Lecture 7: Gene Expression 2 Flashcards
what is the start codon
AUG
what are the stop codons
UAA, UAG, UGA
what creates a bond between tRNA and its corresponding amino acid
tRNA synthetase
what are ribosomes made out of
- RNA and some accessory proteins
- large subunit and small subunit. tRNAs fit into cleft between the large and small subunits, into E, P and A sites
how is translation initiated
1) small subunit joins onto RNA at 5’ cap end
2) other proteins move ribosome along and take it to the start codon AUG
3) large subunit joins on
4) other tRNAs join up and translation begins
what happens when a ribosome reaches the stop codon
mRNA and ribosome dissociate from the protein, lose 5’ cap and is degraded
what does tetracyline do
blocks binding of aminoacyl-tRNA to A site of ribosome
what does streptomycine do
prevents transition from initiation complex to chain-elongating ribosome. also causes miscoding
what does chlorampenicol do
blocks peptidyl transferase reaction on ribosomes
what does cycloheximide do
blocs translocation reaction
what does rifamycin do
blocks initiation of RNA chains by binding to RNA polymerase
what is congenital deafness caused by
- deletion in connexin 26 gene
- causes frameshift and makes an early stop codon
what do microRNAs do
stop RNAs from being translated and / or degrades the RNA
what do miRNAs bind to
3’ UTR of mRNAs
what is the miRNAs life cycle
- longer precursor made and processed to cut out miRNA
- exported from nucleus to cytoplasm
- one strand finds the mRNA to bind to
- mRNA degraded or translation stopped
what causes lymphocytic leukaemia
- deletion of miRNAs, so overexpression of BCL2, which causes no/slow apoptosis so cells live longer than they should
what does the miRNA-200 family do
promotes growth of tumours and colonises metastases
what does the miRNA-31 family do
inhibits movement and invasion of cancer cells to a new location
what are good miRNA biomarkers
- miRNA-21 overexpressed in glioblastomas
- miRNA-155 overexpressed in forms of B cell malignancy
these can be detected using standard RT-PCR machines, and the number and types of miRNA can be used to estimate prognosis of the disease
where are miRNAs found
- circulating in the blood
- inside lipid particles called exosomes
- bound to proteins
