Exam 2: Translation Flashcards Preview

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Flashcards in Exam 2: Translation Deck (29)
1

codon

3 nucleotide bases representing 1 aa or the stop command

64 possible

2

start codon

AUG

also methionine so every protein starts with met

often met is cleaved later

3

stop codons

UAA

UAG

UGA

4

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

5' to 3'

5

5' to 3' is also...

direction mRNA is synthesized and translated

sequence of the coding strand of dsDNA in transcription units

6

variations in genetic code are found in

mitochondria

some bacteria

7

redundancy in genetic code

64 codons but 20 AAs

for every AA there are 1-6 codons

8

silent sites

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

9

where on mRNA do nucleotides make a codon?

open reading frame only

10

3 steps of translation

initiation

elongation

termination

11

initiation

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

large ribosome subunit joins to form a complete ribosome

12

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

mRNA leader sequence, ribosomal RNA (rRNA)

13

AUG binds...

a special tRNA-methionine

used only at the beginning of a protein

14

larger ribosome subunit cannot attach to the smaller subunit until...

AUG binds tRNA-methionine

15

initiation complex

mRNA + large and small ribosome subunits + tRNA methionine

16

Shine-Dalgarno mRNA sequence

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

provides recognition btw small subunit and mRNA

puts AUG into right place on small subunit

17

main molecules of elongation

mRNA

ribosomes

AAs

tRNA

18

elongation steps

bind new charged tRNA

transfer polypeptide chain

translocate mRNA

19

3 ribosome sites

A, P, E

AA site, polypeptide site, exit site

each same size as one codon on mRNA

mRNA moves across these sites

20

tRNA

transfer RNA

AA come attached on tRNA

has an anticodon complementary to mRNA codon

21

bond transfer

AA had bond transferred from tRNA to lengthening polypeptide

then mRNA and attached tRNA moves ahead 1 codon

22

translocation

moving ahead one codon

stops at a stop codon

23

part 1 of elongation

polypeptide attached to tRNA to mRNA at p-site

a-site holds charged tRNA

e-site holds uncharged tRNA

24

part 2 of elongation

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

P & E sites have uncharged tRNAs

25

part 3 of elongation

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

26

how is tRNA charged

aminoacyl-tRNA synthetase

20 enzymes for 20 AAs

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

27

3 steps of elongation condensed

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

28

termination

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

29

elongation factor EF

subsidiary proteins that help the process at several points

released when codon-anticodon bond forms