BIO 104 5/28/96

Cellular Respiration:
1. To live is to work.
     -all cells require energy
     -energy comes from external sources and begins with sunlight
     -cells harvest energy from food
     -process of cellular respiration produces CO2, H2O and energy
2. What is ATP?
     -adenosine triphosphate
     -contains:
          1. ribose sugar 
          2. adenine 
          3. phosphate group (unstable)
               -energy stored in chemical bonds and is converted to ATP
               -used to drive active transport, power movements, etc.
     -formed from ADP
          ADP + P - ->ATP
3. How cells make ATP
     -substrate level phosphorylation  (e.g., glycolysis)
     See Figure 7.2
          -Phosphate moves from PEP to ADP to form ATP
     -chemosmosis (e.g., citric acid cycle, electron transport)
     See Figure 7.3
          Sources for ATP producing Electrons
          1. sunlight (ATP formation in chloroplasts)
          2. energy of chemical bonds
4. What is cellular respiration?
     -conversion of chemical energy into ATP
     -Three stages:
          1. glycolysis converts glucose into 2 three carbon 
          molecules (Pyruvate) PLUS (substrate level phosphorylation of ATP)
          2. citric acid cycle breaks down glucose into CO2
          3. electron transport chain passes electrons down a 
          chain to eventually bond with hydrogen molecules to
          form water (part of chemiosmosis)
     SEE FIGURE 7.12
5. Substrate Level Phosphorylation
     -glycolysis "splitting of sugar"
     -occurs in cytoplasm of the cell
     -usually product: 2 pyruvate molecules
     -energy costs: 2 ATP molecules
     -energy gain: 4 ATP molecules
          -glycolysis results in a gain of 2 ATP molecules
     -inefficient method
     
     Energy Investment Phase (glycolysis)
     1. Glucose changes into Glucose-6-phosphate when ATP 
     phosphoralates glucose (forming ADP)
     2. Glucose-6-phosphate, with assistance of an enzyme that
     rearranges chemical bonds, turns into fructose-6-phosphate
     3. Fructose-6-phosphate turns into fructose-1-6-di-
     phosphate, because it takes a phosphate from ATP when it
     changes over to ADP
     4. Then that fructose molecule is converted to dehydroxy-
     acetone phosphate because a enzyme cleaves the molecule
     5. Dehydroxyacetone phosphate is converted to 
     glyceraldehyde-3-phosphate (G3P).  It must be in this form
     to continue the process.
     Energy Yielding Phase
     6. G3P gets a phosphate from the cytoplasm and gives a H
     atom to make NAD+ into NADH
     7. 1.3-diphosphoglycerate (DPG) gives a phosphate to form 
     ATP and is reduced to 3-phosphoglycerate (3PG)
     8. The carbon relocates in the 3PG to form 2-phospho-
     glycerate.
     9. The 2-phosphoglycerate gives off water and becomes
     phosphoenolpyruvate (PEP)
     10. PEP gives off a phosphate to form ATP and form 
     Pyruvate
6. Only 2 ATPs?
     -glycolysis releases a very small % of available energy
     -remaining energy stored in pyruvate
     -If oxygen is present the pyruvate will enter the
     mitochondria and enter the citric acid cycle and electron 
     transport cycle
     SEE FIGURE 7.6
7. What happens to Pyruvate
     -If oxygen is present it is converted to Acetyl-CoA and 
     enters citric acid cycle
     -If oxygen is not present is will become lactic acid and
     /or ethanol
8. Anaerobic Metabolism (fermentation) occurs when oxygen is not 
   available.
     -ethanol fermentation (Yeast)
          -Pyruvate is converted to acetaldehyde, by removal of
          CO2.  Which then accepts H from NADH to produce ethyl alcohol.
     -Lactic Acid Fermentation
          -takes H from NADH and attaches it to pyruvate to produce
          lactic acid (Muscles)
9. Oxidative Respiration
     -aerobic metabolism
     -occurs in mitochondria
     -conversion of pyruvate to Acetyl-CoA
     -citric acid cycle
     -electron transport