DNA & RNA Flashcards
Describe the structure of DNA
DNA has a double helix structure made up of complementary polynucleotide chains with minor and major grooves (which can act as receptors for drugs
In what form is DNA stored in nuclei?
DNA is in the form of chromatin
What are the 3 forms of DNA?
A, B and Z form DNA
What form of DNA is the most common?
B form DNA
When in high ethanol concentrations, what is the most commonly found form of DNA?
A form DNA is found, and A form is more compact than B form.
What’s the least compacted form of DNA?
Z form DNA is the least common and least compacted form of DNA.
Besides compactness, how is Z form DNA different to A and B form DNA?
Z form has the 2 antiparallel polynucleotide chains in a left-hand helix, rather than a RH helix
What are the building blocks of chromatin?
Nucleosomes
When first seen down an EM, what were nucleosomes described to look like?
Nucleosomes were said to resemble ‘beads on a string’.
What is DNA replication described as being, due to template strands?
Semi-conservative replication
What’s the name of the specific sites at which DNA replication is initiated, and what are they recognised by?
Replication origins are recognised by an initiation complex
What are the phases of the mammalian cell cycle?
M phase, G1, S and G2
What are the phases of the bacterial cycle?
M phase and S phase
What is the enzyme responsible for synthesising DNA by semi-conservative replication?
DNA polymerase
Cells have multiple DNA polymerases. Name the 3 bacterial DNA polymerases and their general function
DNA polymerase I- repair
DNA polymerase II- repair
DNA polymerase III- replication
Name the 5 eukaryotic DNA polymerases and their general function
DNA polymerase Alpha - replication DNA polymerase Beta- replication DNA polymerase Gamma- mitochondrion
DNA polymerase Delta- replication DNA polymerase Epsilon- replication
In what direction does DNA polymerase act?
DNA polymerase acts in a 5’ to 3’ direction
What are the components required for DNA replication?
DNA polymerase, DNA template strand, a DNA or RNA primer, deoxyribonucleoside triphosphate (dNTP) building blocks and Mg2+ ions
Name the 3 ways in which DNA can be damaged
1) Spontaneously, via random mutations
2) Chemicals- some chemicals can change base structure or insert between bases
3) Radiation- UV light produces thymine dimers, which can be dangerous in DNA replication. Ionising radiation breaks DNA chromosomes and can cause leukaemia.
What are the 4 deoxyribonucleoside triphosphate building blocks?
dATP, dCTP, dGTP and dTTP
As DNA helicase unwinds DNA, what are the 2 strands called due to the antiparallel nature of DNA?
There’s a leading strand, with which the new strand is formed in the direction of the replication fork, and a lagging strand, in which the replication fork is at the 3’ end.
In the lagging strand, Okazaki fragments are formed. Explain this
In the lagging strand, the replication fork is at the 3’ end, and because DNA polymerase works in a 5’ to 3’ direction, the new DNA strand must be made discontinuously, away from the replication fork, so fragments of new DNA are formed.
What enzyme joins the Okazaki fragments?
DNA ligase
What’s the function of DNA helicase?
DNA helicase separates the base pairs, producing single strands
What’s the function of topoisomerase?
Topoisomerase goes in front of DNA helicase and gets rid of the coils in DNA
What’s the function of primase?
Primase lays down some RNA (produces 3’-OH) so that DNA polymerase knows where to start replicating
What’s the function of DNA ligase?
DNA ligase splices DNA fragments together
What’s the function of replicative DNA polymerase?
Replicative DNA polymerase copies the parental strand
What’s the function of repair DNA polymerase?
Repair DNA polymerase repairs the fragments and takes out the RNA so it will be a full DNA strand
What’ the function of DNA binding proteins?
DNA binding proteins stabilise the single stranded DNA, stopping it from re-annealing to the other parental strand
What does DNA polymerase have to ensure that DNA replication proceeds with high fidelity?
DNA polymerase has a proof-reading and mismatch repair system that checks for mistakes and can repair them
With the proof-reading and mismatch repair system, what’s the error rate for DNA replication?
Approximately 1 in 10^8
Name the 2 major differences between DNA and RNA
RNA contains the sugar ribose, while DNA contains the sugar deoxyribose
Where DNA has the nucleotide base thymine, RNA has uracil
Define gene
A unit of heredity that contains instructions for an organism’s phenotype.
A DNA segment containing instructions for making a particular product
What are transcription factors?
Transcription factors are proteins required to initiate or regulate transcription in eukaryotes. They assemble on a promoter to position RNA polymerase II.
What’s a TATA box?
A type of promoter sequence that indicates where a DNA sequence can be read and decoded
What are the 3 steps of RNA processing?
Capping, polyadenylation and splicing
Why are capping and polyadenylation important?
They give mRNA stability so its degraded less easily.
They allow the mRNA to be transported to the cytoplasm.
They provide integrity prior to translation, so only fully formed mRNA is translated.
What are the 2 parts to the splicing process or pre-mRNA?
Cleavage, and ligation of exons.
What are the enzymes responsible for splicing called?
Spliceosomes
How can a gene code for multiple different proteins?
Exon skipping
