3_DNA_Replication_Flashcards
What is DNA replication?
The process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.
Why is DNA replication essential?
It ensures that daughter cells inherit the same genetic information as the parent cell.
How was the process of DNA replication discovered?
Using radioactive labeling with ³H-thymidine in the 1960s to track newly synthesized DNA.
What is semi-conservative replication?
Each parental strand serves as a template for a new complementary strand.
What is bidirectional replication?
Replication proceeds in two directions from the origin of replication.
What is an origin of replication?
Specific DNA regions where replication begins.
Why are A-T rich regions found at replication origins?
A-T pairs have two hydrogen bonds, making them easier to separate than G-C pairs.
How many replication origins do bacteria and humans have?
Bacteria have one; humans have 30,000–50,000.
What is the replisome?
A protein complex that carries out DNA replication.
Name key components of the replisome.
Helicase, DNA polymerase, gyrase/topoisomerase, SSBPs, and primase.
What template is required for replication?
The parental DNA strand.
What are the substrates for DNA replication?
dNTPs (dATP, dCTP, dGTP, dTTP) and Mg²⁺ ions.
How fast does DNA replicate in bacteria?
1000 base pairs per second per fork.
How long does the S phase last in mammalian cells?
Approximately 8 hours.
Who discovered DNA polymerase?
Arthur Kornberg in the 1950s.
What are the main activities of DNA polymerase?
5’-3’ polymerase activity and 3’-5’ exonuclease proofreading activity.
What is the direction of DNA synthesis by DNA polymerase?
5’ to 3’.
What is replication fidelity?
The accuracy of DNA replication, with an error rate of 1 per 10 billion bases.
What contributes to replication fidelity?
DNA polymerase proofreading and mismatch repair mechanisms.
What is the function of primers in DNA replication?
They provide a starting point for DNA polymerase.
What synthesizes RNA primers?
Primase.
What is the first step in DNA replication?
Initiation, where the DNA strands are separated at the replication fork.
What happens during elongation?
DNA polymerase adds nucleotides to synthesize the new DNA strand.
What completes the replication process?
Termination, where RNA primers are replaced and Okazaki fragments are joined.
What is the leading strand?
The DNA strand synthesized continuously in the 5’ to 3’ direction.
What is the lagging strand?
The DNA strand synthesized discontinuously in Okazaki fragments.
What does helicase do?
Unwinds the DNA double helix.
What is the role of topoisomerase?
Relieves strain caused by DNA unwinding.
What do single-strand binding proteins (SSBs) do?
Stabilize unwound single-stranded DNA.
What does ligase do?
Joins Okazaki fragments by forming phosphodiester bonds.
What are telomeres?
Repetitive DNA sequences at chromosome ends that protect against DNA loss.
What enzyme synthesizes telomeres?
Telomerase.
What is the human telomere sequence?
TTAGGG.
Where does DNA replication occur in prokaryotes?
In the cytoplasm.
Where does DNA replication occur in eukaryotes?
In the nucleus.
How do replication origins differ between bacteria and humans?
Bacteria have one origin, while humans have thousands.
What are the three DNA polymerases in prokaryotes?
DNA Polymerase I, II, and III.
Which DNA polymerase is the main replicating enzyme in prokaryotes?
DNA Polymerase III.
What are the key eukaryotic DNA polymerases?
DNA Polymerase Alpha, Delta, and Epsilon.
What forms at the origin of replication?
Two replication forks.
What is the function of the replication fork?
It serves as the site where DNA is actively unwound and replicated.
What is the melting temperature (Tm) of DNA?
The temperature at which half of the DNA is denatured.
What are Okazaki fragments?
Short DNA fragments synthesized on the lagging strand.
What is the role of dNTPs?
They are the building blocks of DNA synthesis.
Why is telomerase active in germ cells?
To prevent telomere shortening and ensure full DNA replication.
How does telomerase activity relate to cancer?
Increased telomerase activity is a hallmark of cancer cells.
What prevents DNA strands from reannealing during replication?
Single-strand binding proteins (SSBs).
What is the Hayflick limit?
The number of times a somatic cell can divide before telomere shortening stops replication.
How long are Okazaki fragments in eukaryotes?
Approximately 150–200 base pairs.
What is the overall error rate of DNA replication?
About 1 mutation per 10 billion bases replicated.
