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MCM II > Functions and dysfunctions of protein processing > Flashcards

Functions and dysfunctions of protein processing Flashcards

1
Q

What is the genetic code?

A

-“set of Rules” that convert the nucleotide sequences of a gene into the aa sequences of a protein using mRNA as an intermediary

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2
Q

Why is the genetic code said to be degenerate?

A

some aa can be coded by more than 1 codon, and three codons do not code for any aa

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3
Q

Silent mutation

A

does not change the amino acid

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4
Q

Missense mutation

A

changes amino acid in the protein, with either no effect on protein function or a protein with vastly different function

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5
Q

Nonsense mutation

A

codon changes into a stop codon, causing premature chain termination.
-also called null mutation. protein either degraded or formed as TRUNCATED VERSION

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6
Q

Frameshift Mutation

A

one or more nucleotides are deleted or inserted into ORF. out of frame causes change in the codon sequence and consequently alteration in the amino acid sequence (E.g. Duchenne Muscular dystrophy, beta thalassemia)

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7
Q

Sickle Cell Anemia

A

Arises in a missense mutation of 6th codon in the allele of the gene for human beta-globib (HBB), a subunit of adult hemoglobin.
-changes GAG to GTG –> substitutes Val (hydrophobic0 for Glu (neg and hydrophillic)

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8
Q

Duchenne Muscular Dystrophy

A

Large in-frame and out-of-frame (OOF) deletions to the DYSTROPHIN GENE –> leads to partially non functioning dystrophin protein. Muscle wasting.

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9
Q

Becker muscular dystrophy

A

In-frame shift resulting in truncated form of dystrophin and milder MD

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10
Q

mRNA

A

codons (present in the coding region)

  • 7-methylguanosine cap at 5’ end
  • poly(A) tail at 3’ end
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11
Q

tRNA

A

-serve as adaptors (binding sites for both codons (mRNA) and amino acid

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12
Q

structure of tRNA

A

Cloverleaf

  • unpaired nucleotides
  • anticodon loop
  • complementary codon
  • 3’ CCA terminal region
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13
Q

Aminoacyl tRNAs

A
  • complex of tRNA with AA
  • AA needs to be activated
  • catalyzed by the enzyme AMINOACYL tRNA SYNTHETASES
  • serve as second genetic code
  • each tRNA charged with the correct AA to maintain fidelity of protein synthesis
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14
Q

Activation of Amino Acids

A
  1. Aminoacyl tRNA synthetase catalyzes addition of AMP to COOH end of AA
    2AA transferred to cogenate tRNA
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15
Q

Ribosomes

A
  • translational machinery assembled on ribosomes
  • large complexes of proteins and rRNA
  • have a large and small subunit which assemble in the presence of mRNA
  • Antibiotics can target prokaryotic translational machinery
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16
Q

Ribosomal complex (Three Important Sites)

A
  • Acceptor (A) site- where mRNA codon exposed to receive aminoacyl tRNA, except the met tRNA.
  • Peptidyl (P) site - where aminoacyl tRNA is attached
  • Empty (E) or exit site - location occupied by empty tRNA before exiting ribosome
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17
Q

Initiation

A

formation of mRNA, small ribosomal subunit and initiator tRNA pre-initiation complex

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18
Q

Elongation

A

activated AA attached to initiating Met by forming a peptide bond

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19
Q

Termination

A

peptide chain is released from ribosomal complex

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20
Q

What are the stop codons that trigger termination

A

UAA, UAG, and UGA

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21
Q

Polysomes

A

clusters of ribosomes simultaneously translating a single mRNA molecule

  • each synthesizing a polypeptide
  • makes protein synthesis more efficient
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22
Q

what subunits are involved in prokaryotic translation

A
  • 30S Subunit

- 50S Subunit

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23
Q

What subunits are involved in eukaryotic translation

A
  • 40S Subunit

- 60S Subunit

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24
Q

Streptomycin binds to what subunit to disrupt the initiation of translation

A

binds to 30S subunit interferes with the binding fmet-tRNA. Interferes with 30S subunit association with 50S subunit

25
Q

Shiga toxin (from shigella dysenteriae) and Ricin (toxon from castor oil plant) binds to what subunit to disrupt elongation

A

binds to large 60S subunit (euk.), blocking entry of aminoacyl-tRNA to ribosomal complex

26
Q

Clindamycin and erithromycin bind to what subunit to disrupt translocation of the ribosome

A

biinds to large 50S subunit (pork), blocking translocation of the ribosome
ERYTHROMYCIN IS COMMONLY USED TO TREAT PURTUSSIS

27
Q

Tetracyclines bind to what subunit to disrupt elongation

A

binds to small 30S subunit (prok.), blocking the entry of aminoacyl-tRNA to ribosomal complex

28
Q

where is peptidyl transferase activity housed

A

in the large subunits

29
Q

What does initiation require?

