DNA Flashcards
How many base pairs are there in a turn of DNA?
10.5
What are major and minor grooves?
Where the DNA wrap into a double helix each twist alternates in length due to one side of the base pair bond being longer than the other
How is DNA packaged?
DNA wraps twice around 4 histones
What are histones?
Positively charged molecules that condense DNA
How is bacterial DNA different to eukaryotic DNA?
Its circular
How is DNA replication initiated in bacteria?
Begins at 1 unique origin and proceeds bidirectionally, slow
How is DNA replication initiated in eukaryotes?
Begins at multiple origins and proceeds bidirectionally, much quicker
What is DNA polymerase?
An enzyme that replicates DNA with a primer
What unwinds the double helix of DNA?
Helicase
What makes the primers?
Primase
What direction does DNA replication occur in?
5’ to 3’
What is telomerase?
An enzyme that has a bit of DNA with RNA on it that can start making DNA without a primer
What is telomerases function?
To allow space for a primer to be added without important DNA being lost
Its activity decreases over time which is why we get old
What are the 4 types of DNA repair?
Mismatch repair
Direct repair
Excision
Nonhomologous end joining
What are the 3 stages of gene expression?
DNA replication
Translation
Transcription
In eukaryotes what does DNA polymerase 1 synthesise?
rRNA
In eukaryotes what does DNA polymerase 2 synthesise?
mRNA
In eukaryotes what does DNA polymerase 3 synthesise?
tRNA
How is mRNA processed after being transcribed?
Spliced to remove the introns
Capped and polyadenylation
What is capping and polyadenylation?
Where a 5’ cap is added so the ribosome cane recognise the start of the gene
What is alternative splicing of mRNA?
When some adjacent exons are removed to produce multiple proteins from one gene
What is a transcription factor?
Regulates transcription
Either activator or repressor of RNA polymerase
What are histone tails?
Chains of amino acids that are positively charged so attract the DNA to wrap around them
How can histones be modified to bring about post translational modification@
Histone acetylation
Histone deacetylation
What is histone acetylation?
transcriptional activation - When acetyl groups are added to the histone tails which neutralises the tails so DNA doesn’t wrap around as well
What is histone deacetylation?
Transcriptional repression - When acetyl groups are removed from histone tails so its more positive and DNA wraps around more
What is epigenetic gene regulation?
When modifications change gene expression without changing the DNA sequence
What forms of epigenetic gene regulation are there?
DNA methylation - silences genes
Histone modification
miRNA related gene silencing
What are aminoacyl-tRNA synthetases?
Enzymes that join tRNA and amino acids together
What are the 3 active sites of ribosomes?
A site - aminoacyl-tRNA
P site - peptidyltransferase
E site - exit
What is a polyribosome?
One piece of mRNA with lots of ribosomes attached to it all translating at once
What are the 3 main checkpoints in the cell cycle?
G1 - before S phase
G2 - after S phase
Mitosis - before cytokinesis
What are cyclins?
Proteins that control the cell cycle
How do cyclins control the cell cycle
They have different levels through the cell cycle
Protein kinase is activated by them which allows the cell cycle to occur
What is an example of cyclins?
Retinoblastoma (Rb) protein
How does Rb protein control the cell cycle?
Binds to the transcription factor that controls the S phase so cycle stops
