d1.2 protein synthesis Flashcards
sense strand
actually contains the genetic material for the polypeptide
antisense strand
complimentary strand
- not codable in the 5’ to 3’ direction
mRNA vs sense strand
mRNA is a copy of the sense strand (T is replaced by U)
gene
segment of dna that contains coded information for synthesising a polypeptide molecule
what does ribosome convert (what to what)
dna to amino acid
what is the only thing that is copied
gene segment
start codon
AUG
what can cells do through gene expression
cells can specialise into different types
what does cell specialisation affect
whether or not a gene will be transcribed for ribosomes to create the necessary polypeptide
transcription
first stage of gene expression, key stage at which expression of a gene can be switched on and off
how does the dna fit in the nucleus
wrapped around histone to form nucleosome
how does nucleosome affect gene expression
by prompting or limiting dna transcription
what does a condensed chromatin mean
no genes are expressed since dna transcription is inhibited
what does an open chromatin mean
genes are expressed since it promotes dna transcription
what does the rna polymerase attach to + what does it do
- unzip the double helix
- attach onto the antisense strand (template strand)
why does the rna polymerase attach to the antisense strand
as it moves, it copies and makes rna that is complementary to the antisense strand
after transcription what does the ribosomes do (+ what do they use)
uses tRNA to synthesise the polypeptide using the mRNA
what do tRNA contain
anticodon that is complementary to the codon in the mRNA
what do ribosomes do after transcription at the 3’ end
carries the amino acid that the codon codes for
2 types of ribosomes
- free ribosomes
- bound ribosomes
where will all mRNA go to first
free ribosomes
how to tell if a gene is expressed
if it is condensed, its not expressed
how is the mRNA identical to the sense strand except T to U
mRNA uses RNA polymerase which attaches to the antisense strand
what would happen is the ribosome is bound on the rough er
polypeptide would go outside of the cell through exocytosis
dna structure of tRNA
clover leaf
brief process of translation
- initiation
- elongation
- termination
detailed process of initiation
- mRNA enters the small unit of the ribosome
- tRNA carrying Met will bind to start codon
- large subunit of ribosome binds and the tRNA will fit into the p site
detailed process of elongation
- another tRNA binds to the next codon at the A site
- amino acid in P site will form a peptide bond with the amino acid of the A site
- ribosome will move from 5’ to 3’ to the next codon
- tRNA in the E site leaves
- repeats until the stop codon hits the A site
detailed process of termination
- when a stop codon enters A site, translation terminates
- ribosome detaches
- polypeptide detaches from the tRNA
what does the polypeptide need to do in order for it to be functional
fold according to its properties
3 types of point mutation affecting protein structure
- base substitution
- base deletion
- base addition
which point mutation has the least impact + why
base substitution
doesnt change all the codons after it (reads in triples)
how does the different amino acid in sickle cell affect the chemical properties
non polar
- hydrophobic so it wants to be on the inside
codon for Met (the starting codon)
AUG
codons for the stop codon
- UAG
- UAA
- UGA
how to determine where to start reading a codon
- the first few codons doesnt have a stop codon
what do non-coding sequences in dna mean
do not code for polypeptides
functions of non-coding sequences in dna
- telomeres
- introns
- base sequences
what are telomeres
structures that form the end of chromosomes in eukaryotes
what are introns
non coding regions within a gene that needs to be edited out
what do only eukaryotes have
introns
what are base sequences
- can be transcribed to produce transfer rna (tRNA), ribosomal RNA (rRNA) that makes up part of a ribosome (ribosome is made up of RNA and proteins
- base sequences used to regulate gene expression (eg. promoters, enhancer and silencer)
- affects gene even tho doesnt code for polypeptide itself
what proteins affects dna transcription
enhancer and silencer regions
what is the promoter proximal elements
proteins need to bind there to allow for transaction to start
mechanism of silencer
bind and stops the promoter or rna polymerase to bind
what does activated protein do
enhances transcription
y is regulation needed
so not all resources are used up
why do only eukaryotes need to do post transcription processing
have introns to be cut out
process of post-transcriptional processing
- splicing
- alternative splicing
- 5’ cap
- poly A tail
splicing
removal of introns using splicesome (small nuclear ribonucleoprotein)
why is alternative splicing needed
to make variations of polypeptide for different functions
function of 5’ cap
- prevents breakdown of the mRNA
- helps regulate the export out of the nucleus
- promotes translation
function of poly A tail
- prevents breakdown of mRNA
- keeps mRNA stable
- results in mature mRNA
conjugated proteins
quaternary + non polypeptide component
name of sequence that tells ribosomes to go to rough er
signal sequence
why does the protein have to go to the rough er
so exocytosis can occur
what is the signal sequence not a part of
insulin
prepoinsulin
chop off signal sequence
3 parts of preproinsulin
- b-b chain
- a-a chain
- connecting polypeptide
how does the preproinsulin start folding
- r group
- disulphide birdges between cystine
what are used to modify the polypeptide
protease
why might proteins no longer be needed
- reaction ended
- proteins changed due to denaturation/mis-folding
- changed due to free radicals or other reactive chemicals
name of recycling protein
proteaosomes
what are proteaosomes
molecular machine that removes and recycles proteins into amino acids
what tags the short protein sequences
ubiquitin
what is needed to break down protein
atp
role of ribosomes in translation
translation is the production of polypeptides/proteins
b. mRNA binds to the ribosome
c. tRNA binds to the ribosome
d. at the site where its anti-codon corresponds to the codon on the mRNA
OWTTE
e. amino acids of «consecutive tRNAs» bind by a peptide link «in the ribosomes»
f. the ribosome moves along the mRNA
OR
continues with elongation of polypeptide chain
