Sesh 2: DNA Structure and Replication Flashcards
What is the central dogma?
DNA–> RNA–> Protein
What is a histone?
An octameric protein that forms the core of a nucleosome. 147 base pairs of DNA wrap around a histone to –> nucleosome.
What type of chromatin is more in the solenoid form?
Heterochromatin. More tightly coiled, so is a way of controlling gene expression.
__________ are further coiled to form chromatin fibres.
Nucleosomes
What is the effect of the main mutation leading to CF?
It is a 3 bp deletion, leading to deletion of 1 amino acid. CFTR misfolds and does not reach the plasma membrane, so you don’t get Cl- conductance.
How many chromosomes are in the human genome?
24- (22 autosomes + X and Y)
What is the genome?
The entire DNA sequence.
Nucleic acids are _________________.
Polynucleotides= linear polymers of nucleic acids
What 3 components make up a nucleotide?
- Base
- Sugar
- Phosphate
What is a nucleoSide composed of?
A base and a sugar….no phosphate group.
What is the difference between ribose and 2-deoxyribose?
Ribose has an OH group on C2, but 2-deoxyribose only has a H on C2.
Ribose forms RNA, and 2-deoxyribose forms DNA.
What carbon of 2-deoxyribose does the nitrogenous base attach to?
C1
The phosphate group of a deoxyribonucleotide connects to carbon ____.
5
How many rings do purines and pyrimidines have?
Purines-2 rings
Pyrimidines- 1 ring
Which bases are purines and which are pyrimidines?
Purines= adenine and guanine Pyrimidines= cytosine, thymine and uracil
Nucleotides are connected by __________ bonds.
Phosphodiester
At the 5’ end of DNA there is a ________, and a _________ at the 3’ end.
- Phosphate
2. Hydroxyl
__ hydrogen bonds form between C and G bases, and __ hydrogen bonds form between A and T/U bases.
- 3
- 2
Due to the bases’ chemical structure, get secondary structure of DNA.
In the duplex DNA structure, the strands are _____________ and run ___________.
- Complimentary
2. Anti-parallel
By convention, DNA is written ___ to ____.
5’ to 3’.
What occurs in each stage of the cell cycle listed below?
- G1
- S
- G2
- M
- G1= cell contents replicated
- S= DNA replication
- G2= check and repair
- M= cell division- mitosis/meiosis
Where do the cell cycle checkpoints occur?
After G1 and G2.
Which enzyme catalyses the formation of phosphodiester bonds in DNA replication?
DNA polymerase
What direction is chain growth in DNA replication?
From 5’ to 3’- DNA polymerase adds nucleotides to the 3’ end.
What drives the reaction of DNA replication?
Pyrophosphate hydrolysis.
What is the structure of DNA in prokaryotes?
It is in the form of a naked circular chromosome.
Sine DNA polymerase can only EXTEND from a 3’ end, a ________ is required to ‘kick start’ DNA replication.
Primase
What direction does DNA polymerase read the template strand?
3’ to 5’ (to make in 5’ to 3’)
The leading strand is made _________, but the lagging strand is made in ________ ___________.
- Continuously
- Okazaki
- Fragments
Which enzyme joins the Okazaki fragments of the lagging strand?
DNA ligase.
Which enzyme unwinds the DNA double helix, for DNA replication?
DNA helicase.
Apart from catalysing DNA replication, what can DNA polymerase do?
Can proofread- corrects 99.9% of its errors.
When does DNA replication terminate in prokaryotes?
When the 2 facing replication forks meet and DNA ligase joins the final fragments.
How many molecules of DNA does replication of 1 chromosome produce?
2 molecules of DNA (chromatids held together by a centromere)- 1 REPLICATED chromosome.
What are the 2 major functions of DNA?
- To replicate itself
2. To store genetic information
What is the definition of a gene?
A stretch of DNA at a specific locus on a specific chromosome, that carries the code for a protein.
Histones can be methylated or acetylated to regulate gene expression. This is termed_________.
Epigenetics.
Phosphodiester bonds are a type of ________ bond.
Covalent.
What is chromatin?
DNA+histone, that allows DNA to be tightly packaged into a small volume.
Why are nucleoSide analogues used instead of nucleoTide analogues, as antiviral and anti cancer drugs?
Nucleosides lack a phosphate group, making it easier for them to pass through the cell membrane. Once in the right place, nucleosides are phosphorylated by kinases–> nucleotides
What is the difference between an exo- and endonuclease?
Exonucleases cleave the end of DNA at the 5’/3’ end.
Endonucleases cleave DNA within the nucleotide chain.
What is the function of an exonuclease domain in DNA polymerase?
Proofreading…detects base pair mismatches, helps remove the incorrect base for it to be replaced with the correct one.
Mutations in this domain can–>errors in DNA replication–>mutations–>cancer
How can nucleoside analogue drugs be used to treat HIV/AIDS?
They act as substrates for DNA polymerase, but when incorporated into the newly-synthesised strand, cannot form phosphodiester bonds, so cause termination of the nucleotide chain…preventing DNA replication.
-In high doses can have adverse effects on continually dividing cells e.g. Skin, GIT
Define precision medicine
An emerging approach for disease treatment and prevention that takes into account individual variability in genes, environment and lifestyle.
What is pharmacogenomics?
The study of how genes affect individual’s response to specific drugs.
