Chapter 14 (ABC) - Energy Generation in Mitochondria and Chloroplasts

NADH & FADH₂ — made from glucose/fats, but not directly usable

What kind of energy is this?

Intermediate energy

Intermediate energy must be converted into ATP to be...

Usable energy

Ancient method to make ATP without oxygen — still used in some species

Fermentation

Modern Respiration used what as a FINAL e- acceptor?

O2

Where do H⁺/e⁻ come from?

NADH & FADH₂, made from glucose/fats

What does the enzyme G3P dehydrogenase do?

Catalyzes redox reaction in glycolysis step 6

During a G3P Dehydrogenase Reaction, what is Oxidized and what does it becomes? What is reduced and what does it become?

O: G3P → 1,3-BPG..... Loses H+

R: NAD⁺ → NADH...... Gains H⁺/e⁻ from G3P

What’s happening during G3P Dehydrogenase Reaction

Electrons are transferred from G3P to NAD⁺, forming NADH — this is oxidation of G3P, reduction of NAD⁺

What is Gluconeogenesis?

When used?

Why important?

- Making glucose from non-carb sources (e.g. pyruvate, lactate, amino acids)

- During fasting, stress, starvation — when glucose is low

- Keeps brain and critical tissues alive when no dietary glucose is available

How do we convert "gift card" energy into usable ATP?

Through oxidative phosphorylation in mitochondria (and chloroplasts in plants)

So stuff like Glucose/fats only give a small amount of ATP/GTP aka usable energy. What is most energy stored as?

Most energy stored as NADH/FADH₂ (activated carriers = “gift cards”)

Permeable to small molecules

Outer Membrane

Houses ETC + ATP synthase; impermeable to ions

Inner Membrane

Folds that increase surface area for energy reactions

Cristae

Contains enzymes for pyruvate/fatty acid oxidation + CAC

Matrix

Where H⁺ is pumped to build gradient for ATP synthesis

Intermembrane Space

Why only Eukaryotes maximize energy?

They have mitochondria with compartmentalized structure → enables efficient ATP production

Where does pyruvate go after glycolysis?

It’s pumped into the matrix → enters CAC

How do cells obtain most of their energy?

By using a membrane-based mechanism that converts electron energy into ATP.

What do electron carriers do in this process?

They release electrons (e⁻) to membrane proteins in the electron transport chain (ETC).

What is the purpose of pumping H+ across the membrane?

To build an electrochemical gradient by pumping H⁺ ions across the membrane, increasing potential energy.

What does the electrochemical gradient do?

It powers ATP synthase, which uses the flow of H⁺ ions to synthesize ATP.

Where do the electrons come from?

From NADH and FADH₂, which are made during glycolysis and the citric acid cycle (CAC).

Where does this process take place?

In the inner mitochondrial membrane (and in the thylakoid membrane of chloroplasts for photosynthesis).

What happens to the electrons after they pass through the ETC?

They are transferred to oxygen (O₂), the final electron acceptor, forming water (H₂O).

What is the role of the proton gradient?

It’s the stored energy that drives ATP production when H⁺ flows back through ATP synthase.

What’s the big picture of this process?

➡️ Electron energy → proton gradient → ATP synthesis

➡️ This is how cells convert food energy into usable ATP, especially in mitochondria and chloroplasts.

What is the first stage of the ETC process?

Building a proton gradient by pumping H⁺ across the inner mitochondrial membrane

What molecules donate electrons to the ETC?

NADH and FADH₂

What does the ETC require to function?

Oxygen (O₂) as the final electron acceptor

What happens as electrons move through the ETC?

H⁺ ions are pumped out of the matrix → builds electrochemical gradient (= high potential energy)

Where do NAD⁺ and FAD⁺ get electrons?

From oxidation reactions in the citric acid cycle

What is the result of this stage? (stage 1)

A high potential energy gradient and formation of H₂O

What is the second stage of the ETC process?

ATP synthesis using the H⁺ gradient via chemiosmosis

What enzyme makes ATP?

ATP synthase

What are the two parts of ATP synthase?

Channel (moves H⁺) and catalytic subunits (make ATP)

What is chemiosmotic coupling?

Using H⁺ gradient to power ATP production

How can cells increase ATP output?

By having more mitochondria and more cristae

What does the Channel do in ATP synthase?

Moves H⁺ down gradient → releases energy

What does the Catalytic subunits do in ATP synthase?

Use energy to add P to ADP → ATP

What increases ATP capacity?

More mitochondria and more cristae

More folds = more surface area = more ATP potential

What is chemiosmosis?

Movement of H⁺ ions across membrane to drive ATP synthesis

Where does the ETC take place?

In the mitochondria, specifically the inner membrane

What types of cells have more mitochondria?

Cells with high ATP demand (e.g. muscle, kidney, liver)

What makes mitochondria unique?

They have own DNA, ribosomes, and can divide/fuse

How much energy from glucose is recovered in glycolysis?

Less than 10% — most is recovered in mitochondria

Do mitochondria vary by cell type?

Yes — structure and number vary depending on energy needs

Mitochondria = ___ site

ETC

More mitochondria = ?

