
Q

Elongation at replication
fork requires:

A

1.Helicase to unwind DNA

2.SSB to protect single nucleotide strands and
prevent secondary structures.

3.DNA gyrase to remove strain

  1. Primase to synthesize primers with a 3’-OH group
  2. DNA polymerase to synthesize the nucleotide
    strands.
35
Q

Bacterial DNA Replication: Termination

A

In some DNA molecules, termination occurs
whenever two replication forks meet.

In others, specific termination
sequences (Ter sites) block
further replication.

36
Q

Replication at the Ends
of Chromosomes

A

single-celled eukaryotes and early embryonic cells –chromosomes do not shorten!

ends of linear chromosome replicated by telomerase

37
Q

Nucleosomes assembly

A

Nucleosomes reassemble quickly following replication.

38
Q
  • Creation of nucleosomes requires:
A

‒ 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
Q

Initiator protein

A

Binds to origin and separates strands of DNA to initiate
replication

40
Q

DNA helicase

A

Unwinds DNA at replication fork

41
Q

Single-strand-binding
proteins

A

Attach to single-stranded DNA and prevent secondary
structures from forming

42
Q

DNA gyrase

A

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
Q

DNA primase

A

Synthesizes a short RNA primer to provide a 3’-OH group
for the attachment of DNA nucleotides

44
Q

DNA polymerase III

A

Elongates a new nucleotide strand from the 3’

45
Q

DNA polymerase I

A

Removes RNA primers and replaces them with DNA

46
Q

DNA ligase

A

Joins Okazaki fragments by sealing breaks in the sugar–
phosphate backbone of newly synthesized DNA

47
Q

The Fidelity of DNA replication

A

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
Q

Mismatch repair:

A

corrects errors after replication is
complete (will discuss more in Ch. 18).

49
Q

Eukaryotic DNA Replication Differs in
Several Aspects

A
  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
Q

Eukaryotic Origins of Replication

A

Origins of replication vary greatly in sequence

Research suggests origins in eukaryotes are
defined by modifications to the chromatin structure

51
Q

Origin-recognition complex (ORC);

A

a multiprotein
complex, serves as initiator

Initiator ORC recruits and loads the helicase
right to the double-stranded DNA at the origin!

52
Q

In eukaryotic cells – replication is

A

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
Q

The licensing of DNA Replication

A

Thousands of origins of replication allows entire
eukaryotic genome to be replicated in a timely
manner.

53
Q

The precise replication is accomplished by separation of
the initiation of replication into two distinct steps

A
  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
Q

Eukaryotic Unwinding

A

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
Q

Three DNA polymerases carry out most of the nuclear DNA
synthesis during replication

A

alpha, delta, and epsilon

Genetics (19 decks)

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