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MCM Exam 2 > Functions and Dysfunctions of proteins > Flashcards

Functions and Dysfunctions of proteins Flashcards

1
Q

Each group of 3 consecutive nucleotides in RNA is called a _______

A

Codon

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2
Q

Mutation that does not change the amino acid.

A

Silent

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3
Q

Mutation that changes amino acid in the protein with vastly different function.

A

Missense

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4
Q

Example of disease caused by missense mutation

A

Sickle Cell Anemia On 6th codon in the allele of the gene for human β-globin (HBB), a subunit of adult hemoglobin.

GAG (Glu) to GTG (Val)

Negatively charged hydrophilic to hydrophobic

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5
Q

Codon changes into a stop codon causing premature chain termination.

A

Nonsense Mutation (null mutation)

Protein either degraded or formed as a truncated version.

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6
Q

What mutation causes Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy?

A

Nonsense mutations in the dystrophin gene lead to partially or non-functional dystrophin protein.

Out of frame deletions cause DMD.

In frame cause BMD (truncated forms)

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7
Q

Deletion or insertion where one or more nucleotides are deleted or inserted into the open reading frame.

Out of frame causes change in the codon sequence and consequently alteration in the amino acid sequence

A

Frameshift.

E.g. Duchenne Muscular Dystrophy, beta thalassemia

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8
Q

Components of mRNA

A
  1. Codons (present in coding region)
  2. 7-methylguanosine cap at the 5′ end
  3. Poly(A) tail at the 3′ end.
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9
Q

What makes up the structure of tRNA?

A

Set of 3 consecutive nucleotides that pair with mRNA.

3’ CCA terminal region which binds the amino acid that matches the corresponding codon.

“Cloverleaf”

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10
Q

How are amino acids bound to tRNA “ativated”?

A

Catalyzed by enzymes called aminoacyl tRNA
synthetases which help to add AMP to COOH end of amino acids.

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11
Q

Units of Eukaryotic Ribosomes in size.

A

Large 60s

Small 40s

Total 80s

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12
Q

Units of prokaryotes in size

A

50S Large

30S Small

70S Total

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13
Q

What does the A site of a ribosome do?

A

mRNA codon exposed to receive aminoacyl tRNA, except the met tRNA

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14
Q

What does the P site of a ribosome do?

A

Where aminoacyl tRNA is attached.

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15
Q

What does the E site do?

A

Location occupied by empty tRNA before exiting ribosome

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16
Q

How do Eukaryotes identify the start of translation?

A

mRNA 5’ cap, 3’ poly-A tail, the Kozak sequence and an ATP-dependent mRNA scan

mRNA molecules also contain signals that define the beginning of there polypeptide chain

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17
Q

How do Prokaryotes identify the start of translation?

A

Shine Dalgaro sequence or AGGAGG

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18
Q

What are the initiation factors mentioned in eukaryotic translation?

A

elF4E

elF4G

elF2

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19
Q

What is an intiator tRNA?

A

Bound to GTP and attaches to P site of small subunit

Codon is AUG (codes for methione)

N-formylmethioninyl tRNA in
prokaryotes and methioninyl tRNA in eukaryotes

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20
Q

What happens when the initiator tRNA’s GTP is hydrolyzed in initiation?

A

The large subunit binds to DNA and translation begins

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21
Q

What are the steps of elongation in translation?

A

The incoming aminoacyl tRNA is attached to a GTP-bound elongation factor.

Loading of an aminoacyl tRNA anticodon so it base pairs at the A site with codon

Loading accompanied by GTP hydrolysis and release of factor from aminoacyl tRNA

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22
Q

How is the peptide bond formed between the A and P site in elongation?

A

Catalyzed by peptidyl transferase.

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23
Q

What are the stop codons?

A

UAA, UAG and
UGA

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24
Q

What is a Release Factor?

A

Promote the release of a complete protein from tRNA

Bind to A site of ribosome containing the stop codon
and cleaves the ester bond between the C terminus of
the polypeptide and the tRNA.

Catalyze the addition of water instead of AA
Large ribosomal subunit leaves with hydralyzation of GTP

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25
Q

At the very end of translation, what fuels the dissociation of the ribosomal complex?

A

GTP hydrolysis

26
Q

Prokaryote Elongation inhibitors

A

Streptomycin - 30s (30s and 50s association)

Tetracycline - 30s (aminoacyl-tRNA to complex)

Chloramphenicol -peptidyl transferase

Clindamycin and erythromycin - 50s (translocation of ribosome)

(STCCE)

“sticky”

27
Q

What is erthromycin used to treat?

A

Purtussis

28
Q

Inhibits peptidyl transferase

A

Cycloheximide

29
Q

Toxin from Streptomyces griseus: inhibits peptidyl transferase (euk.)

A

Cycloheximide

30
Q

From Corynebacterium diphtheriae: inactivates GTP-bound eEF-2, interfering with ribosomal translocation (euk.)

A

Diptheria toxin

31
Q

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

A

Shiga toxin and ricin

32
Q

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

A

Puromicin

Enters A site of ribosome and creates puromycylated chains.

33
Q

Pathway where synthesis begins and ends on free ribosomes in the cytoplasm.

Can be triggered by the absence or presence of certain translocation signals.

A

Cytoplasmic pathway

34
Q

Pathway of protein sorting destined for the ER, lysosomes, plasma membranes, or for secretion.

