Peroxisomes

Question 1

Where are peroxisomes made?

Answer 1

Free ribosomes

Question 2

What kind of reactions do peroxisomes carry out?

Answer 2

oxidative reactions

Question 3

Cells in what organs have abundant peroxisomes?

Answer 3

Liver & kidney

Question 4

What is the tag to get enzymes into the peroxisome?

Answer 4

SKL

Question 5

What is the pH of peroxisome?

Answer 5

7.5

Question 6

What tissues are peroxisomes present in?

Answer 6

All of them

Question 7

Why do peroxisomes generate H2O2?

Answer 7

oxidative purposes

Question 8

What is in peroxisomes to turn H202 into water?

Answer 8

catalase

Question 9

What is another name for catalase?

Answer 9

peroxidase

Question 10

How do peroxisomes divide?

Answer 10

Fission

Question 11

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

Answer 11

cytoplasm

Question 12

What terminus is SKL sequence usually located?

Answer 12

C-terminus

Question 13

PTS1 is another name for what?

Answer 13

SKL sequence

Question 14

What recognizes SKL?

Answer 14

peroxins

Question 15

Import into peroxisome requires what?

Answer 15

ATP

Question 16

Where are proteins that are destined for peroxisome folded?

Answer 16

cytoplasm

Question 17

What are peroxins?

Answer 17

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

Question 18

What amino acids make up the SKL sequence?

Answer 18

Ser-Lys-Leu

Question 19

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

Answer 19

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

Question 20

What three biosynthetic functions do the peroxisome have?

Answer 20

Plasmalogen synthesis
Bile acid synthesis
Lipid biosynthesis

Question 21

What is plasmalogen and why is it important?

Answer 21

It’s a phospholipid, especially important in Schwann cells

Question 22

Name two examples of lipid biosynthesis in peroxisome

Answer 22

Cholesterol & dolichol

Question 23

What are the 3 degradative functions of peroxisome?

Answer 23

VLCFA beta oxidation
purine cataboilsm
H2O2

Question 24

What does VLCFA stand for?

Answer 24

Very long chan fatty acid

Question 25

Where is the only place that VLCFA breakdown can occur?

Answer 25

Peroxisome

Question 26

What is purine catabolism?

Answer 26

breakdown of purine

Question 27

Peroxisomes use O2 to remove what from organic substrates?

Answer 27

H atoms

Question 28

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

Answer 28

organic compounds

Question 29

H202 is needed in peroxisomes to do what?

Answer 29

oxidise toxins

Question 30

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

Answer 30

alcohol

Question 31

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

Answer 31

24 or more

Question 32

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

Answer 32

10

Question 33

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

Answer 33

Until it has 10 C tail length

Question 34

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

Answer 34

beta oxidation

Question 35

fatty acid oxidation is a major source of metabolic ____

Answer 35

energy

Question 36

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

Answer 36

fatty acids → AcetylCoA → cytosol

Question 37

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

Answer 37

uric acid

Question 38

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

Answer 38

xanthine oxidase

Question 39

What is Hyperuricaemia?

Answer 39

Gout

Question 40

What is hypoxanthine?

Answer 40

It makes xanthine

Question 41

Key words: hyperuricemia, Allopurinol are what disease?

Answer 41

Gout

Question 42

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?

Answer 42

Gout

Question 43

What is the mechanism for gout?

Answer 43

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

Question 44

What causes the swollen toe in gout?

Answer 44

urate crystal deposits

Question 45

What is allopurinol?

Answer 45

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

Question 46

What is plasmogen and why is it important?

Answer 46

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

Question 47

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

Answer 47

phospholipid

Question 48

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

Answer 48

Zellweger syndrome

Question 49

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?

Answer 49

Zellweger syndrome

Question 50

PEX genes encode what?

Answer 50

Peroxins

Question 51

What lysosomal disease is zellweger syndrome similar to?

Answer 51

I-cell

Question 52

What is mechanism for zellweger syndrome?

Answer 52

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

Question 53

What is the mode of inheritance for zellweger syndrome?

Answer 53

Autosomal recessive, congenital

Question 54

Where is the defect/mutation in zellweger syndrome?

Answer 54

PEX mutation - leads to defective peroxin

Question 55

XALD stands for what?

Answer 55

X-linked Adrenoleukodystrophy

Question 56

What is XALD?

Answer 56

defective membrane protein that imports VLCFAs

Question 57

How is XALD caused in zellweger syndrome?

Answer 57

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

Question 58

Why is there muscle weakness in pts with zellweger?

Answer 58

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

Question 59

Why is there hepatomegaly in pts with zellweger?

Answer 59

accumulation of VLCFA in liver cells

Question 60

Why is there abnormal brain development in pts with zellweger?

Answer 60

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

Question 61

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

Answer 61

X-linked Adrenoleukodystrophy (XALD)

Question 62

What is mode of inheritance for XALD?

Answer 62

X-linked

Question 63

What is mechanism for XALD?

Answer 63

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

Question 64

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

Answer 64

XALD

Question 65

What is the defect in XALD?

Answer 65

import protein defect, VLCFA are not imported into peroxisome

Question 66

Where is especially important locations that VLCFAs accumulate?

Answer 66

Brain cells & adrenal cortex

Question 67

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

Answer 67

Breakdown of myelin

Question 68

Because VLCFAs accumulate in the adrenal cortex, what happens?

Answer 68

adrenal atrophy

Question 69

What is the usually the first symptom in XALD?

Answer 69

behavioral changes