LECTURE 24 - MIDTERM 3

Question 1

What are the hormones that primarily regulate the storage and utilization of glucose?

Answer 1

– insulin

– glucagon

Question 2

How many mols of ATP can be yielded with the complete oxidation of 1 mol of glucose?

Answer 2

– 30 -32 mols

– depending on the transport system from cytoplasm

Question 3

What are the activated carriers used during ATP production?

Answer 3

– Glycolysis:

             - 1, 3-bisphosphoglycerate = 2 ATP produced per mol glucose
             - phosphoenolpyruvate = 2 ATP produced per mol glucose (-2 ATP that are used up)
             - NADH (cytoplasmic) x2 = 3-5 (depending on shuttle)

• • Pyruvate
    - NADH (mito) x2 = 5 ATP produced per mol glucose

– CAC

           - NADH (mito) x6 = 15 ATP produced per mol glucose
           - FADHS   x2  = 3 ATP produced per mol glucose 
           - GTP = 2 ATP produced per mol glucose 

Total = 30-32 ATP produced per mol glucose

(1 NADH = approx. 1.5 or 2.5 ATP; 1 FADH2 = approx 1.5 ATP)

Question 4

What are 3 examples of ATP production via substrate level phosphorylation?

Answer 4

– 1, 3-bisphosphoglycerate plus ADP yields 3-phosphoglycerate and ATP.

– phosphenolpyruvate plus ADP yields pyruvate and ATP.

– succinyl coA plus inorganic phosphate plus GDP yields succinate and coA and GTP. \
Although GTP is not exactly ATP, GTP can easily be converted to ATP via the enzyme, nucleoside diphosphokinase.

Question 5

What are 3 examples of ATP production via substrate level phosphorylation?

Answer 5

– 1, 3-bisphosphoglycerate plus ADP yields 3-phosphoglycerate and ATP.

– phosphenolpyruvate plus ADP yields pyruvate and ATP.

• • succinyl coA plus inorganic phosphate plus GDP yields succinate and coA and GTP. \
    - -> Although GTP is not exactly ATP, GTP can easily be converted to ATP via the enzyme, nucleoside diphosphokinase.

Question 6

Where do the other 26-28 ATP come from?

Answer 6

– Through the Citric Acid Cycle, there is a net production of 4 ATP (2 ATP from Glycolysis and 2 ATP from the Citric Acid Cycle) in the form of GTP.

– The other ATP will come from the accumulated reduced electron carriers, NADH and FADH2 –> in oxidative phosphorylation

Question 7

T or F, ATP production via oxidative phosphorylation yields 30-32 ATP

Answer 7

True; variability is dependent upon which cytoplasmic shuttle system the reduced electron carrier NADH uses to enter the inner mitochondrial membrane

– For instance, if cytoplasmic NADH uses the Glycerol-3-phosphate shuttle, it yields 1.5 ATP.

– Cells using the G3P shuttle incur an energy loss because the electrons from cytosolic NADH enter the respiratory chain as FADH2.

– However, if cytoplasmic NADH uses the malate-aspartate shuttle, it will yield 2.5 ATP.

– FADH2 is already present in the mitochondria (so no shuttling occurs), this yields 1.5 ATP.

Question 8

What is the purpose of the big burst of energy that occurs when O2 is reduced by NADH?

Answer 8

– this big burst of energy will contribute to protons being pumped to the intermembrane space and to the proton motive force that will subsequently drive ATP synthesis

Question 9

How much energy is inherent in the proton-motive force across the inner mitochondrial membrane?

Answer 9

– 20.9 kJ/mol of H+

– represents the total free energy change of transporting a proton from matrix to intermembrane space

Question 10

How many protons are pumped from NADH during oxidative phosphorylation?

Answer 10

– Electron transfer from NADH to O2 releases -220 kJ/mol

– Each proton that is pumped across inner membrane stores - 21 kJ/mol

– From this we conclude that each NADH derived electron pair pumps 10 protons across the inner membrane

NADH (mito) – each NADH in matrix yields - 2.5 ATP

Question 11

Where do the 10 protons pumped per NADH molecule in terms of the complexes?

