EXAM 2 Flashcards
What is the final electron acceptor of ETC
Oxygen
What are two ways to move electrons on NADH from cytoplasm into mitochondria? List the differences
Malate/ Aspartate shuttle
- completely reversible
- cytoplasmic NADH → 3 ATP
Glycerol phosphate shuttle
- irreversible
- cytoplasmic NADH → 2 ATP
where does electron transport and oxidative phosphorylation occur?
Inner mitochondrial membrane
The inner membrane is permeable only to
- H2O
- CO2
- O2
(everything else must have a transporter)
What enzyme of TCA is also part of the ETC , specifically Complex II, found in the IMM
Succinate DH
when will the malate aspartate shuttle be active
in a relaxed state
when will the glycerophosphate shuttle be active
active when we need to make ATP as fast as possible ( doing physical activity)
What energy sources are being used in the cytoplasm vs IMM during the glycerol phosphate shuttle?
NADH in cytoplasm and FADH2 in IMM
How does the Km and Vmax look like when Ca2+ pours in from cytoplasm → mitochondria vs mitochondria → cytoplasm?
cytoplasm ➜ mitochondria:
↑ Km
↑ Vmax
mitochondria → cytoplasm:
↓ Km
↓ Vmax
What happens to Ca2+ levels in the cytoplasm during muscle contraction?
Ca2+ levels increase
Why does Ca²⁺ need to enter the mitochondria during muscle contraction?
To activate pyruvate dehydrogenase (Pyr DH) and the TCA cycle
Electron transport oxidation vs reduction
oxidation:
NADH + H⁺ → NAD⁺ + 2e⁻ + 2H⁺
reduction:
1/2 O₂ + 2e⁻ + 2H⁺ → H₂O
ETC
How do you calculate ∆E’ in ∆G’ = -nF(∆E’)
E’(acceptor) - E’ (donor)
Explain the general mechanism for ETC
(NADH in mitochondria) drop it into Complex I and pump 4H⁺ OUT, hand it off to Coenzyme Q, which will take it to Complex III (4H⁺), hand it to Cytochrome C → complex IV (2H⁺)
how many protons total are pumped out of the mitochondria?
10 H⁺ total
4- complex I
4- complex III
2- complex IV
Explain what is oxidized/ reduced in each complex
Complex I
reduced by: NADH
oxidized by: coenzyme Q
Complex III
reduced by: QH2
oxidized by: Cyt C
Complex IV
reduced by: Cyt C
oxidized by: O2
What ion is needed in Complex IV and what is the disease name for the lack of this ion?
Copper; Menke’s disease
Draw Q, QH*, QH2 structures
lec 5, slide 26
What does Q cycle allow for?
Allows complex III to transport 4 H⁺ with only 2e-
___prosthetic groups are used for high energy electrons in ETC
Iron sulfur
Explain the Q cycle
Step 1: Two Electrons from Ubiquinol (QH₂)
Ubiquinol (QH₂), which carries two electrons, enters Complex III.
QH₂ donates its two electrons:
One electron goes to cytochrome c (which can only accept one electron at a time).
The other electron goes to another molecule of ubiquinone (Q), converting it into a partially reduced intermediate called semiquinone (Q*⁻).
At the same time, QH₂ releases two protons (H⁺) into the intermembrane space (this is part of the proton gradient formation).
Step 2: Second Ubiquinol (QH₂) Enters
A second QH₂ molecule enters Complex III and donates its two electrons.
Again, one electron goes to another cytochrome c molecule.
The second electron goes to the previously formed semiquinone (Q*⁻), fully reducing it to ubiquinol (QH₂).
Step 3: Protons and Electron Transfer
The two cytochrome c molecules (each carrying one electron) move on to Complex IV.
Two more protons (H⁺) are pumped into the intermembrane space from the second QH₂.
Net Result:
✦2 electrons are transferred to 2 cytochrome c molecules
✦4 protons (H⁺) are pumped into the intermembrane space.
