Structure and Replication of DNA Flashcards
What is DNA
A nucleic acid and macromolecule. Made up of two polynucleotide chains.
What does a nucleotide consist of?
A 5-carbon sugar (deoxyribose), a nitrogen containing base and a phosphate group
What is a nucleoside?
A sugar and a base
Why are the bonds between bases H bonds
They are easy to break and allow flexibility to unravel and allow transcription
How many H bonds are there between C and G?
Three
How many H bonds between T and A?
2
What is a purine?
A base with two rings (adenine and guanine)
What is a pyrimidine?
A base containing one ring (thymine and cytosine)
Why is a purine bonded to a pyrimidine in both the base pairings?
Both A+T and G+C take up similar space inside the nucleus making it easier to package
What are the major and minor grooves important for?
Enzyme binding
What must you do when writing a sequence of DNA?
Identify the 5’ end
How does asexual reproduction occur in prokaryotes?
- The entire genome is on one circular chromosome
- The chromosome replicates once to produce two identical chromosomes
- The two identical daughter chromosomes move toward opposite ends of the cell
- When the cell divides each daughter chromosome ends up in each cell.
How does asexual reproduction occur in eukaryotes?
- DNA replication occurs during S phase
- Gene expression occurs during G1 and G2
- Nuclear division occurs during mitosis
- Cell division (cytokinesis) occurs at the end of mitosis
Why does no transcription occur during metaphase?
Chromsomes too compact and the major and minor grooves are unavailable for enzyme docking
What is the first enzyme in DNA replication and what is it’s role?
DNA helices unwinds the double stranded DNA
What is the second enzyme used in DNA replication and what is it’s role?
A single-stranded binding protein binds to and stabilises the single DNA strand to keep it unwound. Lays down the primer.
Why is DNA replication semi-conservative?
Parent strand is used to make daughter strand
What direction does primase work in?
5’ to 3’ (connects to 3’ end)
What is the third enzyme used in DNA replication?
DNA polymerase, which lies down complementary nitrogenous bases to the parent strand and will check that the bases are correct.
What does DNA polymerase require?
All 4 dNTPs
Template
Primer
How fast does DNA polymerase work?
1000 base pairs per second
What is the role of exonuclease?
Removes nucleotides from the end of DNA. Removes RNA primer.
Can work in either direction
What is the role of ligase?
Joins ends of single stranded DNA strands by making new phosphate bonds.
Why is there a leading and a lagging strand?
Lagging strand is made up of small Okazaki fragments and has to wait for H bonds to be broken so the primer can be added
What other methods can DNA replication enzymes be used for?
PCR
Making recombinant DNA
Detecting mutations at molecular level
How long would it take to replicate the whole mammalian genome?
8 hours
What is the role of gyrase?
It relaxes supercoils (cause by polymerase) produced when the molecule is twisted during replication. It also facilitates unwinding at the beginning of replication.
What is the role of telomerase?
It uses a short RNA template to add short DNA repeats to the short ends of linear chromosomes when the last primer is removed using RNA template
What happens at the telomerase ends of all chromosomes
They contain non-coding DNA that protects the genetic information
