Lecture 10: the central dogma Flashcards
Why is it beneficial for DNA to be double stranded?
- it ensures that essential information is not lost. If one copy is damaged then the other strand can be used as a template for repair.
- It reduces the dangers inherent in transmitting genetic information –> if a single chain is present, genetic information might be lost
What phase of mitosis does DNA replication occur?
S phase
How does semiconservative DNA replication work?
2 strands in a parent DNA molecule are separated and each strand acts as a template for the synthesis of a new daughter strand.
DNA polymerase has the general structure of a ____________________.
Right hand
DNA polymerase has the general structure of a ____________________.
Right hand
Which direction does DNA synthesis occur in?
The growing strand is synthesized in the 5’ to 3’ direction
DNA polymerase needs ______________ to facilitate catalysis?
metal ions
What are the functions of the parts of DNA polymerase?
- “Fingers” : interact with incoming dNTP and template DNA
- “Palm” : the site where bond formation is catalysed
- “Thumb” : positions duplex DNA
What is the bond that DNA polymerase forms?
It catalyses the formation of a phosphodiester bond between the 3’ -OH of the growing strand and the 5’ phosphate group of the incoming dNTP
What is the structure of helicase?
It is made u of 6 proteins arranged in a ring shape
What is the function of helicase?
It unwinds the DNA double helix into 2 strands
What is the replication fork?
The point where the DNA is separated into single strands
What is the function of single stranded binding proteins (SSBs)?
- SSBs coat the newly exposed DNA strands during replication
- They prevent the 2 polynucleotide strands from joining back together.
What is the function of primase?
It synthesizes short RNA primers which are needed to start the replication process
What is the function of the sliding clamp protein?
- It helps to hold the DNA polymerase onto the DNA strand during replication.
What is the function of RNAse H?
It removes the RNA primers that previously began the DNA strand synthesis.
What is the function of DNA ligase?
It links the DNA together to form one continuous strand
The lagging strand is synthesized in small fragments called ______________
Okazaki fragments
How long are okazaki fragments?
1000-5000 bp
How does RNAase H remove the primers?
- It recognises RNA-DNA hybrid helices
- It degrades the RNA by hydrolyzing the phosphodiester bonds
What is the origin of replication?
A stretch of DNA sequence in the genome at which DNA replication is initiated
How can acyclovir act as an anti cancer agent?
- It has a nucleoside like structure –> with the same nucleic acid base, but without the complete sugar ring
- It can get incorporated into the elongating DNA strand, but more nucleotides cannot be added to it –> it prevents DNA elongation
What is the (general) function of DNA topoisomerase?
It acts of DNA to reduce supercoiling stress caused by unwinding during replication.
What are the 2 ways DNA topoisomerase can reduce supersoiling stress?
- Type I: single stranded cut –> unwind –> join back together
- Type II: double stranded cut –> unwind –> join back together
How does camptothecin act as an anticancer drug?
- It forms hydrogen bonds with DNA and tipoisomerase I, forming a stable ternary complex
- This complex prevents DNA religation
- Interferes with DNA replication
How does fluoroquinolones act on bacteria?
- It inhibits bacterial topoisomerase II (but not human)
- Causes accumulation of clevage complexes hat lead to bactericidal effect
