Lec 11 - gene expression Flashcards
How does DNA, genotype, RNA, proteins ect all fit together ?
Genotype is the code, the phenotype is what is expressed
genes on chromosomes are what codes for proteins in cytoplasm
Proteins have an N and C terminus,
DNA and mRNA are coded 5’ to 3’
DNA is replicated, DNA is transcribed to make mRNA (in nucleus), mRNA is translated by ribosomes into proteins (in cytoplasm
How is a polypeptide made ?
Ribosome uses amino acids as protein building blocks
template is mRNA
initiation, elongation, termination
what factors influence the transcription of DNA into mRNA ?
in transcription there is a gene/transcription unit that codes for a gene.
initiation - protein (transcription factor) recognises the TATA box - this is called the PROMOTER
binding of transcriptor decides direction of gene transcription and where transcription starts
RNA polyermase then attaches to the trancription factor - in the decided direction
explain the concepts of upstream and downstream
+1 is the starting point of transcription and downstream is everything beyond this that will be trancribed , ie +2,+3,+4 ect
-1 is before is point, and everything before +1 (-1,-2,-3 ect) is upstream (before) where is transcribed
what are promoter sequences
are upstream of tata box transcription site, that can influence gene transcription is some way, ie when to be transcribed, or rates if transcription
an activatior can bind to this bit, that can cause interactions with the transcription via mediators
explain how coding strands ,template strands, promoters, transcription site work to produce mRNA
Promoter is either upstream of the transcription site or the transcription site itself,
TATA box when transcription factor (protein) binds.
it will bind to the template stand, and RNA ployemrase will then bind to the transcriptor
the mRNA will then be transcribed in opposite way to template strand so it 3’-5’ template strand, then the new strand is transcribed 5’-3’
therefore it will be opposite in nucleotides to the template strand, and be an exact match to the coding strand of DNA
the coding strand of DNA will separate in a bubble to allow the mRNA space to be coded for by template strand
which is more stable DNA or RNA
DNA
RNA is prone to desegregation
explain the process of capping
capping occurs on the 5’ end - protects against degregation as RNA is an unstable molecule
capping is the creation of a 5’-5’ linkage, that will also play a role in translation - this protects 5’ end of mRNA
explain the process of tailing/ polyadenylation
tailing occurs on the 3’ end, and protects the RNA from degregation
a specific sequence is the termination site that a specific endoneuclease can recognise and cut off abit downstream
then a ployA polymerase can use ATP to add many Adenine bases, this is polyadenylation
this is a polyA and the longer it is, the longer the RNA life, as it takes time to degrade
can act as a timer on RNA life length, and hence controls how much of a specific protein is produced - good for regulation
explain splicing
once transcribed the mRNA is called pre mRNA
it is made of introns and exons
splicing occurs in the middle of mRNA
introns have specific sequences to singal to cut at the introns (which are useless in themselves)
the exons are the active sections of mRNA but are separated and hence inactivated by the introns
the pre-mRNA is spliced to remove the intorns, leaving just the exons, which means the now mature mRNA is activated
this is beneficial as it can control when a mRNA is activated into use - ie an enzyme that would destroy the cell needs to exit the cell before activation
a mutation in the splice site of introns, can mean it is not removed from mRNA and hence the protein will not be functional
what are the main types and purposes of RNA
rRNA - ribosomal RNA - makes up part of the strucutre of the ribosome
mRNA - messenger RNA, - information of ribosomes to translate to proteins
tRNA - transfer RNA - used in translation
each has a different RNA polymerase to make them
what is a polysome ?
a stretch of mRNA with many ribsomes attached, translating polypeptides
prokaryotes and eukaryotes have different ribsomes
was just a bonus
they are made of different subsunits of different lengths
mutations are possible in ribosomes
antibiotics can specifically attack prokaryote (bacterial) ribosomes.
translation - the genetic code, what is it
a degenerate (so multiple patterns can code for the same amino acid) triplet code (read in threes)
it is non overlapping
there are initiation (AUG) and termination/stop (UAA,UAG,UGA) codons
change from DNA language (4 base pair) to 20 letter protein language means we go from 5’-3’ to N to C polypeptide chain extension
the adaptor molecule that we need is tRNA
what is the role of tRNA in translation ?
tRNA has a clover structure and is single stranded
H bonds form between anti-parallel complementary sequences to make stem loops
they have an anticodon in the middle
this anticodon is the opposite of a codon on mRNA and hence can bind to it
at the final A on the 3’ end has an amino acid bound to it - tRNA is specific for each amino acid - each has a different anti codon that responds to a specific codon
inosine is the wobble position - can bind to U,C or A
this provides the degeneracy for the genetic code - hence it the 3rd base of the genetic code doesn’t matter and can all code for same base
specific enzmyes have two sites that recognise specific tRNA and specific amino acid to form the active complex - aminocyl tRNA synthases