Synthesis begins at the ribosomes, ends at the ER

First 20 amino acid residues of the polypeptide have ER
targeting signal sequences

A

Secretory pathway

35
Q

Signal for transportation into mitochondria and its purpose.

A

N terminal alpha-helix

Helps them to interact with chaperone proteins (heat shock family)

Translocation sequences recognize TIM and TOM on the mitochondrial membrane

36
Q

How are large proteins >40 kDa moved into the nucleus?

A

Nuclear localization signals

37
Q

What do nuclear localization signals have as AA residues?

A

Lys and Arg

38
Q

What is the signal sequence for ER Lumen proteins?

A

KDEL

K=lysine

D=aspartic acid

E=Glutamate

L=Leucine

39
Q

What is the signal sequence for lysosomal proteins?

A

Mannose 6-phosphate

40
Q

Signal sequence for membrane proteins

A

N terminal a polar region

41
Q

The signal sequence for secretory proteins.

A

Tryptophan

42
Q

What does each protein in the secretory pathway have?

A

An ER targeting signal peptide

43
Q

What are the features of an ER target signaling peptide?

A

15-60 amino acids at N terminus of protein

1 or 2 basic amino acids (Lys or Arg) near N terminus

Hydrophobic sequence (10-15 residues) on C terminus of the basic residues

44
Q

______ wraps itself around the ribosome-mRNA-peptide complex, tethering it to the ER membrane, halting it and redirecting it to the ER lumen.

A

Signal recognition particle (SRP)

Enzymes on luminal side cleave the protein.

PTM mods then occur in ER or GA

45
Q

What is a disease in which tagging of lysosomal proteins with mannose 6p is defective?

A

I-cell disease

A severe form of lysosomal storage disease

High plasma levels of lysosomal enzymes

By 6 months: failure to thrive and developmental delays and physical manifestations

Abnormal skeletal development, coarse facial features, restricted joint movement,
stiff claw-shaped hands, short-trunk dwarfism, clouding on the cornea

Hepatomegaly, splenomegaly, occasionally heart valves

Development delays of their motor skills, cognitive delays

Recurrent respiratory tract infections:

Death frequently occurs by age 7, usually due to congestive heart failure or recurrent respiratory tract infections

46
Q

Proteins that help protect large proteins and assist in folding them into their proper shape.

A

Chaperons

47
Q

Large barrel shape compartments for unfolded proteins that catalyze their folding in an ATP-dependent manner.

A

Chaperonins

48
Q

Converts inactive forms to active enzymes by
unmasking active site.

&

Converts nascent precursor proteins to mature
ones

A

Proteolic cleavage

49
Q

What is essential to the enzymes involved in the post-translation modification of collagen?

A

Ascorbic acid is essential for the activity of lysyl and prolyl hydroxylases.

50
Q

What types of proteins are glycosylated?

Where are they glycosylated?

A

Extracellular proteins

the ER lumen, processed to mature protein as traveled through ER and Golgi.

51
Q

What are the O glycosidic proteins links?

A

O-links are formed with the hydroxyl groups of Ser or
Thr residues.

52
Q

What are the N-glycosidic protein links?

A

N-linked are always with Asparagine. Precursor sugar
transferred from phospho Dolichol

53
Q

Formation of an ester bond between phosphate and OH of an amino acid

A

The activity of serine/threonine and tyrosine kinase

54
Q

Where are disulfide bonds formed?

What facilitates their formation?

A

The ER Lumen

Protein disulfide isomerases

55
Q

Where are proteins usually acetylated?

A

Lysine residues.

56
Q

What are the three modifications in collagen?

A

Lysines in collagen modified to form 5-hydroxylysines

Some lysines deaminated to aldehydes

Some prolines hydroxylated to hydroxyprolines.

57
Q

Defects in lysyl hydroxylases

A

Ehlers-Danlos Syndrome - overly flexible joints, walls of blood
vessels, intestines or uterus may rupture

Epidermolysis Bullosa Simplex – blisters on skin

58
Q

Characteristics of Alzheimer’s

A

Amyloid precursor protein (APP) breaks down to form
amyloid beta peptide (Aβ)

Misfolding/Aggregation of Aβ forms plaques in the brain
(extracellular)

Hyperphosphorylation of Tau (neurofibrillary tangles)
(intracellular)

59
Q

What is the cause of familial vs sporadic Alzheimer’s.

A

Mutations APP and Tau are familial form

Aging is common in sporadic form

60
Q

A disease characterized by the aggregation of α-synuclein (AS) protein forms insoluble fibrils which deposit as Lewy bodies in dopaminergic neurons in the substantia nigra

Symptoms due to reduced availability of dopamine.

A

Parkinson’s disease

Familial = Mutations in AS

61
Q

What disease is characterized by CAG triplet repeats?

What do these triplets result in?

A

Huntington’s disease (mutation in Huntingtin gene)

Results in Polyglutamine repeats, which form H-bonds and misfold and aggregate

Basial ganglia cell death

62
Q

Disease caused by misfolding of prion proteins

What type of encephalopathy is this?

A

Creutzfeldt-Jakob disease (HD)

Spongiform - appearance of infected brains, filled with holes
and resemble sponges under a microscope.

MCM Exam 2 (14 decks)

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