Lecture 6 (Ch 9)

Question 1

Describe the structure of AA

Answer 1

Central carbon, amino group (NH3+), carbonyl group (COO-), and R-group

Question 2

There are __ AA

Answer 2

20

Question 3

The bond between AA that form a peptide chain is the ___, which connects ___ with ___. The bond is catalyzed by ___

Answer 3

peptide bond; NH3+ and COO- of two AA;

enzyme of the ribosome

Question 4

Conserved function of ribosome (3):

Answer 4

1. bind mRNA and i.d. start codon
2. facilitate complementary base pairing of mRNA codon with tRNA anticodon
3. catalyze formation of peptide bonds between AA

Question 5

Conserved structure of ribosome

Answer 5

Large subunit + small subunit = ribosome

Question 6

Structure of bacterial ribosome v. eukaryotic ribosome

Answer 6

50s + 30 s = 70s

60s + 40s = 80s

Question 7

Each subunit contains ___ and ___, which are created by ___ and ___

Answer 7

protein and rRNA;

RNA Pol II and mostly RNA Pol I

Question 8

The 3 regions of ribosome are:

Answer 8

E, P, and A

Question 9

The funct’n of the 3 regions of ribosome are:

Answer 9

1. Peptidyl site holds tRNA to which PP is attached
2. Aminoacyl site binds new tRNA molecule holding AA to be addd to PP chain
3. Exit site - empty, uncharged tRNA exits

Question 10

tRNA’s post-transcription modification is (1) ___, which causes a ___ structure, and (2) ___, which acts as a ____.

Answer 10

2’ structure via base-pairing with itself;
stem-loop structure;
CCA codon that acts as a AA attachment site.

Question 11

initiator Met-tRNA has two special bases, which are ___

Answer 11

psy (psuedoA) and a T (!)

Question 12

Maximum number of different tRNA produced are seen in ___, and is ___; however, most organisms produce ___ due to ____.

Answer 12

some eukaryote; 61 (64 - 3 stop codons);

30-40 tRNA due to third base wobble.

Question 13

Three phases of translation are: ____. They each involve factors ___.

Answer 13

1. Initiation, IF
2. Elongation, EF
3. Termination, RF

Question 14

The main difference in translation processes in bacteria and eukarya is ____

Answer 14

how the start codon is identified

Question 15

Initiation: begins by ___ binding near the ___ end of mRNA. ___ must be Id’d.

Answer 15

small ribosomal subunit; 5’;

AUG

Question 16

Initiation: Any tRNAmet can initiate translation. T/F

Answer 16

False– structural differences

Question 17

Initiation: ends when ___

Answer 17

large subunit joins small subunit

Question 18

Initiation: beginning in the right codon is controlled for with 3 different methods, which are___

Answer 18

1. tRNA-met start codon being different structurally
2. 5’ cap & consensus sequence is the recognition site for eIF4 complex, which recruits the small subunit
3. Shine-Delgarno/Kozak sequences for bacteria and eukarya

Question 19

Initiation: differences between bacteria and eukarya

Answer 19

Bacteria: Shine-Delgarno seq upstream of AUG;
Eukarya: Kozak seq upstream of AUG
&
Bacteria: initiator tRNA= fMet
Eukarya: initiator tRNA = Met

Question 20

Initiation: How does the eIF4 make sure that it is starting the translation in the right place in eukarya?

Answer 20

recognizes 5’ cap & consensus sequence upstream of AUG

Question 21

Elongation: begins with ___

Answer 21

EF recruitment

Question 22

Elongation: EF uses ___ to do 3 things:

Answer 22

GTP hydrolysis;

1. recruit tRNA to A-site
2. form Peptide bonds between AA
3. translocate ribosome in 3’ direction along mRNA (down the mRNA)

Question 23

Initiation: In bacteria, how does it compensate for a lack of 5’ cap to start transcription?

Answer 23

IF3 complex binds to 5’ mRNA, and Shine-Delgano sequence base-pairs with 16s rRNA in small subunit to position AUG at P-site.

Question 24

Elongation: the 4 steps of elongation are:

Answer 24

1. charged tRNA recruitment at A site
2. charged tRNA-codon pairing at A-site
3. GTP hydrolysis
4. Peptide bond formation

Question 25

Elongation: When is EF-Tu-GTP within the ribosome? When is EF-Tu-GDP within the ribosome? Out?

Answer 25

with tRNA recruitment
after tRNA recruitment
when mRNA translocation occurs

Question 26

Elongation: What catalyes the formation of peptide bond? Where is the AA chain created?

Answer 26

Peptidyl transferase;

A-site

Question 27

Termination: What are the 3 steps?

Answer 27

1. RF recruitment
2. PP release
3. Ribosome dissocation and mRNA release

Question 28

Termination: what triggers RF recruitment?

Answer 28

when stop codon enters A-site

Question 29

Termination: what triggers PP release? How?

Answer 29

eRF1 fills A-site; hydrolysis of GTP triggers release of PP from the P-site

Question 30

T/F: Transcription & translation happen simultaneously in bacteria

Answer 30

T

Question 31

T/F: Transcription & translation happen simultaneously in eukarya

Answer 31

F, due to nucleus

Question 32

T/F: Kozak sequence is always upstream of AUG

Answer 32

F. AUG can be embedded within the sequene (ACCAUGG)

Question 33

The lack of complete 61 different tRNA can be explained by the presence of ___ tRNAs– they have different anticodons, but ___

Answer 33

isoaccepting;

accept the same AA

Question 34

the third wobble tends to be within ___, or contain a special base called ___ that can base pair with ___

Answer 34

the purines or the pyrimidines (i.e. UCA and UCG anticodon tRNA may be read by one tRNA);
I (Inosine); pyrimidine C U and purine A.

Question 35

tRNA is charged by ___, which adds ___ to tRNA.

Answer 35

tRNA synthetase; AA

Question 36

T/F each tRNA synthetase is specific for each codon

Answer 36

F– for each AA

Question 37

What kind of bond is formed between what molecules by tRNA synthetase?

Answer 37

covalent bond;

COOH on AA and 3’ OH of AMP nucleotide (post-transcriptionally added ACC)