Cellular Respiration

Breakdown of glucose to carbon dioxide and water

Redox reaction

Hydrogen atoms consist of a hydrogen ion and an electron (H+ and e-)

Glucose is oxidized when the hydrogen is removed Oxygen is reduced when it gains hydrogen and

becomes water Exergonic reaction – glucose is a high energy

molecule water and carbon dioxide are low energy molecules

ATP

Build up of ATP = endergonic Glucose is broken down slowly, ATP

produced gradually Maximum production of ATP = 36 – 38 39% efficiency from glucose to ATP

Coenzymes

NAD+ (nicotinamide adenine dinucleotide) Accepts 2 electrons and 1 hydrogen = NADH

FAD (flavin adenine dinucleotide) Accepts 2 electrons and 2 hydrogens = FADH2

Phases of cellular respiration

Glycolysis – outside mitochondria, anaerobic, splitting of glucose – 2 pyruvate, yield 2 ATP

Preparatory reaction – in mitochondria, pyruvate oxidized to 2 – C acetyl group, preps for citric acid cycle

Citric acid cycle – (Krebs) in matrix of mitochondria, yield 2 ATP

Electron transport chain – cristae, oxygen is final electron acceptor and forms water, result in 32 – 34 ATP

Glycolysis

Outside of mitochondria in cytoplasm Glucose 2 pyruvate Does not require oxygen, anaerobic

Energy investment

2 ATP are used to activate glucose and break down into 2 C3 molecules of G3P.

Energy harvesting

Electrons removed (oxidation) with hydrogen ions. NAD picks up Hydrogen and electrons = NADH Substrate level phosphorylation – production of ATP

via an enzyme passing a high energy phosphate to ADP = 4 ATP

Investment of 2 ATP minus 4 ATP = 2 net ATP

Prep Reaction

Pyruvate (2 C3 molecules) is converted to an acetyl group (C2) that is attached to coenzyme A (CoA)

CO2 is a product Oxidation occurs, electrons from pyruvate are

removed, NAD NADH Reaction occurs twice since there are 2 pyruvate

per glucose molecule

Prep reaction

Inputs: 2 pyruvate, 2 NAD+, 2 CoA Outputs: 2 CO2 (Product), 2 NADH,

2 acetyl CoA

Citric Acid Cycle

Matrix of mitochondria C2 (acetyl CoA) joins with C4 molecule = C6

citrate molecule. Each acetyl group is oxidized to 2 CO2

molecules = 4 CO2 total released Cycle goes around 2 times

Citric Acid Cycle

Substrate Level phosphorylation - An enzyme passes a high energy phosphate to ADP = ATP

Inputs: 2 acetyl CoA, 6 NAD, 2 ADP/P, 2 FAD

Outputs: 4 CO2 (product), 6 NADH, 2 FADH2, 2 ATP

Prep reaction Citric acid cycle Cycle goes around 2 times

Electron Transport Chain

Electrons are carried by NADH and FADH2 Oxidation-reduction reaction starts the ETC. High

energy electrons enter the chain, low energy electrons leave.

There is a series of carriers that transport the electrons, first reduced when it accepts the electrons, then oxidized when it releases them.

Carriers

3 protein complexes (NADH-Q reductase, cytochrome reductase and cytochrome oxidase)

2 carriers that transport electrons on ETC– coenzyme Q and cytochrome c

Cytochrome – protein that has a tightly bound heme group with a central atom of iron.

Oxidative phosphorylation

Hydrogen ions are pumped out of the matrix into the intermembrane space, H+ flow back through membrane due to H+ gradient = chemiosmosis

Production of ATP as a result of energy released by the ETC = 32 – 34 ATP

Production of ATP via substrate phosphorylation is 4 ATP Total ATP = 36 – 38 ATP 39% efficiency of cellular resp.

ETC

For each NADH that is oxidized, 3 ATP molecules are produced

For each FADH2 that is oxidized, 2 ATP are produced, (due to the fact that they follow NADH and electrons are at a lower energy level).

Electron transport chain

Oxygen is the final electron acceptor in the ETC

Receives last electrons and combines with the hydrogen ions to form water (product)