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Test 1 FTM > Lecture 15 > Flashcards

Lecture 15 Flashcards

1
Q

What are the requirements for translation?

A
  1. mRNA
  2. ribosomes
  3. Charged tRNA
  4. initiation factors
  5. GTP
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2
Q

Basic components of translation?

A
  1. activation of the monomer
  2. initiation
  3. elongation
  4. termination
  5. processing the polymer
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3
Q

How does tRNA become charged tRNA?

A
  1. enzyme bound amino acid- adenylate
  2. Formation of the aminoacyl-tRNA

reaction is driven by the hydrolysis of pyrophosphate

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4
Q

What is the first AA in prokaryotes and in mitochondria?

A

N-formylmethionine (fMet)

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5
Q

What is the role of fMET?

A

It allows for initiation

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6
Q

Prokaryotes have two tRNA’s for methionine?

A
  1. one allows for the formation of fMAT

2. allows for AUG codon

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7
Q

Two tRNA’s that recognize AUG in eukaryotes?

A
  1. The first codon also uses MET, and it has a special tRNA for this first codon (but the MET amino acid is not
    formylated) .
  2. Normal MET for internal codons
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8
Q

What is the purpose of the Shine Dalgarno sequence?

A

This sequence is purine rich

found in prokaryotes to allow for correct alignment of the AUG codon

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9
Q

How do eukaryotes align the mRNA with the ribosome?

A

lack Shine Dalgarno sequence

eukaryotic small ribosome binds close to the cap at the 5’ end, scans until it encounters the AUG start codon.

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10
Q

The steps to protein synthesis -initiation?

A
  1. Initiation factors (IFs) aid in the formation of the 30S initiation complex.
  2. The charged initiator tRNA is brought to the P site of the 30S subunit by IF-2-GTP.
  3. GTP on IF-2 is hydrolyzed and initiation factors are released when the 50S subunit arrives to form the
    70S initiation complex
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11
Q

Protein synthesis- elongation

A
  1. Elongation factor EF-Tu-GTP brings the appropriately charged tRNA to the codon in the empty A site (decoding). GTP on EF-Tu is hydrolyzed.
  2. Peptidyltransferase activity of the 23S rRNA of 50S subunit catalyzes peptide bond formation, transferring
    the initiating amino acid (or peptide chain) from the P site to the amino acid at the A site (transpeptidation).
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12
Q

protein synthesis - translocation

A
  1. EF-G-GTP facilitates movement of the ribosome three nucleotides along the mRNA in the 5’ to 3’
    direction.
  2. Steps are repeated until a termination codon is encountered at the A site.
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13
Q

Protein synthesis- termination

A

A termination codon is recognized by a release factor (RF-1 or RF-2), which results in release of the newly synthesized protein. GTP on RF-3 is hydrolyzed. The synthesizing complex dissociates.

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14
Q

In prokaryotes the mRNA is what?

A

polycistronic

contains multiple genes

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15
Q

What is the toxin Diphtheria toxin?

A

inactivation of EF-2 by ADP-ribosylation

this prevents translocation during protein synthesis

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16
Q

Streptomycin

A

Prevents assembly of ribosome (binds to 30s subunit)

17
Q

Tetracycline

A

Block elongation by preventing aminoacyl-tRNA access to the A-site

18
Q

Erythromycin

A

Binds to the 50S subunit of the complete (70S) ribosome

prevents ribosome translocation

19
Q

Chloramphenicol

A

Inhibits peptidyl transferase activity in prokaryotes

At high levels, may inhibit mitochondrial translation

20
Q

Cycloheximide

A

Inhibits eukaryotic peptidyl transferase activity

21
Q

Puromycin

A

Causes premature termination of translation in both prokaryotes and eukaryotes

22
Q

What are the 6 major post-translational modifications?

A
  1. protein folding
  2. covalent alterations
  3. proteolytic processing
  4. addition of prosthetic groups
  5. prenylation
  6. protein degradation
23
Q

zymogen activation

A

Activation by enzymatic cleavage of peptide bonds of the zymogen molecule

nonactive to active

24
Q

protein phosphorylation by a kinase

A

phosphate is transferred from ATP to AA side chain

occurs on OH groups

most common post-translational modification

25
Q

What are the two types of glycosylation?

A
  1. N-linked- addition of N to asparagine

2. O-linked- sugar is attached to serine or theonine

26
Q

Lipid anchoring?

A

The cell targets Ras protein to the cytosolic face
(inner leaflet) of the plasma membrane by a lipid
anchor mechanism - with the aid of farnesyl groups.

27
Q

What protein is essential for proper insulin folding?

A

C-peptide

28
Q

Proteolytic Processing of Insulin

A
  1. gene for insulin is transcribed into mRNA
  2. translation of that mRNA
  3. Translation of the polypeptide is directed into the lumen of the rER and forms “preproinsulin”
  4. The signal sequence is cleaved in the lumen of the rER – forms “proinsulin”
  5. Proinsulin is moved from the rER to the golgi, where it is cleaved to form insulin and C-peptide
  6. insulin and C-peptide go into secretory vesicles
  7. secreted by exocytosis

Test 1 FTM (35 decks)

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