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Flashcards

DNA IV - Replication

Deleted user User has deleted their subject information English 28 cards

Cards in this deck (28)

  1. 1Where does DNA replication begin in bacterial DNA? (3)DNA replication beings at a particular site known as the origin of replication.
    This area is rich in A-T base pairings as these regions have fewer hydrogen bonds needed to break in order to unwind DNA.
  2. 2Draw a diagram of Bacterial DNA replication.S
  3. 3What class of enzymes are responsible for DNA synthesis?DNA polymerase
  4. 4How many DNA Pol' does E. Coli have? Which are of most importance in replication? (3)5.
    DNA Pol' I + DNA Pol' III are of most importance
  5. 5What does a DNA Pol' need in order to synthesise DNA?The four dNTP's
    A template DNA strand
    A Primer
  6. 6What is a primer?A short piece of nucleic acid, base-paired to the template DNA strand
  7. 7What is the function of a primer?Acts as a starting point from which DNA Pol' may synthesise new strands of DNA
    Must have an accessible 3'OH group.
  8. 8Draw a diagram of the addition of a dNTP to the template strand of DNAS
  9. 9Draw a diagram of the DNA Polymerase reactionPhosphodiester bond labelled
    Primer labelled
    Template strand labelled
    5' -> 3'
    Nucleophilic addition of O: shown
  10. 10What is the function of DNA Pol' i?Can degrade DNA via exonuclease activity, cleaving DNA from its exposed ends in a 5'-3' orientation.
  11. 11Draw a diagram showing exonuclease degradation of DNAS
  12. 12What conditions are necessary for exonuclease degradation by DNA Pol' i? (2)No dNTPs or Primer DNA present
  13. 13What is "nick translation?"When the 5'-3' exonuclease activity and DNA Polymerase activity take place simultaeneously on the same strand of DNA
  14. 14Draw a diagram showing nick translation (4)Phosphodioester bond missing
    Base being added to OH group
    Degradation from 5'-3'
    Extension of nick, nick still exists
  15. 15What is the function of 3'-5' exonuclease activity?Allows DNA Pol' i/iii to remove incorrect nucleotides from the newly formed DNA (proof reading)
    Opposes DNA synthesis
  16. 16Draw a diagram showing 3'-5' exonuclease activityIncorporation of incorrect nucleotide
    DNA synthesis stopping
    Removal of mis-matched nucleotide
    DNA synthesis resuming
  17. 17Compare DNA Pol' i/iii (8)Pol' i Pol' iii
    5'-3' e. act. ✓ X
    3'-5' proof reading ✓ X
    Polymerisation rate 16-200 250-1000
    (nucleotides per s) Processivity* 3-200 750,000
    *(no. nucl. incorporated
    b4 enzyme dissociates from template)
  18. 18Why does DNA Pol' iii have a much higher processivity?Because DNA Pol' iii will only dissociate when a whole sequence of DNA has been processed
  19. 19What allows DNA Pol' iii to be so processive?A hexameric B-subunit which forms a sliding clamp surrounding the template strand of DNA
  20. 20Draw a diagram showing the appearance of a Replication fork5'-3' Leading strand
    3'-5' Lagging strand
  21. 21What direction does DNA synthesis occur in?5'-3' direction
  22. 22Describe Stage 1 of DNA replication (5)1.Partial unwinding by DNA Helicase
    2.Due to partial unwinding + supercoiling occurs in the template strand
    3.These supercoils are corrected by DNA Gyrase (Topoisomerase)
    4.single stranded DNA-binding proteins prevent strands from rebinding
    5.(Diagram)
  23. 23Describe Stage 2 of DNA replication (5)1.Synthesis of primers by primase occurs
    2.In vivo RNA Primase is necessary, a specialised RNA polymerase
    3.Unlike DNA polymerase, RNA polymerase can start from scratch and doesn't requires a short strand of DNA to operate.
    4.Primers arrange themselves antiparallel to the template strand, with exposed OH groups for dNTP addition.
    5.(Diagram)
  24. 24Describe Stage 3 of DNA replication (8)1.DNA Pol' iii polymerises the nucleophilic addition of the exposed OH to dNTPs.
    2.New DNA is synthesised 5'-3'
    3.DNA Helicase causes unwinding of the DNA molecule and DNA Gyrase corrects supercoils.
    5.After a gap of ~1000 nucleotides a second RNA Primer arranges itself antiparallel to the newly exposed bases.
    6. New DNA is synthesised catalysed by DNA Pol' iii, with a phosphodiester gap existing between the 2 newly synthesised strands of DNA.
    7. These fragments of DNA are known as Okazaki fragments.
    (8) Diagrams
  25. 25Describe Stage 4 of DNA replication (3)1.RNA primers are removed via nick translation, which in turn is catalysed by DNA Pol' i and RNase H.
    2.The primer is degraded by 5'-3' exonuclease activity and simultaneously replaced with DNA using upstream Okazaki fragments as primers
    3.(Diagrams)
  26. 26Describe Stage 5 of DNA replication (3)1.The gaps between Okazaki fragments are sealed using DNA ligases.
    2. DNA ligases achieve this via formation of phosphodioester bonds between the DNA replacing the RNA primer as a result of DNA Pol' i polymerisation action.
  27. 27What is AZT?Azido-dideoxythymidine
    An inhibitor DNA polymerase, used to treat retroviruses such as H.I.V.
  28. 28How do DNA polymerase inhibitors work?(5)1.The nucleoside of this class of inhibitors has its usual 3'-OH group replaced by N3 or H.
    2.(Diagram)
    3.Once incorporated into DNA, they prevent further DNA synthesis as there is no OH group available for phosphodiester bonds to form with a successive nucleotide.
    4.Our bodies recognise AZT as abnormal and don't try to incorporate it during DNA synthesis.
    5.(Diagrams)

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User has deleted their subject information Flashcards on DNA IV - Replication, created by Deleted user on 17/12/2017.
Created by
Deleted user · Dec 2017
Updated
Dec 17, 2017
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20
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  • Created by J yadonknow · Dec 16, 2017
  • Copied by J yadonknow · Dec 17, 2017
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