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8.1 Cellular Respiration                                 http://home.earthlink.net/~dayvdanls/index.html

1. State that oxidation involves the loss of electrons from an element, whereas reduction involves gain in electrons; and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen.

Oxidation Reduction electrons loss gain hydrogen loss gain energy loss gain oxygen gain loss 2. Outline the process of glycolysis, including phosphorylation, lysis, oxidation, and ATP formation.

click for an animation of glycolysis: http://instruct1.cit.cornell.edu/courses/biomi290/ASM/glycolysis.dcr

• glycolysis: takes place in the cytoplasm
• phosphorylation: glucose is reduced with the addition of 2 ATP
• lysis: glucose is split into two 3-carbon molecules
• oxidation: glucose is oxidized to pyruvate; NAD+ is reduced to NADH + H+
• ATP formation: energy released from glucose produces 4 ATP
• Net gain: 2 ATP, 2 NADH + H+, 2 pyruvate

4. Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain, and the role of oxygen.

link reaction: oxidative decarboxylation of pyruvate:

• each 3-carbon pyruvate loses 1 CO2
• forming a 2-carbon acetyl fragment, carried by CoA as acetyl-coenzyme A
• and NADH + H+

Krebs cycle:

• 2-carbon acetyl joins with 4-carbon molecule, forming 6-carbon molecule,
• which is oxidized, releasing 2 CO2,
• allowing reduction of ADP to ATP, FAD to FADH2, 3 NAD to 3 NADH + H+

electron transport chain (ETS):

• mitochondrial inner membrane proteins form a transport chain for electrons and protons
• NADH + H+ arrives at the first carrier and transfers 2 e-s and 1 H+
• another H+ is picked up from the matrix solution
• the 2 e-s and 2 H+s are carried from the inner to outer face,
• where the 2 H+s are deposited in the intermembrane space;
• the 2 e-s return, pick up another pair of H+s and repeat the trip 2 more times,
• for a total of 3 round trips;
• FADH2 enters into the ETS further along,
• and thus pumps only 2 pairs of H+s into the intermembrane space

oxygen:

• oxygen is the final electron acceptor at the end of the ETS;
• as oxygen accepts a pair of electrons, it also accepts two protons,
• which join with the electrons to produce the two hydrogen atoms,
• thus forming water

click for an animation of the ETS: http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/oxidative/oxidativephosphorylation.html

5. Explain oxidative phosphorylation in terms of chemiosmosis.

click for an animation of the ETS: http://www2.nl.edu/jste/electron_transport_system.htm

• the effect of the ETS proton pump was to concentrate H+s in the intermembrane space,
• where pH = 4 (compared to matrix, pH = 8);
• this proton gradient is an electrochemical imbalance;
• as H+s leak from the intermembrane space through special protein complexes back into the matrix,
• the energy dissipated is used by ATP synthetase to convert 1 ADP to 1 ATP for each pair of H+s;
• thus, each NADH + H+ pumped 3 pairs of H+s, which produces 3 ATP,
• and each FADH2 pumps 2 pairs of H+s, which produces 2 ATP

6. Explain the relationship between the structure of the mitochondrion and its function.

outer membrane:

• impermeable to H+s,
• facilitates diffusion of pyruvate,
• shuttles 2 e-s from glycolytic NADH + H+ to inside of mitochondrion

intermembrane space:

• low pH = high concentration of H+s from ETS/proton pump

inner membrane:

• folded into cristae, increasing SA for ETS and ATP synthetase;
• permeable to H+s

matrix:

• contains enzymes for oxidative decarboxylation and Krebs cycle

• VIII. CATABOLISM OF OTHER MOLECULES

  1. Introduction
     1. Respiration is flexible in the fuels it can oxidize to make ATP.
     2. Organisms obtain most calories from fats, proteins, disaccharides and polysaccharides.
     3. These complex molecules must be enzymatically hydrolyzed into simpler molecules or monomers that can enter an intermediate reaction of glycolysis or the Krebs cycle.
  2. Carbohydrates
     1. Glycolysis can accept a wide range of carbohydrates for catabolism.
     2. Starch is hydrolyzed to glucose in the digestive tract of animals.
     3. In between meals, the liver hydrolyzes glycogen to glucose.
     4. Enzymes in the small intestine break down disaccharides to glucose or other monosaccharides.
  3. Proteins
     1. Proteins are hydrolyzed to amino acids.
     2. Organisms synthesize new proteins from some of these amino acids.
     3. Excess amino acids are enzymatically converted to intermediates of glycolysis and the Krebs cycle. Common intermediates are pyruvic acid, acetyl CoA and alpha-ketoglutaric acid.
     4. This conversion process deaminates amino acids, and the resulting nitrogenous wastes are excreted.
  4. Fats
     1. Fats are excellent fuels because they are rich in hydrogens with high energy electrons.
     2. Oxidation of one gram of fat produces twice as much ATP as a gram of carbohydrate.
     3. Fat sources may be from the diet or from storage cells in the body.
     4. Fats are digested into glycerol and fatty acids.
     5. Glycerol can be converted to glyceraldehyde phosphate, an intermediate of glycolysis.
     6. Fatty acids are converted into acetyl Ca which can enter the Krebs cycle.