Lecture 22

Question 1

Define oxidative phosphorylation

Answer 1

the method of generating ATP which is dependent on the transport of protons across the mitochondrial membrane

Question 2

What are the 2 stages of oxidative phosphorylation?

Answer 2

Stage 1 : high energy electrons are transferred down the electron transport chain which pumps protons across a membrane, generating an electrochemical gradient

Stage 2: Protons flow back down their electrochemical gradient through ATP synthase to produce ATP

Question 3

Define chemiosmotic coupling

Answer 3

it is a mechanism that uses energy stored in a transmembrane gradient to drive an energy requiring process (like generating ATP)

Question 4

provide details about the mitochondria

Answer 4

• evolved from bacteria that was engulfed by ancestral cells
• can undergo fission
• contains its own DNA
• can change shape, location and number in response to cells metabolic demands

Question 5

Mitochondrial structure

Answer 5

• outer membrane is permeable to most small molecules as a result of a protein called porin
• inner membrane is impermeable to most small molecules because it has many infolding known as cristae
• the intermembrane space is located between the outer and inner membrane
• the interior space is known as the matrix

Question 6

Generation of high energy electrons

Answer 6

• acetyl-CoA that is generated from fatty acids, sugars and amino acids can enter CAC and produce large amounts of the activated carriers like NADH and FADH2
• electrons from NADH and FADH2 can be passed down the electron transport chain, causing protons to be pumped from the mitochondrial matrix to the intermembrane space

Question 7

How are electrons from NADH and FADH2 passed down the electron transport chain

Answer 7

through using respiratory enzyme complexes

Question 8

What is complex I

Answer 8

Name: NADH dehydrogenase complex
- transfers a pair of electrons from NADH to coenzyme Q (Q –> ubiquinone)
- transfer of electrons are energetically favoured
- pumps protons into the intermembrane space

Question 9

Coenzyme Q

Answer 9

• lipophilic tail allows it to enter hydrophobic core of mitochondrial membrane
• complete reduction requires 2 H+ and 2e-

Question 10

What is complex III

Answer 10

Name: cytochrome c reductase complex
- receives electrons from reduced coenzyme Q (QH2 –> ubiquinol) and transfers them onto cytochrome c
- pumps protons into intermembrane space

Question 11

What is complex II

Answer 11

Name: FADH2 dehydrogenase complex
- It takes electrons from FADH2 generated during the CAC and transfers them to ubiquinone
- complex II does not pump protons

Question 12

What is complex IV

Answer 12

Name: cytochrome c oxidase complex
- accepts electrons from cytochrome c and directs them to the 4 electron reduction of O2 to form H2O
- pumps protons into intermembrane space

Question 13

proton pumping

Answer 13

• complex 1, 3, and 4 pump protons from the mitochondrial matrix into the intermembrane space creating a H+ gradient and a voltage gradient across the inner mitochondrial membrane
• it is very favourable for protons to flow back into the mitochondrial space due to the difference in pH and mostly because of the difference in membrane potential

Question 14

what is proton-motive force

Answer 14

the combines contribution of change in voltage and change in pH

Question 15

what is complex V

Answer 15

Name: ATP synthase
- it is a large multi subunit protein embedded in the inner mitochondrial matrix that uses energy stored in the electrochemical gradient to produce ATP
- head faces mitochondrial matrix
- when protons flow through it causes central stalk to turn

Question 16

What are the 3 conformations of ATP synthase

Answer 16

1. B-ADP (loose) –> ADP and Pi bind
2. B-ATP (tight) –> conformation with high affinity for ATP. ATP is formed
3. B- empty (very loose/open) –> conformation with low off affinity for ATP. ATP is released

• each conformation is caused by the movement of central stalk as protons flow through
• each full rotation produces 3 molecules of ATP

Question 17

ATP synthase can operate in reverse

Answer 17

• ATP can be hydrolyzed to pump protons from the matrix back into the intermembrane space

Question 18

Couples transport

Answer 18

1. exchange ATP for ADP
2. import of pyruvate
3. import of phosphate

Question 19

Rapid conversion of ADP to ATP

Answer 19

• ADP is rapidly converted into ATP in the mitochondria to maintain a high ATP/ADP ratio in the cell
• ATP can shuttle in and out of mitochondrion several times in a minute

Question 20

NADH transfers vs FADH2 transfers

Answer 20

• NADH transfers electrons to NADH dehydrogenase which in turn
  transfers electrons to ubiquinone
• FADH2 transfers electrons to Complex II which in turn transfers
  electrons to ubiquinone. This bypasses NADH dehydrogenase,
  meaning that fewer protons are pumped across into the
  intermembrane space and thus, fewer ATP produced.

Question 21

How is cell respiration efficient

Answer 21

• 2.5 ATP can be produced per NADH
• 1.5 ATP can be produced per FADH2
• almost 50% of energy released from food is capture and stored as ATP

Question 22

Why are protons unique

Answer 22

because hydrogen is so abundant

Question 23

When a molecule is reduced, it is often accompanied
by the ___________ of a proton/protons
When a molecule is oxidized, it is often accompanied by the _______ of a proton/protons

Answer 23

1. addition
2. loss