BIOL 100: Topic 8 - Cellular Respiration/Fermentation

Cellular respiration

A catabolic process that converts glucose into ATP using oxygen.

Main purpose of cellular respiration

Produce ATP for cellular work.

Type of pathway cellular respiration is

Catabolic (breaks down molecules).

Overall chemical formula of cellular respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP.

Reactants of cellular respiration

Glucose and oxygen.

Products of cellular respiration

Carbon dioxide, water, and ATP.

ATP

Cell’s main energy currency; powers biological work.

ADP

Adenosine diphosphate; product when ATP loses a phosphate.

NAD+

Oxidized form of an electron carrier; accepts electrons.

NADH

Reduced form of NAD+; carries high-energy electrons.

FAD

Another electron carrier; oxidized form.

FADH2

Reduced form of FAD; carries electrons to ETC.

Stages of cellular respiration

Glycolysis, pyruvate oxidation, Krebs Cycle, and ETC.

Location of glycolysis

Cytoplasm.

Glycolysis

First stage; breaks glucose into 2 pyruvate molecules.

Glucose

6-carbon sugar; main fuel source in cellular respiration.

ATP used in glycolysis

2 ATP used in investment phase.

ATP produced in glycolysis

4 ATP produced; net gain of 2 ATP.

NADH produced in glycolysis

2 NADH per glucose.

End products of glycolysis

2 pyruvate, 2 NADH, and 2 ATP net.

Pyruvate

3-carbon molecule formed at end of glycolysis.

Location of pyruvate oxidation

Mitochondrial matrix.

Pyruvate oxidation

Conversion of pyruvate to acetyl-CoA, CO2, and NADH.

NADH from pyruvate oxidation

1 NADH per pyruvate; 2 per glucose.

CO2 from pyruvate oxidation

1 CO2 per pyruvate; 2 per glucose.

Acetyl-CoA

Product of pyruvate oxidation; enters Krebs Cycle.

Krebs Cycle

Also called Citric Acid Cycle; completes glucose breakdown.

Location of Krebs Cycle

Mitochondrial matrix.

ATP from Krebs Cycle

1 ATP per turn; 2 per glucose.

NADH from Krebs Cycle

3 NADH per turn; 6 per glucose.

FADH2 from Krebs Cycle

1 FADH2 per turn; 2 per glucose.

CO2 from Krebs Cycle

2 CO2 per turn; 4 per glucose.

Number of Krebs Cycle turns

2 turns per glucose molecule.

Total ATP from glycolysis

2 net ATP.

Total NADH from glycolysis

2 NADH.

Total ATP from Krebs Cycle

2 ATP (1 per turn).

Total NADH from Krebs Cycle

6 NADH (3 per turn).

Total FADH2 from Krebs Cycle

2 FADH2 (1 per turn).

Total NADH before ETC

10 NADH (2 glycolysis, 2 pyruvate ox., 6 Krebs).

Total FADH2 before ETC

2 FADH2 (Krebs only).

Electron Transport Chain (ETC)

Series of proteins that pass electrons from NADH/FADH2 to oxygen.

Location of ETC

Inner mitochondrial membrane (cristae).

Purpose of ETC

Create a proton gradient to power ATP synthesis.

What donates electrons to ETC

NADH and FADH2.

Final electron acceptor in ETC

Oxygen (O2).

What oxygen becomes in ETC

Water (H2O).

What happens if no oxygen in ETC

Electron flow stops, no ATP made in oxidative phosphorylation.

Protons pumped by ETC

Into intermembrane space, forming gradient.

Chemiosmosis

Flow of protons back through ATP synthase to make ATP.

ATP synthase

Enzyme that uses H+ gradient to make ATP.

Oxidative phosphorylation

ATP production via ETC + chemiosmosis.

ATP yield from oxidative phosphorylation

About 26–28 ATP.

ATP yield from glycolysis

2 net ATP.

ATP yield from Krebs Cycle

2 ATP.

Total theoretical ATP per glucose

Approximately 30–32 ATP.

Fermentation

ATP production without oxygen; relies only on glycolysis.

Location of fermentation

Cytoplasm.

Why fermentation is needed

Regenerates NAD+ for glycolysis.

NAD+ role in glycolysis

Electron acceptor; must be regenerated to continue glycolysis.

ATP from fermentation

2 ATP per glucose (from glycolysis only).

End product of fermentation in animals

Lactic acid.

End product of fermentation in yeast

Ethanol and CO2.

Lactic acid fermentation equation

Glucose → 2 lactic acid + 2 ATP.

Alcoholic fermentation equation

Glucose → 2 ethanol + 2 CO2 + 2 ATP.

Organisms that use lactic acid fermentation

Muscle cells and some bacteria.

Organisms that use alcoholic fermentation

Yeast and some bacteria.

Anaerobic respiration

Uses ETC but not oxygen as final electron acceptor.

Difference between fermentation and anaerobic respiration

Fermentation has no ETC; anaerobic respiration has ETC with different acceptors.

Why glycolysis can occur without oxygen

It doesn't require mitochondria or oxygen.

Why fermentation is inefficient

Only produces 2 ATP per glucose.

Why aerobic respiration is efficient

Produces about 15 times more ATP than fermentation.

Proton gradient

Created by ETC pumping protons into intermembrane space.

Importance of proton gradient

Drives ATP synthesis through ATP synthase.

Cristae

Inner folds of mitochondrial membrane that increase surface area for ETC.

Mitochondrial matrix

Location of pyruvate oxidation and Krebs Cycle.

Intermembrane space

Area between inner and outer mitochondrial membranes where protons accumulate.

Redox reaction in ETC

Electrons are transferred from NADH/FADH2 to oxygen through proteins.

Oxidation in respiration

Loss of electrons (e.g., glucose to CO2).

Reduction in respiration

Gain of electrons (e.g., O2 to H2O).

Gluconeogenesis

Process of generating glucose from non-carbohydrate sources.

Why NADH must be oxidized

To regenerate NAD+ for use in glycolysis.

What happens to pyruvate without oxygen

Converted to lactate or ethanol through fermentation.

What happens to pyruvate with oxygen

Converted to acetyl-CoA and enters the Krebs Cycle.

How oxygen affects ATP production

Allows full oxidation of glucose, maximizing ATP yield.

What happens if ATP synthase is blocked

ATP production via oxidative phosphorylation stops.

Uncoupling proteins

Allow protons to flow without making ATP, generating heat.

Example of ATP used in mechanical work

Muscle contraction.

Example of ATP used in transport work

Active transport of ions across membranes.

Example of ATP used in chemical work

Building polymers like proteins or DNA.

Role of coenzymes in respiration

Carry electrons (e.g., NAD+, FAD).

What is produced from NADH in ETC

ATP and water.

Why mitochondria are important for energy

They contain the machinery for aerobic respiration and ATP synthesis.