gene expression and protein synthesis Flashcards
central dogma of molecular biology
DNA-mRNA via transcription
mRNA-protein via translation
what are the potential products of mRNA
rRNA, tRNA, ribozymes, microRNAs and proteins
what are ribozymes?
RNA that act as enzymes
how does the double helix provide a copying mechanism?
A-T and C-G for DNA replication via complementary base pairing with hydrogen bonds
antiparallel strands 5 prime to 3 prime
nucleotides held in place by phosphodiester bonds
sense strands via antisense strands
sense strands code, (5’ to 3’) antisense is the opposite to sense (3’ to 5’)
what does ATG code for?
met- start codon
what do TAA, TAG and TGA code for?
stop codons
gene structure
5’ to 3’
promoter initiates gene expression
coding sequence starts with ATG and finishes TAG (e.g)
either side are untranslated regions (5’ UTR and 3’UTR)
function of UTRs
regulation
eukaryotic vs prokaryotic gene structuree
eukaryotic DNA has introns and exons, prokaryotic is only exons
introns make sequence non-continuous
TATA box/INR
sequence in some eukaryotic genes (30%)
part of promoter region- initiation of gene expression
enhancers
enhance expression of molecules to modulate gene expression
turn up or turn down gene expression (+ve or -ve)
where do initial transcription factors bind?
TATA box
how do we make mRNA from DNA?
RNA polymerase II makes mRNA from DNA and binds to promoter region
what makes up the transcription initiation complex?
regulatory enhancers/silencers, RNA polymerase II and TFs
what strand is used for transcription?
primary RNA transcript made from antisense strand
template strand complementary ro primary RNA transcript
post-transcriptional mRNA processing (5’ capping)
during transcription, guanine added to the 5’ end via 5’-5’ link
guanine is then methylated – 7mG
prevents degradation of mRNA by 5’-3’ nucleases and promotes nuclear export
how is post-transcriptional mRNA processing regulated?
5’ capping and 3’ polyadenylation
how does 5’ capping prevent degradation?
5’ endonucleases cannot bind to 5’-5’ link initially
steps of polyadenylation
initiated immediately transcription is terminated
poly A tail can be VERY long – hundreds of bases
enhances stability of mRNA – 3’-5’ nucleases are common
required for translocation out of the nucleus
what does the poly A tail prevent binding of?
3’-5’ nucleases
how are introns removed?
splicing (pre-mRNA to mature mRNA)
steps of translation
- takes place on 80S ribosomes in the rough endoplasmic reticulum
- ribosomes have two subunits - rRNA and protein complexes
- mRNA is moved through a groove at the junction of the two RNA molecules
- tRNA with complementary codon sequences bring the
relevant amino acids - translation terminates at the STOP codon (e.g. UAG)
tRNA is a copy of what strand?
antisense strand because it is complementary to mRNA
how do you get selective expression of a gene in a neuron?
promoter allows for cell-specific expression (certain TF can bind)
what do all primary proteins start with?
methionine
how do TF control suites of genes?
expression of TF in different cells
genes can be common across cells (e.g cytoskeleton and mitochondria)
how do you get selective expression of a gene in a neuron?
pluripotent stem cells can diffrentiate into any type of cell
certain TF can turn this into a neuron
this can determine the type of neuron (e.g spinal motor and cranial motor)
elements of cranial and motor neurons
Hb9=spinal motor TF
Phox2b=cranial motor TF (accessory nerve)
Tuβ3=common to all neurons
what are microRNAs (miRNA)?
post-transcriptional regulators
small non-coding RNA sequences
produced as long hairpin structures
processed to produce short sections of RNA <30 bases in
length
bind to RISC (RNA-induced silencing complex)
cleaves target mRNA
leads to down-regulation of protein expression
