Homework questions to be emailed to valenciabiologyhw@gmail.com

1. Explain why ATP is required for the preparatory steps of glycolysis

2. Describe how the carbon skeleton of glucose changes as it proceeds through glycolysis

3. Explain how the exergonic "slide" of electrons down the electron transport chain is coupled to the endergonic production of ATP by chemiosmosis

4. Describe the fate of pyruvate in the absence of oxygen

5. Distinguish between aerobic and anaerobic metabolism

Respiration is an Oxidation-Reduction process
•Oxidation-reduction (Redox) reactions are chemical reactions where there is a transfer of one or more electrons (e-) from one reactant (donor) to another (recipient).
•Oxidation and reduction occur together.
Respiration is an Oxidation-Reduction process

– Loss of electrons from one substance = oxidation.
– Addition of electrons to a substance = reduction.
– Oxidizing agent - accepts electrons.
– Reducing agent - gives up electrons.
•Oxygen - very strong oxidizing agent (hence: “oxidizing” or “oxidation”)
Redox reactions
E.g. Na + Cl -> Na+ + Cl-
The reactions of respiration
•Glycolysis
•Krebs/Tricarboxylic acid (TCA) Cycle
•Electron transport chain & oxidative phosphorylation
Respiration is a series of reactions
•The cell doesn’t want to release all of the energy trapped in food at once.
Cell Respiration: Two Types
• Anaerobic: process that breaks down organic molecules (food) partially and produces some (ATP) without the assistance of oxygen.
– Bacteria & Yeast.
• Aerobic: process that breaks down organic molecules (food) completely and produces (ATP) with the assistance of oxygen.
– All eukaryotes.

Aerobic respiration
• Cellular respiration is similar to the combustion of gasoline in an automobile engine.
• The overall process is:
– Organic compounds + O2 -> CO2 + H2O + Energy
• Carbohydrates, fats, and proteins can all be used as the fuel, but it is traditional to start learning with glucose.
– C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)
Gylcolysis(stage 1): Splitting Sugar
•Process that begins with glucose and occurs in the cytoplasm
•Consumes 2 ATP
•Produces 2 NADH, 4 ATP, 2 Pyruvate molecules


•Glycolysis
•Anaerobic Phase
•Cytosol
•No CO2 Loss
•Very Little Energy Released
•Prepares Carbon Molecules
•for Complete Oxidation

Fermentation: Two types
•Alcoholic: produces ethyl alcohol (2C’s) and CO2
– Champaign
•Lactic Acid (3C’s)
– Yogurt
– Muscle Cramps
– Krebs Cycle(stage 2)
•Process that breaks down pyruvic acid (3C’s) into 3 molecules of CO2 that occurs in the matrix of the mitochondria.
•Produces 1ATP, 1FADH2, 4NADH Molecules


1  Krebs Cycle
•Reactions of Pyruvate
•Formation of Oxaloacetate
•Formation of Acetyl-CoA
•Reactions of Krebs Cycle
•Regulation of Krebs Cycle

2  Pyruvate to Oxaloacetate ®
•Pyruvate àOxaloacetate
•First step in gluconeogenesis
•Requires CO2

3  Pyruvate to Acetyl-CoA
•Reaction occurs inside mitochondria
•Partial Net Reaction:
CH3 -C(O)-COO - à  CH3 -C(O)-S-CoA + CO2
•Pyruvate oxidized: Oxidative decarboxylation
•Lipoic acid undergoes reduction of disulfide group
•Dihydrolipoic acid + FAD à lipoic acid + FADH2

4  Pyruvate Dehydrogenase
Pyruvate Dehydrogenase Complex contains three 'enzyme activities', with multiple copies of each.
•E. Coli - 24, 24, & 12 copies in a single complex
•Mammals - (20-30), 60, & (20-30) copies
Compact arrangement allows complex reaction sequence to occur very rapidly

5  Krebs Cycle reactionsKrebs
 Cycle
Net Reaction:
Acetyl-CoA
2 CO2 + CoA
GDP + Pi
GTP + H2O
3 NAD + + FAD
3 NADH + 3 H + + FADH2

6  Citrate Metabolism
Citratemit. àCitratecyt.
Citratecyt. à Oxaloacetate + Acetyl-CoA
Oxaloacetate + NADH à Malate + NAD +
Malate + NADP + àpyruvate + NADPH + CO2
•High [citrate] in cytosol only if cell's energy requirements are low.
•Acetyl-CoA and NADPH used for fatty acid synthesis
Electron Transport Chain
(stage 3)
• A series of protein molecules located with in the inner membrane (cristae) of the mitochondria.
• High energy electrons are transported from NADH & FADH2 to the ETC.
• As the electrons are transported from protein to protein, their energy is used to pump H+ions through the membrane.
• As the H+ions diffuse back into the matrix they result in the production of ATP

Key points:
• Protons are translocated across the membrane, from the matrix to the intermembrane space
• Electrons are transported along the membrane, through a series of protein carriers
• Oxygen is the terminal electron acceptor, combining with electrons and H+ ions to produce water

Key points:
4. As NADH delivers more H+ and electrons into the ETS, the proton gradient increases, with H+ building up outside the inner mitochondrial membrane, and OH- inside the membrane.

Overview of respiration reactions
– Breakdown of glucose into 2 pyruvate.
– Occurs in cell cytosol.
– No molecular oxygen involved.
•Krebs/Tricarboxylic acid (TCA) Cycle
– Decomposes pyruvate derived to CO2.
– Occurs in mitochondrial matrix.
– Produces intermediate compounds that can be used in synthetic pathways (protein, lipids).
Overview of respiration reactions
– No molecular oxygen involved.
•Electron transport chain & oxidative phosphorylation
– Generates bulk of ATP.
– Stepwise series of oxidations.
– Oxygen involved.