BIOLOGY- respiration processes

The krebs cycle

1 acetyl CoA delivers an acetyl group that combines to another two carbon acetyl group forming a four carbon oxaloacetate to form a six carbon citrate

2 the citrate molecule undergoes decarboxylation and dehydrogenation producing one reduced NAD and carbon dioxide which forms a five carbon compound

3 the five carbon compound undergoes decarboxylation and dehydrogenation further eventually regenerating oxaloacetate and so the cycle continues. more carbon dioxide, two more reduced NADs and one FADH are produced and ATP is also produced by substrate level phosphorylation

The link reaction (oxidative decarboxylation)

This is where each pyruvate is converted to acetyl which binds to coenzyme A. in the process NAD is reduced into NADH and carbon dioxide is produced as pyruvate is decarboxylated

Acetyl CoA delivers the acetyl group to the next stage of respiration the krebs cycle then the reduced NAD is used in oxidative phosphorylation to synthesis ATP

Glycolysis

1 Phosphorylation- the first step of glycolysis requires two ATP molecules. two phosphates are released from the two ATP molecules they are then attached to a glucose molecule forming hexose bisphosphate

2 Lysis- this destabalises the molecule causing it to split into two triose phosphate molecules

3 Phosphorylation- another phosphate group is added to each triose phosphate forming two bisphosphates, these phosphate groups come from free inorganic phosphate ions present in the cytoplasm

4 Dehydrogenation and formation of ATP- the two triose bisphosphate molecules are oxidised by the removal of hydrogen atoms. NAD coenzymes accept the removed hydrogen then are reduced forming two NADH molecules

Oxidative phosphorylation

• the hydrogen atoms that have been collected by the coenzyme NAD and FAD are delivered to the electron transport chains present in the membranes of the cristae of the mitochondria

• the hydrogen atoms dissociate into hydrogen ions and electrons, the high energy electrons are used in the synthesis of ATP by chemiosmosis then energy is released during redox reactions as the electrons reduce and oxidise electron carriers as they flow along the electron transport chain. this energy is used to create a proton gradient leading to the diffusion of protons through ATP synthase resulting in the synthesis of ATP

• at the end of the electron transport chain the electron combines with hydrogen ions and oxygen to form water, oxygen in the final electron acceptor and the electron chain cannot operate unless oxygen is present