A

It requires hydrolysis of one GTP

30
Q

What does elongation require?

A

It requires hydrolysis of two GTP per amino acid added

31
Q

How does diptheria toxin work?

A

It works by inactivating GTP bound eEF-2, interfering with ribosomal translocation

32
Q

What does termination require?

A

It requires hydrolysis of one GTP

33
Q

cycloheximide

A

(toxin from streptomyces griseus) inhibits peptidyl transferase (euk.)

34
Q

Puromycin (from streptomuces alboniger)

A

causes premature chain termination (prok/euk)

  • stops the ribosome
  • reassembles the 3’ end of the aminoacylated-tRNA
  • Enters the A site and adds to the growing chain
  • forms a puromycylated chain that leads to premature release
35
Q

What are the two major pathways for protein sorting

A

Cytoplasmic pathway

Secretory pathway

36
Q

Cytoplasmic pathway

A
  • for proteins destined for cytosol, mitochondria, nucleus, and peroxisomes
  • protein synthesis begins and ends on free ribosomes in cytoplasm
  • absence or presence of certain translocation signals play role in final target
37
Q

Secretory pathway

A
  • for proteins destined for ER, lysosomes, plasma membranes, or for secretion
  • translocation begins on free ribosomes but terminates on ribosomes sent to ER
  • First 20 amino acid residues of the polypeptide has ER targeting signal sequence
38
Q

In mitochondrial protein import proteins are passed across the mitochondrial membranes via what two translocator complexes

A

-transporter outer membrane (TOM)
-transporter inner membrane (TIM)
(unfolded proteins are protected by binding to chaperones, in particular heat shock proteins 70 (HSP70)

39
Q

For what is KDEL a signal sequence

A

ER Lumen proteins

  • K (Lysine)
  • D (Aspartic acid)
  • E (glutamic acid)
  • L (leucine)
40
Q

For what is Mannose-6-phosphate a signal sequence

A

lysosomal proteins

41
Q

For what is the N terminal apolar region a signal sequence

A

membrane proteins

42
Q

For what is the tryptophan a signal sequence

A

secretory proteins

43
Q

I-cell disease

A

severe form of lysosomal storage disease

  • tagging of lysosomal proteins with mannose 6P is defective
  • high plasma levels of lysosomal enzymes
44
Q

Protein folding

A

small proteins can fold into native conformations spontaneously
-large proteins cannot and are at risk for (a) aggregation and (b) proteolysis

45
Q

What do large proteins need

A

auxiliary proteins called CHAPERONES

46
Q

what do chaperones do

A

protect the protein and help fold into the proper tertiary structure

47
Q

What are chaperonins

A

barrel shaped compartments that admit unfolded proteins and catalyze their folding in an ATP dependent manner

48
Q

Proteolytic cleavage

A

converts inactive form to active enzymes by unmasking active site (trypsinogen and chemotrypsen to trypsin and chemotrypsin, respectively)
-converty nacent precursor proteins to mature ones (proinsulin to insulin)

49
Q

What are the four types of post-translational covalent modifications

A
  • glycosylation
  • phosphorylation
  • disulfide bond formation
  • acetylation
50
Q

What rersidues are affected in O-glycosylation

A

Ser, Thr

51
Q

What residues are affected in N-glycosylation

A

Asn

52
Q

Phosphorylation

A

Formation of an ester bond between phosphate and OH.
-regulates enzyme activity and protein function particularly in signaling (also in cell growth, proliferation, differentiation, oncogenesis)

53
Q

Disulfide bond formation

A

Inter and intra-molecular disulfide bonds stabilize many proteins.

  • these bonds form between thiol (SH) group of 2 cysteine residues
  • Formation and reorganization of these bonds occur in the ER lumen
  • Facilitated by protein disulfide isomerases
54
Q

What usually catalyzes acetylation reactions

A

Histome acetyltransferase (HAT) or histome deacetylase (HDAC)

55
Q

Alzheimer’s disease (AD)

A

loss of memory, cognative function, language

56
Q

Parkinson’s disease (PD)

A

Impairment of fine motor control

57
Q

Huntington’s disease (HD)

A

Loss of movement and cognitive functions and psychiatric problems

58
Q

Crutzfeldt-Jacob disease (CJD)

A

failing memory, behavioral changes, lack of coordination and visual disturbances.
-Late stages involve mental deterioration blindness, weakness of extremities, and coma.

MCM II (3 decks)

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