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Biology Exam 2 > Cytoskeleton Protein Defects > Flashcards

Cytoskeleton Protein Defects Flashcards

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1
Q

fragile cytoskeleton of RBCs

A

hemolytic anemia

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2
Q

complete absence of cytoskeletal protein dystrophin

A

Duchenne’s muscular dystrophy

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3
Q

dystrophin protein is present but abnormal

A

becker’s muscular dystrophy

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4
Q

hemolytic anemia characterized by spherical and …….

A

fragile RBCs that lyse and release hemoglobin

hereditary spherocytosis

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5
Q

in types of anemia, bone marrow cannot work fast enough to produce RBCs, so …..

A

the spleen will begin producing RBCs as well

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6
Q

hereditary spherocytosis cause

A

caused by mutations in genes for the erythrocyte membrane skeleton of RBCs

spectrin

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7
Q

osmotic fragility test

A

test the membrane strength of RBCs in a hypotonic solution

HS RBCs will burst

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8
Q

osmotic fragility curve

A

doing the osmotic fragility test over several trials w/ increasing hypotonic concentrations (decreased [NaCl])

normal RBCs will withstand the tests longer (closer to water) than HS RBCs

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9
Q

HS is the most common

A

most common hemolytic anemia in people of northern European descent

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10
Q

HS genes

A

most are identified but 10% of diseased - we do not know why they have HS

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11
Q

treatments for HS

A
  1. blood transfusions
  2. splenectomy - which removes spherocytes from circulation
  3. increase RBC# and Hb
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12
Q

DMD is the most common …..

A

fatal neuromuscular disorder
no cure
early 20s

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13
Q

DMD treatments

A
  1. nothing can alter course of disease

2. treatments to maintain general health and quality of life

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14
Q

DMD genetics

A
  • x linked recessive
  • dystrophin gene mutations
  • genetic defect present at birth but does not show symptoms to ~3 yrs of age
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15
Q

function of dystrophin

A

provide structural stability to muscle cell membranes during contractions

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16
Q

dystrophin protein

A
  1. has 4 functional domains
  2. N-terminus binding to actin
  3. long spectrin like repeats
  4. cysteine rich
  5. bind to transmembrane proteins at c-terminus
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17
Q

dystrophin C-terminus

A

cysteine rich

binds to dystroglycans and syntrophins - transmembrane proteins

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18
Q

dystrophin is localized to

A

inner surface of muscle membrane

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19
Q

loss of dystrophin

A

results in destabilization of entire actin to membrane complex

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20
Q

dystrophic myopathy

A

progressive muscle degeneration with loss of functional muscle tissue over time w/ resulting weakness

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21
Q

clinical presentation of DMD

A
  1. elevated creatine kinase in blood (50-100x normal)
  2. slow walking, general weakness
  3. age of diagnosis ~5 years
  4. wheelchair dependent by 13 yrs
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22
Q

physical presentation of DMD

A

–necrosis of muscle fibers — replaced by fat or CT

leads to pseudohypertrophy

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23
Q

gower maneuver

A

because of weakened leg muscles, boys w/ DMD have a distinct way of rising from the floor

using their hands to walk up their legs

24
Q

EMG

A

electromyography
test that is used to record the electrical activity of muscles

CRDs

25
Q

CRDs

A

complex repetitive discharges

abnormal/spontaneous firing APs associated w/ membrane instability
seen on EMGs

26
Q

significance of CRD presence

A

indicative of muscle membrane instability and muscle pathology

hallmark of testing for dystrophies

27
Q

becker muscular dystrophy

A
  • -milder form than Duchenne
  • -similar symptoms to dmd but milder
  • -wheelchair at 16
28
Q

MD etiology

A
  • -x linked recessive
  • -dmd–dystrophin gone
  • -bmd–50-80% of protein present
29
Q

associated w/ frameshift mutations

A

dmd

30
Q

western plot

A

or protein blot

indicates presence or absence of proteins

31
Q

DMD dystrophin presence

A

<0.30%

32
Q

BMD phenotype

A
  • -variable in symptoms
  • -no frameshifts
  • -dystrophin present and abnormal in quantity or size
  • -walk till 16
  • -lifespan 45 yrs
33
Q

