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SFM > Functions and Dysfunctions of Protein Processing > Flashcards

Functions and Dysfunctions of Protein Processing Flashcards

1
Q

Why is it important to study the difference in protein synthesis between prokaryotes and eukaryotes? (2)

A
  1. to be able to selectively inhibit prokaryotic protein synthesis (clinical use - molecular basis for development of abx)
  2. to be able to understand the mechanism of human diseases (research use - allow for the development of treatment and/or prevention)
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2
Q

Streptomycin binds to ____ subunit to disrupt initiation of translation

  • interferes w/ binding of fmet-tRNA and impairs initiation
A

30S (prok)

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3
Q

Shiga toxin and Ricin binds to the ____ subunit to disrupt elongation

  • blocks entry of aminoacyl-tRNA ribosomal complex
A

60S (euk)

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4
Q

Clindamycin and erythyromycin bind to the ____ subunit to disrupt translocation of the ribosome

A

50S (prok)

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5
Q

Tetracyclines bind to the ____ subunit to disrupt elongation

  • blocks entry of aminoacyl-tRNA to ribosomal complex
A

30S (prok)

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6
Q

peptidyl transferase activity is housed in the _____ subunits

A

large

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7
Q

diphtheria toxin inactivates _______ and inhibits _______

  • interferes with ribosomal translocation
A
  • EF2-GTP
  • elongation
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8
Q

Chloramphenicol inhibits ______ ________ activity and impairs ______ bond formation

A
  • peptidyl transferase
  • peptide
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9
Q

Cycloheximide inhibits ______ ________ (euk) and impairs _______ bond formation

A
  • peptidyl transferase
  • peptide
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10
Q
  • causes premature chain termination (prok/euk)
  • resembles 3’ end of the aminoaceylated-tRNA
  • enters the A site and adds to the growing chain
  • forms a puromycylated chain, leading to premature chain release
  • more resistant to hydrolysis
  • stops the ribosome from functioning
A

puromycin

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11
Q

What are the 4 types of genetic mutations?

A
  1. silent: does not change amino acid
  2. missense: changes amino acid in protein with either no effect on protein function or a protein with vastly different function
  3. nonsense (null mutation): codon changes into a stop codon causing premature chain termination, protein either degraded or formed as a truncated version
  4. frameshift: one or more nucleotides are deleted or added into ORF, out of frame causes change in the codon sequence and consequently alteration in the amino acid sequence of the protein (e.g. Duchenne muscular dystrophy, β-thalassemia)
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12
Q
  • arises from a missense mutation of 6th codon in the allele of gene for human β-globin (HBB), subunit of adult hemoglobin
  • mutation changes GAG to GTG which changes glutamic acid (negatively charged, hydrophillic) to valine (hydrophobic)
  • alters conformation of HbA which causes it to aggregate and form rigid, rod-like structures
  • deforms the RBC’s into sickle-like shape
  • deformed erythrocytes have poor oxygen capacity and tend to clog capillaries, further restricting blood supply to tissues
A

sickle cell anemia

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13
Q
  • large in frame and out of frame deletions to the dystrophin gene leads to partially or non-functioning dystrophin protein
  • OOF deletions result in little/no expression of dystrophin protein, gives rise to the severe form of condition
  • presented in 1:3,500 males
  • leads to muscle wasting (wheelchair by age 12, death by respiratory failure within 10 years, sx onset by years 3-5)
  • in frame deletions result in expression of truncated forms of dystrophin, giving rise to a milder for of the disease called Becker ______ _______
A

Duchenne muscular dystrophy

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14
Q

What are the 2 types of protein sorting?

A

cytoplasmic and secretory

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15
Q
  • type of protein sorting for proteins destined for cytosol, mito, nucleus, and peroxisomes
  • protein syn begins and ends on free ribosomes in cytoplasm
  • absence or presence of certain translocation signals play role in final targeting
A

cytoplasmic pathway

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16
Q
  • type of protein sorting for proteins destined for ER, lysosomes, plasma membranes, or for secretion
  • translation begins on free ribosomes but terminates on ribosomes sent to ER
  • proteins have N-terminal hydrophobic α-helix ER targeting signal sequences present on the first 20 amino acid residues of the polypeptide
A

secretory pathway

17
Q

How does the cytoplasmic pathway know where to send mito, nucleus, and peroxisome proteins?

