Link, Krebs cycle, oxidative phosphorylation and anaerobic respiration

Link reaction

The pyruvate made in glycolysis is oxidised to acetate. NAD picks up the hydrogen and becomes reduced NAD

One carbon has been removed, so we’ve formed one carbon dioxide molecule

Acetate combines with coenzyme A to produce acetylcoenzyme A to enter the Krebs cycle

Link reaction occurs twice for every glucose molecule so: 2x acetylcoenzyme A , 2x CO2 released, 2 reduced NAD

Krebs cycle

Acertyl-coA reacts with a 4 carbon molecule, releasing coenzyme A and producing a 6 carbon molecule that enters the kreb cycle

Then there are a series of redox reactions where we go from having a 6 carbon molecule back to the four carbon molecule

Carbon compounds are being oxidised

Coenzymes FAD and NAD are being reduced

3 reduced NAD made and one reduced FAD

Going from 6 carbon to 4 carbon molecule means we’ve lost two carbons to create two molecules of carbon dioxide

Also releases one molecule of ATP

Products per cycle- 3x reduced NAD, 1x reduced FAD, 1x ATP, 2x CO2

Products per glucose molecule- 6x reduced NAD, 2x reduced FAD, 2x ATP, 4x CO”

Oxidative phosphorylation

This is the final stage of aerobic respiration, where most ATP is synthesised and oxygen is used

The stage involves the transfer of electrons down the electron transfer chain and the movement of protons across the inner mitochondrial membrane

All the reduced coenzymes accumulate in the mitochondrial matrix, where they release their protons (H+) and electrons (e-)

The electrons are passed down a series of electron carrier proteins embedded in the inner mitochondrial membrane, losing energy as they move (electron transport chain)

Oxidative phosphorylation 2

The small amounts of energy the electrons release pump protons from the mitochondrial matrix into the intermembrane space

This creates an electrochemical gradient across the membrane, therefore the protons move down the electrochemical gradient back into the matrix via ATP synthase

And that enables ATP synthase to phosphorylate ADP + Pi into ATP - this movement of H+ is known as chemiosmosis

Oxygen is the final electron acceptor in the electron transfer chain

The oxygen combines with the electrons and protons to form water

This enables the process to continue so more ATP can be made

Anaerobic respiration

In the absence of oxygen respiration occurs anaerobically - it occurs in the cytoplasm of the cell only

The pyruvate produced in glycolysis is reduced to form ethanol and carbon dioxide (in plants and microbes) or lactate (in animals) by gaining the hydrogen from reduced NAD

This oxidised NAD can be reused in glycolysis and ensure that more ATP is continued to be produced

The pyruvate produced in glycolysis is reduced to form lactate in animals by gaining the hydrogen from reduced NAD

Exactly the same happens in plants and microbes but ethanol and carbon dioxide are produced