DNA Replication & Repair Flashcards
Base pair allows for ________
DNA Replication
Each strand of DNA that contains a certain type of nucleotide sequence can be a ______ used to make a new strand
Template (allows cells to replicate genes before dividing up)
Semiconservative replication
Since each parent strand of DNA is a template for each daughter strand of DNA double helix, the duaghter helix will have one of the parent strand (old strand strand) & a new strand
DNA synthesis begins at ______
Replication origins
Replication origins
Specific DNA sequence that initiator proteins bind to start DNA synthesis (unzip/ open up a DNA strand & its just an area where DNA is opened)
__________ form at each replication origin
Two replication forks
Replication fork
The y shaped junctions that allows a replication machine to move along the DNA (they continuously open DNA strands up in opposite direction)
__________ synthesizes DNA using a parental strand as a template
DNA polymerase (is whats copying the DNA strands as the replication forks is continuously opening up the DNA strand)
DNA polymerase 3
An enzyme that builds the new strand of DNA using the old strand as a template (Builds it in the 5’ to 3’ direction)
The new DNA strand is made (synthesized) in what direction by the DNA polymerase?
The DNA polymerase makes the new DNA strand in the 5’ to 3’ direction only (add a new nucleotide triphosphate)
The replication fork is ________ because at each replication fork one new DNA strand is made on a template that runs in 3’ to 5’ direction whereas the other new DNA strand is made in the 5’ to 3’ direction
Asymmetrical
Okazaki Fragments
Small DNA pieces that was made in the opposite direction of the replication fork (made in the 3’ to 5’ direction) & is made disconinuously, they ae the lagging strands
Lagging strand
The DNA strand that is made discontinuously
Leading strand
The DNA strand that made continuously
Since DNA polymerase only goes in the 5’ to 3’ direction it is able to be ________
Self - Correcting
What are the two reasons why DNA is able to be self-correcting and make no wrong base pairs (like A-G or C-T) ?
- The enzyme (DNA polymerase) carefully monitors the base-pairing between each incoming nucleotide triphosphate & template strand
- When DNA polymerase does make a rare mistake & add wrong base pairs togethers it can correct it through proofreading
________ occurs as each new DNA strand is made
Proofreading
Short lengths of _______ act as primers for DNA synthesis
RNA
Primers
A Short nucleic acid sequence that provides a starting point for DNA synthesis
The accuracy of DNA replication depends on the _________ to correctly base - pair the 3’ end before adding on more nucleotides
DNA polymerase
Primase
An enzyme that is used as a starting place to make a new strand of DNA, its made of a short RNA & uses the DNA strand as the template since the A in DNA can pair with the U in RNA the RNA fragment serves as a primer (Starting place) for DNA synthesis (Its a type of RNA polymerase)
RNA contains ______ instead of thymaine (T) but since _____ can pair with A, RNA primer is made on the DNA strand by base - pairing the same way as DNA
Uracil (U)
_________ only starts the replication at the replication origins
RNA primer
Need _______ to form a new strand of DNA from the lagging strands
DNA Ligase
DNA ligase
An enzyme that joins the 5’ end phosphate of one okazi fragment to the adjacent 3’ end hydroxyl end of the next (Seals the gap within the strands)
______ at a replication fork cooperate to form a replication machine
Proteins
What protein (enzyme) continuously open/unzip DNA strand?
DNA helicases
DNA helicases
An enzyme that breaks the hydrogen bond between the base
Single-strand DNA-binding proteins
Prevents the DNA strand from zipping up back up
DNA topoisomerases
Enzyme that relase the tension caused by the helicases continuously prying open DNA causing it to twist even more
________ produces a single-strand cut in the DNA backbone which releases the tensions
DNA topoisomerase
_________ replicates the ends of eukaryotic chromosomes
Telomerase
Telomerase
Are enzymes attached to the end of a chromsome
Telomerase uses its own _________ template which it uses to add multiply copies of repetitive DNA sequence to the lagging - strands so the lagging strand doesn’t get shorter & shorter so that DNA isn’t lost in each cell divison
RNA template
________ & __________ prevents linear eukaryotic chromosomes from shortening with each cell division
Telomers & telomerase
DNA damage occurs in cells since DNA molecules undergo _____ with other molecules
Collisions
Depurination
Process where purine bases (A & G) is lost from DNA in the cells of the body (Just removes the purine bases)
Deamination
Loss of a an amino group from a cytosine in DNA to produce the base Uracil
Thymine dimer
Type of damage to DNA by UV radiation from the sun which causes covalent linkage between two adjacent pyrimidine bases
What are the different types of chemical changes?
- Depurination
- Deamination
- Thymine dimer
If chemical modification are left unpaired it can cause _________
Mutations
What are the steps for repairing DNA?
- When the damage is recognized, nucleases will cut out the damage nucleotide sequence from the DNA strand leaving a gap on the strand
- A repair DNA polymerase binds the 3’ hydroxyl end of the cut DNA strand where the enzyme fill up the gap by making a complementary copy of the nucleotide sequence in the damage strand
- When the repair DNA polymerase filled up the gap the break in the sugar-phosphate backbone is fixed by DNA ligase
A DNA _______ system removes replication errors that escape proofreading
Mismatch repair system
Mismatch repair
Corrects the mistakes that were left after proofreading
Mismatch
Mispaired nucleotide (like A-G or C-T)
If nucleotides on one strand of DNA is damaged it can be fixed using _______________
Nucleotide sequence in the complementary strand as a template
What are the strategies used to repair double-strand break?
- Nonhomologous end joinging
- Homologous Recombination
Nonhomologous end joining
Sticking the broken ends back together before the fragment drift apart but also can lose nucleotides at the repair site as well (Risky process)
Homologous Recombination
Flawlessly repairs DNA double -strand break (safer process)
What is the steps for homologous steps?
- Nuclease digest the 5’ end of the broken strand
- Strand invasion by complementary base-pairng
- Repair polymerase synthsizes DNA using undamaged complementary DNA as a template
- Invading strand released complementary base-pairing allows broken helix to reform
- DNA synthesis using complementary strands from damaged DNA as a template
- DNA ligation
SSB proteins
Protect the two separated DNA strand & stablize them which prevent them from snapping back together
DNA replication occurs where in eukaryotic cell?
In the nucleus
DNA polymerase 1
Removes the primer from the lagging strand and replaces it with DNA (Move in the 5’ to 3’ direction & have exonuclease activity which has a role in DNA repair)
