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molecular biology of the cell > DNA replication > Flashcards

DNA replication Flashcards

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1
Q

what were the 3 main theories on DNA replication?

A
  • conservative: complete transmission of DNA to daughter cells (which are perfectly identical to mother cells)
  • semi-conservative:1 DNA -> generate 2 molecules of DNA (1 parental strand and a newly formed)
  • dispersive: patched replication of DNA
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2
Q

describe meselson’s and stahl’s experiment and what it proved

A

proof of semiconservative replication (only replication)

  • N15 (heavy isotope)
  • N14 (light isotope)
  • both added to bacteria through centrifugal force
  • DNA will position at the density similar to its own (heavy-low, light-top)
    • intermediary DNA forms after a single replication
    • 2nd replication: chains form half intermediate density and half light density
  • DNA is replicated in semiconservative way and the chromosomes derive from parent and new strand
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3
Q

what is DNA polymerase

A

main replication enzyme (works with other enzymes to unwind, replicate and re-close strand)

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4
Q

describe the actions of DNA polymerase in replication

A
  • 5’ to 3’ nucleotide chains added
  • contain multiple origins of replication
    • complete replication faster for cell division
  • fork of replication is asymmetrical: the speed of replication on the strands is different
  • DNA polymerase always needs a free prime OH to add nucleotide chains
    - RNA polymerase synthesises directly along DNA -> DNA polymerase recognises 3’ OH and starts polymerising DNA
    • created many times in lagging strand to initiate fragment
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5
Q

describe the theta models

A
  • 1 strand has 3’-OH allows for straight replication (leading strand)
    • polymerase is linear and progresses without interruption (towards the helicase splitting fork)
  • 1 strand has opposite configuration so polymerase moves in the same direction in segmented strand (lagging strand, Okazaki fragments formed)
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6
Q

replication components: topoisomerase

A

prevent DNA tangling and supercoiling during replication (problem of topology) - DNA rotates on itself before the bond is recreated

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7
Q

replication components: helicase

A

moves around DNA (1000bp/s, very high speed) using hydrolysis of ATP to unzip the DNA strands in front of replication fork

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8
Q

replication component: single strand DNA binding protein

A

bind DNA where its open (single strand) to protect it - polymerase removes it when it starts the replication

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9
Q

replication components: DNA primase

A

synthesis of primer (RNA)

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10
Q

replication components: DNA polymerase

A

recognises the primase and starts the polymerisation of DNA

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11
Q

replication components: ligase

A

consuming ATP reforms the phosphodiester bond between ribose and phosphate between okazaki fragments (lagging strand)

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12
Q

proofreading mechanism of replication

A

avoid change in coding sequences in DNA

  • polymerase incorporates a nucleotide and check the perfect match -> if its incorrect stops and starts degrading the DNA
  • removes small piece of DNA and starts synthesising again
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13
Q

cell cycle

A
  • G1 phase: where the cell lies
  • S: DNA duplication (6-8 hours)
  • G2: preparation for cell division
  • M: mitotic division
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14
Q

what is the lac operon?

A

repressor/promoter mechanism for RNA synthesis -> create balance between proteins - happens with lactose

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15
Q

describe the RNA synthesis from DNA

A

RNA has the same sequence as the coding strand of DNA

  • RNA polymerase acts from 5’ to 3’ strand
  • opens DNA, reads sequence and synthesises the new RNA transcript in a single strand
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16
Q

what is RNA polymerase?

A

different polymerases act to transcribe different genes

17
Q

describe the components involved in RNA synthesis

A

transcription unit: gene
TATA box: site of attachment for polymerase (TA bond is easier to break) (30 base pair further from TSS)
- causes DNA to bend (>90 degrees) to open the binding site for polymerase
gene regulatory proteins: regulate activity of polymerase to control levels of transcription
activator proteins -> activated by enhancer (sequence of DNA which acts as binding site for protein)
- mediator: allows interaction between simpler transcription proteins and enhancer (activates transcription)
TSS: Transcription start site
- TFIID -> necessary for transcription start
- tail in RNA polymerase: phosphorylation of ATP for energy production

18
Q

what are general transcription factors?

A

each element has a specific sequence which triggers a general transcription factor

19
Q

what is superhelical tension?

A

caused by unbinding in transcription

  • DNA with free end: doesn’t cause alteration in structure
  • DNA with fixed ends: causes supercoiling -> topoisomerase II stops superhelical structure

molecular biology of the cell (3 decks)

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