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19 Cards in this Set
- Front
- Back
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1. Nitrogenous bases -
Purines- Pyrimidines |
= Composed of two fused heterocyclic rings
- The purines are the bases Adenine and Guanine = Composed of a single heterocyclic ring- The pyrimidines are the bases Cytosine, Thymine and Uracil |
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2.Sugar
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- A 5-C sugar or pentose- Ribose- Deoxyribose- Nitrogenous bases are attached to the 1′-carbon of the sugar
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3. Phosphate
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- One or more phosphates could be attached to the 5′-carbon of the sugar
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• Base + Sugar =
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Nucleoside
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Base + Sugar + Phosphate =
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Nucleotide• Adjacent nucleotides are linked by 5′-3′ phosphodiester bonds
==> At one end of the linear DNA chain, the nucleotide will have a free 5′-phosphate and at the other end, the nucleotide will have a free 3′-hydroxyl |
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- G and C are connected by-
A and T are connected by |
three hydrogen bonds
two hydrogen bonds |
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• The enzymes that synthesize new DNA using DNA as a template are termed
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DNA dependent polymerases
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• Bacteria
- E. coli has five main DNA polymerases, designated DNA pol I through pol V - All five have 5′ → 3′ _____activity - All five have 3′ → 5′_____activity - Only DNA pol I has 5′ → 3′_____activity - DNA pol I = Plays an essential, albeit secondary role in replication - DNA pol III = The major replication enzyme - The other polymerases are involved in DNA repair and rescuing stalled replication forks |
polymerase
exonnuclease exonnuclease |
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• Eukaryotes DNA pol α →
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nuclear dna synthesis
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• Eukaryotes- DNA pol β →
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DNA Repair
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Eukaryotes DNA pol γ →
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Mitochondria DNA synthesis
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Eukaryotes DNA pol δ →
DNA pol ε → |
Nuclear DNA synthesis
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- The other polymerases are involved in DNA repair and translesion synthesis
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- DNA pol ζ - DNA pol η
Zeta/Eta |
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• The process of DNA replication is divided into three phases:
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1) Initiation, which takes place at the origin
2) Elongation, which takes place at the replication fork 3) Termination, which takes place at the terminus |
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DNA POL III is a multicomponent enzyme
- It is capable of ____and so minimizes mistakes and improves fidelity - Occasionally an incorrect nucleotide is incorporated during replication - This is corrected by ____exonuclease activity (contained in the ___subunit) followed by ____polymerase activity (contained in the ____subunit) |
proofreading/ 3'-->5'/eta/5'--->3'/alpha
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1) Sequestration of oriC
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- The protein SeqA binds to oriC and inhibits ill-timed initiations
- It is “assisted” by the protein Dam - Dam methylates the adenine residue in the palindromic sequence GATC that is repeated 11 times in oriC |
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- Semi-conservative replication of fully methylated oriC DNA yields _____- ____preferentially binds to these sites
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hemimethylated oric
SeqA- Eventually, Dam will methylate the new strands and decrease SeqA binding |
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2) Titration of DnaA-
The chromosomal locus ____contains five DnaA boxes |
datA-
This locus can actually bind a large number of DnaA molecules, thus reducing the number of DnaA molecules available for initiation at oriC. |
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3) Inactivation of DnaA-ATP- The _____and a protein called _____are involved
These two proteins interact with DnaA-ATP to induce its intrinsic_____The resulting DnaA-ADP is inactive- This process has been termed________ |
BetA clamp/ HDA
ATPaseactivity- RIDA -Regulatory Inactivation of DnaA |
