Bioenergetics I and II- Lectures 70-71

Question 1

Energy derived from the oxidation of glucose, fatty acids, and amino acids is converted to the high-energy phosphate bonds of ATP by the process of ______.

Answer 1

oxidative phosphorylation

Question 2

The electron transport chain is fueled by _____ and _____.

Answer 2

NADH and FADH2

Question 3

What are the components of the respiratory chain?

Answer 3

Complex I: NADH-CoQ (ubiquinone) Reductase
Complex II: Succinate-COQ REductase
Complex III: Reduced QH2- Cytochrome C Reductase
Complex IV: Cytochrome Oxidase
Complex V (F0 and F1 components): ATP Synthase

Question 4

Which complexes in the respiratory chain pump protons?

Answer 4

Complex I (4H+ per electron)
Complex III (2H+ per electron)
Complex IV (4H+ per electron)

Question 5

Why are protons pumped by the respiratory chain?

Answer 5

to generate a proton gradient to be harnessed for energy by Complex V

Question 6

Describe ATP synthase.

Answer 6

complex V of the respiratory chain
composed of a proton pore and a catalytic head-piece
protons enter via the pore –> conformational change in the catalytic head-piece –> releases ATP bound to one site while catalyzing the formation of a new ATP from ADP plus Pi at another site (which can be transferred to the bound site for release with next proton)

Question 7

What is the rate of respiration?

Answer 7

the rate at which electrons are transferred and O2 is reduced

Question 8

What regulates the rate of respiration?

Answer 8

rate of ATP synthesis
deltaP
other bioenergetic work functions which use the delta P

Question 9

What are uncoupling agents?

Answer 9

chemicals that make the mito membrane damaged and leaky to protons

Question 10

What happens when the mito membrane becomes damaged and leaky to protons?

Answer 10

deltaP will be immediately dissipated
inhibition of ATP synthesis (and any other mechanisms that use the proton motive force)
O2 uptake increases because respiratory chain activity increases to reestablish the pmf (but no ATP is being created)

Question 11

Provide examples of uncoupling agents.

Answer 11

UCP1: associated with heat production in brown adipose tissue; important for thermoregulation of infants and hibernating animals
UCP3: present in skeletal muscle; targeted for weight loss drugs that “waste” deltaP as heat rather than harness it to support biosynthetic reactions such as fat synthesis

Question 12

Describe the flow of electrons for complex I of the respiratory chain.

Answer 12

NADH –> FMN –> FeS centers –> ubiquinone (Q) –> QH2 (reduced Q)

Question 13

Describe the flow of electrons for complex II of the respiratory chain.

Answer 13

succinate –(succinate dehydrogenase)–> FAD –> QH2 (reduced Q)
OR
FADH2 (from beta oxidation) –(electron transfer flavoprotein)–> QH2 (reduced Q)

Question 14

_____ is the only component of the electron transport chain that is not protein-bound.

Answer 14

Ubiquinone (CoQ)

Question 15

How is ubiquinone synthesized?

Answer 15

from an intermediate produced during cholesterol synthesis

Question 16

NADH and FADH2 transfer _____ electrons to Q, however Q can only accept _____ electrons at a time.

Answer 16

2

1

Question 17

What are cytochromes?

Answer 17

proteins containing hemes in which iron in the heme undergoes oxidation-reduction

Question 18

Describe the flow of electrons for complex III of the respiratory chain.

Answer 18

QH2 (one e- at a time)–> cytochrome b (Fe 3+) –> FeS –> cytochrome c1 –> cytochrome c

Question 19

Describe the flow of electrons for complex IV of the respiratory chain.

Answer 19

cytochrome 2 –> CuA –> cytochrome a –> CuB –> cytochromea3 –> H2O
four electrons are needed

Question 20

About ____ ATPs are synthesized per mole of NADH and about _____ ATPs are synthesized per mole of FADH2. Thus, about ____% of the available energy from the oxidation of NADH/FADH2 is trapped in ATP.

Answer 20

2.5
1.5
25-30

Question 21

What other uses does the deltaP have?

Answer 21

energized calcium uptake into mito
adenine nucleotide translocase
reversed electron transport
transhydrogenase activity

Question 22

What is transhydrogenase activity?

Answer 22

the ability of NADH to reduce NADP+ to produce NAD+ and NADPH

Question 23

Describe an inhibitor of complex 1.

Answer 23

rotenone- reduces FMN and iron sulfur centers of complex I accumulate and electrons are not passed to Q
deltaP cannot be maintained –> ATP not synthesized

Question 24

Describe an inhibitor of complex III.

Answer 24

Antimycin A- QH2 accumulates and cytochrome c is not reduced

Question 25

Describe an inhibitor for complex IV.

Answer 25

cyanide/ carbon monoxide- reduced cytochrome c accumulates

on a plot, O2 consumption would flatline (no O2 consumption) and pmf would start to dissipate

Question 26

Describe an inhibitor for complex V.

Answer 26

oligomycin/ DCCD- bind the ATP synthase complex and block proton pore
on a plot, O2 consumption would increase (negative slope) as would pmf but no ATP is produced