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MCB1 Block 3 > Peroxisomes > Flashcards

Peroxisomes Flashcards

1
Q

Where are peroxisomes made?

A

Free ribosomes

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2
Q

What kind of reactions do peroxisomes carry out?

A

oxidative reactions

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3
Q

Cells in what organs have abundant peroxisomes?

A

Liver & kidney

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4
Q

What is the tag to get enzymes into the peroxisome?

A

SKL

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5
Q

What is the pH of peroxisome?

A

7.5

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6
Q

What tissues are peroxisomes present in?

A

All of them

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7
Q

Why do peroxisomes generate H2O2?

A

oxidative purposes

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8
Q

What is in peroxisomes to turn H202 into water?

A

catalase

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9
Q

What is another name for catalase?

A

peroxidase

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10
Q

How do peroxisomes divide?

A

Fission

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11
Q

Most transmembrane proteins and peroxisomal enzymes are carried to the peroxisome from where?

A

cytoplasm

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12
Q

What terminus is SKL sequence usually located?

A

C-terminus

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13
Q

PTS1 is another name for what?

A

SKL sequence

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14
Q

What recognizes SKL?

A

peroxins

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15
Q

Import into peroxisome requires what?

A

ATP

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16
Q

Where are proteins that are destined for peroxisome folded?

A

cytoplasm

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17
Q

What are peroxins?

A

peroxisomal translocaters AKA they bind to proteins that have SKL signal sequence and bring them to peroxisome

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18
Q

What amino acids make up the SKL sequence?

A

Ser-Lys-Leu

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19
Q

Once the peroxin takes the enzyme/protein to peroxisome, how does it enter the cell?

A

There are also peroxins that form channels in membrane that the protein goes through to enter cell

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20
Q

What three biosynthetic functions do the peroxisome have?

A

Plasmalogen synthesis
Bile acid synthesis
Lipid biosynthesis

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21
Q

What is plasmalogen and why is it important?

A

It’s a phospholipid, especially important in Schwann cells

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22
Q

Name two examples of lipid biosynthesis in peroxisome

A

Cholesterol & dolichol

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23
Q

What are the 3 degradative functions of peroxisome?

A

VLCFA beta oxidation
purine cataboilsm
H2O2

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24
Q

What does VLCFA stand for?

A

Very long chan fatty acid

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25
Q

Where is the only place that VLCFA breakdown can occur?

A

Peroxisome

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26
Q

What is purine catabolism?

A

breakdown of purine

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27
Q

Peroxisomes use O2 to remove what from organic substrates?

A

H atoms

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28
Q

Uric acid, aas, fas, purines are all examples of what

A

organic compounds

29
Q

H202 is needed in peroxisomes to do what?

A

oxidise toxins

30
Q

What is an example of a toxin a peroxisome could use H202 to oxidise?

A

alcohol

31
Q

Fatty acids with a carbon tail length of what can only be degraded in peroxisome?

A

24 or more

32
Q

A fatty acid tail of what length can be degraded by mitochondria?

A

10

33
Q

A peroxisome breaks down a VLCFA until it reaches what point?

A

Until it has 10 C tail length

34
Q

What is the name of the reaction for how peroxisomes break down VLCFA?

A

beta oxidation

35
Q

fatty acid oxidation is a major source of metabolic ____

A

energy

36
Q

How are fatty acids used for energy (describe the pathway, fatty acids →)

A

fatty acids → AcetylCoA → cytosol

37
Q

One thing peroxisome does is purine catabolism. What are purines A and G degraded to?

A

uric acid

38
Q

What is an important catalyst for purines A and G to be degraded to uric acid?

A

xanthine oxidase

39
Q

What is Hyperuricaemia?

A

Gout

40
Q

What is hypoxanthine?

A

It makes xanthine

41
Q

Key words: hyperuricemia, Allopurinol are what disease?

A

Gout

42
Q

Characteristics: Inflammation of big toe due to deposits of uric acid crystals; can be treated with Allopurinaol – xanthine oxidase inhibitor → inhibits degradation of purines to uric acid is what disease?

