From DNA to proteins Flashcards
How is DNA unwounded and separated before replication?
Prior to cell division, topoisomerase unwinds DNA and DNA helicases separates DNA apart to expose two single DNA strands and create two replication forks. DNA replication then takes place simultaneously at each form
What coats the single DNA?
Single stranded binding protein (SSB’s) coat the single DNA strands to prevent reannealing or snapping back together
What does the primate enzyme then do?
The primate enzyme then uses the original DNA sequence on the parent strand to synthesise a short RNA primer. Primers are necessary since DNA polymerase can only extend a nucleotide chain, not start one.
How is new DNA synthesised?
DNA polymerase begins to synthesise a new DNA (via complementary base pairing using free floating nucleotides) strand by extending an RNA primer in 5’ and 3’ direction. Each parental strand is copied by one DNA polymerase (lead strand and lagging strand).
What does RNAse H do?
As replication proceeds RNAse H recognizes RNA primers bound to the DNA template and removes the primers by hydrolyzing the RNA
- DNA polymerase can then fill the gap left by RNAse H
How is the DNA replication process completed?
DNA replication process completed when the ligase enzyme joins the short DNA pieces (Okazaki fragments) together into one continuous strand.
What are the 4 stages of the synthesis of mRNA from DNA?
- Preparation
- Production
- Termination
- Modification (splicing)
What happens during the preparation phase?
- Topoisomerase unwinds the double helix by relieving the supercoils.
- DNA helicase then separates the DNA apart exposing the nucleotides.
- Single stranded binding proteins (SSBP’s) coat the single DNA strands to prevent DNA re-annealing
What sequence is the recognition signal for starting?
TATA
and then AUG is the start codon
How is mRNA produced?
- Free mRNA nucleotides line up next to their complimentary bases on the template strand
- U&T, C&G
- Coding strand runs 5’ to 3’
- Template strand runs 3’ to 5’
How is the sequencing terminated?
- Transcription is stopped at the stop codon – UAA/UAG/UGA
What does RNA polymerase do?
- RNA polymerase (specifically RNA polymerase 2) joins the mRNA nucleotides (catalysing phosphodiester bonds between them)
- Forms antiparallel mRNA strand (with a 5’CAP head and a 3’Poly A tail) - starting at a promoter (specific sequence that RNA polymerase binds to - initiation of transcription.
What happens in the modification/ splicing?
The removal of introns
Leaves exons – the coding part
How does the mRNA leave the nucleus?
Via the nuclear pores
What does mRNA attach to once it has left the nucleus?
80s ribosome with large and small subunits
(APE section in large subunit - A at the 5’ end of mRNA)