✦1 molecule of ubiquinol (QH₂) is oxidized, and 1 molecule of ubiquinone (Q) is regenerated.
Complex IV Cytochrome C oxidase pumps ___ H⁺/e⁻ across mito. inner membrane but always works in batches of ___e⁻
2; 4
1 round of the TCA cycle pumps __H⁺ across the membrane
36
citrate→succinate via TCA cycle produces___ATP worth of energy
7
1 round of the TCA cycle in cells treated with amytal pumps___ H⁺ across the membrane
6
List the four basic rxns involving free radicals
✭O₂ + 1 e⁻ → O₂⁻ (superoxide radical)
✯O₂ + 1 e⁻ + 2H⁺ → (hydrogen peroxide)
✭ H₂O₂ + 1e- → OH⁻ + *OH (hydroxyl radical)
✯ H⁺ + *OH + 1e⁻ → H2O
draw the TCA cycle including its intermediates (NADH, FADH₂)
lec 4, slide 50
name the enzyme in which the mechanism involves a hydride removal by FAD
Succinate DH
(succinate→fumarate)
alcohols have higher/lower energy/
lower
NADH (3 ATP *2.5)
FADH₂ (2ATP *1.5)
How many protons does the ETC push out (NAD vs FAD)?
NADH :10 protons.
FADH₂ : 6 protons.
What is the significance of the Glycerol Phosphate shuttle?
Glycerol Phosphate Shuttle is irreversible, feed electrons from cytoplasmic NADH directly into the mitochondria electron transport chain, and results in 2 ATP per NADH
Complex 1 can be selectively inhibited by ____ and ____.
How so?
rotenone & amytal
Stops e- transfer from NADH in mitochondrial matrix, but NOT from succinate DH or glycerol P shuttle
T/F rotenone & amytal stops e- transfer from NADH in matrix, along with succinate DH and glycerol P shuttle.
FALSE; it is from NADH, but NOT from succinate DH or glycerol P shuttle
Rotation of the 𝜸 subunit distorts___. this changes …?
⍺ and β subunits
changes binding affinity for ADP + Pi and ATP
Movement of 𝜸 subunits causes ⍺β subunits to have ___ distinct conformations. These are…?
O= nonbinding sites⇒ ejection of ATP
L= loose binding site⇒ADP + Pi binds
T= tight binding site⇒ ATP generated and transfered to O ( ADP + Pi go to T)
ADP + Pi ☞ Kd ≈ 10⁻⁵ M
ATP ≈ 10⁻¹² M
Walk me through the process of this 𝛾 rotation
✯ 𝛾-subunit again rotates 120° powered by 3H+
✯ 3H+ per active site make 1 ATp
✯ 3 active sites bc ⍺/β dimers need to bind
✯ 9H+ to run all 3 active sites
9H⁺
↓
3 x 120° (or 360°) movements
↓
1 revolution
↓
3 (ADP+ Pi→ ATP)
Where exactly is the ATP synthase pump located?
Inner membrane of the mitochondria
What do uncouplers do exactly?
Drain H+ gradient without making ATP → heat
what is the role of 2,4- Dinitrophenol (DNP)?
It acts as an uncoupler in cellular respiration. It disrupts the proton gradient across the mitochondrial membrane by allowing protons to flow back into the mitochondrial matrix without producing ATP. This “drains” the H+ gradient, which typically powers ATP synthesis, and instead releases the energy as heat. This has been used as a weight loss tool, as it inc. metabolic rate, but it can be dangerous due to its impact on energy efficiency and heat production in cells.
Humans have multiple UCP. name and give descriptions of them
UCP1
*Keeps babies (and adults) warm
* Brown fat → heat
* Knock out mice are cold sensitive
UCP2
* Broadly expressed (including brain)
* Proposed to protect neurons against free-radical induced death
UCP3
* Expressed in muscle
* Over-expression → lean mice
T/F, only babies have brown fat; we dissolve it as we get older
FALSE; adult humans DO have brown fat. it is just more in young and lean than old and fat
What antiporters does the malate/aspartate shuttle require to functoin?