DMD phenotype

A
  • -frameshifts
  • -no dystrophin
  • -wheelchair by 12
  • -lifespan up to 25 yrs
34
Q

inheritance risk for MD

A

50% risk for affected sons
50% risk for daughters to be carriers

when mother is carrier

35
Q

MD manifestation in females

A
  1. mild
  2. slight elevation of CK
  3. weak back, arms, legs
  4. fatigue easily
  5. heart problems/shortness of breath
36
Q

cellular pathophysiology of MD

A
  1. sarcolemmas sustain mechanical injury
  2. Ca influx/oxidative stress
  3. reduced resting potential (close to threshold)
  4. fiber degeneration
  5. irreversible necrosis – replaced by fat or CT
37
Q

How does MD result in fatality?

A

progressive respiratory weakness
chronic hypoxia

result in cardiac and respiratory failure

38
Q

diagnostic tools for MD

A
  1. EMG
  2. blood test
  3. biopsy
  4. DNA study
  5. quantitative dystrophin analysis
39
Q

prenatal MD diagnosis

A
  1. use fetal DNA – molecular analysis

2. preimplantation genetics – checking blastomere in IVF – transfer only healthy embryos

40
Q

treatments for DMD

A
  1. use growth factors
  2. use gene therapy
  3. gene therapy microdystrophins
  4. exon skipping
  5. nonsense stop codon read-thru
41
Q

describe DMD option 1 gene therapy

A
  1. replace dystrophin gene

but is too large for adeno-associated viruses

also try utrophin

ultimately does not work — immune issues

42
Q

DMD usage of growth factors

A
  1. myostatin inhibits muscle cell growth
  2. knockout myostatin
  3. muscles grow very large
  4. but does not change that we are just making more DMD compromised muscle
43
Q

utrophin

A

homologous dystrophin like protein

44
Q

DMD option 2 gene therapy

A
  1. use microdystrophins
    generate a protein like dystrophin but w/ less spectrin like repeats

works little but still immune issues

45
Q

problem of dystrophin immunity

A

immune system has never seen this protein before so generates a response

T-cell mediated immunity against dystrophin proteins

46
Q

DMD exon skipping

A

–in dmd deletions in gene cause frameshift mutations

therapy to skip the exons to get back into frame

works little but still immune issues

47
Q

DMD stop codon skipping

A

–premature stop codon mutations which result in single nuc substitution

use a drug to skip or suppress the stop codon
–read-thru stop codon

works little but still immune issues

48
Q

overall treatment strategies for DMD conclusions

A

all approaches have problems, typically immune responses

KCU investigating the dystrophin gene itself

49
Q

dystrophin gene

A

has several different products by different promoters

dif. dystrophin sizes depending on where in the body it is
ex. muscle vs. retinal dystrophin

50
Q

Dp260

A

retinal dystrophin

similar but basically smaller

51
Q

DMD treatment w/ dp260

A

works in mice

but do not know the promoter for dp260 yet

52
Q

describe how the osmotic fragility test indicates a patient has hereditary spherocytosis

A

–using this test we subject RBCs to a hypotonic solution to test the strength of their membranes

–in hs RBC membranes are weakened and will show up much weaker in a of test

53
Q

describe the function of the erythrocyte membrane cytoskeleton and how defects in the EMS cause hereditary spherocytosis

A

–the cytoskeleton is responsible for giving RBCs their biconcave shape which gives them structural integrity which is important for them to survive the mechanical stress of passing thru the circulatory system

defects in ems result in deformed shapes of RBCs, which weakens them and greatly shortens their lifespan

54
Q

EMS

A

erythrocyte membrane cytoskeleton

55
Q

differentiate Duchenne muscular dystrophy vs. becker muscular dystrophy

A

Duchenne — dystrophin protein is absent

becker — dystrophin protein is abnormal in quantity or size

56
Q

describe 2 therapeutic strategies to attempt to treat Duchenne muscular dystrophy

A
  1. treat patient with growth factors to knockout myostatin (which prevents muscle cell growth) to allow muscles to grow large but the muscles are still weakened by dmd
  2. gene therapy by using microdystrophins, creating a dystrophin-like protein, treating patient with this. works a little bit but the patient will have an immune response since the immune system has never encountered this protein before

Biology Exam 2 (9 decks)

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