Bioenergetics

Question 1

The catabolic pathways of carbs, proteins and fats converge at ………..

Answer 1

Acetyl-CoA , which is oxidized in the mitochondria via citric acid cycle.

Question 2

Oxidation of NADH and FADH2 by molecular oxygen is an ……… process, with the energy released used to ……

Answer 2

1. exergonic

2. Drive the phosphorylation of ADP to ATP (endergonic)

Question 3

The citric acid cycle and the oxidative phosphorylation are both regulated by the…..

Answer 3

presence of molecular O2

Question 4

Summarize the oxidation process:

Answer 4

1. metabolic fuels are hydrolyzed to their building blocks.
2. Building blocks degraded to the common intermediate, Acetyl-CoA
3. Oxidation of Acetyl-CoA to CO2 and the transfer of electrons to electron carriers NADH and FADH2
4. Oxidative phosphorylation and synthesis of ATP

Question 5

Delta G is equal to ?

Answer 5

the difference in energy between the products and the reactants. The free energy (delta G) change predicts the direction of the reaction
Delta G = G products - G reactants
*Negative results means exergonic
*Positive results means endergonic
*Zero means equilibrium

Question 6

What are the requirement for coupled reaction system (endergonic/exergonic)?

Answer 6

The product of the first reaction must be the substrate for the second reaction

Question 7

Define substrate level phosphorylation. with examples

Answer 7

The formation of ATP from a path different than oxidative phosphorylation.

• Phosphoenolpyruvate & 1.3 bisphosphoglycerate are both intermediates in glycolysis and have higher energy than ATP
• Creatine phosphate is a reservoir of high energy in muscles

Question 8

……. percent of redox energy is conserved in ……

Answer 8

40, ATP

Question 9

Oxidation is……… . Reduction is ……..

Answer 9

loss of electrons, gain of electrons

Question 10

Define the standard reduction potential E

Answer 10

a constant that describes the tendency of a compound to be reduced. Expressed in volts and measured under standard conditions.

Question 11

Stronger donors have a more negative reduction potential. T/F?

Answer 11

True. The less the E value, the less the tendency of a compound to be reduced and the higher to be oxidized.

Question 12

What is the relation between reduction potential and free energy change?

Answer 12

Delta E = E electron acceptor - E electron donor
Delta G = - nF * delta E

where n is the number of electrons
F is Faraday constant (23kcal/volt*mol)

Question 13

Oxidation potential is the same as reduction potential with the sign reversed. T/F?

Answer 13

True

Question 14

For REDOX to be spontaneous and exergonic, delta E must be a ……….?

Answer 14

positive value

Question 15

The major carrier of electrons in reductive reactions is ………..?

Answer 15

NADPH

Question 16

Hydride ion is……?

Answer 16

2 electrons and proton

Question 17

NAD+ function is?

Answer 17

accepting a hydride ion to form NADH

Question 18

FAD function is?

Answer 18

electron acceptor in reactions involving oxidation of two adjacent carbon atoms.

Question 19

NADPH function?

Answer 19

is the major reducing power in extramitochondorial reactions

Question 20

Define amphibolic pathway?

Answer 20

has both catabolic and anabolic pathways

Question 21

Complete oxidation of one Acetyl-CoA molecule gives…..?

Answer 21

12 ATP molecule

see p.460

Question 22

Intermediates in citric acid cycle:

1. Citrate
2. Oxaloacetate
3. Succinyl-CoA
4. Oxaloacetate and alpha-ketoglutarate

Answer 22

1. Substrate for fatty acid synthesis
2. first substrate in gluconeogenesis
3. required for heme synthesis
4. Substrates for amino acid synthesis.. Also amino acids can be reconverted to alpha-ketoglutarate to enter the TCA cycle.

Question 23

what happens to Acetyl-CoA upon entry into TCA?

Answer 23

it condenses with Oxaloacetate to form Citrate. The enzyme responsible is citrate synthase

Question 24

Where are the enzymes for Kreb’s cycle located?

Answer 24

All enzymes are located in the mitochondrial matrix except for succinate dehydrogenase which is located in the inner mitochondrial membrane.

Question 25

What is the rate limiting step in Kreb's cycle?

