5-2 Respiration

Question 1

What is aerobic respiration?

Answer 1

• Aerobic respiration is the splitting of a respiratory substrate, to release carbon dioxide as a waste product.
• Hydrogen is reunited with atmospheric oxygen with the release of a large amount of energy.

Question 2

What is anaerobic respiration?

Answer 2

• Anaerobic respiration occurs in the absence of oxygen.

Question 3

What are the stages of respiration?

Answer 3

1. Glycolysis.
   a. First process of both aerobic and anaerobic respiration.
   b. It takes place in the cytoplasm of the cell.
   c. Glucose is phosphorylated to produce 2 molecules of ATP and 2 molecules of NADH.
   d. In anaerobic respiration the pyruvate is further converted into lactate with the help of NADH.
   e. Lactate is then converted back to pyruvate in the liver.
   f. From one molecule of glucose 2 molecules of ATP, 2 molecules of reduced NAD and 2 molecules of pyruvate are formed.
2. Link Reaction
   a. In the link reaction the 2 molecules of pyruvate are actively transported into the mitochondria.
   b. The enzyme decarboxylase then removes a molecule of CO2 with a hydrogen also being lost, going on to reduce NAD.
   c. The acetate formed then combines with coenzyme A to form a molecule of acetyl coenzyme A.
   d. Per glucose molecule 2 molecules of acetyl coenzyme A are formed and 0 ATP.
3. Krebs Cycle
   a. The Krebs Cycle occurs in the matrix of the mitochondria.
   b. The acetyl coenzyme A gives the 2-carbon acetate to a 4-carbon molecule already present.
   c. The 6-carbon molecule that is formed then undergoes a series of reactions.
   d. Eventually the starting 4 carbon molecule is regenerated to accept another acetate molecule.
   e. The Krebs Cycle turns 2 times per molecule of glucose and therefore per molecule of glucose, 2 ATP molecules, 6 NADH molecules, 2 FADH molecules and 4 CO2 molecules are produced.
4. Oxidation Phosphorylation
   a. Reduced NAD from the Krebs Cycle binds to protein complex 1, releasing its hydrogen atoms as protons and electrons.
   b. The NAD hydrogen carrier then goes back to the Krebs Cycle to be used again.
   c. Reduced FAD binds to complex 2.
   d. It also releases its hydrogen atoms as protons and electrons.
   e. The protons move into the mitochondrial matrix whilst the electrons released go into the electron chain.
   f. The electrons are then passed down a chain of protein complexes, 1 to 4, each having a higher affinity than the previous.
   g. In complexes 1,3 and 4, the energy from the electron is used to pump across protons.
   h. For each hydrogen released by NADH 4 protons are pumped across.
   i. The protons are pumped into the intermembrane space.
   j. After the electrons have pumped across the protons, they are accepted by the final acceptor oxygen.
   k. The electrons combine with a proton to form a hydrogen atom, which then combines with oxygen to form water.
   l. The pumping of the protons from the mitochondrial matrix to the intermembrane space creates a proton gradient.
   m. The protons therefore move across the membrane through a protein channel called a stalked particle.
   n. The proton motive force provides energy for ATP synthase to produce ATP.