More ATP

Glycolysis = ?; mitochondria = ?

Small energy

Big energy

What are the "games balls" of ETC?

NADH & FADH2

What are NADH and FADH₂?

Reduced coenzymes that carry high-energy electrons to ETC

Where are they located? (NADH & FADH2)

Mostly in the mitochondrial matrix

What do they do in the ETC? (NADH & FADH2)

Donate electrons to ETC → helps make ATP

What kind of reaction is this?

Oxidation — electrons and H⁺ are released

What is a hydride ion (H⁻)?

A particle that carries 2 electrons + 1 proton

Who conducts the electron donation reaction?

ETC enzymes in the inner membrane

Where is the ETC located?

In the inner mitochondrial membrane, which is impermeable

How many structures pass electrons?

5 molecular structures transfer electrons through the ETC

Why do we need oxygen?

It’s the final electron acceptor in cellular respiration — major use of all O₂ we breathe

What happens to electrons as they move?

They lose energy, which is used to pump H⁺ ions

How many ETC complexes pump protons?

Three complexes pump H⁺ across the membrane

What does proton pumping create?

A proton gradient = high potential energy

What are the fixed complexes in the ETC?

- Complex I: NADH dehydrogenase

- Complex III: cytochrome b-c1

- Complex IV: cytochrome oxidase

What are the 2 mobile molecules that carry e- b/w complexes?

- Ubiquinone

- Cytochrome c

What do these fixed complexes do?

They pump H⁺ ions across the membrane

What are the mobile electron carriers? What is their role?

Ubiquinone and cytochrome c

They carry electrons between fixed complexes — like trucks

What is the ETC also called?

The respiratory chain

Is oxidative phosphorylation the only way to make ATP?

No — SLP also makes ATP in glycolysis, but it’s less efficient

What starts the ETC process?

NADH/FADH₂ donate electrons to the chain

What does electron flow do?

Powers H⁺ pumping → builds gradient

What is the gradient used for?

Drives ATP synthase to make ATP

What is oxidative phosphorylation?

"Oxidative" = builds gradient

"Phosphorylation" = converts gradient to ATP

Why does H⁺ want to move back into the matrix?

Because of ΔV (charge difference) and ΔpH (concentration difference) — together they form PMF

What creates the proton motive force (PMF)?

The electrochemical gradient formed by pumping H⁺ ions into the intermembrane space during the electron transport chain (ETC)

What are the two components of PMF?

1. ΔV (membrane potential) — electrical gradient; matrix is more negative Major force

2. ΔpH (pH gradient) — chemical gradient; matrix is more basic Minor Force

Which component is stronger?

ΔV — the electrical gradient is the larger force driving H⁺ movement

Where does the proton gradient form?

Across the inner mitochondrial membrane, with H⁺ accumulating in the intermembrane space

What is the protein gradient?

H⁺ ions pumped into intermembrane space → high [H⁺] outside inner membrane

What is the electrochemical gradient

Combo of ΔV + ΔpH → total proton motive force

What happens if H⁺ flows back into the matrix without ATP synthase?

The stored energy is released as heat — this is wasteful, but used by hibernating animals and for body warmth

How do most cells use the gradient?

To make ATP via ATP synthase

What are the Gradient components

- ΔΨ = membrane potential

- ΔpH = pH gradient

- ΔμH⁺ = total electrochemical gradient

How do most cells capture the energy from the proton gradient?

By using ATP synthase to convert ADP + Pi → ATP

Which ETC complexes pump protons?

Complexes I, III, and IV pump H⁺ into the intermembrane space

Large, multi-subunit enzyme embedded in inner mitochondrial membrane

ATP Synthase

Form H⁺ channel — allow H⁺ to flow into matrix

Transmembrane subunits

What is the role of the stalk?

It connects the channel to the catalytic head and rotates as H⁺ flows through

What happens when the stalk rotates?

It triggers the catalytic subunits to phosphorylate ADP → ATP and release ATP

Where is the catalytic component located?

In the mitochondrial matrix, attached to the stalk

How many catalytic subunits are there?

Three — they work together to make ATP

How does ATP get out of the matrix?

Via antiport exchange with ADP — driven by voltage gradient

How do ADP, Pi, and pyruvate get in?

- ADP: exchanged with ATP

- Pi: co-transported with H⁺

- Pyruvate: co-transported with H⁺

What powers both ATP synthesis and metabolite transport?

The electrochemical proton gradient created by the ETC

How does ATP leave the mitochondrial matrix?

Through an antiport transporter that exchanges ATP out for ADP in, using the voltage gradient

How does ADP enter the matrix?

It’s exchanged with ATP via the same antiport system

How does phosphate (Pi) enter the matrix?

It’s co-transported with H⁺ ions via a symport transporter

How does pyruvate enter the matrix?

It’s also co-transported with H⁺ ions using a symport mechanism

Why is this transport important?

It brings in substrates for the citric acid cycle (CAC) and sends ATP to the cytosol where it’s needed

What dictates direction? (ATP synthase)

The electrochemical gradient and energy demand — strong gradient favors ATP synthesis, weak gradient or high ATP favors ATP hydrolysis