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Flashcards in Molecular mechanisms in inherited disorders Deck (81):
1

Mutation in what proteins results in Cystic Fibrosis?

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

2

What is CFTR?

membrane protein that acts as a chloride channel

3

CFTR belongs to what group of transporters?

group of ATP Binding Cassette (ABC) transporter

4

Describe the structure (domains) of CFTR?

It has 2 membrane spanning domains, two ATP binding domains and a regulatory domain that can be phosphorylated.

5

What causes activation of CFTR?

phosphorylation of regulatory domain by PKA

6

Why is there low Na and H20 in the lumen (mucous)?

the mutant CPTR can't transport Cl from the cell into the lumen therefore Na will stay in cell to balance Cl's negative charge.

7

Why is the mucous thick and viscid in pts w/ Cystic Fibrosis?

due to the low water and electrolyte concentration in the mucous.

8

Why do CF pts have a higher risk of developing respiratory infections?

The thick viscid mucus are prone to developing bacterial infections.

9

Respiratory infections are common causes of what in CF pts?

mortality and morbidity

10

How does the mutant CFTR effect the pancreas?

Leads to thick pancreatic secretions which obstruct pancreatic duct and destroy tissue. Results in deficiency of pancreatic enzymes.

11

What type of tissues replace pancreatic tissue in pts with cystic fibrosis?

Fibrotic tissue and fat

12

What symptoms are found in pts with CF?

Malabsorption, sterility, salty sweat, chronic pancreatitis, secondary biliary cirrhosis and recurring resp infections

13

Why is there defective protein digestion in pts with CF?

Blockage of pancreatic duct results in deficient secretion of pancreatic enzymes like lipase, trypsin, and chymotrypsin

14

Why is there steatorrhea in pts w/ CF?

B/C of the maldigestion of nutrients and the excretion of fat in stool due to deficiency of fat soluble vitamins esp Vit K (not stored in liver)

15

Why do many children w/ CF have protein malnutrition and delay in growth?

B/C of the deficient secretion of pancreatic enzymes which aid in the digestion of proteins

16

How is it possible to restore normal digestion and nutrition in pts w/ CF?

by providing pancreatic enzyme supplements

17

The viscid secretions in the intestine of CF pts causes what in kids?

meconium ileus and intestinal obstruction

18

Why are more than 95% of males with CF infertile?

B/C they don't have a vas deferens; called Congenital bilateral absence of the vas deferens (CBAVD)

19

What is the normal role of CFTR in sweat glands?

to reabsorb NaCl from the sweat.

20

How is the role of CFTR different in sweat glands compared to that in lungs/ pancreas?

CFTR reabsorbs NaCl in sweat glands while in other tissues, it secretes Cl (opposite fxns)

21

The presence of excessive salt in sweat is diagnostic of what condition?

Cystic fibrosis

22

What chromosome contains the mutation for CFTR?

chromosome 7

23

What is the most common position for the mutation that results in CFTR?

position 508 (F508)

24

Is Cystic Fibrosis a x-linked disorder?

No, autosomal recessive disorder

25

What is the most common CFTR mutation and on what domain is it on?

3 bp deletion that eliminates phenylalanine residue from the ATP binding domain 1

26

What is the effect of phenylalanine deletion at position 508 on CFTR structure?

doesn't cause change in reading frame but prevents protein from maturing and from reaching the plasma membrane

27

What drug is used to stimulate sweat glands in the sweat chloride test?

pilocarpine - used to collect sweat to measure chloride concentration in diagnosis of CF

28

What molecular diagnostic tests an be used to determine CF if the mutation is known?

ASO and Allele specific PCR test

29

Why is it possible to use PCR and Southern blotting to detect F508 mutations in pts w/ CF?

B/C the mutant gene (60 bp) is shorter than the normal gene (63pb) by 3 bp

30

Describe the G protein pathway involved in CFTR.

activated G-protein coupled receptor will activate adenylate cyclase which will increase levels of cAMP. this activates protein kinase A (PKA) to phosphorylate CFTR. This opens channel so that Cl can leave.

31

What type of mutation causes sickle cell anemia?

point mutation in 6th position of B-globin chain of hemoglobin where glutamic acid is replaced by valine

32

At what position does the point mutation occur?

postion 6 of B-globin chain of Hb

33

What effect does the substitution of valine for glutamic acid have on the structure of Hb?

Will create a hydrophobic pocket on the exterior surface of Hb b/c valine is hydrophobic and glutamic acid is hydrophobic

34

Why does Hb tend to aggregate, forming long filament like structures in pts w/ sickle cell anemia?

the mutation will create a hydrophobic pocket "sticky patch" forming site of attachment for nearby Hb molecules.

35

What effect does aggregation of Hb molecules have on the structure of RBC?

Distorts structure of RBC- sickled shape

36

What is the effect of sickled RBC on Bl flow?

blocks bl flow b/c can't flow freely

37

Why do pts w/ sickle cell disease have anemia?

b/c the spleen removes the sickled and distorted RBCs often

38

Why would splenomegaly be present in pts w/ sickle cell disease?

B/c spleen is responsible for removing the sickled RBCs

39

What type of hyperbilirubinemia in found in sickle cell disease?

