Lec 10: Protein Synthesis Flashcards
what is the purpose of transcription? why does it occur in the nucleus?
Transcription is the process by which DNA is copied (transcribed) to mRNA, which carries the information needed for protein synthesis
it occurs in the nucleus because this is where the DNA is located
what is the template strand? state the other name given to this polymer
single strand of mRNA
antisense strand/non conding strand
what is the cap for Pre-mRNa composed of?
phosphorylated 7 ‐methyl guanosine
what adds the cap to pre-mRNA. where is the cap place on the mRNA molecule?
guanyltransferase adds the cap to the 5’ end of the mRNA
what is the importance of pre-mRNA capping?
– Ensures mRNA is exported out of nucleus
– Blocks degradation of mRNA by 5’ exonucleases
– Promotes translation
what is the polyadenylation of Pre-mRNA and why is this important in transcription
this is where appr.200 adenosine residues are added to pre-mRNA
So:
- pre-mRNA is cleaved by an endonuclease near a signal AAUAAA sequence at the 3’ end
- the adenosine residues are added at the cleavage site by poly‐A polymerase
importance:
- poly‐A‐tail protects the mRNA from degradation by 3’ exonucleases
- aids in termination of transcription
- ensures export from the nucleus
what are the difference between exons and introns?
*EXtra special & *IN the way
exons code for proteins
introns do not code for proteins so need to be spliced out to produce the final mRNA
what is alternative splicing?
this is where the pre-mRNA sequence is spliced to produce different proteins from the same gene
what is mature mRNA
mRNA that has been spliced and processed
and is ready for translation
what does mature mRNA consists of?
Mature mRNA consists of:
- 5’ cap
- 5’ UTR (untranslated region)
- Coding Region (to be translated into a protein)
- 3’ UTR (untranslated region)
- Poly(A) tail
what is the name given to 3 bases e.g ACG
DNA base triplet
what is the name given to base triplets in mRNA
codons
how many mRNA codons are there?
64 (43)
what is meant by degenerate with respect to the genetic code?
More than one codon codes for each of the 20 amino acids
why are the first two codons most crucial?
gives tolerance against mutation
state the bases that code for the START and STOP codons
– START codon: AUG (methionine)
– STOP codons: UAG, UAA, UGA
how does a mutation in the amino acid sequence affect haemoglobin?
change in amino acid sequence causes haemoglobin to crystallise when oxygen levels are low, causing the sickle shape which gets stuck in small blood vessels
what is the consequence of sickle cell anemia in terms of red blood cell function?
compared to normal red blood cells, sickle red blood cells can not move as easily through the blood stream
resulting in;
– Downstream tissue ischaemia, causing pain and infarction
– In severe cases, organ damage and ischaemic stroke
in sub-saharan africa what does sickle cell anemia provide protection against
malarial parasite
what is meant by frameshift mutation?
small deletions or insertions into a DNA sequence can resulting in significant changes of protein sequence
what is translation? where does it occur?
genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain
in the ribosome
what is a ribosome composed up of?
60S subunit and smaller 40S subunit
what name is given to the triplet bases complementary to the codon on a mRNA molecule
anticodon
what is a aminoacyl tRNA molecule?
a tRNA molecule bonded to an amino acid
what is a deacylated or uncharged tRNA molecule?
tRNA molecule that has had its amino acid removed
what is a peptidyl tRNA?
a tRNA molecule bound to a growing polypeptide chain
what is initiation?
binding of ribosome to 5’ end of mRNA and hydrogen binding of the anticodon of an aminoacylated tRNA carrying methionine on the AUG start codon
what is elongation?
the addition of further amino acids to the growing polypeptide chain brought by corresponding aminoacylated tRNAs.
what is the function of peptidyl transferase?
creates covalent peptide bonds between amino acids
what is termination?
when the stop codon (UAG, UAA, UGA) is reached and the peptide and ribosomal subunits are released
where do proteins synthesised on free ribosomes end up?
cytoplasm
where do proteins synthesised on ribosomes attached to RER end up?
secreted our of the cell
how are proteins secreted?
proteins are incoporated into vesicles
for transport to the golgi apparatus
post translational modification of proteins occurs in the goldi cavaties e.g glycosylation
modified proteins traverses the GA and is packaged into secretory vesicles
these vesicles move to the cell membrane, fuse with it and expel their contents into the extracellular space (excytosis)
