Mod 7: Protein synthesis

Question 1

in prokaryotes, what type of ribosome and what subunits are they made up of

Answer 1

70s ribsomes

Large subunit = 50s = 23s rRNA + 5s rRNA + 31 proteins

Small subunit = 30s = 16s rRNA + 21 proteins

Question 2

in eukaryotes, what type of ribosome and what subunits are they made up of

Answer 2

80s ribosomes

Large subunit = 60s =
28s rRNA + 5.8s rRNA + 6s rRNA +48 proteins

Small subunit = 40s =
18s rRNA + 33proteins

Question 3

what does s stand for in the sixing of ribosomes

Answer 3

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

Question 4

what needs to happen before AA can bind to DNA?

Answer 4

must bind with ATP first

Question 5

what process allows AA to bind with ATP and explain x

Answer 5

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

Question 6

initiation - whawt is Shine-Dalgarno sequence

Answer 6

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

Question 7

what is the equivalent to the Shine-Dalgarno sequence in eukaryotes

Answer 7

Kozak sequence

Question 8

how many tRNAs are there for methionine and what are their functions

Answer 8

one for initiation (to start translation)
one for elongation (so within the gorwing polypeptide chain)

Question 9

for process of translation and diagram, see onenote

Answer 9

:)

Question 10

what are the initiation factors involved in translation

Answer 10

IF1
IF2
IF3

Question 11

IF1 function

Answer 11

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

Question 12

IF2 function

Answer 12

tags the initiator tRNA and regulates its entry into ribosome

Question 13

IF3 function

Answer 13

stops premature association of 30s and 50s

stabilises free 30s

accuracy check to make sure tRNAi-met is bound in the right place

Question 14

Elongation:

what site does the tRNAi Met associate with on the large subunit

Answer 14

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

Question 15

what does the A site do

Answer 15

where new amino acyl tRNAs come and slot in during elongation

Question 16

what does the A site do

Answer 16

where new amino acyl tRNAs come and slot in during elongation

remember it by A for amino acyl idk

Question 17

what is the elongation factor that brings in the amino acid

Answer 17

EFTu
coupled with GTP

so it forms a aminoacyl tRNA-EFTU-GTP complex

Question 18

once the new aminoacyl tRNA binds, what is ejected

Answer 18

EF-TU-GDP (so it’s been converted from GTP, but this will be recycled and goes back into process)

Question 19

what kind of bond forms between the AAs

Answer 19

peptide bond duh

Question 20

what happens when peptid bond gets formed

Answer 20

first tRNA (tRNAi Met) gets ejected from P site

Question 21

what is the other accessory factor involved in translocating the ribosome along the mRNA strand

Answer 21

EF-G-GTP

which then turn into EF-G-ADP after it’s ejected

Question 22

recap then, what are the 2 elongation factors and their functions

Answer 22

EF-Tu
mediate aminoacyl-tRNA entry into ribsome

EF-G mediates translocation

Question 23

see onenote for diagram and deatil on elongation

Answer 23

:)

Question 24

Termination:
what are the release factors used in this process and their functions

Answer 24

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)

Question 25

what happens once the release factor is bound

Answer 25

hydrolysis of polypeptid chain from tRNA and chain released and tRNA dissociates

Question 26

what is GTP

Answer 26

guanosine triphosphate

Question 27

what does GTP do

Answer 27

provides energy (via hydrolysis) GTP -> GDP + Pi

most initiation factors, elongation factors and release factors are bound covalently to GTP