Intro to Cellular Respiration, Glycolysis & Krebs CycleChapter 9.1-9.3

LEARNING TARGET 1

I can explain how catabolic pathways yield energy by oxidizing organic fuels.

Cellular Respiration

• C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy (ATP)• Type of coupled oxidation-reduction (redox) reaction• OIL RIG• Oxidation Is Losing electrons• Reduction Is Gaining electrons

Electron Carrier Molecules• B-vitamin coenzymes• NAD+ + 2H → NADH + H+

• FAD + 2H FADH2

oxidized form

reduced form

reduced form

oxidized form

Cellular Respiration Overview• Occurs mainly in mitochondria (begins in cytoplasm)1. Glycolysis

1. “Prep Step”2. Krebs Cycle (Citric Acid Cycle)3. Oxidative Phosphorylation & Chemiosmosis (ETC)

LEARNING TARGET 2

I can explain how glycolysis harvests chemical energy by oxidizing glucose into pyruvate.

1. Glycolysis• “glykos” = sweet; “lysis” = split apart• Occurs in cytosol• Aerobic or anaerobic process

• Glucose is oxidized into 2 pyruvate• Requires 2 ATP to get started• Produces 4 ATP (net gain 2 ATP)• Produces 2 NADH

Summary of Glycolysis• One glucose (6C) converted

into two pyruvates (3C)• Net yield of 2 ATP• 2 NAD+ are reduced into 2

NADH & 2 H+

LEARNING TARGET 3

I can explain how the citric acid (Krebs) cycle completes the energy yielding oxidation of organic molecules.

Oxidation of Pyruvate to Acetyl CoA(“Prep Step”)

• Preps pyruvate for Krebs Cycle (linking glycolysis and citric acid cycle)

• Occurs in mitochondria• 3 step oxidation process1. Carboxyl group (COO) is removed

from pyruvate• Releases 1 CO2 (per pyruvate)

2. Remaining 2C fragment is oxidized, producing acetate and NADH• Creates 1 NADH (per pyruvate)

3. Coenzyme A attaches to acetate, forming Acetyl CoA• Forms 1 Acetyl CoA (per pyruvate)

“Prep” Step Summary• Started with 2 pyruvates• Ended with:• 2 CO2 released to air, • 2 NADH that will go to ETC,

and • 2 Acetyl CoA molecules (2

C) that will move on to Krebs Cycle in the mitochondrial matrix

2. Krebs Cycle (AKA Citric Acid Cycle)• Complete oxidation of

glucose• Cycle because it occurs

twice – once for each Acetyl CoA

• 8 step pathway occurring in mitochondrial matrix• Each catalyzed by specific

enzyme• Step-wise catabolism of 6C

citrate molecule• All remaining H, O, and C

from glucose released

Krebs Cycle Summary• At the end of 2 turns of the

Krebs cycle: • 6 NADH are generated • 2 FADH2 are generated • 2 ATP are generated • 4 CO2 are released

• If the yield is only 2 ATP, then why?• Value of NADH and FADH2

• Krebs cycle produces large quantities of these electron carriers, which are reduced molecules and store energy that will go to the ETC

• ETC will produce mass ATPs

Glucose is now completely oxidized

Count the carbons!