Block 1 - Mitochondria (L11-13)

Question 1

What are the two major roles of the mitochondria?

Answer 1

cellular respiration/ATP homeostasis

programmed cell death/apoptosis

Question 2

What is the basic structure of a mitochondria?

Answer 2

• rod shaped/round
• two membranes
• outer membrane is the boundary
• inner membrane is folded into cristae that project inward

Question 3

What are the three proteins in the inner membrane of the mitochondria?

Answer 3

• electron transport chain molecules (NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase)
• ATP synthase
• Transport proteins

Question 4

What is in the mitochondrial matrix?

Answer 4

• enzymes for oxidation of pyruvate and fatty acids and use in citric acid cycle
• mitochondrial DNA
• mitochondrial ribosomes
• tRNAs and enzymes needed for expression of the mitochondrial genes

Question 5

What things do mitochondria and bacteria have in common?

Answer 5

circular DNA, double membrane, and similar electron transport chain

Question 6

Mitochondria generate —– from —— for use in ——-.

Answer 6

generate energy from OxPhos for use in many pathways

Question 7

Where does glycolysis occur?

Answer 7

cytoplasm, outside the mitochondria

Question 8

Where does the Krebs/citric acid cycle occur?

Answer 8

inside the mitochondria

Question 9

What drives ATP synthesis in the mitochondria?

Answer 9

NADH and FADH2 transport H+ protons into the intermembrane space (between the inner and outer membranes) via the electron transport chain

The proton gradient is used in chemiosmotic coupling to generate ATP

Question 10

What is chemiosmotic coupling?

Answer 10

the process mitochondria use to harness energy

link between chemical bond-forming reactions that generate ATP and membrane transport

Question 11

What are the two main steps of generating ATP in the mitochondria?

Answer 11

1. electron transport chain shifts protons to create a gradient
2. proton gradient is harnessed by ATP synthase to make ATP

Question 12

What is the pathway leading up to ATP synthase

Answer 12

complex 1 - NADPH oxidase
complex 2 - succinate reductase
complex 3 - cytochrome bc1
complex 4 - cytochrome oxidase

NADH —> complex 1 —> Q
OR
succinate —–> complex 2 —–> Q
THEN
Q —> complex 3 —-> cytochrome c —-> complex 4

Question 13

What is the final electron acceptor in the ETC?

Answer 13

oxygen

Question 14

Is the plasma membrane voltage greater or less than the inner mitochondrial membrane voltage?

Answer 14

less than - the high protein gradient across the inner mitochondria creates a voltage that is much higher than the voltage across the plasma membrane

Question 15

Where are ATP created, and how many?

Answer 15

glycolysis (2)
ox phos (34, but need O2)
= 36 ATP

Question 16

A single cell consumes roughly —- ATP per second.

Answer 16

10 million

Question 17

How many protons cause ATP synthase to spin once and generate 1 ATP?

Answer 17

10 protons = 1 spin = 1 ATP

Question 18

Mitochondrial proton gradients are good sensors of…

Answer 18

cellular health

Question 19

Mitochondria do not actually make new ATP, they…..

Answer 19

continually recycle ADP to ATP

Question 20

Why is ADP recycled instead of just making new ATP?

Answer 20

We would need 10 million molecules of ATP per second, or 60 kg ATP per day

That’s too much to make new every day, so we reuse throughout the day

Question 21

Does the citric acid/Krebs cycle generate ATP?

Answer 21

no, it makes precursors which are then used to make ATP

Question 22

Mitochondria can divide in a process called…

Answer 22

fission

Question 23

How do mitochondria get their proteins?

Answer 23

essential proteins that are coded by mtDNA are synthesized in the mitochondria
but MOST proteins are imported from the cytosol and are coded by nuclear DNA

Question 24

What happens to old/worn out mitochondria?

Answer 24

autophagy (phagocytosis of large particles):
- endoplasmic reticulum wraps around it
- fusion with a lysosomal vesicle
- mitochondrion is digested

Question 25

What happens to new mitochondria?

Answer 25

they can be transported around the cell by motor proteins along microtubules of the cytoskeleton

Question 26

Mitochondrial DNA, as opposed to nuclear DNA, is...

Answer 26

circular

Question 27

What is needed for proteins to be translocated into the mito?

Answer 27

translocation contact sites and specialized translocon structures are needed TOM (translocon of the outer membrane) TIM (translocon of the inner membrane)

Question 28

How do TOM and TIM work together to translocate proteins?

