MCBG gene expression. topic 13 Flashcards
which is the 5’ and 3’ end of tRNA?
5’-left. shorter.
3’ right
(see photo google)
to which end of tRNA molecule is an amino acid attached?
the 3’ OH
amino acid attachment site
which enzyme catalyses the charging of a tRNA molecule with its cognate activated amino acid
amino acyl tRNA synthetase
what is the role of amino acyl tRNA synthetase? describe process
Charging of tRNA
1) amino acid and ATP bind to enzyme
2) amino acid is coupled to AMP forming aminoacyl-AMP. two phosphates lost.
3) uncharged tRNA binds to enzyme
4) amino acid transferred from aa-AMP to tRNA to form aminoacyl tRNA (charged tRNA)
> products released. enzyme returns to original state.
which bases can purine nucleoside inosine (I) complementary bind to?
A/C/U
what is the difference between nucleotide and nucleoside
nucleotide- phosphate, sugar, base
nucleoSIDE- sugar AND base (NO phosphate)
which bases are purine which are pyrimidine?
purine-
Adenine
Guanine
(All Girls are pure)
pyrimidine-
Thymine/ Uracil
Cytosine
(all contain a Y)
key feature about tRNA anticodon
anticodon= 5’ UAC 3’ codon=?
recognises ANTIPARALLEL complementary codon
codon= 3’ AUG 5’
compare and contrast DNA to RNA
- RNA has ribose sugar (C2 OH group)
- RNA contains U instead of T
- RNA single stranded
- RNA forms stem loops ( complementary, antiparallel strands which form mini helix)
- RNA can form non standard base pairing, complex 3D structure (e.g. 3 linked base pairs)
describe the relative amount of each type of RNA and the amount of different kinds and copies of each
rRNA
- most abundant
- few kinds, many copies
tRNA
- 15% of total RNA
- 100 kinds, many copies
mRNA
- least abundant
- 1000s of kinds, few copies
what does a gene contain
coding region
AND regulatory sequences around it (promoter, transcription initiation/ terminator, transcription termination)
where is the promoter in relation to transcription initiation?
promoter is UPSTREAM
what are the other minor types of RNA
- non coding RNA
- snRNA > splicing
- miRNA > regulation of gene expression
- antisense RNA > complimentary copy of mRNA
role of transcription factor
TF binds promoter
binding is directional on the TATA box (specific sequence on all eukaryotic promoter sequences)
more TF bind to upstream sequences
RNA polymerase recruited (beginning initiation)
for transcription elongation which strand is coding and which is non coding?
non transcribed DNA= coding strand
transcribed DNA = non-coding strand (template)
what is the role of capping?
5’ cap. put on 5’ to 5’ phosphodiester bond
- provides protection
- role in translation
role of tailing? enzyme involved?
3’ polyA tail
- protection
- regulation
endonuclease
splicing carried out by?
spliceosomes
what are the 3 sites on the large ribosomal subunit
5’ EPA 3’
only two sites occupied at one time
which enzyme catalyses the peptide bond formation in translation elongation
peptidyltransferase
Describe translation initiation in detail
1) met cap is recognised by tRNA* met
> finds AUG start codon
2) initiation factors removed
3) large ribosomal subunit recruited producing functional ribosome complex
E
P site- contains tRNA met bound to AUG
A- free ready for elongation
describe translation elongation in detail
1) P site already occupied. binding of aminoacyl-tRNA on A site
2) peptide bond formation between 2 amino acids
3) peptidyl tRNA moves to P site (translocation), freeing up A site
> pushes the now uncharged tRNA to E site
describe translation termination in detail
1) P site contains peptidyl-tRNA. empty A site.
2) stop codon recognised by release factor causing hydrolysis reaction resulting in uncharged tRNA in P site and free peptide
> peptide leaves ribosome through exit tunnel in large ribosomal subunit
3) dissociation of ribosome into subunits
compare prokaryote and eukaryote ribosomes
prokaryote- 30s and 50s subunits
70s
eukaryote - 40s and 60s subunits
80s
describe features of RNA polymerase in prokaryotes
RNAP CORE enzyme- has 5 subunits
HOLOenzyme - has 6 subunits (core enzyme + sigma)
non specific DNA binding by core enzyme
sigma subunit needed to make specific RNA
what additional molecules required for translation
initiation factors
elongation factors
release factors
energy GTP/ATP
