Peroxisomes and Mitochondria

Question 1

What are Peroxisomes?

Answer 1

Small single membrane organelles found in all cells

Peroxisomal Proteins are all nuclear encoded

Question 2

What metabolic reactions do peroxisomes carry out?

Answer 2

Oxidative reactions using molecular oxygen

E.g. breakdown normal metabolites and harmful compounds

Synthesis of bile acids and plasmalogens

Question 3

What is Catalase?

Answer 3

Enzyme in peroxisomes that removes excess H2O2

Question 4

What are the two mechanisms of peroxisome formation?

Answer 4

Vesicles budding from the ER and fuse

Growth and division of existing peroxisomes (more rapid)

These two mechanisms allow response to different metabolic needs

Question 5

Where are peroxisome matrix proteins synthesized?

Answer 5

Free ribosomes and imported as folded polypeptides

Question 6

What is Peroxisomal targeting sequence 1?

Answer 6

Ser-Lys-Leu

Labels peroxins for import via ER pathway

Question 7

What recognizes the PTS1 signal and what is the next step?

Answer 7

Pex5 receptor

Pex5/Cargo complex binds to a docking complex on the peroxisome

Question 8

What is mPTS?

Answer 8

Targeting signal on peroxins that is recognized by Pex19

Question 9

How are oxidized flavins regenerated in peroxisomes?

Answer 9

Regenerated with oxygen in a reaction that produces hydrogen peroxide

Question 10

Why do 2-carbon units oxidized in the peroxisomes produce fewer ATPs?

Answer 10

Enzyme transfers liberated electrons directly to oxygen instead of the electron transport chain

Question 11

What is FAD-dependent acyl-CoA oxidase?

Answer 11

Catalyzes the initial double bond formation in peroxisomal B-oxidation

Inactive with carbon chains of 8 or fewer

Short-chain products must be transferred to mitochondria to be broken down

Question 12

Where are plasmologens made?

Answer 12

Peroxisomes

Protective versus oxidant stress

Question 13

What are the recessive genetic disorders associated with Peroxin mutations?

Answer 13

Rhizomelic Chondrodysplasia punctata type 1 (RCDP type 1)

Zellweger spectrum disorders

Question 14

Describe Zellwegger Spectrum Disorders.

Answer 14

Disrupted peroxisome assembly

Peroxisomes absent in hepatocytes and fibroblasts

Accumulation of VLCFA, phytanic acid, plasmologen deficiency

Question 15

What are the symptoms of Zellwegger Syndrome?

Answer 15

Craniofacial, neurologic, and ocular abnormalities

Impaired neuronal migration and severe demyelination

Question 16

What is Neonatal Adrenoleukodystrophy (NALD)?

Answer 16

Milder form of ZS

Patients have milder ZS symptoms with adrenal atrophy

Question 17

What is Infantile Refsum’s Disease?

Answer 17

No neonatal abnormalities and only mild dysmorphia

Mental retardation, retinitis pigmentosa, neurosensory deafness, growth retardation

Question 18

Describe mitochondrial fusion and fission.

Answer 18

Happens dynamically

Fusion allows exchange of genetic material

Fission is important in distribution of mitochondria between daughter cells at cell division

Question 19

What four processes does the mitochondria carry out?

Answer 19

Oxidation of nutrients in TCA cycle

Energy generation - Oxphos

Integrator of cellular death signals - apoptosis

Transcription/Translation

Question 20

Where does mitochondrial protein import occur?

Answer 20

Regions where the outer and the inner membranes are close together

Question 21

How many different types of signal sequences are there for mitchondrial protein import and what is their general structure?

Answer 21

4

Predominantly positive AA’s, often in an alpha helix

Question 22

What is responsible for making the mitochondrial outer membrane fairly permeable?

Answer 22

Porins or voltage dependent anion channel

Question 23

What is the role of Hsp70?

Answer 23

Maintain protein in a semi-folded state in the cytosol

Question 24

What is the function of TOM complex?

Answer 24

Mediates protein transport across the outer membrane

Question 25

What is the function of TIM23 complex?

Answer 25

Mediates protein transport across the inner membrane into the matrix

Question 26

What is the function of matrix processing peptidase?

Answer 26

Cleaves the targeting pre-sequence within the matrix

Question 27

What is the function of Mim1?

Answer 27

Responsible for inserting proteins into the outer membrane with a single transmembrane domain

Question 28

How do B-barrel proteins get inserted into the outer membrane?

Answer 28

Pass through TOM

Bound by Tim9-Tim10 and carried to SAM

SAM mediates their insertion into the outer membrane

Question 29

How are proteins with multiple transmembrane domains that have an internal import signal transported?

Answer 29

After transport through TOM, tim9-10 bring them to Tim22

Tim22 then facilitates transfer into the inner membrane

Question 30

What is the function of Oxa1?

Answer 30

Responsible for mediating the insertion of inner membrane proteins that are transcribed in the mitochondria

Question 31

What is Human Deafness Dystonia Syndrome?

Answer 31

X-linked neurodegenerative disorder

Defect in Tim8

Question 32

What are the symptoms of Human Deafness Dystonia Syndrome?

Answer 32

Postlingual progressive sensorineural deafness

Dystonia

Spasticity, Dysphagia

Mental deterioration

Cortical blindness

Question 33

What is cardiolipin?

Answer 33

Lipid that contains four fatty acyl chain and is found almost exclusively in the inner mitochondrial membrane

Essential for the optimal function of numerous enzymes

Question 34

What is Barth Syndrome?

Answer 34

Infantile cardiomyopathy linked to the X-chromosome

Associated with decrease in tetralinoleoyl species of cardiolipin and accumulation of monolysocardiolipin

Metabolic defect involves phospholipid acyltransferase

Question 35

What are the symptoms of Barth Syndrome?

Answer 35

Cardiomyopathy

Skeletal myopathy

Neutropenia

Growth retardation