Answer 28

- the cytosolic protein has a signal sequence on the end - signal sequence is recognized by TOM - TOM inserts the protein into the membrane, where it contacts TIM - TIM translocates the protein into the matrix of the mito - signal peptidase (inside the mito matrix) cleaves the signal sequence from the protein to create the mature mitochondrial protein

Question 29

Why is mito DNA inherited from the mother?

Answer 29

sperm has very few mito compared to the oocyte, and most are in the tail which does not even become part of the embryo also, sperm mito may be programmed to die after fertilization

Question 30

What cytoskeletal element helps sperm swim?

Answer 30

microtubules (because the tail is a flagella)

Question 31

Why is mitochondrial inheritance risky business? Why is everything still okay though?

Answer 31

Risky: while nuclear genes are recombined every generation, mito DNA is passed asexually and therefore is 50x as prone to mutations However: mito defects are so lethal that natural selection tends to prevent dysfunctional mito from establishing in a population

Question 32

What is heteroplasmy? Why is it able to happen in mito?

Answer 32

Heteroplasmy: a cell or tissue contains more than one type of mitochondrial genome Each mitochondrion contains multiple copies of mtDNA, and a mutation does not necessarily affect all the copies, so some can be mutated while others are not. The dose of a mutation is important when considering the inheritance pattern of a mitochondrial disease.

Question 33

Besides energy homeostasis, what other functions do the mito have?

Answer 33

- programmed cell death (apoptosis) - heat production - generation of reactive oxygen - calcium store - role in some diseases (impaired function from ntDNA mutations)

Question 34

What is apoptosis?

Answer 34

programmed cell death, orderly cellular self-destruction about 100 thousand cells are produced every second, so 100 thousand also die every second by apoptosis

Question 35

Evolutionarily, why do cells undergo apoptosis?

Answer 35

bacteria evolved a mechanism to ensure that they died quickly when infected with a virus this evolved into the mitochondrial pore which is part of the apoptosis machinery

Question 36

Describe the basic mechanism of mitochondrial apoptosis

Answer 36

- the permeability transition pore opens and cytochrome c exits - cyt c activates Apaf-1 - Apaf-1 activates caspases (family of proteases that begin the process of degrading cellular components)

Question 37

Where is cytochrome c located in the mito?

Answer 37

on the intermembrane space side of the inner membrane

Question 38

cytochrome c is crucial for apoptosis, but also...

Answer 38

the electron transport chain

Question 39

What are the stages of classic apoptosis?

Answer 39

- healthy cell receives a death signal (extrinsic or intrinsic) - cell undergoes commitment to die (reversible) - cell is executed (irreversible) and condenses/crosslinks to become a dead cell - engulfment by macrophages and neighboring cells where it is degraded

Question 40

What role do mito play in glucose sensing/insulin release?

Answer 40

- in pancreatic b cells, mito link glucose exposure to insulin release 1. GLUT2 transporters introduce glucose to the cell, and mito increases the ATP:ADP ratio 2. K+ gates close which depolarizes the cell 3. voltage sensitive Ca++ channels open 4. exocytosis of ins. storage granules to the bloodstream

Question 41

How are the B-cells impaired (causing loss of glucose-stimulated insulin release)?

Answer 41

- superoxide radicals induce UCP-2 (uncoupling protein 2) upregulation - uncoupling causes proton leak, decreased ATP:ADP ratio, and loss of glucose stim. insulin release

Question 42

What are UCPs (uncoupling proteins)?

Answer 42

- transmembrane proteins in mito that decrease the proton gradient generated in oxidative phosphorylation - they create a leak pathway that allows protons to cross the mito inner membrane, bypassing ATP synthase - basically, H+ gradient is uncoupled from ATP generation

Question 43

What is UCP1 vs. UCP2?

Answer 43

UCP1: - brown adipose tissue - babies and hibernating mammals - diverts energy from ATP generation to thermogenesis (heat release) in response to cold - decrease mito production of damaging reactive oxygen species UCP2: - white adipose tissue - humans during feeding - metabolic adaptation to fasting regardless of weight - non-thermogenic uncoupling

Question 44

Mitochondrial mutation can cause disease in what systems?

Answer 44

nervous, cardiovascular, liver, kidneys, eyes, skeletal muscle, digestive, and pancreas

Question 45

How can a three person baby be made (in order to eliminate mito mutations)?

Answer 45

- mother egg is enucleated - donor egg is enucleated - the nucleus of the mother's egg is put into the enucleated donor egg with normal mito - sperm fertilizes that "new" egg

Question 46

When a three person baby is made, where does each part come from?

Answer 46

nucleus comes from mother, mito/rest of the egg comes from donor, sperm from father