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DNA IV - Replication
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- 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. - 2Draw a diagram of Bacterial DNA replication.S
- 3What class of enzymes are responsible for DNA synthesis?DNA polymerase
- 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 - 5What does a DNA Pol' need in order to synthesise DNA?The four dNTP's
A template DNA strand
A Primer - 6What is a primer?A short piece of nucleic acid, base-paired to the template DNA strand
- 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. - 8Draw a diagram of the addition of a dNTP to the template strand of DNAS
- 9Draw a diagram of the DNA Polymerase reactionPhosphodiester bond labelled
Primer labelled
Template strand labelled
5' -> 3'
Nucleophilic addition of O: shown - 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.
- 11Draw a diagram showing exonuclease degradation of DNAS
- 12What conditions are necessary for exonuclease degradation by DNA Pol' i? (2)No dNTPs or Primer DNA present
- 13What is "nick translation?"When the 5'-3' exonuclease activity and DNA Polymerase activity take place simultaeneously on the same strand of DNA
- 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 - 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 - 16Draw a diagram showing 3'-5' exonuclease activityIncorporation of incorrect nucleotide
DNA synthesis stopping
Removal of mis-matched nucleotide
DNA synthesis resuming - 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) - 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
- 19What allows DNA Pol' iii to be so processive?A hexameric B-subunit which forms a sliding clamp surrounding the template strand of DNA
- 20Draw a diagram showing the appearance of a Replication fork5'-3' Leading strand
3'-5' Lagging strand - 21What direction does DNA synthesis occur in?5'-3' direction
- 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) - 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) - 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 - 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) - 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. - 27What is AZT?Azido-dideoxythymidine
An inhibitor DNA polymerase, used to treat retroviruses such as H.I.V. - 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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- El usuario ha eliminado su información de asignaturas Fichas sobre DNA IV - Replication, creado por Usuario eliminado el 17/12/2017.
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- Creado por J yadonknow · 16 dic 2017
- Copiado por J yadonknow · 17 dic 2017
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