Protein Synthesis and Processing Flashcards

1
Q

Steps in Synthesis of Protein– Initiation (common to all organisms)

A
  • Initiation complex including mRNA and initiator tRNA(met) is assembled on small subunit of ribosome, then large subunit binds
  • All proteins start with methionine (which can be removed later)
  • In bacteria, formyl-methionine (fMet) is used for initiation
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2
Q

Steps in Synthesis of Protein-Elongation (common to all organisms)

A
  • Aminoacyl tRNA recognizes a code and delivers an amino acid
  • Peptide bond is formed
  • The growing peptide is translocated by three nucleotides
  • Above 3 steps are repeated as ribosome moves along mRNA
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3
Q

Steps in Synthesis of Protein- Termination (common to all organisms)

A
  • Release factors recognize termination codons

- Peptide chain is released from ribosome

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4
Q

Initiation in Prokaryotes

A

-fMet used
-Initiation factors: IF1, IF3 (keeps ribosome subunits apart)
IF2–binds aminoacyl-fMet-tRNA and GTP

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5
Q

Elongation factors in E.coli

A
  • Eu-Tu
  • EF-Ts
  • EF-G
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6
Q

EF-Tu

A

binds GTP and aminoacyl tRNA (the GTP is converted to GDP)

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7
Q

EF-Ts

A

exchanges the GDP on Tu for GTP

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8
Q

EF-G

A

mediates translocation step

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9
Q

RFs

A

Release factors. Recognize termination or STOP codons

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10
Q

Release factors in E. coli

A

RF1, RF2, RF3

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11
Q

RF1

A

recognizes UAA, UAG

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12
Q

RF2

A

recognizes UAA, UGA

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13
Q

RF2

A

GTPase, helps bind RF1 or RF2 to ribosome

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14
Q

Initiation factors-Humans

A

eIF-2, eIF-3, eIF4E, eIF-4F

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15
Q

eIF-2

A

binds Met-tRNA, GTP

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16
Q

eIF-3

A

ribosome dissociation

17
Q

eiF-4E

A

binds mRNA cap structure

18
Q

eIF-4F

A

mRNA binding and helicase unwinding activity

19
Q

eEF1-alpha

A

analogous to EF-Tu (aa-tRNA binding)

20
Q

eEF1betagamma

A

analogous to EF-Ts (GTP exchange)

21
Q

eEF-2

A

analogous to EF-G - translocation

22
Q

Post-translational modifications

A
  • Removal of signal sequence
  • Disulfide bond formation
  • Glycosylation
  • Amino acid side-chain modification
  • Proteolytic cleavage
  • —Insulin, glucagon, and other polypeptide hormones
23
Q

Dolichol phosphate

A

Lipid carrier molecule, transfers high mannose blocks of sugar