cellular energetics

Define catabolism and give an example

Catabolism breaks down molecules to release energy. Example: formation of pyruvate from glucose in glycolysis.

What is the role of activated carriers (like NADH, FADH₂, ATP)?

They capture energy from energy-releasing reactions and transfer it to drive energy-requiring processes

Why does ATP hydrolysis have a negative ΔG°?

Products (ADP + Pi) are lower in free energy due to relief of electrostatic repulsion and resonance stabilization.

Where does glycolysis occur?

cytosol

What are the inputs and net outputs of glycolysis per glucose?

inputs: 1 glucose, 2 NAD⁺, 2 ADP + Pi.
Outputs: 2 pyruvate, 2 NADH, 2 net ATP (4 ATP produced, 2 consumed).

How many NADH are generated in glycolysis?

2 NADH per glucose.

Does glycolysis require oxygen?

No, it is anaerobic.

What happens to pyruvate if oxygen is low?

Fermentation regenerates NAD⁺.
• Yeast: pyruvate → ethanol + CO₂.
• Animal muscle: pyruvate → lactate.

Where does oxidative decarboxylation occur?

Mitochondrial matrix.

What are the products per pyruvate?

1 acetyl-CoA, 1 NADH, 1 CO₂ (no ATP directly).

Where does the citric acid cycle occur?

Mitochondrial matrix.

Inputs per acetyl-CoA?

1 acetyl-CoA, 3 NAD⁺, 1 FAD, 1 GDP (or ADP), 2 H₂O.

Outputs per acetyl-CoA?

3 NADH, 1 FADH₂, 1 GTP (≈1 ATP), 2 CO₂.

Total products per glucose (two acetyl-CoA)?

 6 NADH, 2 FADH₂, 2 GTP (≈2 ATP), 4 CO₂.

Where is the ETC located?

Inner mitochondrial membrane (cristae).

What is the primary function of the ETC?

Oxidize NADH/FADH₂, transfer electrons to O₂, and pump protons to create a proton-motive force.

What is the ultimate electron acceptor?

Oxygen, forming H₂O.

Which complexes pump protons?

I (NADH-CoQ reductase), III (CoQ-cytochrome c reductase), IV (cytochrome c oxidase).

Which complex does NOT pump protons?

II (succinate-CoQ reductase).

How many H⁺ are pumped per NADH? per FADH₂?

~10 H⁺ per NADH (≈3 ATP); ~6 H⁺ per FADH₂ (≈2 ATP).

Function of ATP synthase?

Uses the proton gradient to convert ADP + Pi → ATP.

How many H⁺ needed for one ATP?

~3–4 H⁺.

Total ATP per glucose from aerobic respiration?

~30–32 ATP (Glycolysis ~2, Citric Acid Cycle substrate-level ~2, Oxidative phosphorylation ~26–28).

Which ion is high inside cells and low outside?

K+

Mutation of NDUFA1 (Complex I subunit) causes what accumulation?

NADH (cannot be oxidized efficiently), leading to inhibited glycolysis due to lack of NAD⁺.

Why do plants need mitochondria if they produce ATP in chloroplasts?

They still require ATP at night and for cellular processes that cannot use light energy directly.

How many ATP are made directly (substrate-level) in glycolysis + TCA per glucose?

4 net (2 from glycolysis + 2 GTP from TCA).

Why does FADH₂ yield less ATP than NADH?

It donates electrons at Complex II, bypassing Complex I and pumping fewer protons.

What is the role of activated carriers in cells?

They capture energy from energy releasing reactions and transfer it to other reactions

The inner mitochondrial membrane (cristae) contains proteins that

Synthesize ATP
B. Pump protons
C. Transport pyruvate

Fermentation of glucose to ethanol in S. cerevisiae also produces:

Both carbon dioxide and NAD+

Which of the following is a reason why ATP hydrolysis has a negative ΔG0?

The removal of the phosphate is energetically favorable

What is NADH?

The reduced form of NAD+, which carries electrons to the electron transport chain

Which type of membrane transport uses ATP directly?

Primary active transport

Which of the following components of the electron-transport chain do NOT act as a proton pump?

Succinate-CoQ reductase (Complex II)

NADH is produced by this reaction. Briefly explain the role of NADH in energy
production by the cell.

activated carrier in cell

-transport chemical energy

-Nad+ accepts an electron and becomes reduced to NADH. NADH donates electron to complex 1 to become oxidized. The movement of electrons in the ETC facilitate the formation of. A proton gradient between the intermembrane soace and matrix. This gradient drives change in the ATP synthase enzyme producing ATP.

these products are considered activated carriers. In what form do these molecules
carry energy?

They carry electrons in the form of a hydride ion

Why are these products essential for oxidative phosphorylation

The electrons carried by NADH and FADH2 are passed through enzymes in the ETC to molecular oxygen. The H+ produced are pumped through these same complexes (1, 3, 4) to create a chemiosmotic gradient across inner membrane of the mitochondria. The gradient is then used to drive the formation of ATP from ADP and inorganic phosphate using ATP synthase.

What molecule(s) is/are likely to accumulate in the mitochondrial matrix in cells with a
mutated NDUFA1 gene?

NAD+

Why would a mutation inNDUFA1lead to inhibition of glycolysis?

Likely leads to defective mitochondrial complex 1, without this NADH cant be converted into NAD+. The NAD+ produced normally in the mitochondria is transported back to the cytosol where it serves as an activated carrier in glycolysis. Some NAD+ can be produced in the cell by lactic acid fermentation, it is unlikely that the system could provide adequate NAD+ for energy needs of the cell.

What steps in glycolysis are likely inhibited in cells with a mutatedNDUFA1gene?

The step that would be affected in glycolysis is step 6, the transformation of glyceraldehyde-
3-phophate to 1,3-bisphosphoglycerate using glyceraldehyde-3-phosphate dehydrogenase

These cells can be rescued by inserting a yeast gene,NDI1, into the mammalian cells. ND1
functions as an NADH-CoQ oxidoreductase without pumping protons out of the matrix.
Why would NDI1 rescue the cells?

ND1 would allow for the regeneration of NAD+, which could then participate in glycolysis.
This means that the cell could then produce pyruvate, which would allow the citric acid cycle
and the electron transport chain to function, producing ATP for the cell

Do you think the rescued cells would produce the same amount of ATP per molecule of
glucose as wild type cells? Why or why not

No, the cells would not produce the same amount of ATP per glucose molecule as normal
cells. This is because NDI1 does not pump protons across the mitochondrial inner membrane.
Therefore, the chemiosmotic gradient between the intermembrane space and the matrix
would be less per molecule of glucose. Normally, complex 1 moves four H+ protons across the
membrane per molecule of NADH converted to NAD+. Since protons are not pumped through

NDI1, the chemiosmotic gradient would only be formed by the oxidation of FADH2 to FADH in
complex 2. Since complex 2 also does not pump protons, only 6 protons would move across
the membrane per molecule of acetyl CoA, only two molecules of ATP would be produced per
one turn of the citric acid cycle in the ETC instead of 15 molecules of ATP that would be
produced if complex I was working normally