Exam 3 (Topic 12) Flashcards
Each daughter DNA molecule contains one parental strand and one daughter strand
Semiconservative Replication
DNA backbone gets broken, and strands are copied and rejoined
Dispersive Replication
After replication, parent helix forms back together and daughter strands join together
Conservative Replication
How did Melson and Stahl disprove two of the hypothesis?
The used a density gradient centrifugation of DNA from cultured bacteria with 14N (light) and 15N (heavy). The conservative test was disproved because a mixture of light and heavy was observed. Dispersive was disproved because when heat was applied there was a separate heavy band and a separate light band, confirming the semiconservative hypothesis.
Why is DNA synthesized 5’–>3’?
Because it is endergonic which releases enough energy when broken from the 5’ triphosphate for the polymerization reaction to occur.
What is the function of the origin of replication?
To be a position where the DNA is first opened for DNA replication
What is characteristic about the origin of replication’s DNA sequence?
DNA sequences attract initiator proteins and DNA that are easy to open
How many replication forks does a eucaryotic chromosomes that is undergoing replication contain?
2 replication forks are formed at each replication origin
What is the purpose of the Okazaki fragments and why are they made?
To eventually form a continuous new DNA strand and to connect to the leading strand to make the strand continuous
Would you fine on DNA polymerase in a replication fork?
No, you would find them at the 5’ end of all Okazaki fragments. Since there can be many Okazaki fragments, there must be DNA polymerase for each fragment.
What is the function of the Helicase?
Uses ATP energy to unwind the double helix at the replication fork
What is the function of the single-strand binding protein?
Binds to the newly formed single-stranded DNA and prevents it from base pairing
What is the function of the sliding clamp protein?
Protein that binds to DNA polymerase and keeps it attached to the single-stranded DNA
What is the function of the clamp loader?
Uses ATP to assemble and attach the sliding clamp
Which of the four proteins from replication require ATP to perform its function?
Helicase and Clamp Loader
What is the function of primase?
An RNA polymerase that makes a short 10 nucleotide primer of RNA bound to the DNA template; makes a short primer that DNA polymerase can add nucleotides to
Is primase a DNA or RNA polymerase
RNA
Why must DNA replication begin with an RNA primer?
Because DNA polymerase cannot initiate replication without an existing nucleotide to build from
What three other enzymes are required to remove the primer and complete DNA replication?
Nuclease, Repair Polymerase, DNA Ligase
What is the function of Nuclease?
erases the RNA primer
What is the function of Repair Polymerase?
fills the RNA gap made by nuclease
What is the function of DNA Ligase?
joins the two DNA fragments
Why can’t DNA polymerase replicate the ends of the chromosomes?
Because it does not have an existing strand with a 3’ hydroxyl group to replicate on
What are telomeres?
special repetitive noncoding sequence that are added to end chromosomes
What is the function of telomerase? How does it do it?
A DNA polymerase with a built in RNA template to synthesize new DNA. It replenishes the nucleotides that are lost by adding multiple copies of the same DNA sequence.
Why is telomerase called a ribonucleoprotein?
because it contains RNA and protein reverse transcriptase subunit
When cells do not have telomerase expressed anymore, what happens when the ends of their chromosomes lose a certain amount of DNA?
You lose the ends of your chromosomes and senescence (stop dividing) and apoptosis (programmed cell death) occur
Programmed cell death
apoptosis
Stop dividing
Senescence
