Lecture 7 - Cellular Respiration

What is cellular respiration? (also known as carbohydrate metabolism)

• Purpose: metabolic rxns and processes to transfer chemical energy (mainly glucose) from nutrients to ATP

• Overall Equation:
  C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP + heat

• Type: Catabolic (breaks down molecules to release energy)

What is the overall reaction of carbohydrate metabolism (cellular respiration)? –

All cellular respiration involving glucose is carbohydrate metabolism,
but not all carbohydrate metabolism is cellular respiration.

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP and heat)

What are the 4 stages of cellular respiration?

1. Glycolysis

2. pyruvate oxidation

3. krebs cycle (TCA cycle)

4. oxidative phosphorylation – slide 9

What is used from glucose and other macromolecules during cellular respiration?

High energy e- (and their associated H +) from glucose and other macromolecules are used to to do work

What is happening in glycolysis?

GLUCOSE TO 2 (TWO) PYRUVATE

What is pyruvate oxidation?

1. Acetyl coA produced

What 3 stages occur in the mitochondrion? –

1. pyruvate oxidation

2. citric acid cycle

3. oxidative phosphorylation

(*glycolysis occurs in cytosol)

What is happening in oxidative phosphorylation?

ELECTRON TRANSPORT AND CHEMIOSMOSIS

What is an oxidation reduction reaction?

A redox rxn that is a chemical reaction that involves a transfer of electrons between 2 species

(also **HYDROGEN ATOMS = ENERGY )

What is oxidation

• loss of electrons

• less H (less energy)

• compound is more oxidized

(reactant in oxidation = reducing agent / has electrons)

What is reduction – compound is reduced and gains electrons

• gain of electrons

• more H (rich in energy)

• compound is more reduced

(reactant in reduction = oxidizing agent - no electrons)

What are the 2 electron carriers that link ALL stages of cellular respiration?

NADH (nicotinamide adenine dinucleotide) AND FADH2

What is the first step of cellular respiration? –

glycolysis (glyco - sugar, lysis - breakdown)

• breakdown of glucose into 2 pyruvate molecules in cytosol

• Anaerobic — does not require O₂

Two stages:

• Energy Investment Reactions

• Energy Harvesting Reactions

Input: 1 glucose, 2 ATP, 2 NAD⁺

Output: 2 pyruvate, 4 ATP (gross), 2 ATP (net), 2 NADH, 2 H₂O

What happens in the energy investment phase of glycolysis?

• 2 ATP used to phosphorylate glucose

• Key enzymes: hexokinase, phosphofructokinase

• Forms fructose 1,6-bisphosphate

What happens in the energy harvest phase of glycolysis?

Produces:

• 4 ATP total (net gain: 2 ATP)

• 2 NADH

• 2 pyruvate and 2 H2O

What occurs in the cytosol in the cell?

glycolysis and fermentation

Structural features of mitochondria

• 2 membranes: (Outer membrane and Inner membrane)

• Intermembrane space: space between membranes

• Matrix: space WITHIN inner membrane

• Cristae: Wrinkles in inner membrane, part of intermembrane space

What is happening in Pyruvate oxidation?

1. (*2) Pyruvate (from glycolysis) goes into mitochondrion and undergoes oxidation (loses e^-)

2. One carbon is removed as CO₂ (decarboxylation)

3. NAD⁺ is reduced to NADH (electron carrier)

4. 2-carbon molecule left is attached to Coenzyme A → producing Acetyl CoA.

What is produced in pyruvate oxidation?

ONE glucose (which gives 2 pyruvate):

• 2 NADH are produced

• 2 CO₂ are released

• 2 Acetyl CoA are formed

Pyruvate (3C) → Acetyl CoA (2C) + CO₂

Generates: 1 NADH per pyruvate, or 2 NADH per glucose

What is the citric acid cycle?

1 Acetyl CoA (from pyruvate oxidation) combines with oxaloacetate (4C) → forms citrate (6C)

🔄 Main Events per turn (1 Acetyl CoA):

• 3 NAD⁺ reduced → 3 NADH

• 1 FAD reduced → 1 FADH₂

• 1 ATP (or GTP) made via substrate-level phosphorylation

• 2 CO₂ released

• Oxaloacetate is regenerated

What is FADH2?

reduced electron carrier , similar to NADH2

What is produced in Krebs cycle?

• 6 NADH

• 2 FADH₂

• 2 ATP (from GTP)

• 4 CO₂

bc 1 glucose → 2 pyruvate → 2 Acetyl CoA, so the cycle turns twice per glucose

What are the 2 stages of oxidative phosphorylation?

– electron transport and ATP synthesis/chemiomosis

How does the ETC work? –

Where: Inner mitochondrial membrane
Purpose: Create a proton gradient by pumping H⁺ into the intermembrane space

• NADH and FADH₂ donate high-energy electrons to the chain

• Electrons flow through protein complexes I–IV

• This powers H⁺ pumps that move protons into the intermembrane space (IMS)

• Final electron acceptor: O₂, which forms H₂O

🧠 Key result:

• A proton gradient (high H⁺ in IMS, low H⁺ in matrix) = stored energy, called the proton motive force (PMF)

What is the proton gradient? –

“proton motive force” (PMF) – gradient= stored potential energy, like a dam

What is happening in chemiosmosis?

Where: Inner mitochondrial membrane
Purpose: Use the PMF to make ATP

💥 What happens:

• H⁺ ions flow down their gradient (from IMS to matrix) through ATP synthase

• This flow spins the ATP synthase, like a turbine

• The spinning drives ADP + Pᵢ → ATP

💡 Analogy: (ATP synthase is like a hydroelectric dam — H⁺ = water, flow = energy)

🧠 Key result:

• Most of the ATP in cellular respiration is made here

What are the two gradient?

– electromical (+/- charge) and H+ concentration (pH)

How much ATP is produced throughout each stage of respiration?

• Glycolysis: 2 ATP

• Pyruvate Oxidation: 0 ATP

• Citric Acid Cycle (Krebs): 2 ATP (as GTP)

• Oxidative Phosphorylation: ~26–28 ATP
  ➡ Total: ~30–32 ATP per glucose

Why isn’t any ATP produced for pyruvate?

• pyruvate oxidation is a preparatory step that converts pyruvate into acetyl-CoA and generates NADH for later ATP production during oxidative phosphorylation

• It doesn't directly generate ATP

What is fermentation?

• – the breakdown of glucose to generate ATP without oxygen SLIDE 26

• anaerobic respiration (NO OXYGEN AVAILABLE so cellular respiration can NOT occur)

• Fermentation is useful short-term when oxygen is scarce.

What are the difference between cellular respiration and fermentation?

• Cellular Respiration: Uses O₂, makes ~30–32 ATP, happens in mitochondria, ends with CO₂ + H₂O.

• Fermentation: No O₂, makes 2 ATP, stays in cytoplasm, ends with lactic acid or ethanol.

• Main difference: Oxygen use & ATP yield.

Things to know:

• If a molecule gains H, it's reduced (NAD⁺ → NADH)

• If a molecule loses H, it's oxidized (succinate → fumarate)

• Most energy comes from oxidative phosphorylation, not glycolysis!