Pre-hepatic (hemolytic type)

40

What type of bilirubin accumulates in pts w/ Sickle cell anemia?

unconjugated (direct) and total bilirubin

41

Why will jaundice be present in pts w/ sickle cell anemia?

b/c of the excessive removal of sickled RBC from the bloood

42

Why is the urine of pts w/ sickle cell anemia normal?

the high levels of unconjugated bilirubin can't be excreted in urine b/c bound to albumin

43

Why will people w/ sickle cell anemia develop pigmented gall stones?

b/c large amounts of conjugated bilirubin are secreted into bile

44

In electrophoresis, why would HbS (sickle cell form) move slower than HbA toward the positive end?

HbS has valine which is less negative than the glutamate in HbA (normal)

45

Why is it useful to use ASO test to detect sickle cell disease?

Makes it possible to identify carriers

46

What does RFLP analysis reveal about sickle cell disease and carriers in relation to restriction sites?

Normal: 3 restriction sites; in sickle cell anemia: loss of central restriction site producing longer fragment generated which will travel more slowly than normal band

47

What gene is mutant in Duchenne muscular dystrophy and Becker muscular dystrophy?

Dystrophin gene

48

Almost complete absence of functional dystrophin results in what disease?

Duchenne Muscular Dystrophy (DMD)

49

What causes Becker Muscular Dystrophy?

production of abnormal dystrophin or decreased amts of dystrophin

50

Why is Duchenne Muscular Dystrophy more common in males?

X-linked recessive disease

51

What is the most common muscular dystrophy?

DMD

52

Which muscular dystrophy is more milder? which muscular dystrophy has a later onset?

Becker Muscular Dystrophy for both b/c DMD will occur between ages 2-6 and most pts die in early 20s.

53

What is the differences between DMD deletions and BMD deletions?

DMD: cause frameshift mutations resulting in large deletions of exons (almost no protein)

BMD: in-frame mutations therefore protein is shorter but translated

54

Why will pts w/ DMD and BMD have trouble rising, climbing stairs and maintaining balance?

b/c DMD and BMD affects pectoral muslces, trunk and upper/lower legs -muscle weakness

55

What is Gowers' maneuver?

distinctive way of risking from floor: get on hands/knees first, raise posterior, then "walk" hands up legs to raise their upper body

56

Gowers' manuever is characteristic of what disease and why?

Duchenne muscular dystrophy; b/c of weakened leg muscles

57

What would lead to pseudohypertrophy and in what disease is it found?

replacement of normal muscle w/ connective tissue / fat; in pts with DMD

58

The largest gene encodes for what protein and where is it found?

Encodes for dystrophin; expressed in smooth, cardiac and skeletal muscle w/ lower levels in the brain

59

Why would cardiac abnormalities be found in pts w/ DMD resulting in their early death?

b/c gene for dystrophin also expressed in cardiac muscle

60

Describe structure of Dystrophin

has two globular heads with flexible rod-shaped center. One head binds to actin; other head (C-terminal domain) binds to protein in plasma membrane

61

How does Dystrophin anchor cystoskeleton of muscle cells to extracellular matrix?

by linking actin filaments to transmembrane proteins of muscle cell plasma mem.

62

Why is Dystrophin important?

Its role in anchorage of cytoskeleton to EC matrix stabilizes plasma mem and helps cell to withstand stress of muscle contraction.

63

What does the loss of dystrophin result in?

oxidative cellular injury and myonecrosis

64

How can we differentiate between DMD and BMD in western blot?

DMD: no band b/c of frameshift deletion; BMD: smaller protein size and decreased quantity when compared to normal

65

Microscopy of BMD/ DMD will show what when compared to normal?

increase in adipocytes and fibrous tissue

66

What will immunofluorescense microscopy show in pts w/ DMD, BMD?

BMD: reduced quantity of dystrophin; DMD: complete absence

67

What are serum creatine kinase (MM) in pts w/ muscular dystrophy?

high b/c CK MM indicates muscle damage

68

What is the serum CK-MM levels in females who are carriers for DMD?

high levels

69

Gowers' manuever is characteristic of what disease and why?

Duchenne muscular dystrophy; b/c of weakened leg muscles

70

What would lead to pseudohypertrophy and in what disease is it found?

replacement of normal muscle w/ connective tissue / fat; in pts with DMD

71

The largest gene encodes for what protein and where is it found?

Encodes for dystrophin; expressed in smooth, cardiac and skeletal muscle w/ lower levels in the brain

72

Why would cardiac abnormalities be found in pts w/ DMD resulting in their early death?

b/c gene for dystrophin also expressed in cardiac muscle

73

Describe structure of Dystrophin

has two globular heads with flexible rod-shaped center. One head binds to actin; other head (C-terminal domain) binds to protein in plasma membrane

74

How does Dystrophin anchor cystoskeleton of muscle cells to extracellular matrix?

by linking actin filaments to transmembrane proteins of muscle cell plasma mem.

75

Why is Dystrophin important?

Its role in anchorage of cytoskeleton to EC matrix stabilizes plasma mem and helps cell to withstand stress of muscle contraction.

76

What does the loss of dystrophin result in?

oxidative cellular injury and myonecrosis

77

How can we differentiate between DMD and BMD in western blot?

DMD: no band b/c of frameshift deletion; BMD: smaller protein size and decreased quantity when compared to normal

78

Microscopy of BMD/ DMD will show what when compared to normal?

increase in adipocytes and fibrous tissue

79

What will immunofluorescense microscopy show in pts w/ DMD, BMD?

BMD: reduced quantity of dystrophin; DMD: complete absence

80

What are serum creatine kinase (MM) in pts w/ muscular dystrophy?

high b/c CK MM indicates muscle damage

81

What is the serum CK-MM levels in females who are carriers for DMD?

higher levels