⍺-KG and Glu/Asp
What molecule enters the mitochondria in the malate-aspartate shuttle, and what exits as a balance?
Malate (2e-) enters the mitochondria, and (𝛼-KG) exits to maintain balance across the mitochondrial membrane
Where is the malate-aspartate shuttle primarily located?
A:
In the inner mitochondrial membrane, where it facilitates the transfer of reducing equivalents (NADH) from the cytosol into the mitochondria for ATP production.
Which molecule exits the mitochondria in the malate-aspartate shuttle, and what molecule enters as a counterpart?
Aspartate exits the mitochondria, while glutamate enters to keep the cycle in balance.
What is the primary purpose of the malate-aspartate shuttle?
To transfer reducing equivalents from NADH in the cytosol into the mitochondria for ATP synthesis without directly moving NADH across the mitochondrial membrane.
Explain how the ATP synthase pump works
❇︎Location and Purpose: The ATP synthase pump is located in the inner membrane of the mitochondria. Its main job is to make ATP, the energy “currency” of the cell.
❇︎Proton Gradient: The electron transport chain, which is right before ATP synthase in the process of cellular respiration, pumps protons (H⁺ ions) from the mitochondrial matrix to the intermembrane space, creating a high concentration of protons outside.
❇︎Flow of Protons: These protons naturally want to flow back into the matrix where their concentration is lower, and ATP synthase is like a gate that lets them back in. The protons move from the intermembrane space into the matrix through a channel in ATP synthase.
How Movement Drives ATP Synthesis:
☞As protons flow through ATP synthase, they cause part of the enzyme to rotate—specifically, the c-ring and the gamma subunit (central stalk). Think of it like turning a crank!
☞This rotation pushes and changes the shape of another part of ATP synthase where ADP and Pi (inorganic phosphate) are waiting. The change in shape squeezes ADP and Pi together to form ATP.
Stable vs. Rotating Parts:
The rotating part is the c-ring and the gamma subunit.
The stable part, which doesn’t move, is the F 1 complex (where ATP is actually made) and the stator that holds it in place.
What is moving and what is stationary in the ATP synthase pump
☞The “head” (F1 complex, which includes the alpha and beta subunits where ATP is produced) stays stationary.
☞The “stalk” (central gamma subunit and the c-ring in the F 0 part) does rotate.
What direction of the protons flowing in the ATP synthase pump?
✯Protons (H⁺ ) move from the intermembrane space into the mitochondrial matrix. This movement follows the proton gradient created by the electron transport chain, which pumps protons into the intermembrane space, building a high concentration of protons outside the inner mitochondrial membrane.
As protons flow down their gradient through the F0 subunit of ATP synthase, they cause the c-ring and attached gamma subunit to rotate. This rotation drives conformational changes in the F1 subunit, where ADP and inorganic phosphate (Pi) are combined to form ATP.
How is fat turned into heat (step format)
✦ Fat
→ acetyl-coA
→NADH, FADH₂
→ H⁺ gradient
→ drain via UCP
➜ HEAT
write anti-oxidant mechanisms
Super-oxide dismutase
2 O2-* + 2H+ → H2O2 + O2
Amyotrophic lateral sclerosis (ALS, Lou Gehrig)
Catalase
2 H2O2 → 2 H2O + O2
Glutathione peroxidase
2 GSH + R-O-O-H → GSSG + ROH + H2O
(GSSG + NADPH → 2 GSH + NADP+)
recall discussion of people with
↓G6PDH activity (Ch 15, pentose-P)
* Se, Vit E, Vit C, uric acid
Where do light reactions occur?
In chloroplasts
instead of H+ being pumped across the inner membrane as in mitochondria, where are these protons being pumped in light reactions?
into (inside) THYLAKOID COMPARTMENT
