Test 3: ETC and ATP

Question 1

What 3 types of work does a cell do?

Answer 1

• mechanical work
• transport work
• chemical work

Question 2

What is ATP?

Answer 2

• Adenosine TriPhosphate
• nucleotide with unstable phosphate bonds that the cell hydrolyses for energy to drive endergonic reactions.

Question 3

What does ATP consist of?

Answer 3

ATP (nucelotide):
- 3 phosphate groups
- ribose
- adenine

Question 4

How is energy released from ATP?

Answer 4

terminal phosphate bond is hydrolysed:
- inorganic phosphate group (Pi) is removed
- ADP is produced

Question 5

Explain the strength of phosphate bonds of ATP. Why?

Answer 5

• called “high-energy phosphate bonds”
• weak covalent bonds
• unstable

weak because each phosphate group has a negative charge –> instability due to repulsion

Question 6

The hydrolysis of ATP is coupled directly to what kind of processes? How?

Answer 6

• endergonic processes
• by transferring the phosphate group to another molecule

Question 7

What happens when a phosphate group is transferred to another molecule?

Answer 7

the molecule is:
- phosphorylated
- more reactive!

Question 8

How can ATP be synthesised? By what processes?

Answer 8

• glycolysis
• oxidative phosphorylation
• substrate-level phosphorylation

Question 9

What is substrate level phosphorylation? How does it occur? What does it form?

Answer 9

• chemical reaction
• forms ATP
• direct transfer and donation of phosphoryl group (-PO32-) to ADP

Question 10

Where does substrate level phosphorylation occur? Under what conditions?

Answer 10

location: cytoplasm (glycolysis)
conditions: aerobic and anaerobic

Question 11

What is the primary difference between substrate level phosphorylation and oxidative phosphorylation?

Answer 11

substrate level phosphorylation:
- oxidation and phosphorylation are not joined!

Question 12

What is oxidative phosphorylation? What does it form? What happens?

Answer 12

• chemical process
• forms ATP
• transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers

Question 13

What enzyme complexes take part in oxidative phosphorylation?

Answer 13

• ATP synthase
• the electron transport chain

Question 14

Where does oxidative phosphorylation take place in eukaryotes?

Answer 14

mitochondria

inner mitochondrial membrane: ETC, ATP synthase

mitochondrial matrix: pyruvate dehydrogenase complex, cirtric acid cycle, fatty acid oxidation

Question 15

What is the ETC?

Answer 15

• set of membrane proteins allowing for oxidative phosphorylation of O2.
• highly exergonic reduction of O2 by NADH and FADH2
• occuring in a number of electron transfer reactions

Question 16

How is the ETC organized?

Answer 16

4 complexes:
I: NADH-coenzyme Q reductase / NADH dehydrogenase
II: succinate-coenzyme Q reductase / succinate dehydrogenase
III: coenzyme Q reductase
IV: cytochrome C reductase

Question 17

Where are all of the ETC complexes located?

Answer 17

embedded in the inner mitochondrial membrane

Question 18

Explain how electrons are carrier (of both NADH and FADH2)

Answer 18

NADH:
I –> II (+ ‘ubiquinone’ coenzyme Q) –> III –> IV

FADH2:
II (+ ‘ubiquinone’ coenzyme Q) –> III

Question 19

What is ‘ubiquinone’?

Answer 19

‘ubiquinone’ = reduced form of coenzyme Q

Question 20

Where are FADH2 electrons generated?

Answer 20

in the succinate dehydrogenase (Citric Cycle)

Question 21

What is an oxidation-reduction couple? State examples.

Answer 21

Pair of molecules of which one is reduced and the other is oxidized.
- lactate & pyruvate
- NADH & NADH+
- FADH2 & FAD

Question 22

What is complex I? How many electrons does it transfer? From what to what?

Answer 22

NADH-Coenzyme Q reductase / NADH dehydrogenase
- transfers 2 electrons from NADH to coenzyme Q
- contains FMN prosthetic group
- NADH + FMN –> NAD+ +FMNH2

Question 23

What is complex II? What is it composed of?

Answer 23

• succinate dehydrogenase
• enzyme of the citric acid cycle
• 4 subunits (2Fe-S and 2 FAD)

Question 24

State the overall reaction for complex II.

Answer 24

succinate + CoQ –> fumarate + CoQH2

Question 25

What is complex III? What is it composed of?

Answer 25

coenzyme Q-cytochrome c reductase
- passes electrons by the Q-cycle
- 2 b-type cytochromes, 1 c-type cytochrome

Question 26

What is a cytochrome?

Answer 26

• iron-containing electron transferring proteins
• heme proteins

Question 27

What do cytochromes undergo?

Answer 27

reduction:
all: Fe3+ –> Fe2+
cytochrome a3: Cu2+ –> Cu+

Question 28

What is complex IV? What is it composed of?

Answer 28

Cytochrome c oxidase
- a proton pump

• 2 heme centers, cytochrome a, cytochrome a3 and 2 copper proteins

Question 29

Explain the reaction process with cytochrome IV.

Answer 29

• Cytochrome IV + O2 –> … + 2H2O
• O2 is reduced into H2O

Question 30

What does the chemiosmotic theory create?

Answer 30

• an electrical gradient (more e- on the outside of the membrane)
• pH gradient (outside is more acidic)

Question 31

What is Complex V? What does it do?

Answer 31

ATP synthetase / ATPase
- synthesizes ATP through the proton gradient (proton motive force) generated by the ETC
- spontaneous H+ flux

Question 32

Explain the cycle of ATP-ase. What are the three conformations?

Answer 32

• driven by H+ flow
• conformation of each B subunit changes (as it interacts with the rotating shaft)

loose conformation: active site can bind ADP+Pi
tight conformation: substrates bound and ATP is formed
open conformation: favours ATP release

Question 33

What would happen if no membrane potential or pH gradient exists?

Answer 33

the reverse reaction would occur:
- ATP hydrolysis

Question 34

State examples of inhibitors of ATPsynthase. What do they do?

Answer 34

block H+ transport coupled to ATP synthesis / hydrolysis:
- ogliomycin
- DCCD

Question 35

What is the energetic yield of ETC (oxidative phosphorylation)?

Answer 35

Oxidation of NADH: 3ATP (ADP and Pi)
Oxidation of FADH2: 2ATP (ADP and Pi)