Cellular Respiration
Cellular Respiration…What is it?
-process by which cells make ATP by
breaking down organic compunds.
Why is it important?
-cells need usable forms of energy to
function and maintain homeostasis.
It all starts with: Glycolysis

Cellular Respiration begins with a biochemical pathway
called glycolysis. (no oxygen is present.)
-one glucose molecule is broken down (oxidized) to
produce two molecules of pyruvic acid.
-The net yield of glycolysis is two ATP molecules.
-After glycolysis, the oxidation process continues in
the presence or absence of oxygen.
Fermentation (Anaerobic) no oxygen

Fermentation occurs after glycolysis when
oxygen is absent within the cells.
-No ATP is generated. However, NAD+ is
regenerated which is needed in glycolysis.
-Two common fermentation pathways:
1. Lactic Acid Fermentation
2. Alcoholic Fermentation
1. Lactic Acid Fermentation

Enzymes convert pyruvic acid into lactic
acid.
-Lactic Acid Fermentation is important in
the manufacturing of various foods.
(yogurt, cheese)
-Athletes also experience Lactic Acid
buildup…cramping and fatigue.
2. Alcoholic Fermentation

Enzymes convert pyruvic acid into ethyl
alcohol.
-Process is done by some plants and
yeast.
-This process is important in the bread,
beer and wine industry.
Aerobic Respiration
oxygen present
Occurs in the presence of oxygen.
 Net ATP production is much greater!


Two major steps:
1. Krebs Cycle (citric acid is formed)
2. Electron Transport Chain
In prokaryotes, occurs in the cytoplasm.
 In eukaryotes, occurs in the mitochondria.

Krebs Cycle
(Citric Acid Cycle)

When pyruvic acid enters the
mitochondria, acetyl CoA is formed.

The Krebs Cycle breaks down the acetyl
CoA producing CO2 , hydrogen atoms, and
ATP. (NADH, FADH2)

Each glucose molecule yields only two
molecules of ATP through the Krebs Cycle.
Electron Transport Chain

So far, not much ATP has been produced. The Krebs
Cycle produces NADH and FADH2 which drives the
Electron Transport Chain.

Occurs in the membrane of the mitochondria. After the
ATP is produced, it diffuses into the cytoplasm.

ATP is produced by the release of hydrogen atoms from
NADH and FADH2. (chemiosmosis)

Oxygen is necessary and ends up forming water.
Final Thoughts…

Net production of ATP through aerobic
respiration…36 ATP.

The oxidation of glucose can be summarized in
the following equation:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)

Not only does Cellular Respiration provide ATP,
it also makes carbon ‘skeletons’ that can be
made into larger molecules needed by the cells.