quiz 12 Flashcards
DNA is a polymer made of
nucleotides
In what order do the following processes occur during DNA synthesis?
Topoisomerase (Gyrase) relieves the stress created by the unraveling of the DNA double helix
Primase synthesizes the first primer
DNA polymerase begins synthesis of the leading strand
Primase synthesizes primers for lagging strand synthesis
DNA helicase denatures double stranded DNA
DNA polymerase I removes the primers
Once replication has begun DNA helicase continues to open the replication bubble
Ligase connects all the newly replicated strands of DNA
DNA helicase denatures double stranded DNA
Topoisomerase (Gyrase) relieves the stress created by the unraveling of the DNA double helix
DNA polymerase begins synthesis of the leading strand
Primase synthesizes the first primer
Once replication has begun DNA helicase continues to open the replication bubble
Primase synthesizes primers for lagging strand synthesis
DNA polymerase I removes the primers
Ligase connects all the newly replicated strands of DNA
2
4
3
6
1
7
5
8
Why is an RNA primer necessary to initiate DNA synthesis?
DNA polymerase requires a 3’ hydroxyl to add a new nucleotide
Denatures double stranded DNA
helicase
Removes primers
DNA polymerase I
Synthesizes a primer made of RNA
Primase
Connects fragments of DNA produced during DNA synthesis
Ligase
Relieves stress created by the denaturation double stranded DNA
Gyrase
What does DNA polymerase require?
A single stranded DNA to act as a template
A free 3’ hydroxyl
Unbound nucleotides
DNA synthesis
Each of the two existing strands act as a template to produce new double strands
What enzyme best synthesizes a new strand of DNA?
DNA polymerase
How can DNA polymerase be the source of mutation?
It may incorrectly match nucleotides
Why is ionizing radiation a mutagen?
It can break double stranded DNA
How do oxygen radicals create mutagens?
They attach to cytosine to make a nucleotide that pairs with adenine rather than guanine
Why is ultraviolet light a mutagen?
It can fuse two adjacent thymine nucleotides and change the topology of the DNA molecule
What is the exonuclease activity of DNA polymerase
Its ability to remove nucleotides and correct base pairing mistakes
What is the outcome of a genetic mutation?
A loss of protein function leading to a recessive phenotype
A gain of protein function leading to a new dominant phenotype
Or nothing at all
What is the role of an existing double stranded helical DNA in the synthesis of new strands?
Serves as a template for its own replication
What direction does DNA polymerase synthesize a new strand?
5 to 3
What direction does DNA polymerase read the strand?
3 to 5
What does DNA Polymerase I do?
Removes RNA primers and replaces them with DNA by way of exonuclease activity
What is the difference between lagging and leading strand synthesis?
Leading - continous 5 to 3 uninterupted synthesis
Lagging - upstream of leading - production of small fragments of DNA upstream of the leading strand to prevent degredation of single-stranded DNA
Why is lagging strand synthesis necessary?
Without it a large portion of DNA would go unreplicated/unsynthesized
What is genetic mutation?
A change in DNA nucleotide sequences
Mutations can be good bad, or neutral
What sources of DNA mutation did we cover?
DNA polymerase may mistmatch base pairs during replication - Single Nucleotide Polymorphism
Mutagens
How does a DNA polymerase usually repair a mismatched base pair?
Exonuclease
What is the difference between polymerase and exonuclease?
Exo = removal, Poly = adding
What is a mutagen?
Environmental phenomena that alters or changes DNA
How does ultra-violet damage DNA?
uses adjacent thymines to create thymine dimers - changes shape of DNA molecule
What is the general repair mechanism that fixes damaged or mismatched base pairs?
Excision repair
What is the process of excision repair?
Nucleases make cuts on both sides of mutation, stretch of DNA w/ mutated nucleotides is removed, DNA polymerase fills in the nucleotides that were removed
