MOLECULAR BIOLOGY OF THE GENE Flashcards
what processes occur in the nucleus?
transcriptional control
processing control
what processes can gene expression be regulated?
transport control, translational control, mRNA degradation control, protein degradation control
what is transcriptional control?
t
what are interim regions?
i
what is ‘junk’ DNA needed for?
needed for organism plasticity, control of gene expression
describe the gene structure
Promoter
Transcriptional ‘start’ and ‘stop’ signal
Exons and introns
Upstream regulatory regions
what does the promoter do?
stitches a gene on
why aren’t genes all expressed infall cells at the same time?
some genes may be expressed in response to an external stimulus, others during a particular point in the cell cycle, development etc. (timing is important)
How does a cell keep control over which genes are expressed or not?
the promoter
what are transcriptional activators?
t
what is gene expression driven by?
RNA polymerase II
why are transcription factors needed?
In order for a gene to be expressed (switched on) a number of DNA-binding proteins TF bind in and around promoter region
how is gene expression fine-tuned?
via the binding of other DNA-binding proteins to distal regions termed upstream enhancer sequences
what is open chromatin?
o
what do activators do?
Activators bind
to enhancer sequence and increase expression significantly than without them (basal/low expression)
what does transcription create?
mRNAs, tRNAs and rRNA
what produces mRNAs, tRNAs and rRNA?
enzyme RNA polymerase
what is RNA polymerase I?
responsible for the production of the large ribosomal RNA
what is RNA polymerase II?
responsible for the production of mRNA
what is RNA polymerase III?
responsible for the production of tRNA and the small ribosomal RNA molecules
how does RNA polymerase bind to promoter?
RNA p molecules collide randomly with the DNA in the nucleus and bind with specific DNA sequences called promoters, the TATA sequence/box
what does RNA polymerase open?
opens up a short length of the DNA double helix exposing a specific section of DNA on each strand.
what are the 2 types of transcriptional repressors?
Interacts with activator - binding site next to activator - blocks function
Overlapping binding sites (activator, repressor) - stops activator from binding
what is the 5’ end of the mRNA molecule capped by?
addition of methylated G nucleotide
3’ end is cleaved at a specific site and a poly – A tail added
how is methylated G nucleotide added to 5’ end?
by removal of a phosphate by a phosphatase
addition of a GMP via a guananyl transferase addition of a mythyl group via a methyl transferease
what are introns?
non coding regions
what are exons?
coding regions
how are introns removed?
by RNA splicing
what is RNA splicing ?
s
what is alternative splicing?
a
what is the 1st AA in a polypeptide?
AUG (methionine) -start codon
what is translational control?
t
how does translational control occur?
mRNA associates with ribosomes which translate the RNA sequence into a polypeptide chain (protein)
Many ribosomes attach to each mRNA (multiple bubbles)
what is the purpose of the half-life of mRNA?
another way in which the cell can regulate gene expression levels
how does translational initiation occur?
an initiator tRNA carrying a methionine associates with a small ribosomal unit in association with eukaryotic initiation factor 2 ( eIF2).
what occurs after tRNA binds to eIF2?
The small ribosomal unit recognises the a 5’ end of a mRNA capped with two additional initiation factors eIF4G and eIF4E, and scans along the mRNA for a start codon (AUG), which then allows the large subunit bind.
what is stage 1 of translational elongation?
An aminoacyl – tRNA binds to the A site and the tRNA molecule at the E site is released
what is stage 2 of translational elongation?
Carboxyl end of the polypeptide chain is uncoupled from the tRNA in the P site and joined by a peptide bond to the AA attached to the new tRNA molecule in the A site via a peptide transferase enzyme.
what is stage 3 of translational elongation?
Large ribosomal sub unit steps one codon along the mRNA
what is stage 4 of translational elongation?
Small ribosomal subunit steps one codon along so that the new peptidyl –tRNA in the A site moves to the P site as and the tRNA that occupied the P site of the ribosome moves 1 codon along the mRNA molecule and becomes the new E –site. This generates a new A site.
what is translational elongation driven by?
Elongation factors EF1 and EF2
what is translational termination?
t
what occurs in translational termination?
Protein synthesis stops when the ribosome encounters a stop codon (UAA, UAG, UGA). Cytoplasmic release factors bind to the stop codon and free the carboxyl end of the growing polypeptide chain.
what is the one gene-one protein hypothesis?
o
what are isoforms?
Alternative mRNAs of a single gene (e.g. Casp8)
