CH 23: Anabolism of nucleic Acid (DNA Synthesis/DNA replication) Flashcards
DNA Replication
What is the template for DNA?
The Parent DNA, 2 strands allows for 2 templates using DNA synthase
DNA Replication
How is DNA replication semiconservative?
Half of the new templates is from the parent and half is newly synthesized DNA (so not fully new)
DNA Replication
What direction is the DNA replication?
5’ to 3’
DNA Replication
Is base pairing more determined by hydrogren bonds or shape?
by shape (A to T, C to G)
learned by testing with similar shaped analong that cannot hydrogen bond but it would still recuit the same pairing as if it was the correct molecule
DNA Replication begins at the origin site
How many origin sites so bacteria have?
1
DNA Replication begins at the origin site
Do the replication forks go the same direction or opposite?
opposite
DNA polymerase catalyzes DNA synthesis
How many structural classes of DNA polymerase do E.coli have?
at least 5
DNA polymerase catalyzes DNA synthesis
Which polymerase number is the main for replication (E.coli)?
DNA Polymerase III: principal replication
Polymerase I (most abundant): clean RNA primers
Polymerase II, IV, and V: DNA repair
Eukaryotic DNA Polymerase
How many polymerase have we found so far for Eukaryotes?
6 (5 in nucleus and 1 in mitochondria. 3 for replication and 3 for repair)
Errors during synthesis
How are errors during DNA synthesis corrected?
using 3’ to 5’ exonuclease activity (proofreeds for mismatched base pairs, it gets rid of just placed nucleotide so the polymerase can try again)
RNA polymerase doesn’t have a proofreeding function
Beginning DNA Synthesis
What is needed to start DNA Synthesis?
Primers (Primase synthesises RNA Primer)
RNA Fragment that is used to extend DNA polymerase
Beginning DNA Synthesis
What removes this RNA fragment?
DNA pol I removes the RNA then it gets replaced by DNA and is sealed by DNA ligase
NIck or Gap
What is the difference between a nick and a gap?
Nick: breakage in phophdiester bond between nucleotides
Gap: one to multi-nucleotide spacing in DNA strand
Leading and Lagging Strand Synthesis
How is the template read for DNA synthesis?
From 3’ to 5’
SInce DNA must be synthesized 5’ to 3’
Leading and Lagging Strand Synthesis
What is the leading strand?
DNA strand being continuously replicated, only needs 1 primer
Leading and Lagging Strand Synthesis
What is the lagging strand?
DNA strand being synthesized discontinuously in short sections (okazaki fragments) opposite to where the replication fork moves
Many primers needed
Other Necessary Proteins at a Replication Fork
What does Helicase do?
opens the double helix and uncoils it using ATP
Other Necessary Proteins at a Replication Fork
What does Single-strand binding proteins (SSB) do?
keep strands seperated (large amount of protein needed)
Other Necessary Proteins at a Replication Fork
What does the sliding clamp (B2 subunit of DNA pol III in E.coli) do?
Helps the polymerase slide along the strand processively
Other Necessary Proteins at a Replication Fork
What does Topoisomerase do?
breaks the covalent bonds of the backbone to allow unwinding ahead of the replication fork and relieves stress by relaxing the supercoils
Type I: cleaves one strand, doesnt require ATP
Type II: cleaves both strands, requires ATP
Eukaryotic Chromosomes
What does telomere/telomerase do in eukaryokes regarding the primer areas?
The telomerase will replicate the 3’ end of the linear chromosomes using a built in template
Types of DNA Damage
Mismatches
arise frmo occasional incorporation of incorrect nucleotides
Types of DNA Damage
Abnormal bases
arise from spontaneous deamination, chemical alkylation, or exposure to free radicals
Types of DNA Damage
Pyrimidine Dimers
form when DNA is exposed to UV light
