Cellular Respiration & Energy Production

• Cellular respiration maximizes energy extraction from glucose through Glycolysis, the Citric Acid Cycle, the Electron Transport Chain, and Oxidative Phosphorylation.

Cellular Respiration Overview

• Glycolysis breaks down glucose.
• Pyruvate metabolizes into acetyl-CoA, which enters the citric acid cycle.
• The electron transport chain utilizes accumulated NADH to pump protons.
• Oxidative phosphorylation produces ATP using chemiosmosis of protons.
• The overall reaction for aerobic catabolism of glucose is Glucose + 6 O₂ → 6 CO₂ + 6 H₂O + energy (38 ATP).

Cofactors and Coenzymes

• These molecules bind to enzymes to aid in catalysis and have extremely wide usage.
• Vitamins and minerals such as Coenzyme A, NADH, and FADH₂ are coenzymes.
• Zinc, iron, and manganese are also important.
• They are small molecules bound in the middle of alpha helices in proteins.

Oxidation and Reduction

• Reduction is defined as gaining electrons (and binding a hydrogen).
• Oxidation refers to losing electrons, which involves adding oxygen.
• Oxygen takes the electrons in oxidation reactions.

Coenzymes: NAD (Nicotinamide Adenine Dinucleotide)

• NAD binds to enzymes and functions as an electron carrier.
• NAD is reduced to NADH by accepting electrons and binding hydrogen.
• NADH stores energy in electrons for later use.
• Related compounds include NADP and FAD, which also act as electron carriers.
• NAD is made from vitamin B3 which is niacin.
• FAD is made from vitamin B2 which is riboflavin.
• The reduction of NAD to NADH stores energy from the breakdown of glucose.

Coenzyme A

• Coenzyme A carries 2-carbon acetyl groups and acts as a carrier or shuttle for 2 of the 3 carbons in pyruvate within the citric acid cycle.
• Its precursor is vitamin B5, also known as pantothenic acid.

Glycolysis

• A metabolic pathway occurs in the cytosol which uses 10 enzymes to extract energy, electrons, & pyruvate from glucose. – Overall Glycolysis Reaction: Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 pyruvate + 2 ATP + 2 NADH within the cytosol.
• ATP stores energy and NADH stores electrons within the cytosol.
• Glucose is a sugar with a lot of energy.
• ATP - is an energy carrying molecule used in metabolism
• NAD - is an electron carrier where electrons carry energy
• The regeneration of NAD+ from NADH is required for the continued breakdown of glucose, so the electrons taken from glucose must be shuttled somewhere in order for more glucose to be used.

Cellular Respiration in Detail

• Glycolysis extracts energy from glucose, storing it as ATP and NADH.
• The Citric Acid Cycle extracts energy from pyruvate, storing it as ATP and NADH as well.
• Oxidative Phosphorylation extracts energy from NADH and oxygen, storing it as ATP

Relationship to Citric Acid Cycle

• Pyruvate feeds into the citric acid cycle, producing energy, electrons, and CO2.

Electron Transport Chain

• The Electron Transport Chain (ETC) uses the energy of the electrons stored in NADH and FADH₂ to pump protons across the cell.

Oxidative Phosphorylation

• Oxidative phosphorylation involves the transfer of electrons to O₂ and the creation of ATP from ADP and Pi.

ATP Synthase

• ATP Synthase uses the flow of protons down an electrochemical gradient to synthesize ATP

Cyanide Inhibition

• Cyanide inhibits cytochrome c oxidase (Cyt c) in the electron transport chain.