DNA Replication/Transcription Flashcards
DNA replication is an example of _____________ replication
Semi-conservative
Which direction does DNA synthesis occur?
5’ —> 3’
Which enzyme initiates DNA replication?
DNA helicase
How does the enzyme that initiates DNA replication start the process?
Separates the paired strand to from a replication fork
What does DNA polymerase do?
Synthesises new strand of DNA by adding free DNA nucleotides onto a complementary RNA primer
Why is a RNA primer necessary?
Starting place for DNA polymerase
Difference between the leading strand and lagging strand
Leading strand will be synthesised continuously whereas the lagging strand cannot as template is limited
What is an Okazaki fragment?
A fragment of DNA formed from the lagging strand
What is a sliding clamp?
Keeps DNA polymerase firmly attached to the strand but is released when reaches a double strand
Talk through the steps of DNA synthesis
DNA primes is used to synthesise short RNA primers
Each primer is extended by DNA polymerase
RNA primer is erased by ribonuclease H and replaced by DNA
DNA ligase joins the 3’ end of new fragment with 5’ of old one if in lagging strand
What is ribonuclease H?
An enzyme that erased RNA primer and replaces them with DNA
What is DNA ligase?
An enzyme that joins together the phosphate sugar backbone of DNA
Which enzyme produces RNA primers?
DNA primase
What does SSBP stand for?
Single stranded DNA-binding protein
What do SSBPs do?
Maintain unwound parental DNA strands in single-stranded conformation to ease replication fork process
How do SSBPs aid in the lagging strand?
Stabilise the ssDNA to prevent formation of short helices –> prevent impediment of DNA synthesis
What is transcription?
DNA –> mRNA
What are the two major steps of gene expression?
1) Transcription
2) Translation
What does semi-conservative replication mean?
Each new double helix is made up of one strand from the parental helix plus one newly synthesised strand
Where does transcription occur?
In the nucleus
Why is it necessary for DNA –> mRNA?
mRNA is small enough to leave through a nuclear pore
Process of transcription in eukaryotes
RNA polymerase II moves stepwise 5’ –> 3’ along the DNA, unwinding the DNA helix just ahead of the active site to produce a copy of mRNA.
Termination of the process occurs when reaches a terminator region
What is pre-mRNA?
Precursor mRNA is mRNA which hasn’t yet been splice so still contains introns
What is the initiator step in transcription?
RNA polymerases bind to promoter region
What is the elongation step in transcription?
When an mRNA transcript of DNA is being yielded
What is the termination step in transcription?
When RNA polymerase encounters a terminator region which promotes the dissociation of RNA polymerase
What do general transcriptions factors aid?
- Positioning of promoter
- Pulling apart two strands of DNA for transcription
- Release RNA polymerase from promoter –> start transcribing
What carries out RNA splicing?
Spliceosome
What is a spliceosome made up of?
snRNAs with protein
– five snRNPs and numerous proteins make up the core
What do spliceosomes do?
Remove intron sequences from pre-mRNA
What is an advantage of RNA splicing?
Splicing occurs in different ways which means that the same gene is able to produce different proteins
–> increases coding potential of the genome
How the is the coding potential of the genome increased?
RNA splicing
