1.7 - Cellular Respiration

1.7 - Cellular Respiration

1. Stage 1 - Glycolysis

   • Occurs in the cytoplasm
   • Occurs in the presence or absence of oxygen
   • Phase 1 - Energy Investment
     • ATP broken down
       • This provides energy
     • First phosphorylation occurs
       • Addition of phosphate to a molecule
       • Phosphate from breakdown of ATP is added onto glucose
         • Forms intermediate compounds
           • Intermediates can continue onto a number of pathways
   • Phase 2 - Energy Pay Off
     • ATP generated
       • Net gain of 2 ATP
     • Second phosphorylation occurs
       • Phosphate added to intermediates to form pyruvate
     • Catalysed by phosphofructokinase
     • Irreversible reaction leading to glycolytic pathway
   • Dehydrogenase enzymes remove hydrogen ions and electrons which are passed onto coenzyme NAD
     • Forms NADH

2. Stage 2 - Citric Acid Cycle

   • Occurs in the matrix of the mitochondria
   • Requires the presence of oxygen
   • Pyruvate is broken down into an acetyl group
   • Acetyl group combines with coenzyme A
     • Forms acetyl coenzyme-A
   • Acetyl Co-A is transferred to the citric acid cycle
   • Acetyl Co-A combines with oxaloacetate
     • Forms citrate
   • A series of enzyme mediated steps converts citrate back to oxaloacetate
   • Cycle produces CO2 and generates ATP
   • Dehydrogenase enzymes remove hydrogen ions and electrons which are passed onto conezymes NAD and FAD
     • Forms NADH and FADH2

3. Stage 3 - Electron Transport Chain

   • Occurs on a collection of proteins (cristae) attached to the inner mitochondrial membrane
   • Coenzymes NADH and FADH2 release high energy electrons to the electron transport chain
   • High energy electrons pass along the chain and release energy
     • Energy is used to pump hydrogen ions across the inner mitochondrial membrane
   • Hydrogen ions flow black through the membrane
     • ATP is synthesised using the membrane protein ATP synthase
       • Provides the bulk of ATP generated by cellular respiration
   • The final electron acceptor is oxygen
   • Oxygen combines with hydrogen ions and electrons
     • Forms water

4. Respiratory Substrates

   • Starch and glycogen are broken down to glucose
   • Other sugar molecules are converted to glucose or a glycoloysis intermediate
   • Proteins can be broken down to amino acids
     • Converted to intermediates of glycolysis and citric acid cycle
   • Fats can be broken down to intermediates of glycoloysis and citric acid cycle