A
  • mito: N-terminal hydrophobic α-helix signal peptide
  • nucleus: KKKRK signal sequence (Lys, Arg rich)
  • peroxisome: C-terminal SKL signal sequence (Ser, Lys, Leu)
18
Q

How does the secretory pathway know where to send ER lumen, lysosome, secretory, and membrane proteins?

A
  • ER lumen: C-terminal KDEL retention signal (Lys, Asp, Glu, Leu)
  • lysosome: mannose 6-phosphate signal group (I-cell disease)
  • secretory: tryptophan-rich domain signal region, absence of retention motifs
  • membrane: N-terminal apolar region (stop transfer sequence)
19
Q

How are mitochondrial proteins imported?

A
  • unfolded proteins protected by binding to chaperones such as heat shock proteins 70 (HSP70)
  • translocation sequences recognized by transporters present in the mito membrane
  • proteins are passed across TOM and TIM
20
Q

How are nuclear proteins imported?

A
  • via nuclear pores
  • small proteins able to pass through specific pores
  • large proteins (>40 kDa) require nuclear localization signals
  • four continuous basic residues (Lys and Arg)
21
Q

What is the process of secretory pathway protein processing?

A
  • each protein has ER-targeting signal peptide that is 15-60 amino acids at N terminus of protein
  • signal peptide: 1 or 2 basic amino acids (Lys or Arg) near N terminus, extremely hydrophobic sequence (10-15 residues) on C terminus of basic residues
  • signal recognition particle (SRP) binds to ER targeting signal and ribosome during translation
  • SRP wraps itself around ribosome-mRNA-peptide complex, tethering it to ER membrane and halting translation temporarily
  • translation resumes when protein is directed into ER lumen
  • enzymes on luminal side cleave the signal to release the protein
  • protein undergoes post translational mods in ER and/or golgi
  • additional signal sequences serve to guide each protein to final location
22
Q
  • disease caused by lysosomal proteins not tagged with M6P
  • defective or missing GIcNAc phosphotransferase (enzyme that adds M6P to lysosomal hydrolases), enzymes are not phosphorylated and hence not sorted into vesicles and not delivered into lysosomes
  • enzymes are carried to cell surface and secreted (into blood)
  • high plasma levels of lysosonal enzymes
  • by 6 months: failure to thrive, developmental delays, physical manifestations
  • developmental delays more pronounced than cognitive delays
  • hepatomegaly, splenomegaly, defective heart valves
  • death by age 7, usually due to congestive heart failure or recurrent respiratory tract infections
A

inclusion cell disease (I cell disease)

23
Q

Describe the process of protein folding in terms of small and large proteins

A
  • small proteins can fold into native conformations spontaneously
  • large proteins cannot and are at risk for aggregation and proteolysis
  • large proteins need auxiliary proteins, chaperones which protect the protein and help fold into proper tertiary structure
  • other proteins, chaperonins, have barrel shaped compartments that admit unfolded proteins and catalyze their folding in an ATP-dependent manner
24
Q
  • type of post-translational processing
  • converts inactive forms of protein to active enzymes by unmasking active site (e.g. trypsinogen and chymotrypsinogen to trypsin and chymotrypsin)
  • converts nascent precursor proteins to mature ones (e.g. proinsulin to insulin)
A

proteolytic cleavage

25
Q

What are the 4 types of post-translational mods?

A
  • glycosylation
  • phosphorylation
  • disulfide bond formation
  • acetylation
26
Q
  • type of post-translational modification that involves a covalent linkage to an amine (NH3+)
  • residue affected: Lys
  • acetyl group donor is usually acetyl CoA
  • histones are acetylated and deacetylated on their N terminal lysines, critical for gene regulation
  • rxn catalyzed by histone acetyltransferase (HAT) and deacetylation by histone deacetylase (HDAC) enzymes
  • regulates protein function
  • also facilitates crosstalk w/ other types of modifications such as phospho, methylation, ubiquination, etc for dynamic control of cellular signaling
  • pattern of histone mods are heritable (epigenetics)
A

acetylation

27
Q
  • type of post-translational modification for proteins that are destined for cell surface and plasma
  • covalently linked to sugar residues in the ER lumen
  • functional group: (OH)
  • residue affected: Ser and Thr for O-linkage, Asn and Gln for N-linkage
  • O-links are formed with the hydroxyl groups of Ser or Thr residues
  • N-links are always with Asn
A

glycosylation

SFM (21 decks)

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