DNA Flashcards
(30 cards)
What is the name of the bond that joins nucleotides together?
The phosphate backbone is made of phosphodiester bonds between sugar phosphates.
Which carbon atoms are involved in the bond between adjacent nucleotides?
5′ and 3′ carbons of the deoxyribose sugar molecule.
Give three differences between DNA and RNA structure.
DNA is double stranded, whereas RNA is normally single stranded.
DNA contains deoxyribose sugars, whereas RNA contains ribose sugars.
DNA contains thymine, whereas RNA contains uracil.
Role of DNA primase?
Lays down a short strand of RNA to act as a primer for DNA synthesis (DNA primase is an RNA polymerase).
Role of DNA polymerase I ?
This enzyme synthesizes new DNA strands on the lagging strand and during DNA repair.
Role of DNA polymerase III ?
This enzyme synthesizes new DNA strands on the leading strand.
Role of single stranded binding proteins ?
These proteins bind to single stranded DNA at the replication fork to stabilize the single strands (ie stop them reannealing)
Role of DNA helicase ?
This enzyme unzips the two strands of DNA at the replication fork.
Why is DNA replication said to be semiconservative?
Each new molecule of DNA contains one original strand and one newly synthesized strand of DNA.
What are the requirements for DNA synthesis by DNA polymerase?
Template, free 3′-OH group, all four dNTPs
What are Okazaki fragments?
The short fragments of DNA synthesized on the lagging strand of DNA as the replication fork progresses. They contain an RNA primer. The primer is subsequently removed by DNA polymerase I (or eukaryotic equivalent) and fragments joined by DNA ligase.
How does the DNA polymerase reduce the frequency of errors from 1 in 105 to 1 in 107?
The polymerase has a 3′ to 5′ proofreading activity that checks if the correct base has been inserted before the next base is inserted. 1 in 100 error.
What is the function of the enzyme uracil N-glycosylase?
Why does this help to reduce mutations in DNA?
Uracil-N-glycosylase cuts (excises) uracil from DNA. Uracil can arise in DNA by the deamination of cytosine.
In Sanger DNA sequencing how is the growing chain of DNA terminated?
When a dideoxynucleotide is inserted; as it has no free 3′-OH group, the polymerase cannot continue adding bases
What is the definition of a polymorphism?
A sequence variation that occurs in at least 1% of the population.
A-T has how many H bonds?
2 T for two
G-C has how many H bonds?
3 G-C Three!
What is the TATA box?
A sequence that binds transcription factors to help initiate transcription.
is mRNA a replica of antisense or sense strand?
Sense, it carries the message
What direction is RNA synthesised?
5’ to 3’
Name three modifications of mRNA in eukaryotes?
5′- cap, polyA tail, splicing out introns.
To which end of the tRNA molecule is the amino acid attached?
3’
Two sub units of eukaryotic ribosomes?
60s and 40s
What is the role of the E, P and A sites in the ribosome?
Docks in the A sites, attached in P leaves in E (exit)
