Mod 7: Protein synthesis Flashcards
in prokaryotes, what type of ribosome and what subunits are they made up of
70s ribsomes
Large subunit = 50s = 23s rRNA + 5s rRNA + 31 proteins
Small subunit = 30s = 16s rRNA + 21 proteins
in eukaryotes, what type of ribosome and what subunits are they made up of
80s ribosomes
Large subunit = 60s =
28s rRNA + 5.8s rRNA + 6s rRNA +48 proteins
Small subunit = 40s =
18s rRNA + 33proteins
what does s stand for in the sixing of ribosomes
Svedberg
a measure of sedimentation rate of suspended particles centrifuged (in standard conditions)
not determinant of the mass of molecule but the shape and size
what needs to happen before AA can bind to DNA?
must bind with ATP first
what process allows AA to bind with ATP and explain x
transesterification
hydroxyl group from the carboxy end of an AA is lost and is joined onto ATP
which leads to loss of 2 phosphates (gamma and beta)
1 remains (alpha)
leaves amino acyl AMP
this then gets joined to the correct tRNA at the tRNA 3’ acceptor arm
see onenote
initiation - whawt is Shine-Dalgarno sequence
sequence of bases with AUG (methionine initiator codon) embedded
used to recognise and pair w/ 30s subunits
specifically the 16s ribosomal RNA, which scans the mRNA until it finds this sequence and binds
what is the equivalent to the Shine-Dalgarno sequence in eukaryotes
Kozak sequence
how many tRNAs are there for methionine and what are their functions
one for initiation (to start translation)
one for elongation (so within the gorwing polypeptide chain)
for process of translation and diagram, see onenote
:)
what are the initiation factors involved in translation
IF1
IF2
IF3
IF1 function
makes sure the tRNA only binds to large subunit on correct side (P site)
cuz theres 2 sides, and IF1 blocks the A site
also inhibits premature interaction between 30s and 50s
IF2 function
tags the initiator tRNA and regulates its entry into ribosome
IF3 function
stops premature association of 30s and 50s
stabilises free 30s
accuracy check to make sure tRNAi-met is bound in the right place
Elongation:
what site does the tRNAi Met associate with on the large subunit
the P site
this is the only one that can do this
other amino acyl tRNAs that are involved in elongation associate with A site
what does the A site do
where new amino acyl tRNAs come and slot in during elongation
what does the A site do
where new amino acyl tRNAs come and slot in during elongation
remember it by A for amino acyl idk
what is the elongation factor that brings in the amino acid
EFTu
coupled with GTP
so it forms a aminoacyl tRNA-EFTU-GTP complex
once the new aminoacyl tRNA binds, what is ejected
EF-TU-GDP (so it’s been converted from GTP, but this will be recycled and goes back into process)
what kind of bond forms between the AAs
peptide bond duh
what happens when peptid bond gets formed
first tRNA (tRNAi Met) gets ejected from P site
what is the other accessory factor involved in translocating the ribosome along the mRNA strand
EF-G-GTP
which then turn into EF-G-ADP after it’s ejected
recap then, what are the 2 elongation factors and their functions
EF-Tu
mediate aminoacyl-tRNA entry into ribsome
EF-G mediates translocation
see onenote for diagram and deatil on elongation
:)
Termination:
what are the release factors used in this process and their functions
RF1 = recognises UAA/UAG
RF2= recognises UAA/UGA
RF3= helps the other 2 bind to the ribosome (coupled with GTPase, so is a G protein)
what happens once the release factor is bound
hydrolysis of polypeptid chain from tRNA and chain released and tRNA dissociates
what is GTP
guanosine triphosphate
what does GTP do
provides energy (via hydrolysis) GTP -> GDP + Pi
most initiation factors, elongation factors and release factors are bound covalently to GTP
