Cellular Respiration

Cellular Respiration

  1. In cells, the chemical energy from food is broken down into other forms of energy through a process called Cellular Respiration which occurs as a series of reactions.
  1. The energy in food is measured in calorie. This is the amount of energy needed to raise the temperature of 1 gram of water by 1degree Celsius.
  1. The first step in respiration is Glycolysis(takes place in cytoplasm) in which one molecule of glucose is broken into 2 molecules pyruvic acid(3-carbon compound), an electron carrier called NADH and ATP. It does not require O2.

All living things carry out Glycolysis – It does not need O2, takesplace in cytoplasm.

  1. The reactions then continue as aerobic or anaerobicrespiration.
  • Aerobic pathway - requires the presence of O2.

Glycolysisis followed by Kreb cycle and and Oxidative phosphorylation (Electron transport chain + Chemiosmosis) .

  • Anaerobic pathway – does not require O2.

Glycolysisis followed by Fermentation.

  1. Aerobic Respiration – Glycolysis, Kreb cycle (citric acid cycle), and Oxidative phosphorylation (Electron transport chain + Chemiosmosis) together make up cellular respiration.
  • Cellular respiration is a process that releases energy by breaking down food in presence of O2 (electron acceptor).
  • The purpose of cellular respiration is to capture the energy from food (glucose) a little at a time and hold it in the chemical bonds of ATP.
  • C6H12O6 + 6O2 ------ 6CO2 + 6H2O + Energy
  • Glucose is broken down in the process and recombines with oxygen to form new substances. Energy is released.

  • Glycolysis takes place in cytoplasm
  • Kreb’s cycle takes place in mitochondrial matrix
  • Oxidative phosphorylation (Electron transport chain + Chemiosmosis) takes place in cristae (inner mitochondrial membrane).
  • Glycolysis supplies pyruvic acid to Kreb’s cycle and high energy electronsvia NADH to electron transport chain which converts ADP into ATP.

Summary Aerobic Respiration

  1. requires the presence of oxygen,takes place in the mitochondria of the cell
  1. Glycolysis followed by Krebs cycle and Oxidative phosphorylation (Electron transport chain + chemiosmosis)
  1. Krebs cycle converts pyruvate to ATP, CO2, NADH (carrying high energy e-)
  1. Electron transport chain and chemiosmosis produce H2O, ATP (energy).
  1. produces 36 ATP molecules and heat energy

When O2is NOT present:

  1. Anaerobic Respiration - Glycolysis is followed by different pathway, combined together they are known as Fermentation.
  • During Fermentation, cells convert NADH to NAD+by passing high energy electrons back to pyruvic acid allowing glycolysis to continue producing a steady supply of ATP
  • The purpose of Fermentation is to replenish NAD+ so glycolysis can continue.
  • Anaerobic Respiration
  • does not require oxygen
  • occurs in the cytoplasm of the cell
  • energy is produced from glycolysis
  • produces only 2 ATP molecules

  1. Two types of Fermentations
  1. Alcoholic Fermentation
  2. occurs in unicellular fungi and yeasts
  3. produces carbon dioxide and ethanol
  4. the alcohol molecule contains much unused energy
  1. Lactic acid Fermentation
  2. occurs in animal cells
  3. pyruvate from glycolysis is converted to lactic acid
  4. occurs during strenuous exercise when muscles run out of oxygen
  1. only 2 ATP are produced