Cellular Respiration

• • Food serves as a source of raw materials for cells and as a source of chemical energy (glucose)
  • However, the glucose in food must be converted to free energy (ATP) in order for cells to use it for cell activities like active transport
  • This process is called Cellular Respiration
  • Cellular Respiration occurs in both autotrophs and heterotrophs (all organisms)
  • final stages happen in the mitochondria
• There are two ways to convert food molecules into free energy:

  • Aerobic Cellular Respiration
  • occurs with oxygen
  • releases a LOT of energy (36 ATP)
  • Anaerobic Cellular Respiration (Fermentation)
  • occurs without oxygen
  • releases a little bit of energy (2 ATP)
  • no oxygen required to release a small amount of ATP (2 molecules)
• Aerobic Cellular Respiration

  • Cellular respiration is the set of reactions that releases free energy (ATP) by breaking down glucose and other food molecules (like fats) in the presence of oxygen
  • Three Step Process
  • Glycolysis
  • Krebs Cycle
  • Electron Transport Chain
• Aerobic Cellular Respiration

  • Why Cellular Respiration?
  • Each step is catalyzed by enzymes
  • Each step releases free energy which is stored in ATP
  • Breaks down glucose in a series of reactions (steps) to avoid releasing too much energy and heat all at once and cooking the cells
  • Chemical formula for Aerobic CR
  • 6O2 + C6H12O6 -> 6CO2 + 6H2O + Energy (ATP)
• Aerobic Cellular Respiration

  • 3 steps in Aerobic CR
  • Glycolysis
  • Both aerobic & anaerobic pathways start with this process
  • It happens in the cytoplasm (outside mitochondria)
  • Doesn't require oxygen
  • One molecule of glucose is broken in half, producing two 3-carbon molecules called pyruvic acid (pyruvate) that can be used in the next steps of respiration
  • Happens so fast that cells can produce thousands of ATP molecules in a few milliseconds
  • Each glucose produces only 2 ATP molecules
  • IMPORTANT: NAD+ forms many NADH (electron carriers like NADPH in photosynthesis) to be used later
• Aerobic Cellular Respiration

  • 3 steps in Aerobic CR
  • Krebs Cycle
  • Pyruvic acid molecules from glycolysis enter the mitochondria and start the Krebs Cycle reaction
  • Happens in the matrix of the mitochondria
  • Pyruvic acid forms and releases carbon dioxide (CO2)
  • Makes just 2 ATP molecules
  • IMPORTANT: Makes MANY more high energy electron carrier (NADP and FADH2) for making a lot of ATP in the final step
• Aerobic Cellular Respiration

  • 3 steps in Aerobic CR
  • Electron Transport Chain
  • After the Krebs Cycle all the high-energy electrons stored in NADH and FADH2 are donated and passed by one protein carrier to the next in a chain. This happens in the inner membrane of the mitochondria.
  • Every pair of electrons released from NADH and FADH2 and passed through the chain creates energy to form 2 ATP molecules from ADP+
  • Oxygen is required for the chain to work and make ATP - water is formed as waste and released into the cell
• Aerobic Cellular Respiration

  • The Totals
  • Glycolysis produces just 2 ATP molecules per molecule of glucose
  • Energy Totals in Aerobic Respiration
  • Glycolysis produces just 2 ATP molecules per molecule of glucose
  • The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP
• Anaerobic Respiration (Fermentation)

  • When oxygen is not present, cells preform anaerobic respiration (A.K.A fermentation)
  • There are two types of fermentation, Lactic Acid and Alcoholic
• Anaerobic Respiration (Fermentation)

  • Lactic Acid Fermentation
  • During strenuous exercise, muscles cannot get oxygen into the body fast enough as the need for ATP increases
  • Muscle cells switch from CR to anaerobic respiration
  • Glucose is not completely broken down and lactic acid builds up in muscles & causes "the burn" and fatigue during exercise
  • Other uses:
  • Turn cabbage into sauerkraut
  • Soybeans into soy sauce
  • Some cheeses & yogurt
• Anaerobic Respiration (Fermentation)

  • Alcoholic Fermentation
  • Yeasts and a few other microorganisms use alcoholic fermentation
  • Forms ethyl alcohol and carbon dioxide as wastes
  • This process makes alcoholic beverages like beer and wine
  • Helps bread rise (carbon dioxide gas)
• Total Energy Gain in Anaerobic vs Aerobic Respiration

  • 1 molecule of glucose broken down and releases energy for 2 ATP and lactic acid or alcohol
  • Not a lot of ATP for one molecule of glucose (compared to aerobic = 36 ATP per glucose) which is better than no ATP!