Mbb 331 Lec 21

Front 1

Is transcription and translation coupled in eukaryotes? is it in prokaryotes?

Back 1

prokaryotic RNAP and ribosomes work on the same mRNA (coupled), in eukaryotes it is not coupled, they are spatially and temporary seperated

Front 2

what's a polyribosome?

Back 2

a cluster of ribosomes that is connected by a strand of messenger RNA and is active in protein synthesis. (can be translated simultaneously by multiple ribosomes)

Front 3

what does the peptidyl transferase reaction do?

Back 3

which forms peptide bonds between adjacent amino acids using tRNAs during the translation process of protein biosynthesis.

Front 4

what 3 things are necessary for translation initiation in prokaryotes?

Back 4

1. ribosome must be recruited

2. initiator tRNA must be charged and placed into the P site of the ribosome

3. ribosome must be precisely positioned over the start codon

Front 5

what is the initiating aminoacyl-tRNA called?

Back 5

N-formyl-methionine (fMET)

Front 6

what are the ribosomes three tRNA binding sites?

Back 6

A site: for binding of the aminoacylated-tRNA

P site: binding for peptidyl-tRNA

E site: binding site for the tRNA that is released after the growing polypeptide chain has been transferred to the aminoacyl-tRNA (E for exiting)

Front 7

what are the 3 initiation factors (IFs) that direct the assembly of the 30S initiation complex?

Back 7

IF1, IF2, IF3

Front 8

Describe bacterial translation initiation

Back 8

1.IF3 to 30S at E site - this prevents 50S reassociation

2.IF1, IF2, GTP bind alongside IF3

3.binding mRNA to fMet-tRNA forming 30S initiation complex

4. loss of IF3 and binding of 50S large subunit

5. GTP hydrolysis, IF2 and IF1 dissociation

Front 9

what does IF1 do in bacterial translation initiation?

Back 9

IF1 influences dissociation of 70S ribosome to prevent 50 S and 30S and prevents tRNA from binding to the A-site of the small 30S subunit

Front 10

what does IF2 do in bacterial translation initiation?

Back 10

IF2 is a GTPase that interacts with 30S, IF1 and fMet-TRNA, to facilitate association of initiator tRNA with 30 S

Front 11

binding between 30S prokaryotic ribosomal subunit and the initiation site of a message depends on base pairing between?

Back 11

shine-dalgarno sequence and complementary RNA sequence at 3' end of 16S RNA of the 30s subunit, IF3 helps with this

Front 12

describe translational control in ribosomal proteins in terms of in the presence of rRNA and absence

Back 12

in the presence of rRNA-> both ribosomal proteins expressed from the operon bind to the rRNA and assist in the proper assembly of the riboswitch

in the absence of rRNA-> ribosomal proteins have no rRNA to associated with, this causes ribosomal protein 2 to bind to the ribosomal binding site and overlapping ribosomal protein 1 translation site

Front 13

what are sRNA's? what's their function?

Back 13

small baterial regulatory RNAs, they can repress or activated translation

Front 14

describe the MS2 RNA phage and what its involved in

Back 14

translational control via access to initiation sequences,

the initiation codon for the replicase gene in MS2 RNA phage is buried in a ds secondary structure that involves part of the coat gene

Front 15

describe riboswitches, describe how they work

Back 15

they are regulatory elements that bind and respond to ligands in controlling gene transcription and translation

it works by the aptamer binding the ligand (metabolite) causing a change in the structure of the expression platform (this is how control occurs)

Front 16

describe SAM-sensing riboswitches in terms of absence and presence of it (in transcription) and describe it in translation

Back 16

S-adenosylmethionine-sensing riboswitch

absence: transcription is on, regions on the RNA form one stem loop

in translation: ribosome binding site not affected

presence: two stem loops are formed, one becomes a terminator, transcription is off

in translation: ribosome binding site is on the second loop, blocking it from binding

Front 17

how is antisense rna translational control done?

Back 17

antisense rna complementary to mRNA forms a dsRNA with target mRNA. this prevents ribosome binding, targetting bound mrna and causes premature transcriptional termination

Front 18

describe translation initiation scanning model in eukaryotes

Back 18

40s ribosomal subunit locates start codon by binding to the 5'cap and scanning downstream to find first favorable AUG (NO SDG/RBS)

which is purine in -3 position and G in +4 position

Front 19

what does a hairpin past an AUG (near 5'end) do to translation? a stable stem loop between cap and initiation site?

Back 19

hairpin can force a pause by ribosomal subunit which may stimulate translation

stable stem loop between cap and initiation site blocks scanning and inhibits translation

Front 20

describe the eukaryotic initiation factors (eIFs) in translation initiation

Back 20

eIF2 binds Met-tRNA^met to ribosomes, eIF2B activates eIF2 replacing GDP with GTP

eIF1 and eIF1A aid in scanning to initiation codon,

eIF3 binds to 40S ribosomal subunit and inhibits reassociation with 60S subunit

eIF4F multi-subunit (A,G,E) helps 40s subunit bind 5'end of mRNA

eIF5 helps 60s ribosome subunit associate with 48S complex

eIF6 binds 60s subunit, blocks 40s subunit reassociation

Front 21

describe the eIF4F multi-subunit complex

Back 21

eIF4G adaptor protein that binds to:

eIF4E (cap binding protein),

eIF3 (40S ribosomal subunit-binding protein)

eIF4A (helicase) unwinds hairpins found in the 5' leader

-Pab1p (polyA-binding protein, PABP)

Front 22

for translation control in eukaryotes, what gets phosphorylated? give an example of how this works in hemoglobin

Back 22

eIF2alpha,

heme-starved molecules activate HCR (heme-controlled repressor) which phosphorylates the alpha unit of eIF2, this inhibits initiation via tight interaction with eIF2B which can no longer change GDP to GTP

Front 23

what is the rate limiting step in mRNA translation in eukaryotes?

Back 23

cap binding by eIF4E

eIF4G has to compete with 4E-BPs to bind to eIF4E

Front 24

how it translation controlled by mTOR phosphorylation?

Back 24

mTOR targets and phosphorylates 4E-BP1 which causes it to dissociated from eIF4E and releases it to activate translation initiation (allows it to do cap binding)