Releasing Chemical Energy
• All organisms must have energy to
carry out life processes.
• Where does this energy come from?
Autotrophs collect energy
from the sun and store it as
The Need for Energy
• No Energy
= no work
•Energy = Work
Metabolism is all of the chemical
reactions in the body.
These reactions are either:
1. Synthesis – combining small molecules to
make complex molecules OR
A + B ---> AB
8 Fe + S8 ---> 8 FeS
2. Decomposition reactions – breaking down
molecules into simpler forms.
AB ---> A + B
2 H2O ---> 2 H2 + O2
• Synthesis reactions require energy –
• Decomposition reactions release
• This energy can be used to make ATP
• ATP is a small, useable packet of
• Cell Respiration is a decomposition reaction
that provides the energy cells need to
• In this series of reactions, sugars, proteins,
and lipids are broken down (decomposed)
and energy is released.
Types of Cellular
There are two types of cell respiration
– aerobic and anaerobic.
1. Aerobic respiration occurs in the
presence of oxygen.
2. Anaerobic respiration occurs in the
absence of oxygen.
Raw Materials for Cell
• What are the raw
materials for cell
• How does the food
become the raw
•Food is digested into
Glucose and Glycogen
• Glucose is the form in
the blood stream.
• Glycogen is the form
in which it is stored in
• Glycogen is stored in
the liver and muscles.
are the energy
• Cellular Respiration occurs in the mitochondriaan organelle in the cytoplasm of cells.
• an outer membrane that encloses the entire
• an inner membrane that encloses a fluid-filled
• between the two is the intermembrane space
• the inner membrane is elaborately folded with
shelf-like cristae projecting into the matrix.
Stages of Cell Respiration
2. Kreb’s Cycle
3. Electron Transport System
• Glycolysis happens in the cytoplasm.
• Glucose is split into 2 three-carbon
• Enzymes partially oxidize glucose and this
partial oxidation releases energy that
forms a small amount of ATP.
• This is an anaerobic process and 2 net ATP
• This ATP is used to start the Kreb’s Cycle.
• The Kreb’s cycle completes the
decomposition and oxidation of glucose to
• The carbon dioxide is released as a gas.
• The oxidation of one glucose molecule
yields up to 38 ATP molecules under ideal
conditions (this occurs infrequently)
• The reaction of acetyl CoA with
oxaloacetate starts the cycle by producing
citrate (citric acid).
• In each turn of the cycle, two molecules of
CO2 are produced as waste products, plus
three molecules of NADH, one molecule of
GTP, and one molecule of FADH2.
• The number of carbon atoms in each
intermediate is shown in a yellow box. (see
picture next slide)
Krebs Cycle Animations
The Electron Transport Chain
• It is composed of the mitochondrial
enzymes that transfer electrons from one
complex to another, eventually resulting in
the formation of ATP.
• In the first part, electrons are transferred
from protein to protein and energy is lost as
free energy along the way.
• This free energy is used to move protons
into the matrix of the mitochondria.
• As they pass through the matrix, they pass
through the ATP –synthetase enzyme.
• This causes a charge differential (gradient)
which drives the forming of ATP from ADP.