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HOW CELLS RELEASE
ENERGY
Chapter 7
All cells (prokaryotic & eukaryotic)
require energy to:
 combat
entropy
 carry out day-to-day functions
 repair/replace worn out organelles
 reproduce
What form of energy do cells use?
ATP
How do cells obtain ATP?
All cells must make their own ATP
from nutrients they have either
synthesized (autotrophs) or consumed
(heterotrophs).
Most cells break down nutrients to
make ATP by:
 Cellular respiration (aerobic process)
 Fermentation (anaerobic process)
A. Cellular Respiration (aka. Aerobic
Respiration)
Biochemical pathways that extract
energy from nutrients, in the
presence of oxygen.
Occurs in cells of most eukaryotes &
some prokaryotes.
General equation for cellular respiration
of glucose:
C6H12O6 + 6O2  6CO2 + 6H2O + 30 ATP
Cellular respiration occurs in 3
stages:
Eukaryotic cells
Cytoplasm
Prokaryotic cells
Glycolysis
Krebs Cycle
Mitochondria
Cytoplasm
Electron
Cell membrane
Transport Chain
1. Glycolysis (“glucose-splitting”)
Glucose (6C) is split into two pyruvate
(3C) molecules.
 does not require oxygen
 energy harvested/glucose:
2 ATP (via substrate-level
phosphorylation)
2 NADH (actively transported into
mitochondria of eukaryotic cells)
First half of
glycolysis
activates
glucose.
Second half
of glycolysis
extracts
energy.
Pyruvic acid
must be
converted to
Acetyl CoA
before it can
enter Krebs
cycle.
2. Krebs Cycle (aka. citric acid cycle)
Acetyl CoA is broken down completely
to CO2.
 cells use carbon skeletons of
intermediates to produce other
organic molecules (amino acids).
 energy harvested per acetyl CoA:
1 ATP (via substrate-level
phosphorylation)
3 NADH
1 FADH2
Thus far, how much useable energy
has been produced from the
breakdown of 1 glucose molecule?
4 ATPs
Need the electron transport chain
to harvest potential energy in
NADHs & FADH2s.
3. Electron Transport Chain (ETC)
Series of proteins & electron carriers
embedded in the inner mitochondrial
membrane (eukaryotes) or cell
membrane (prokaryotes).
 O2 is the final electron acceptor
 H2O is the final product
 energy harvested/NADH: 2.5 ATPs
(via chemiosmotic phosphorylation)
 energy
harvested/FADH2: 1.5 ATPs
(via chemiosmotic phosphorylation)
How many ATPs can 1 glucose yield?
Can cells use proteins & lipids to
produce energy?
B. Fermentation
Biochemical pathways that extract
energy from nutrients, in the
absence of oxygen.
1. Alcoholic fermentation
Pyruvic acid is broken down to ethanol
and carbon dioxide.
Ex. yeast (used in production of baked
goods & alcoholic beverages)
2. Lactic acid fermentation
Pyruvic acid is broken down to lactic
acid.
Examples:
 certain bacteria (used in production of
cheese & yogurt)
 human
muscle cells in oxygen debt
Photosynthesis, glycolysis & cellular
respiration are interrelated.