1. Glycolysis, Link Reaction, and Krebs
Cell Respiration part 3

2. Respiration Process in which organic molecules act as a fuel
Main fuel molecule: Glucose
Secondary sources of fuel: fatty acids, glycerol, amino acids
Organic molecules broken don in a series of stages
Release chemical potential energy
Used to synthesize ATP
Four stages of glucose break down:
Glycolysis
Link Reaction
Krebs Cycle
Oxidative Phosphorylation

3. Review Phosphorylation
Conversion of an energy- rich, but not very reactive, molecule into one that is MUCH more reactive AND whose chemical potential energy can be released and trapped more efficiently

4. CoEnzymes a nonprotein compound
required for an enzyme to be able to catalyze a reaction
NOT a substrate
Do not become part of the reaction
bind with the protein molecule (apoenzyme) to form the active enzyme (holoenzyme)
bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction
function as intermediate carriers of electrons, specific atoms or functional groups that are transferred in the overall reaction
Examples: NAD, NADP, FAD, CoEnzymeA

5. NAD (Nicotinamide adenine dinucleotide)
Co-enzyme
Carrier molecule
2 linked nucleotides, each with a ribose
One nucleotide has adenine
One had nictinamide ring (this accepts hydrogen ion and 2 electrons
Becomes “reduced” because it carries hydrogen ions and electrons
“reduced NAD” aka NADH
Removal of hydrogens is called an oxidation reaction
Molecule that picks up the hydrogens is “REDUCED”

6. Other important coenzymes: FAD and NADP
NADP (nicotinamide adenine dinucleotide phosphate)
Slightly different form of NAD in photosynthesis
Has a phosphate group instead of a hydrogen on carbon 1 of the ribose rings
Called NADP (reduced NADP is NADPH)
FAD (flavin adenine dinucleotide)
Similar in function of NAD
Used in Krebs
Made of two nucleotides
one nucleotide containing ribose and adenine
One nucleotide containing unusual structure involving a linear molecule ribitol (instead of ribose)

7. Glycolysis
Means “splitting glucose”
Starting point for respiration in aerobic AND anaerobic conditions
Aerobic with oxygen
Anaerobic no oxygen present
Location: cytoplasm (cytosol) of cell
Multi-step process
Each step is catalyzed by a specific enzyme (IMPORTANT!!!)
ONE six carbon molecule splits into TWO three carbon molecules called PYRUVATE
Energy required to begin (2 ATPs)
Energy released at end (4 ATPs)
Net total: 2 ATPs
In order for Glycolysis to continue, we MUST have steady supply of NAD

8. ATP ATP 2 ATP 2 H 2 ATP Glucose (Hexose) (6C) Fructose phosphate (6C)
Fructose biphosphate (6C)
2 molecules of triose phosphate (3C)
Intermediates
2 molecules of pyruvate (3C)
ATP
ATP
2 ATP
2 NAD
2 H
2 Reduced NAD
2 ATP

9. Glycolysis
First stage Phosphorylation with ATP (substrate level phosphorylation)
1st ATP to glucose glucose phosphate  fructose phosphate
2nd ATP to fructose phosphate  Fructose bisphosphate
Fructose bisphosphate immediately breaks up into TWO molecules of triose phosphate
Inorganic phosphate added to each triose phosphate creates triose bisphosphates
Second Stage Dehydrogenation
A phosphate is removed from each triose bisphosphate--. Back to 2 triose phosphates
Hydrogen is removed from each triose phosphate by NAD  2 reduced NAD molecules
Reduced NAD travels to mitochondria to be used in oxidative phosphorylation
Third Stage Dephosphorylation
Phosphate from triose intermediates removed to yield TWO more ATP molecules
Product: 2 molecules of pyruvate (contains A LOT of chemical potential energy)
When oxygen available, some of energy will be released via Krebs cycle and oxidative phosphorylation

12. Pyruvate + CoA + NAD   acetyl CoA + CO2 + reduced NAD
The LINK Reaction
Pyruvate enters mitochondria via ACTIVE transport
Through outer AND inner membranes of mitochondria into MATRIX
In the matrix, pyruvate is:
DECARBOXYLATED
Carbon dioxide molecule removed
Diffuses out of mitochondria
DEHYDROGENATED
Hydrogen is removed (via NAD)
Combined with Coenzyme A
Makes a molecule called ACETYL Coenzyme A

14. CoEnzyme A Complex molecule Composed of:
nucleoside
Adenine + Ribose
Vitamin
Pantothenic acid
Acts as a carrier of acetyl groups to the Krebs cycle

15. Other sources of Acetyl CoEnzyme A
Proteins
Amino acids
Fatty Acids
Broken down in mitochondria in a cycle of reactions in which each turn of cycle shortens the fatty acid chain by a two-carbon acetyl group
Each acetyl group can react with CoEnzyme A  Acetyl CoEnzyme A
Acetyl CoEnzyme A can now enter Krebs Cycle
Oxygen MUST be present
In order to BURN fat (break of those acetyl groups in a fatty acid) you must conduct AEROBIC types of exercise

16. Krebs Cycle Citric Acid Cycle Tricarboxylic Acid Cycle (TCA)
1937, Hans Krebs
Closed pathway of enzyme controlled reactions
Location : Matrix of Mitochondria
Most important aspect: the release of hydrogens (that go onto oxidative phosphorylation to make ATP)
In:
Acetyl CoEnzyme A Enters
Out:
Carbon Dioxide released
Reduced NAD released
Reduced FAD released
ATP is made

17. Steps of Krebs Cycle
Acetyl CoEnzyme A combines with four- carbon compound (OXALOACETATE)  six- carbon compound (CITRATE)
Citrate is DECARBOXYLATED (carbon dioxide removed) then DEHYDROGENATED (hydrogen removed by NAD and FAD)
OXALOACETATE regenerated at the end of the cycle so it can happen all over again
Products:
ONE turn of Krebs yields:
TWO carbon dioxide molecules
ONE reduced FAD
THREE reduced NAD
ONE molecule of ATP (via intermediate)