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Biochem Exam IV > Translation > Flashcards

Translation Flashcards

1
Q

Ternary Complex

A
  • -eIF2a, Met-tRNA, GTP

- -eIF2a/GDP complex leaves once initiation complex is formed

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2
Q

Initiation of Translation

A
  • -need tRNA, mRNA bound to small ribosomal subunit

- -phase ends when larger subunit binds

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3
Q

Elongation

A
  • -Met-tRNA binds in P site and next AA/tRNA binds in A site with help of EF1:GTP
  • -after bond formed between both AA’s ribosome moves further down mRNA with help of EF2:GTP opening up A site for next AA/tRNA to bind
  • -need 2 GTP’s for each AA added to polypeptide chain
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4
Q

Termination

A
  • -one of three stop codons reaches A site
  • -protein called eRF (releasing factor) pairs w/ stop codon and is bound w/ GTP
  • -GTP hydrolysis releases peptide from P site
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5
Q

Streptomycin

A
  • -binds to small subunit of ribosome and inhibits initiation
  • -also causes mistranslation of codons
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6
Q

Neomycin and Gentamycin

A

–bind to ribos and cause mistranslation of codons

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7
Q

Tetracycline

A

–blocks A site and prevent tRNA binding to ribo

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8
Q

Chloramphenicol

A

–prevents peptidyl bond formation

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9
Q

Ribosomal Subunits

A
  • -large subunit contains catalytic activity

- -small subunit contains binding areas from mRNA, tRNA

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10
Q

Eukaryote ribosomal toxins

A
  • -ricin: glycosidase the removes adenine bases from various positions of the rRNA in large subunit–decreases catalytic activity
  • -Diphtheria toxin: inactivates EF2 by ADP-ribosylation so it interrupts elongation phase
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11
Q

Regulation of Translation and Mechanisms

A
  • –works extremely quickly to upregulate or down regulate protein production so no time is lost
  • -regulation by preventing the recognition of a start codon: protein binds to 5’ UTR of mRNA so start codon isnt found by ribos: this is more specific regulation
  • -regulating activity of initiation factors: phosphorylation of eIF-2a in repsosne to certain stimuli renders the initiation factor inactive: this is more overall encompassing regulation
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12
Q

Protein folding

A
  • -some proteins can fold fine on their own
  • -others get assistance from chaperone proteins that bind to hydrophobic regions of protein and help fold it, chaperones are found in cytosol and ER, places where protein folding occurs
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13
Q

Charcot Marie Tooth Disease

A

–mutations in HSP genes that encode for heat shock proteins that help refold misfolded proteins

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14
Q

Protein Synthesis and ER

A
  • -proteins that are to e exported are synthesized at ER
  • -give off hydrophobic signal sequence from peptide which binds to signal recognition particle and then docking protein on ER wall
  • -synthesizes peptide into ER
  • -signal peptidase cleaves off signal peptide sequence
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15
Q

Unfolded protein response

A
  • -inhibits protein translation
  • -induces chaperone production
  • -cell considers apoptosis
  • -response mounted when there is accumulation of unfolded proteins in cell
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16
Q

Protein Glycosylation

A
  • -gives proteins physical changes: size, structure, bulk
  • -carbs on protein surface used for recognition sites that direct trafficking of protein and mediate protein-protein interactions
17
Q

Glycosyltransferases

A
  • add sugars via activated sugar molecules to protein
  • -starts in ER and golgi
  • -tons of specific glycosyltransferases for different sugar donors and acceptor molecules and types of bonds formed
18
Q

N-linked Glycosylation

A
  • -starts in ER and attaches sugars to asparagine
  • -synthesis of universal oligosaccharide on dolichol phosphate
  • -transfer of universal oligo to nascent polypeptide chain
  • -highly specific modification of universal oligo in golgi by addition/removal of carbs
  • -modifications yield two distinguishable types of N-glycosylated proteins: high mannose type and complex type (w/ mannose and 5 other carbs)
19
Q

O-linked Glycosylation

A
  • -occurs after protein is folded and has reached golgi
  • -N-acetyl-galactosamine added to -OH group of serine or threonine on surface of protein (protein already folded)
  • -
20
Q

Blood Types and O-linked glycosylation

A
    • A antigen gets GalNAc added to serine

- -B antigen gets Gal added to serine of H-antigen

21
Q

Other modifications Part 1

A
  • -proline modified in collagen (scurvy)
  • -lysine acetylated in histones
  • -thiol group in cysteine converted to aldehyde group to form Calpha-formylglycine: important for function of lysosomal sulfatases
22
Q

CDG’s

A
  • -congenital disorders of glycosylation
  • -affect N-linked glycosylation
  • -CDG I: defective synthesis of lipid-linked oligosaccharide precursor
  • -CDG II: defective trimming of oligosaccharide chain
23
Q

Terminal Modifications of Proteins

A
  • -N-terminal trimming: methionine removed from start
  • -Addition of hydrophobic moieties: tether proteins to inner membrane leaflet
  • -GPI anchor to C-terminus: tether proteins to outer leaflet of membrane
24
Q

Targeting proteins to lysosoes

A
  • -high mannose glycosylated proteins are phosphorylated at mannose residues
  • -phosphomannose is signal to be picked up by lysosomes
25
Q

Protein Import into Mito

A
  • -unfolded mito proteins bound by chaperones to inhibit folding and have a presequence that interacts w/ receptor on outer mito membrane
  • -TOM’s/TIM’s import unfolded protein into matrix and presequence is cleaved off
  • -proteins will contain another sequence that mediate their insertion into membrane or intermembrane space, etc.
26
Q

Deafness-Dystonia Disorder

A

–mutation in a TIM component that impairs cellular energy production-

27
Q

Cystic Fibrosis

A
  • -protein sorting defect
  • -deletion of just one codon from CFTR1 gene
  • -interferes w/ folding and glycosylation of the protein
  • -instead of being routed to plasma membrane it is routed to cytosol and degraded
28
Q

I-Cell disease

A
  • -protein sorting defect
  • -transfer of phosphate to mannose is impaired
  • -therefore lysosomal proteins do not get routed to lysosomes and their function is compromised
  • -accumulation of undegraded proteins in lysosomes
  • -inclusion bodies in fibroblasts
  • -in serum, lysosomal proteins did not reach destiniation and can be observed
29
Q

2 methods for protein degradation

A
  • -lysosome: nonspecific degradation, autophagy (cell digests itself), has high concentrations of hydrolytic enzymes, degrades intra- or extracellular proteins so two pathways
  • -proteosome: specific degradation of cyto proteins, ubiquitin transferred to protein surface to signal proteosome (E1-E3 proteins) transfer ubiquitin in 1-3 order and E3 puts in on protein, need polyubiquitination for degradation, ubiquitin molecules can be reused, done for misfolded proteins and cyclins (which need to be destroyed quickly for cell cycle)

Biochem Exam IV (5 decks)

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