Lecture 35

Question 1

What is translation?

Answer 1

The decoding of genetic information from the 4-letter language of nucleic acids into polypeptides expressed in the 20-letter language of proteins

Question 2

Where does translation happen?

Answer 2

ribosomes

Question 3

What can ribosomes be?

Answer 3

Either be free floating in the cytoplasm or associated with the ER

Question 4

What happens to most proteins that stay inside the cell?

Answer 4

They are synthesized on a free ribosome within the cytoplasm

Question 5

What happens do proteins that do not stay in the cell and exit?

Answer 5

Most likely be synthesized on a ribosome studded to the rough ER

Question 6

How is mRNA translated?

Answer 6

base sequence is “translated” three bases at a time (codon) by base-pairing with a tRNA having a complementary anti-codon

Question 7

What joins the AA delivered by tRNA together?

Answer 7

polypeptides

Question 8

How is mRNA translated?

Answer 8

5 to 3

Question 9

What is the name when there are multiple ribosomes in a transcript?

Answer 9

polysome

Question 10

What happens when ribosomes bind to mRNA?

Answer 10

Aminoacyl-tRNAs bind to specific pocket sites on the ribosome and complement their anticodons to the codons on the mRNA

Question 11

What is the first tRNA brought to ribosomes?

Answer 11

N-formylmethionine-tRNA, which is specific for initiating translation

Question 12

How are polypeptides synthesized?

Answer 12

N to C terminus

Question 13

How many possible codons are there?

Answer 13

64 codons

Question 14

How many codons code for amino acids?

Answer 14

61

Question 15

How many codons are used for STOP codons?

Answer 15

3

Question 16

What is the codon that initiates translation?

Answer 16

AUG for methionine

Question 17

How can 2 amino acids form a peptide bond?

Answer 17

The two tRNA’s must be side by side on the ribosome, with their anticodons hydrogen bonded to the mRNA at adjacent codon

Question 18

What is true about AUG and bacteria?

Answer 18

It is the start codon that codes for N-formylmethionine (fmet)

Question 19

What is the structure of tRNAs?

Answer 19

They are small, have internal base pairing, form stem loops, have ACC sequences in the 3’.

Question 20

What is true about base pairing?

Answer 20

They are specific for the first 2 but not the third

Question 21

What is the wobble mechanism?

Answer 21

states that the tRNA anticodon pairs with the mRNA codon proceeds from the 5’ to 3’ direction of the codon

Question 22

What is true about the 3rd 5’ base?

Answer 22

can typically pair with either a purine or pyrimidine base in the codon

Question 23

What does the activation of tRNA link?

Answer 23

It links the amino acid to the transfer RNA

Question 24

Do polypeptide bonds need energy?

Answer 24

Yes. tRNA and AA need to be loaded with energy. This is needed to form peptide bonds

Question 25

What is aminoacyl-tRNA-synthetase?

Answer 25

It is the enzyme that loads energy to match it with the correct amino acid

Question 26

Where does tRNA synthetase load?

Answer 26

either 2 or 3 OH

Question 27

What is true about the tRNA proofreading technique?

Answer 27

There are 20 tRNA synthetase for each amino acid and each one selects the correct one (amino acid)

Question 28

What is a charged tRNA?

Answer 28

Amino acid and tRNA

Question 29

What are the assembled ribosome # in prokaryotes?

Answer 29

70s

Question 30

What are the assembled ribosome # in eukaryotes?

Answer 30

80s

Question 31

What is true about ribosomes and their history of evolution?

Answer 31

Ribosomes evolved early in the history of life and have remained relatively unchanged. Same with rRNAs.

Question 32

What is true about rRNA

Answer 32

They are used to determine phylogenetic relationships, have been unchanged, and use internal base-pairing.

Question 33

How does translation happen in prokaryotes?

Answer 33

1. It is broken down to EPA(dissociation) 2. IF 1 & 3 help guide to the mRNA 3. binding happens to Shine-Dalgarno 4. when it binds, it finds the adjacent AUG(start) to Shine-Delg. 5. tRNA recognizes AUG 6. binds to fmet and initiate translation and IF dissociate

Question 34

How does elongation happen?

Answer 34

1. tRNA binds/enters to A site and EF-Tu binds to GTP 2. Amino acids joins P site 3. GTP is hydrolyed and EF-Tu GDP is released 4.peptide bond formation 5. peptidyl transferase transfers the growing chain from previous tRNA to the free AA

Question 35

What do release factors do?

Answer 35

RF1 (UAA) or RF2 (UAG,UGA) recognize stop codons (they have shape similar to tRNA)

Question 36

What does RF3 do?

Answer 36

brings GTP and hydrolyzes the ester bond with tRNA

Question 37

What happens during termination?

Answer 37

Polypeptide is release, RF1 and RF2 are release, GTP is hydrolyzed and RFs, tRNA and GDP are released. Ribosome is disassembled and recycled

Question 38

What are the stop codons?

Answer 38

UAA UAG UGA

Question 39

What are the start codons?

Answer 39

AUG

Question 40

What are some elongation factors?

Answer 40

EF-Tu

Question 41

How does EF-Tu work?

Answer 41

it binds to GTP and tRNA and delivers AA2 to acceptor site

Question 42

What does RF1/RF2 do?

Answer 42

It recognizes stop codons (UAA)

Question 43

What does RF3 do?

Answer 43

Brings in GTP and hydrolyzes the ester bond with tRNA

Question 44

What happens when polypeptides are released?

Answer 44

RF1, RF2, RF, tRNA, and GDP are released while GTP is released and hydrolyzed