DNA Structure and Synthesis COPY COPY Flashcards
Describe transformation
when one bacteria changes the characteristics of another
How did transformation lead to the discovery of DNA?
It was discovered that DNA was the transforming factor
What is a bacteriophage?
a virus that uses a bacteria to replicate itself
How did bacteriophage help confirm the role of DNA?
the virus injects DNA into the bacteria to replicate itself which showed that DNA stored genetic information
What is X-ray crystallography?
early technique used to get a visual of DNA
How does X-ray crystallography work?
it diffracts light through a DNA crystal which creates an image
Describe DNA structure
double helix which runs anti-parallel
Describe double helix
two strands twisted around each other
Describe anti-parallel
3’ and 5’ ends run opposite directions
What makes up a nucleotide
base, sugar, phosphate
What makes up a nucleoside
base, sugar
Pyrimidines have ___ ring (s)
one
Purines have ___ ring (s)
two
Pyrimidines consist of what bases?
cytosine, thymine, uracil
Purines consist of what bases?
adenine, guanine
What do Chargaff’s rules state
in any species there is an equal number of A and T bases, and an equal number of G and C bases
Purine + purine would impact the DNA structure how?
too wide
Pyrimidine + pyrimidine would impact the DNA structure how?
too narrow
What is the correct model of DNA replication?
semiconservative model
Describe the semiconservative model
replicated DNA will have one old and one new strand of DNA
Describe the conservative model
the two parent strands rejoin
Describe the dispersive model
each strand is a mix of old and new
Describe origins of replication
where the two DNA strands are separated forming a “bubble”.
Describe the replication fork
the ends of the bubble where new DNA strands begin elongating.
Bacterial DNA is what shape?
circular
Describe helicases
enzymes that untwist the double helix at the replication forks
Describe topoisomerase
goes ahead of replication forks, cuts, unwinds, and rejoins DNA strands
Why is topoisomerase needed?
to keep the DNA strands from being too twisted
Describe single-strand binding protein
holds the DNA strand straight so it can be used as a template
What is a primer
a short strand of RNA that is laid down at the origin of replication
What is primase?
enzyme that lays down the primer
Describe DNA Polymerase III
adds DNA nucleotides to the 3’ end of the primer
The new strands grow in ________ directions.
opposite
DNA polymerases add nucleotides only to the __ ___of a strand
3’ end
a new DNA strand can elongate only in the __ to __ direction
5’ to 3’
Leading strand grows _______the origin of replication
in front of
Lagging strand grows _______ of the origin of replication
behind
Describe Okazaki fragments
a series of primers and new DNA segments
Describe DNA polymerase I
removes the RNA primers and replaces them with DNA nucleotides
Describe DNA ligase
connects the new DNA nucleotides
___ ___________ proofread DNA as it is added
DNA Polymerases
________ can repair __________ based pairs or ________ DNA
enzymes; mismatched; damaged
Describe nucleotide excision repair.
cutting out damaged DNA and replacing it with new DNA
Describe nuclease
an enzyme that cuts out damaged DNA
In nucleotide excision repair, what happens after DNA is cut out?
- DNA Polymerase adds new nucleotides
2. Ligase seals the new nucleotides
Why is DNA cut short after every replication?
DNA can’t be added to 5’ end new strands
How is DNA code protected from being cut?
meaningless code protects the real code
Describe telomeres
repetitive nucleotide sequences at the end of DNA that do not contain genes
Describe telomerase
an enzyme that lengthens telomeres in gamete DNA
Why is telomerase needed?
so a zygote can start off with a full set of telomeres
Describe histones
DNA wrapped around bead like proteins
Describe chromatin
DNA and histones together
What happens into DNA packaging after histones are made?
the Chromatin is coiled together into a larger fiber
