Lecture #4
• Chapter 9~
Cellular Respiration:
Harvesting Chemical
Energy
Date _________
Things to Know
• The difference between fermentation and cellular respiration
• The role of glycolysis in oxidizing glucose to 2 molecules of
pyruvate
• The process that brings pyruvate from cytosol into the
mitochondria and introduces it into the citric acid cycle
• How the process of chemiosis utilizes the electrons from
NADH and FADH2 to produce ATP
Catabolic Pathways
• Catabolic pathways – molecules are broken down and
their energy is released
2 Types of Catabolic Pathways
- fermentation – partial degradation of sugar without the
use of oxygen
- cellular respiration – the most efficient catabolic
pathway, where oxygen is used as a reactant with organic
fuel (called aerobic respiration because it uses oxygen)
Some Background
• Carbohydrates, fats and protein can all be broken down to
release energy in cell. resp., but glucose is the primary
molecule used in cell. resp.
Here’s the equation:
C6H12O6 + 6 O6  6 CO2 + 6 H2O + Energy
The energy released from this is stored by phosphorylating
(adding phosphate) ADP into ATP
Redox Reactions
• The reactions in cell. resp. are a type called oxidationreduction (redox), where electrons are transferred from
one reaction to another
- loss of electrons from reactant are called oxidation
- gain of electrons is
reduction
Redox in Cell. Resp.
C6H12O6 + 6 O6  6 CO2 + 6 H2O + Energy
NAD+ and NADH
• NAD+ is an electron carrier
• NAD+ accepts 2 electrons to form NADH
Cellular Respiration
• There are 3 steps to cellular respiration:
- Glycolysis
- Citric Acid Cycle
- Oxidative Phosphorylation: electron transport &
chemiosis
Glycolysis
• Glycolysis occurs in the cytosol
(cytoplasm)
• Glucose is broken down into 2
pyruvate acid molecules
• In the “Energy Investment phase” 2
ATP are used
• In the “Energy Payoff phase” 4 ATP
are produced
• The Results: 2 ATP, 2 pyruvate acid,
2 NADH
Citric Acid Cycle (aka Kreb’s Cycle)
• Pyruvate acids use transport
protein to enter the
mitochondria
• In the process, pyruvate
acid is converted by
Coenzyme A to make
Acetyl CoA
• Now this Acetyl CoA enters
the citric acid cycle
Citric Acid Cycle (aka Kreb’s Cycle)
• 2 Acetyl CoA enters the cycle and
each go into the cycle
• Results (from 2 rounds): 4 CO2, 6
NADH, 2 FADH2, and 2 ATP
produced
• * note 1 glucose molecule (C6H12O6)
makes 2 rounds
• **note CO2 released is what you
breathe out
• *** note NADH and FADH2 are
electron carriers and will produce a
bunch of ATP in Oxidative
Phosphorylation
Oxidative Phosphorylation
Electron Transport Chain
- embedded in the inner
membrane of the mitochondria
- 3 proteins work as hydrogen
pumps
- step by step process that
pumps H+ that is powered by
the electron carriers NADH and
FADH2
- H2O is produced in Electron
Transport Chain (NO ATP
produced!!)
Oxidative Phosphorylation
Chemiosmosis
- the H+ ions are pumped back in
chemiosmosis through a protein
called the ATP Synthase
- ATP is produced from ADP in
chemiosmosis
IN TOTAL
- Oxidative Phosphorylation
produced 32-24 ATP
- which means cellular respiration
makes a total of 36-38 ATP (2 from
Glycolysis and 2 from Kreb’s Cycle)
Review: Cellular Respiration
•
•
•
•
Glycolysis:
2 ATP (substrate-level
phosphorylation)
Kreb’s Cycle:
2 ATP (substrate-level
phosphorylation)
Electron transport & oxidative
phosphorylation:
2 NADH (glycolysis) = 6ATP
2 NADH (acetyl CoA) = 6ATP
6 NADH (Kreb’s) = 18 ATP
FADH2 (Kreb’s) = 4 ATP
38 TOTAL ATP/glucose
2
Fermentation
• Fermentation is a process to make ATP without the presence of
oxygen
• Glycolysis still occurs, but that’s the only similarity with cell. resp.
• After glycolysis there’s 2 options:
- alcohol fermentation – pyruvate is converted to ethanol
(alcohol), releasing CO2 and NADH
- lactic acid fermentation – pyruvate is reduced by NADH and
lactic acid is waste product
• Facultative anaerobes are organisms that prefer cell resp., but
can do fermentation if no oxygen available