Unit 3 Cellular Energetic: Cellular Respiration

What are catabolic pathways?

Catabolic pathways break down molecules to release energy.

What are the two types of catabolic pathways?

• Fermentation: Partial breakdown of sugars without oxygen.

• Aerobic respiration: Breaks down macromolecules to produce ATP, using oxygen.

What is the equation for aerobic respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (686 kcal/mol of glucose).

How does aerobic respiration produce ATP?

Energy from breaking down glucose phosphorylates ADP to make ATP.

What are redox reactions?

Chemical reactions where electrons are transferred between molecules.

Define oxidation and reduction.

• Oxidation: Loss of electrons and energy.

• Reduction: Gain of electrons and energy.

What does NAD+ do in cellular respiration?

NAD+ accepts electrons and H+ to form NADH, which stores energy.

What are the three stages of cellular respiration?

• Glycolysis

• Pyruvate oxidation and citric acid cycle

• Oxidative phosphorylation

Where does glycolysis occur, and what happens in it?

Glycolysis occurs in the cytoplasm. Glucose is broken into 2 pyruvates, producing 2 ATP and 2 NADH.

What happens during pyruvate oxidation?

Pyruvate enters the mitochondria, loses a CO2, reduces NAD+ to NADH, and combines with Coenzyme A to form Acetyl CoA.

What is the citric acid cycle, and what does it produce?

The citric acid cycle breaks down Acetyl CoA into CO2 and produces 6 NADH, 2 FADH2, 2 ATP (per glucose).

What happens to the carbons in glucose by the end of the citric acid cycle?

All 6 carbons are released as CO2.

Where does the electron transport chain (ETC) occur?

In the inner mitochondrial membrane.

What powers the electron transport chain (ETC)?

Electrons from NADH and FADH2 power hydrogen pumps.

What is the role of oxygen in the ETC?

Oxygen is the final electron acceptor, forming water.

What is chemiosmosis?

Protons flow back into the mitochondria through ATP synthase, producing ATP.

How much ATP is produced by oxidative phosphorylation?

About 26-28 ATP per glucose.

What is fermentation?

A process that allows ATP production without oxygen, regenerating NAD+ for glycolysis.

What are the two types of fermentation?

• Alcohol fermentation: Pyruvate → Ethanol + CO2, regenerates NAD+.

• Lactic acid fermentation: Pyruvate → Lactate, regenerates NAD+.

How do proteins and fats enter cellular respiration?

They are broken down into intermediates that feed into glycolysis or the citric acid cycle.

What does phosphofructokinase (PFK) do?

• PFK is an enzyme that regulates glycolysis.

• High ATP levels inhibit it, slowing down glycolysis.

• Low ATP levels activate it, speeding up glycolysis.

What does NAD+ do in cellular respiration?

• NAD+ acts as an electron carrier.

• It picks up two electrons and one hydrogen ion (H+) to form NADH.

• NADH stores energy and transports the electrons to the electron transport chain (ETC) to produce ATP.

What happens during chemiosmosis?

• Chemiosmosis is the movement of H+ ions across a membrane, driving ATP synthesis.

• Protons are pumped into the intermembrane space of the mitochondria during the ETC, creating a concentration gradient (high H+ outside, low H+ inside).

• These protons flow back into the mitochondrial matrix through ATP synthase, which uses the energy from this flow to phosphorylate ADP into ATP.

What is ATP synthase?

• ATP synthase is an enzyme in the inner mitochondrial membrane.

• It works like a turbine, using the flow of H+ ions (from chemiosmosis) to generate ATP.

• This process is part of oxidative phosphorylation and produces the bulk of ATP in cellular respiration.

Why is oxygen important in cellular respiration?

• Oxygen is the final electron acceptor in the electron transport chain.

• It combines with electrons and hydrogen ions to form water (H2O).

• Without oxygen, the ETC cannot function, and no ATP is produced through oxidative phosphorylation.

What is the purpose of glycolysis? (occurs in cytoplasm)

To break down glucose (6C) into two pyruvate molecules (3C), producing some ATP and NADH.

Step 1 glycolysis: What happens to glucose in the first steps?

Glucose is phosphorylated (using 2 ATP) and split into two 3-carbon molecules.

Step 2 glycolysis: What happens to the 3-carbon molecules?

They’re oxidized to form 2 pyruvate, producing 2 NADH and 4 ATP (net gain = 2 ATP).

What are the products of glycolysis?

2 pyruvate, 2 NADH, and a net gain of 2 ATP.

What is the purpose of the Krebs Cycle?

To generate high-energy electron carriers (NADH and FADH₂) and ATP by breaking down acetyl-CoA.

Step 1 Krebs Cycle: What happens to pyruvate before the Krebs Cycle?

Pyruvate is converted to acetyl-CoA, releasing 1 CO₂ and producing 1 NADH.

Step 2 Krebs Cycle: What happens when acetyl-CoA enters the cycle?

It combines with oxaloacetate (4C) to form citrate (6C).

Step 3 Krebs Cycle: What happens as citrate is broken down?

It’s oxidized, releasing 2 CO₂, producing 3 NADH, 1 FADH₂, and 1 ATP per acetyl-CoA.

How many turns of the Krebs Cycle per glucose?

Two turns (one for each pyruvate).

What are the total products of the Krebs Cycle (per glucose)?

6 NADH, 2 FADH₂, 2 ATP, and 4 CO₂.

What is the purpose of the ETC?

To use electrons from NADH and FADH₂ to generate a lot of ATP.

Step 1 ETC: What happens to NADH and FADH₂?

They donate electrons to the ETC, becoming NAD⁺ and FAD.

Step 2 ETC: What happens as electrons move down the ETC?

Energy is released and used to pump H⁺ ions into the intermembrane space, creating a gradient.

Step 3 ETC: What happens to the H⁺ gradient?

H⁺ flows back into the matrix through ATP synthase, which generates ATP (chemiosmosis).

What is the role of oxygen in the ETC?

It’s the final electron acceptor, forming water (H₂O).

How much ATP is produced in the ETC?

About 34 ATP per glucose.

What are the stages of cellular respiration?

Glycolysis → Krebs Cycle → Electron Transport Chain.

How much ATP is produced in total?

About 36-38 ATP per glucose (2 from glycolysis, 2 from Krebs Cycle, and ~34 from ETC).