Intro to Cellular
Respiration,
Glycolysis & Krebs
Cycle
Chapter 9.1-9.3
Review
• Ecology (Unit 2)
• Heterotrophs get free energy by eating
other organisms
• Autotrophs make their own free energy
from the sun
• Cellular Biology (Unit 4)
• Mitochondria are specialized organelles
for energy capture and transformation
Catabolic pathways yield energy by oxidizing organic fuels
SECTION 9.1
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
reduced form
oxidized form
reduced form
oxidized form
Cellular Respiration Overview
• GOAL: produce ATP (usable, free energy for the cell)
• Occurs mainly in mitochondria (begins in cytoplasm)
1. Glycolysis
1.
“Prep Step”
2. Krebs Cycle (Citric Acid Cycle)
3. Oxidative Phosphorylation & Chemiosmosis (ETC)
Addition of a Pi to ADP happens 2 ways
1. Substrate level phosphorylation
• Addition of phosphate group directly
without a proton gradient and ATP Synthase
• Enzyme-catalyzed reaction transfers Pi to ADP
• Found in glycolysis and Krebs cycle
2. Oxidative phosphorylation
• Using proton gradient created by ETC in
cristae membrane to make ATP
• ETC + Chemiosmosis = oxidative
phosphorylation
Glycolysis harvests chemical energy by oxidizing glucose
to pyruvate
SECTION 9.2
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+
After pyruvate is oxidized, the citric acid cycle completes
the energy-yielding oxidation of organic molecules
SECTION 9.3
Oxidation of Pyruvate to Acetyl CoA
(“Prep Step”)
• Preps pyruvate for Krebs Cycle
(linking glycolysis and citric acid
cycle)
• Pyruvates are transported into the
mitochondria
• 3 step oxidation process
• Each pyruvate
• Releases 1 CO2 (2 total per glucose)
• Makes 1 NADH (2 total per glucose)
• Sends 1 Acetyl CoA to Krebs Cycle
“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!