Respiration

Glycolysis --> A process that:

• Splits a molecule of glucose [6C] into smaller molecules of pyruvate [3C x 2]
• Occurs in the cytoplasm of cells
• First stage of both anaerobic and aerobic respiration

1) Phosphorlyation:

• Glucose is phosphorylated by adding 2 phosphates from two molecules of ATP
• 2 molecules of TP are created (including 2 molecules of ADP)

2) Oxidation:

• TP is oxidised (loses hydrogen) and forms two molecules of pyruvate
• NAD collects hydrogen ions and forms 2 reduced NAD
• 4 ATP are produced but 2 are used up in phosphorylation when the cycle occurs again (has a net gain of 2 ATP)

- Reduced NAD is used in oxidative phosphorylation (Stage 4) and pyruvate is used in the matrix of mitochondria for link reaction (Stage 2)

Link Reaction --> A process that:

• Occurs in the mitochondrial matrix

- Pyruvate is decarboxylated (carbon is removed from pyruvate in the form of CO2)

- NAD is reduced (collects hydrogen from pyruvate as the pyruvate forms acetate)

- Acetate then combines with coenzyme A - forms acetylcoenzyme A

(NO ATP is produced in this reaction)

What happens to the products?

• 2 molecules of acetylcoenzyme A goes into the Kreb's Cycle (Stage 3)
• 2 molecules of CO2 released as a waste product
• 2 molecules of reduced NAD for oxidative phosphorylation (Stage 4)

Pyruvate ---(NAD-Reduced NAD)-> Acetate ---(Add. of coenzyme A)---> Acetlycoenzyme A 

   [3C]                                                      [2C]                                                            [2C]

Kreb's Cycle --> A process that:

• Consists of a series of oxidation-reduction reactions
• Takes place in the mitochondrial matrix
• Only occurs ONCE for every pyruvate (TWICE for every glucose molecule)

1) acetyl-CoA [2C] + Oxaloacetate (4 Carbon Compound) = Citrate (6 carbon compound). Coenzyme A transfer back to the link reaction

2) Citrate converted into a 5 carbon compound [5C] - Decarboxylation (CO2 removed) and dehydrogenation (hydrogen removed) occur. (Hydrogen is used to produce reduced NAD from NAD)

3) 5C compound converted into a 4C compound. Decarboxylation and dehydrogenation occur. 1 molecule of reduced FAD and 2 molecules of reduced NAD are produced. ATP is also produced by the direct transfer of a phosphate group from an intermediate compound to ADP (substrate-level phosphorylation)

• 1 x Coenzyme A - Reused in the next link reaction
• Oxaloacetate [4C] - Regenerated for use in the next Kreb's cycle
• 2 x CO2 - Released as a waste product
• 1 x ATP - Used for energy
• 3 x Reduced NAD - Used in oxidative phosphorylation (stage 4)
• 1 x Reduced FAD - Used in oxidative phosphorylation (stage 4)

Oxidative Phosphorylation:

• 1) Hydrogen atoms are released from reduced NAD & reduced FAD. Atom splits into protons [H+] and electrons [e-]

• 2) Electrons move along the ETC, losing energy at each electron carrier

• 3) Energy released is used by carriers to pump protons from the mitochondrial matrix to the intermembrane space (between inner and out membrane)

• 4) Concentration of protons is now higher in the intermembrane space, forming an electrochemical gradient 

• 5) Protons move down their electrochemical gradient back into the matrix via ATP synthase. Movement drives the synthesis of ATP from ADP and inorganic phosphate

• 6) Movement of H+ ions across a membrane which generates ATP = chemiosmosis

• 7) In the matrix, at the end of ETC,  protons, electrons, and oxygen (from blood) combine to form water. Oxygen is the final electron acceptor

• Doesn't use oxygen
• Only involves Stage 1 (Glycolysis)

Alcohol Fermentation:

• CO2 removed from pyruvate forming ethanal
• Reduced NAD (from glycolysis) transfers hydrogen to ethanal, forming ethanol and NAD
• NAD can then be reused in glycolysis (production of ethanol regenerates NAD so glycolysis can continue)

Pyruvate --CO2 removed--> ethanal --reduced NAD to NAD--> ethanol

Lactate Fermentation:

• Reduced NAD (from glycolysis) transfer hydrogen to pyruvate to form lactate and NAD
• NAD can then be reused in glycolysis (production of lactate regenerates NAD)

Pyruvate -----reduced NAD to NAD--> lactate (lactic acid)