A

Gout

43
Q

What is the mechanism for gout?

A

Xanthine oxidase catalyzed hypoxanthine → xanthine → uric acid reactions; Hyperuricemia → crystallization of uric acid → deposition of crystals in joints (i.e. big toe) → destroys surrounding tissue

44
Q

What causes the swollen toe in gout?

A

urate crystal deposits

45
Q

What is allopurinol?

A

xanthine oxidase inhibitor, a drug used to treat gout, has nasty side affects

46
Q

What is plasmogen and why is it important?

A

It is a phospholipid, it is important for myelin which insulates neurons

47
Q

80-90% of myelin membrane is made of what?

A

phospholipid

48
Q

key words: peroxins don’t recognize SKL, accumulation of VLCFA, hepatomegaly, prominent forehead, large fontanelles, lack of plasmalogen is what disease?

A

Zellweger syndrome

49
Q

Characteristics: neurological dysfunction: hypotonia, hyporeflexia, seizures, mental retardation, dysphagia; Dysmorphic features: prominent forehead, hypertelorism, large fontanelles; hepatomegaly & liver dysfunction; death 6-12 months is what disease?

A

Zellweger syndrome

50
Q

PEX genes encode what?

A

Peroxins

51
Q

What lysosomal disease is zellweger syndrome similar to?

A

I-cell

52
Q

What is mechanism for zellweger syndrome?

A

Defected Peroxin does not recognize SKL → failure to import peroxisomal enzymes → empty peroxisomes → peroxisome deficiency: VLCFA accumulation glial cell membrane → abnormal brain development → neuronal migration defects & hypomelination (lack of plasmalogen); accumulation of VLCFA in liver → hepatomegaly & liver failure; lack of bile acids → decreased fat absorption ! decreased ATP → muscle weakness

53
Q

What is the mode of inheritance for zellweger syndrome?

A

Autosomal recessive, congenital

54
Q

Where is the defect/mutation in zellweger syndrome?

A

PEX mutation - leads to defective peroxin

55
Q

XALD stands for what?

A

X-linked Adrenoleukodystrophy

56
Q

What is XALD?

A

defective membrane protein that imports VLCFAs

57
Q

How is XALD caused in zellweger syndrome?

A

it’s not - they are two separate diseases with two separate causes

58
Q

Why is there muscle weakness in pts with zellweger?

A

lack of bile acids → decreased fat absorption → decreased ATP → muscle weakness

59
Q

Why is there hepatomegaly in pts with zellweger?

A

accumulation of VLCFA in liver cells

60
Q

Why is there abnormal brain development in pts with zellweger?

A

plasmalogen synthesis doesn’t happen as much, plasmalogen is important for schwann cell

61
Q

Key words: VLCFA transport defect, glial accumulation, myeline breakdown, adrenal atrophy, behavioral changes, most common peroxisomal disorder are what disease?

A

X-linked Adrenoleukodystrophy (XALD)

62
Q

What is mode of inheritance for XALD?

A

X-linked

63
Q

What is mechanism for XALD?

A

Defect in transport of VLCFA into peroxisome → defective breakdown of VLCFAs → accumulation of VLCFA: brain (glial cells) → myelin breakdown; adrenal cortex → adrenal atrophy

64
Q

Characteristics: progressive; onset 5-10 years old: apathy, behavioral changes; spasticity, ataxia, visual loss, death few years later are what disease?

A

XALD

65
Q

What is the defect in XALD?

A

import protein defect, VLCFA are not imported into peroxisome

66
Q

Where is especially important locations that VLCFAs accumulate?

A

Brain cells & adrenal cortex

67
Q

Because VLCFAs accumulate in glial (brain) cells, what happens?

A

Breakdown of myelin

68
Q

Because VLCFAs accumulate in the adrenal cortex, what happens?

A

adrenal atrophy

69
Q

What is the usually the first symptom in XALD?

A

behavioral changes

MCB1 Block 3 (15 decks)

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