tRNAs, charging reaction, translation in detail -- Lecture 15

Question 1

structure of a transfer RNA (tRNA):

tRNA molecules (what do they do)

Answer 1

carry amino acids to the ribosome for incorporation into a protein

Question 2

structure of a transfer RNA (tRNA):

the anticodon associates w/ the codon thru ___

Answer 2

complementary base pairing

Question 3

structure of a transfer RNA (tRNA):

parts of a tRNA

Answer 3

amino acid

acceptor stem

anticodon loop

anticodon

Question 4

structure of a transfer RNA (tRNA):

charged tRNA (what is it)

Answer 4

a tRNA w/ an amino acid attached

Question 5

how does the amino acid get attached to the tRNA to make it a charged tRNA?

Answer 5

thru the tRNA charging reaction

Question 6

tRNA charging reaction:

aminoacyl-tRNA synthetase (aaRS) enzymes bind to

Answer 6

an amino acid

an ATP

an ‘uncharged’ tRNA (not bound to an amino acid)

Question 7

tRNA charging reaction:

using the ___, the amino acid is covalently bound to the tRNA ‘charged’

Answer 7

energy from ATP hydrolysis

Question 8

tRNA charging reaction:

using the energy from ATP hydrolysis, the ___

Answer 8

amino acid is covalently bound to the tRNA ‘charged’

Question 9

tRNA charging reaction:

there are ___ aaRS enzymes (one for each amino acid)

Answer 9

20

Question 10

what are the phases of translation?

Answer 10

initiation

elongation

termination

Question 11

phases of translation:

initiation (what happens)

Answer 11

assembly of the ribosome/mRNA/charged-tRNAs

Question 12

phases of translation:

elongation (what happens)

Answer 12

starts at the ‘Start’ codon (methionine)

amino acids are added until the ‘Stop’ codon

Question 13

phases of translation:

termination (what happens)

Answer 13

the new protein is released from the ribosome

the ribosome complex disassembles

Question 14

prokaryotic initiation steps:

1) ___ in the small ribosomal subunit binds the ___ at the ___ (complementary rRNA/mRNA sequences)

Answer 14

rRNA

mRNA

5’ ribosome binding sequence

Question 15

prokaryotic initiation steps:

2) the ___ binds to the ___ codon (AUG) (methionine)

Answer 15

initiator tRNA

start codon

Question 16

prokaryotic initiation steps:

3) the ___ subunit joins and initiation is complete

Answer 16

large ribosomal subunit

Question 17

eukaryotic initiation steps:

1) the ___ subunit + ___ bind to the mRNA 5’ cap

Answer 17

small ribosomal subunit

initiator Met tRNA

Question 18

eukaryotic initiation steps:

2) the complex scans the mRNA until it finds the ___ codon (AUG)

Answer 18

start

Question 19

eukaryotic initiation steps:

3) the ___ ribosomal subunit joins the complex and ___ is complete

Answer 19

large

initiation

Question 20

ribosome tRNA binding sites:

‘P’ site (what is it)

Answer 20

where the initiator tRNA binds

Question 21

ribosome tRNA binding sites:

‘A’ site (what is it)

Answer 21

where the next tRNA binds carrying the next amino acid to be added to the protein

Question 22

ribosome tRNA binding sites:

‘E’ site (what is it)

Answer 22

where spent uncharged tRNAs are ejected

Question 23

elongation overview:

translocation (what is it)

Answer 23

the movement of the ribosome down the length of the mRNA

Question 24

amino acids are joined by ___ bonds

Answer 24

covalent

Question 25

proteins are always synthesized in the ___ to ___ direction

Answer 25

N-terminal to C-terminal direction

Question 26

protein synthesis continues until the ___ codon –> then ___ of translation

Answer 26

‘Stop’

termination

Question 27

translation termination (steps):

1) release factor (definition)

Answer 27

protein that binds to the stop codon (no tRNAs for the stop codons)

Question 28

translation termination (steps):

2) the protein is ___ from the ribosome

Answer 28

released

Question 29

translation termination (steps):

3) the ribosome complex ___

Answer 29

falls apart

Question 30

(summary) steps in elongation:

initiation complete:

Answer 30

the initiator tRNA is bound to the P site

a new charged tRNA binds to the A site

Question 31

(summary) steps in elongation:

formation of the peptide bond:

Answer 31

amino acid chain is transferred form the tRNA in the P site to the tRNA in the A site

the tRNA in the P site now has no AA (uncharged)

Question 32

(summary) steps in elongation:

translocation:

Answer 32

the ribosome moves 1 codon down the mRNA

the uncharged tRNA in the P site shifts to the E site (ejected)

the tRNA in the A site shifts to the P site

a new charged tRNA can now bind to the codon in the A site