Knowledge-16 R

• Cells use ATP as their immediate energy source.
• respiration transfers energy stored in complex organic molecules to ATP by phosphorylation.
• The process of respiration is common in all organism , providing indirect evidence for evolution.
• There are two types of respiration:

  • Aerobic respiration: requires oxygen; produces water , carbon dioxide and many molecules of ATP.
  • Anaerobic respiration: takes place in the absence of oxygen and produces a small amount of ATP. In plants and fungi it also produces carbon dioxide and ethanol , animals produce lactate.
• Aerobic respiration:

  Aerobic respiration is a four-stage process:

  1. Glycolysis- 6 carbon is split into two molecules of 3-carbon pyruvate.
  2. link reaction- 3 carbon pyruvate is oxidized into carbon dioxide and acetyl coenzyme A.
  3. Krebs cycle- Acetyl coenzyme A enters a cycle of redox reactions that produce ATP and large number of electrons stored in reduced NAD and reduced FAD.
  4. Electron transport chain- the electrons stored in reduced NAD from the Krebs cycle are used to generate ATP, with water as a waste product.
• Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm. It is an anaerobic process in three stages.
• Glycolysis:

  1. Phosphorylation of glucose to glucose phosphate. This uses phosphate from the hydrolysis of two ATP molecules; the addition of phosphate activates glucose.
• Glycolysis:

  • 2.) conversion of glucose to two molecules of 3 carbon triose phosphate.
• Glycolysis:

  • 3.)Oxidation of triose phosphate to pyruvate which produces two molecules of ATP from ADP. A pair of hydrogen atoms are also removed from each triose phosphate and transferred to NAD to form reduced NAD.
• Anaerobic respiration:

  if oxygen is not present only anaerobic respiration can occur. There two main types of anaerobic respiration in eukaryotic cells:

  • in some plant cells and micro-organisms such as yeast , pyruvate is converted to ethanol via ethanal. Ethanal accepts a hydrogen atom from reduced NAD.
  • in animals cells, pyruvate is converted lactate by accepting a hydrogen atom from reduced NAD.
• During exercise , lactate can build up in muscles , causing cramp and muscle fatigue. Lactate must be oxidized back to pyruvate , to enter link reaction, or be converted into glycogen in the liver.
• If oxygen is present then the link reaction occurs and this joins glycolysis to the krebs cycle.
• Link reaction:

  1. Pyruvate enters the mitochondrial matrix via active transport.
  2. Pyruvate is oxidized to form acetate , producing reduced NAD and releasing co2.
  3. Acetate combines with coenzyme A to produce acetyl coenzyme A.
• The krebs cycle occurs in the mitochondrial matrix.
• During the Krebs cycle:

  • 3 reduced NAD , 1 reduced FAD molecules and ATP are generated through a series of redox reactions and phosphorylation.
  • Carbon dioxide is lost
• Acetyl coenzyme A reacts with a 4-carbon compound to produce a 6-carbon compound which enters the Krebs cycle, releasing coenzyme A.
• The electron transport chain (ETC):

  1. ATP is synthesized by oxidative phosphorylation , which is driven by the transfer of electrons from reduced NAD down the ETC and the movement of protons across the inner mitochondrial membrane.
• The electron transport chain (ETC):

  1. 2.) As electrons pass through one carrier to another some energy is wasted. This energy is used to pump protons through the inner mitochondrial membrane into the intermembrane space.
• The electron transport chain (ETC):

  1. 3.) The protons diffuse back through the inner mitochondrial membrane via protein channels associated with ATP synthase , which generates ATP from ADP and inorganic phosphate.
• The electron transport chain (ETC):

  1. 4.)At the end of the ETC, the electrons and protons form hydrogen , which reacts with oxygen to form water. Oxygen is therefore final electron acceptor.
• The electron transport chain (ETC):

  1. 5.) The enzymes required for this process , including ATP synthase , are embedded in the inner mitochondrial membrane.
• what happens to pyruvate during anaerobic respiration:

  1. pyruvate is converted to lactate