Answer 11

• • Complex 1 = 4 protons pumped per 2 electrons or 1 NADH
• • Complex III = 4 protons pumped per 2 electrons or 1 NADH
• • Complex IV = 2 protons pumped per 2 electrons or 1 NADH

Question 12

T or F, there are approximately 10 c subunits in F0

Answer 12

True; one c-subunit turns per proton, so approx. 10 protons make a 360 degree cycle, making 3 ATP

– 10 protons = 3 ATP

– Approx. 3.33 protons/ 1 ATP

10 c subunits bound to 10 protons contributes to 3 ATP; meaning it’s 3.33 protons per 1 ATP

Question 13

T or F, need to offset dampening of membrane potential caused by ATP transport

Answer 13

– True; have to offset transfer of ATP by adding an extra proton

Recall: ATP has one more negative charge than ADP – this dampens the membrane potential

– 25% of the energy yield from respiration goes back into regenerating the membrane potential

– we offset transporting ATP with 1 more H+

– it takes 3 protons to make ATP but we need to add one to regenerate –> NADH contributes to 10 electrons so 10/4 = 2.5 ATP (however if it was working at 100% efficiency we wouldn’t need to regenerate it and the extra proton wouldn’t be necessary so it would be 10/3 = 3.33)

Question 14

How are 2.5 ATPs derived from the 10 protons that are pumped with 1 NADH?

Answer 14

– 3 protons to turn gamma to make 1 ATP and 1 additional proton to reset membrane potential after ATP-ADP transport

– 10 protons/NADH – 4 protons used to make 1 ATP = 2.5 ATP from 1 NADH

Question 15

How many ATPs are derived from 1 molecule of FADH2, taking regeneration into consideration?

Answer 15

– 1.5 ATP

– 6 protons are pumped with 1 FADH2 molecule

– 3 protons are used to turn gamma but need to add 1 more for regeneration

– 6/4 = 1.5

Question 16

Why is there a difference between how many protons get pumped between NADH and FADH2?

Answer 16

– the difference lies in where NADH and FADH2 enter the ETC which dictates how many protons get pumped which dictates how much ATP is made

Question 17

Where do the 6 protons pumped per 1 FADH2 go to complex wise?

Answer 17

– Complex III: 4 protons “pumped” per 2 electrons or 1 NADH

– Complex IV: 2 protons “pumped” per 2 electrons or 1 NADH

Question 18

T or F, the inner mitochondrial membrane is impermeable to NADH and NAD+

Answer 18

True; electrons from NADH, but not NADH itself, are carried across the mitochondrial membrane

– Electrons from NADH, but not NADH itself, are carried across the mitochondrial membrane

– Two shuttles move electrons: glycerol 3-phosphate shuttle and malate-aspartate shuttle

Question 19

T or F, energy generate from cytoplasmic NADH molecules depends on the shuttle system used to transfer electrons to ETC

Answer 19

True

Question 20

What are the two shuttles and what are their differences?

Answer 20

– glycerol 3-phosphate shuttle: active in skeletal muscles and brain, electrons enter the ETC via complex II therefore only 1.5 molecules of ATP are produced

    -- 1.5 ATP produced for this NADH because the electrons are transferred to FADH2 instead of NADH, thus pumping 6 protons 

– malate-aspartate shuttle: active in kidney and heart, 2.5 molecules of ATP are produced for this NADH because it enters ETC at Complex 1, thus pumping 10 protons

Differences between shuttles is based on location

Question 21

T or F, the bulk of ATP comes from NADH

Answer 21

True

Question 22

What is the most important factor in determining the rate of oxidative phosphorylation?

Answer 22

– level of ADP

– regulation of rate of oxidative phosphorylation by the ADP level is called respiratory control and can be observed in isolated mitochondria:

—– Aerobic cells have 4-10x more ATP than ADP. Thus respiratory control is dependent on ADP as a substrate for phosphorylation and ATP production

—— For ATP production, electron flow through the respiratory chain is tightly coupled to phosphorylation of ADP (ATP synthesis)

——- Oxygen consumption increases when ADP levels are high. When ADP levels are low, ATP levels are high, O2 consumption goes down

Question 23

T or F, electron transport can be uncoupled from ATP production by uncoupling proteins

Answer 23

True; proton channel, removes the proton gradient, still get electron transport, but no ATP production

Question 24

Why would one not want ATP?

Answer 24

– uncoupling of oxidative phosphorylation generates heat (energy released as heat) to maintain body temperature in hibernating animals, in newborns, and in mammals adapted to cold

– to make energy it would be energy inefficient bc the ATP would be wasted

– uncoupling proteins catalyze a proton leak across the mitochondrial inner membrane and thus dissipate the proton motive force as heat

Question 25

Describe uncouplers.

Answer 25

– they are lipid-soluble aromatic weak acids

– uncouplers deplete proton gradient by transporting protons across the membrane

– 2,4 - Dinitrophenol: an uncoupled (goes back and forth between the different states

– because the negative charge is delocalized over the ring, both the acid and base forms of DNP are hydrophobic enough to dissolve the membrane