Mitochondrial Structure and Function

Question 1

Mitochondria have their own genome. How do mitochondrial ribosomes get into mitochondria?

Answer 1

ribosomal protein are imported and assembled with mitochondrial ribosomal RNAs

Question 2

Do mitochondria import RNA?

Answer 2

No. That’s why they have tRNA and rRNA encoded in the mitochondrial genome

They can import proteins (98% imported)

Question 3

Are all ribosomal genes encoded in the mitochondrial genome?

Answer 3

No, most are encoded in the nucleus

Question 4

Mitochondria are found in most human cells except for?

Answer 4

erythrocytes and mature lens fiber cells

Question 5

Placement of mitochondrial ribosomal RNA in phylogenetic trees shows a strong correlation to what?

Answer 5

alpha proteobacteria

Question 6

Is the outer membrane of the mitochondria porous to small molecules?

Answer 6

yes

Question 7

is the inner membrane permeable to ions and protons?

Answer 7

No

Question 8

Where does cytochrome C reside?

Answer 8

in the inter membrane space

Question 9

What resides on the inner membrane?

Answer 9

the ATP synthase and ETC complexes and a large set of carrier proteins

Question 10

What is the inner membrane dense in?

Answer 10

protein

Question 11

Stage III of mitochondria conformation exists when?

Answer 11

When ADP is high and the mitochondrial matrix is condemned for active respiration

regulated by mitofillin

Question 12

Stage IV of mitochondria conformation exists when?

Answer 12

When ADP is low and the mitochondrial matrix is expanded for a resting state

regulated by mitofillin

Question 13

How are mitochondria involved in apoptosis?

Answer 13

An appropriate signal from pro-apoptotic proteins like BAD, BAX, and BID cause the mitochondria to become leaky and release cytochrome C into the cytosol and fusion of cristae

Cytochrome C units with another protein, APAF1, and together they recruit Caspase IX.

These three proteins comprise a ‘apoptosome’ which triggers a caspase cascade leading to cell death

Question 14

What is the lipid to protein ratio on the outer membrane of mitochondria?

Answer 14

1:1 by weight (similar to plasma membrane)

Question 15

What is A porin?

Answer 15

protein locate on outer membrane of mitochondria (it is a ‘beta-ferrel’ protein) that forms trimers and has opening that allow small molecules to enter the mitochondria. However, this opening does not allow proteins like cytochrome C to pass

Question 16

T or F. the inner mitochondrial membrane has a much higher protein: lipid ratio than the outer membrane

Answer 16

T. (~3:1 by wgt)

Question 17

What is cardiolipin?

Answer 17

a unique phospholipid on the inner mitochondrial membrane that associates with complexes on the membrane. Chains connected by glycerol

Question 18

What is Barth syndrome caused by?

Answer 18

mutation in cardiolipin biosynthesis gene which leads to ineffective mitochondria and muscle weakness

Question 19

What substances can move across the inner mitochondria membrane?

Answer 19

water, oxygen, and CO2

Question 20

How do substances like ADP, ATP, phosphate, pyruvate, and amino acids pass through the inner membrane?

Answer 20

They need special mitochondrial carriers (most of these are antiporters)

Question 21

What are the intermediates of O2 reduction to water during the ETC?

Answer 21

1) superoxide (O2-)- formed by addition of an electron to O2
2) hydrogen peroxide
3) hydroxyl radical

Question 22

What enzyme exists in mitochondria to eliminate superoxide?

Answer 22

superoxide dismutase (it converts it to hydrogen peroxide which is less toxic)

Question 23

What is Lou Gerhig’s disease caused by?

Answer 23

a defect in superoxide dismutase (the cytosolic form, not the mitochondrial form)

Question 24

How is H2O2 converted to water?

Answer 24

catalase in mitochondria

Question 25

How can H2O2 be converted to hydroxyl radical?

Answer 25

by reaction with Fe2+ and e-. Hydroxyl radical is very reactive and destructive

Question 26

What can help eliminate hydroxyl radicals?

Answer 26

vitamin E and C (converts to water)

Question 27

Where is mitofillin found in the mitochondria?

Answer 27

inner membrane. It is a complex that’s involved with connecting the cristae to the inner boundary membrane and thus allow ATP to exit

Question 28

Where is heme synthesized?

Answer 28

in cytosol and mitochondria. RBC’s make heme in their pre-cursor organelles before they are lost

Question 29

Does glycolysis at least partially occur in mitochondria?

Answer 29

No

Question 30

Are cristae in close communication with the inner membrane of the mitochondria?

Answer 30

Now, cristae are thought of as more of tubes and flattened regions with limited connections to the portion of the inner membrane that lines the outer membrane.

Question 31

How do crest communicate with the inner membrane of the mitochondria?

Answer 31

Cristae come into contact with inner membrane via junctions (mitofilin and MINOS complex is important for the formation of these junctions). Cristae change given different signals (ex. when mitochondria receive pro-apoptotic signals). Also, during different stages of respiration, cristae can fuse. This allows “bottlenecks” to diffusion to allow rapid exchange of metobolites with the cytosol.

Question 32

What primary metabolic functions take place in mitochondria?

Answer 32

• Tricarboxylic acid cycle
• Respiration
• Fatty acid beta oxidation
• Ammonia elimination via the urea cycle
• Heme biosynthesis
• Reactive oxygen species removal (protection against oxidative stress)
• RNA, DNA, and protein biosynthesis
• Mitochondrial Biosynthesis
• Molecular Transport
• Calcium Uptake