Exam 2: Translation

Question 1

codon

Answer 1

3 nucleotide bases representing 1 aa or the stop command

64 possible

Question 2

start codon

Answer 2

AUG

also methionine so every protein starts with met

often met is cleaved later

Question 3

stop codons

Answer 3

UAA

UAG

UGA

Question 4

geneticists read and write genetic code in the _’ to _’ direction

Answer 4

5’ to 3’

Question 5

5’ to 3’ is also…

Answer 5

direction mRNA is synthesized and translated

sequence of the coding strand of dsDNA in transcription units

Question 6

variations in genetic code are found in

Answer 6

mitochondria

some bacteria

Question 7

redundancy in genetic code

Answer 7

64 codons but 20 AAs

for every AA there are 1-6 codons

Question 8

silent sites

Answer 8

for 8 AA the 3rd codon letter can be any of the 4 bases

called silent sites b/c the mutation doesn’t affect the AA being coded for

Question 9

where on mRNA do nucleotides make a codon?

Answer 9

open reading frame only

Question 10

3 steps of translation

Answer 10

initiation

elongation

termination

Question 11

initiation

Answer 11

small ribosome subunit binds to ribosome-binding site on leader sequence of mRNA

large ribosome subunit joins to form a complete ribosome

Question 12

it all beings with base-pairing of the ______ with _______

Answer 12

mRNA leader sequence, ribosomal RNA (rRNA)

Question 13

AUG binds…

Answer 13

a special tRNA-methionine

used only at the beginning of a protein

Question 14

larger ribosome subunit cannot attach to the smaller subunit until…

Answer 14

AUG binds tRNA-methionine

Question 15

initiation complex

Answer 15

mRNA + large and small ribosome subunits + tRNA methionine

Question 16

Shine-Dalgarno mRNA sequence

Answer 16

(5’-AGGAGG-3’) in prokaryotes complementary to rRNA

provides recognition btw small subunit and mRNA

puts AUG into right place on small subunit

Question 17

main molecules of elongation

Answer 17

mRNA

ribosomes

AAs

tRNA

Question 18

elongation steps

Answer 18

bind new charged tRNA

transfer polypeptide chain

translocate mRNA

Question 19

3 ribosome sites

Answer 19

A, P, E

AA site, polypeptide site, exit site

each same size as one codon on mRNA

mRNA moves across these sites

Question 20

tRNA

Answer 20

transfer RNA

AA come attached on tRNA

has an anticodon complementary to mRNA codon

Question 21

bond transfer

Answer 21

AA had bond transferred from tRNA to lengthening polypeptide

then mRNA and attached tRNA moves ahead 1 codon

Question 22

translocation

Answer 22

moving ahead one codon

stops at a stop codon

Question 23

part 1 of elongation

Answer 23

polypeptide attached to tRNA to mRNA at p-site

a-site holds charged tRNA

e-site holds uncharged tRNA

Question 24

part 2 of elongation

Answer 24

polypeptide transferred to tRNA on a-site (bond transfer) and gains 1 AA

P & E sites have uncharged tRNAs

Question 25

part 3 of elongation

Answer 25

mRNA translocates 1 codon forward

polypeptide attached to tRNA to mRNA at p-site again

A-site empty

E-site has new uncharged tRNA

old uncharged tRNA leaves from e-site

repeat

Question 26

how is tRNA charged

Answer 26

aminoacyl-tRNA synthetase

20 enzymes for 20 AAs

enzyme must recognize it’s AA and all alternative tRNA’s for that AA

Question 27

3 steps of elongation condensed

Answer 27

bind anticodon of next tRNA to A site

transfer c-terminal aa of pp to new aa on A site

translocate whole mRNA and associated tRNAs by 1 codon length

Question 28

termination

Answer 28

stop codons UAA, UAG, UGA

there is no tRNA to fit stop codon

special protein called release factor attaches to stop codon

translocation occurs w/ no aa attachment

Question 29

elongation factor EF

Answer 29

subsidiary proteins that help the process at several points

released when codon-anticodon bond forms