DNA Replication Flashcards
what were the experimental organisms that enabled scientists to learn about DNA?
bacteria and viruses
what did Griffith work with in 1928?
bacteria that causes pneumonia
what 2 strains did Griffith work with?
S (smooth) Strain - encased in a capsule and pathogenic
R (rough) Strain - lacked a capsule and could be destroyed by the host’s immune/lymphatic system
What happened in the experiment where heat killed S cells were mixed with R cells?
DNA from the heat killed S was picked up by the living R and they “transformed” into pathogenic S cells
what did Griffith’s experiment show?
transformation - when DNA from one source assimilates into another source, causing a change/ “transformation” in genotype and phenotype
who was the first to suggest that DNA was the agent being transferred between bacteria cells?
Oswald Avery
what did most scientists think were the agents?
proteins
what are phages?
viruses that infect bacteria
who proved that it was DNA and not proteins that were responsible for transferring genetic info ? through what work?
Hershey and Chase; through their work with bacteriophages
what are bacteriophages?
viruses that infect bacteria
at minimum, what is a virus?
DNA/RNA in a protein coat called a capsid
protein contain what elements?
CHON
what is different between proteins and DNA?
protein - S
DNA -P
what did batch 1 have?
radioactive S (protein)
what did batch 2 have?
radioactive P (DNA)
what was incorporated in T2 bacteriophages that infect E coli bacteria?
2 different radioactive tags - S and P
what was the result of Hershey and Chase’s experiment?
P appeared in E coli and S didnt, so DNA was being transferred
who noticed the percentages of A,T,C,G in DNA?
Chargaff
A and T ~ 30%
C and G ~ 20%
A=T and C=G equalities are known as
Chargaff’s Rule
the race to discover DNA’s true shape was won by?
Watson and Crick
(Maurice Wilkins also won Nobel Prize)
how was DNA’s shape found?
Rosalind Franklin took X-ray crystallography images taken, and Watson and Crick saw that it was a double helix
the correct model of DNA consists of
sugars (deoxyribose) and phosphates along the sides of the ladder and the N bases along the rungs
bonds between phosphate group and sugar?
covalent phosphodiester
bonds between complementary n bases?
H bonds
bonds bw non complementary n bases?
Van der Waals
how many bonds bw adenine and thymine?
2
how many bonds bw cytosine and guanine?
3
what needs to happen before DNA copies itself?
H bonds bw the nitrogen bases must be broken first
what does a template (old) strand act as?
acts as a guide for the formation of a new complementary strand
what happens in DNA replication?
nucleotides - simple sugar deoxyribose, phosphate group, and a nitrogenous base- line up along the template strand according to base pairing rules
where are the two old strands located in replication?
outside
where are the two new stands located in replication?
inside
when a double helix duplicates, what is the resulting daughter molecules?
2 new helices, with one new and one old- semiconservative model
why was DNA replication first studied in E coli?
they have a single circular chromosome called the nucleoid (5 million base pairs) and can undergo DNA replication in less than an hour
how is DNA replication in humans?
46 chromosomes - 6 billion base pairs
takes a few hours to replicate and divide
how much is known about DNA replication in prokaryotes than eukaryotes?
a lot more is known
in prokaryotes, where does DNA replication begin?
origin of replication and it proceeds in both directions along the circular DNA molecule until entire molecule is copied
how is DNA replication in eukaryotes?
linear and there are 100-1000’s of origins of replications
why do eukaryotes have many origins of replciation?
increase speed of copying very long DNA strands
the opening of 2 strands of DNA does what?
creates bubbles that eventually fuse together forming 2 daughter DNA strands
what is the point where bubbles formed called?
replication fork
who adds nucleotides to the DNA strand?
DNA polymerase
where does the energy to add nucleotide come from?
nucleoside triphosphate- nucleotides but with 3 phosphate groups instead of 1
how does nucleoside triphosphate provide energy?
very negatively charged and unstable, which accounts for the exergonic energy involved to drive reactions
what is the structure of 2 DNA strands?
antiparallel
what does antiparallel mean in terms of DNA?
their sugar-phosphate backbones run in opposite directions
5’ end
phosphate group
3’ end
hydroxyl group
with DNA replication, in which direction does the growing strand grow?
5’ to 3’
when DNA molecule opens up for replication, which what direction does it grow off from?
3’ to 5’ from the template strand
which direction does the daughter strand always grow in?
5 to 3
leading strand
complementary strand of new DNA
overall direction of the DNA replication in replication forks opening left?
towards the left
creating fragments in 5’ to 3’ direction
backstitching
lagging strand
DNA polymerase builds new DNA in 5 to 3 direction, and in a direction opposite to the leading strand and in short segments
short segments of DNA in lagging starnd
Okazaki fragments
how are Okazaki fragments linked?
enzyme DNA ligase
in a bubble, what are the leading and lagging strands?
leading strand - top left, bottom right
lagging strand - top right, bottom left
all replication bubbles fuse to form…
two new strands of DNA on the inside
which enzyme adds nucleotides before DNA polymerase?
primase
in what direction does primase add nucleotides?
5’ to 3’
are the nucleotides added by primase DNA or RNA?
RNA
what is the resulting RNA fragment added by primase called?
RNA primer
which enzyme replaces RNA primer?
2nd diff DNA polymerase (I)
what is the first step of DNA replication?
DNA helicase breaks the H bonds to unzip and unwind the double helix
what happens after DNA unwinds due to helicase?
single strand binding proteins hold open the unwound DNA molecule
what does topoisomerase do?
helps relieve tension created by unwinding DNA
what does primase do after SSBP attach?
arrives to prime/start building the daughter strand, adding about 10 RNA nucleotides in a 5’ to 3’ direction
what happens once RNA nucleotides are added?
DNA polymerase (III) adds complementary DNA nucleotides
DNA polymerase (I) replaces RNA primer with DNA
last enzyme involved in DNA replication
DNA ligase
links Okazaki fragments in lagging strand
how rare are errors in matching base pairs?
one error per billion
what proofreads mistakes that are made in DNA replication?
DNA polymerase
it immediately replaces a nucleotide if the wrong one is added and resumes replication
what causes mutations to existing DNA?
chemicals, radioactivity, UV light, X rays
what correct damaged DNA?
repair enzymes
what does nuclease do?
cuts out damaged DNA segment and DNA polymerase fills the gap and DNA ligase seals it up
what enzymes replace the last fragment of the DNA molecule?
no enzymes can do that
since last fragment of DNA is not replaced, what happens after repeated replication?
shorter and shorter DNA molecules are produced
what solves the problem or DNA molecules getting shorter?
eukaryotes have telomeres on the ends of their DNA
telomeres?
segments at the end of a DNA molecule that do not contain genes, so therefore do not make proteins
what sequence are telomeres?
TTAGGG
what do telomeres protect?
the organism’s genes/DNA from being eroded away through successive rounds of DNA replication
because of telomeres, how are our genes that code for traits?
unaffected until we’re older as the telomeres shorten instead
what does enzyme telomerase do?
helps lengthen the telomere ends
where is telomerase present?
in germ line cells that form eggs andsperm
what are scientists questioning about the relationship between life span and telomeres?
if an organism’s life span is limited by the length of telomeres
what is the downfall of adding telomerase to somatic cells?
increases risk of cancer
