DNA Flashcards
How is DMA packaged in chromosomes?
Wrapped around histones and then wound up tightly to form solenoids. The sole lids are then cooled many times.
What is a gene?
Short section of DNA found on a chromosome that codes for the production of a protein that controls a characteristic
What are the 3 stages in DNA replication?
Initiation, Elongation and termination
In what direction does DNA polymerase read?
From the 3’ to 5’ only
What is the human genome?
The entire DNA sequence for humans (24 chromosomes)
What is the difference between a nucleoside and a nucleotide?
A NUCLEOSIDE has no phosphate group attached.
What is the important of nucleosides?
They can be moved into and around cells easily before being phosphorylated to become a nucleotide
What does DNA and RNA stand for?
DNA = deoxyribonucleic acid RNA = Ribonucleic acid
What are the 2 purine bases?
Adenine and Guanine
What are the 3 pyrimidine bases?
Thymine and Cytosine and uracil
What is the difference between purines and pyrimidines?
Purines are bigger as they have 2 loops
What bonds join the sugar phosphate backbone?
Phosphodiester bonds
What enzyme unwinds the DNA strands during replication?
DNA Helicase
In which direction is the leading strand produced?
In the 5’ to 3’ direction
What are formed by the discontinuous productions of the lagging strand?
Okazaki fragments
What joins the Okazaki fragments together?
DNA Ligase
What is epigenetics?
It is whether or not genes are expressed due to the structure of the chromatin
Why is DNA replication semi-conservative?
Because the new DNA consists of 1 old and 1 new strand
What is the role of topoisomerase in DNA replication?
Unfolds the helix and allows helicase to come in.
What is the role of telomeres on chromosomes?
They prevent genes being lost during replication. They are repeated sequences so protect DNA from degregation
Why do single stranded binding proteins bind during DNA replication?
To prevent the helix reforming
What is the role of DNA primase?
Binds to DNA strand and synthesises an RNA primer at the replication fork
What is the role of DNA Polymerase?
Synthesises a new DNA strand in a 5’ to 3’ direction by adding new nucleotides and then proof reads the nucleotides
What is the function of chromatin?
To package DNA in order to fit it into a small volume and also protect DNA by preventing breakage. Also controls gene expression (epigenetics)
What is a nucleosome?
A section of DNA that is looped around 8 histones twice each
Why can a nucleoside enter a cell but a nucleotide can’t?
A nucleoside doesn’t contain the negative phosphate group that prevents the nucleotide from entering
What is an exonuclease and an endonuclease?
EXONUCLEASE- cleave nucleotides from the end of a DNA stand
ENDONUCLEASE- cleaves nucleotides by breaking phosphodiester bonds in the middle of a chain
Why does DNA polymerase contain an exonulcease domain?
To excise mismatched nucleotides that have been produced by the polymerase
Why might there be a problem producing the final Okazaki fragment?
There is no room the bind the DNA primase to bind and so there’s no room to attach RNA primers meaning the final fragment can’t be produced
What does the enzyme telomerase do?
Extends the chromosome