Answer 25

The conversion of Isocitrate to alpha-ketoglutarate (the enzyme responsible is isocitrate dehydrogenase). This enzyme (along with alpha-ketoglutarate dehydrogenase and citrate synthase) are allosterically inhibited by ATP and NADH, and activated by ADP. These 3 enzymes regulate the irreversible reactions in the cycle

Question 26

Define anaplerotic "filling up" reactions

Answer 26

The reactions occur to replenish the insufficient intermediates. Like conversion of Pyruvate to Oxaloacetate (catalyzed by pyruvate carboxylase) This reaction requires accumulation of Acetyl-CoA (allosteric activator), with the presence of bicarbonate and biotin. see. p 462

Question 27

Define oxidative phosphorylation?

Answer 27

The process of passing electrons from FADH2 and NADH to molecular oxygen through a series of carriers (ETC), with the energy released used to synthesize ATP. The ETC and all the enzymes are located in the inner mitochondrial membrane.

Question 28

What is the ETC made of?

Answer 28

1. NAD+ and FAD+ dehydrogenases 2. Iron sulfur proteins (FeS) 3. Coenzyme Q 4. Cytochromes

Question 29

List the components of the ETC?

Answer 29

1. Four protein lipid complexes | 2. Co Q (ubiquinone)and Cytochrome C. These two are the mobile components that move freely in the lipid bilayer.

Question 30

NADH and FADH2 both arise from mitochondrial oxidation. T/F

Answer 30

True. But some of the NADH arise from cytosolic oxidation as well.

Question 31

Sources of electrons in NADH?

Answer 31

Mostly from mitochondria, and some from cytosolic oxidation. | Oxidation of isocitrate, alpha-ketoglutarate, malate, pyruvate and glutamate

Question 32

Sources of electrons in FADH2?

Answer 32

Almost all of the electrons are from mitochondrial oxidations. Oxidation of succinate, fatty acyl CoA, and alpha-glycerol phosphate.

Question 33

Where is the entry points for NADH and FADH2 along the ETC?

Answer 33

1. NADH electrons enter at complex I | 2. FADH2 electrons enter Co Q

Question 34

Succinate dehydrogenase is complex III in the ETC. T/F?

Answer 34

False. It is complex II in the ETC

Question 35

Types of electron shuttles in the inner mitochondrial membrane?

Answer 35

1. Malate shuttle: cytosolic electrons are incorporated into mitochondrial NADH 2. Alpha-glycerol phosphate shuttle: electrons transported here are incorporated into mitochondrial FADH2

Question 36

How are the components of ETC arranged?

Answer 36

They are arranged so that the reduction potential increases from negative to positive values to ensure the spontaneous flow of electrons to oxygen.

Question 37

How much energy is required to synthesize one ATP molecule?

Answer 37

7.2 kcal/mol

Question 38

FADH2 electrons bypass complex I. T/F?

Answer 38

True.

Question 39

What is the P/O ratio??

Answer 39

The number of ATP produced per O atom reduced. For each NADH oxidized, 3 ATPs are produced. For FADH2, only 2 are produced.

Question 40

In theory, energy produced from oxidation of one NADH is enough for production of 7 ATP. T/F?

Answer 40

True. However only 3 are produced and the rest of the energy is released as heat. Energy for oxidative phosphorylation is only harnessed at complex I, III & IV. That is why only 3 ATP is produced

Question 41

Define the chemiosmotic hypothesis?

Answer 41

The theory proposed for how the electron transport is coupled to ATP synthesis. It is based on the proton gradient across the inner mitochondrial membrane.

Question 42

Explain the chemiosmotic hypothesis

Answer 42

Complexes I, III and IV pump protons to the outside of inner membrane, creating a proton gradient. The protons flow down the gradient through complex V and cause the release of energy to drive the phosphorylation of ADP to ATP (catalyzed by ATP synthase enzyme) Complex II doesn't pump protons!

Question 43

Describe complex V

Answer 43

composed of two subunits. The F0 spans the inner membrane, creating a proton channel. The F1 subunit is inside the matrix and has the synthase activity. see. p 466

Question 44

How is the oxidative phosphorylation controlled by O2?

Answer 44

It is controlled by O2. When O2 is limited, this leads to accumulation of NADH, which in turn inhibits the TCA cycle. This regulation is call "Respiratory Control" In the presence of O2, the regulation depends on the availability of ADP. ADP allosterically activate isocitrate dehydrogenase increasing the rate of TCA cycle, thereby increasing NADH. And hence increasing oxidative phosphorylation.