CELLULAR RESPIRATION: BASIC FACTS
I.
General Characteristics of Cellular Respiration
A. Definition: the process by which the chemical bonds of organic molecules (like glucose)
are broken; energy is released and stored as ATP (Adenosine Triphosphate).
1. Occurs in both plant and animal cells
2. Occurs on the surface of and inside the mitochondria (this is why the
mitochondria is nicknamed the “powerhouse of the cell”).
3. ¼ of a mitochondrion is composed of enzymes.
4. Equation:
Glucose
oxygen
enzymes
C6H12O6 + 6O2
II.
water
carbon dioxide
energy
6H2O + 6CO2 + 36 ATP
Steps of Cellular Respiration
A. Cellular respiration always starts with GLYCOLYSIS
1. First step is called glycolysis
A. Glucose is broken down into two pyruvic acids (AKA pyruvates)
C6H12O6
2 Pyruvic acids + NADH
B. Occurs in the absence of oxygen (anaerobic process)
C. Occurs in the cytoplasm of the cell
2. FERMENTATION occurs if the process continues without oxygen (that is what
anaerobic means, “without oxygen”)
A. In plants and yeast, fermentation produces ethyl alcohol
B. In animals, fermentation produces lactic acid (lactic acid in muscles is
responsible for muscle fatigue, and the soreness you feel afterward!)
GLYCOLYSIS + FERMENTATION = ANAEROBIC RESPIRATION
3. Fermentation Equations:
Alcoholic Fermentation:
Pyruvic Acid + NADH
alcohol + CO2 + NAD+
Lactic Acid Fermentation:
Pyruvic Acid + NADH
lactic acid + NAD+
B. AEROBIC RESPIRATION occurs if oxygen is present at the end of glycolysis.
1. Equation:
enzymes
C6H12O6 + 6O2
2.
3.
4.
5.
6H2O + 6CO2 + 36 ATP
Occurs in the presence of oxygen (that is what aerobic means)
Occurs in the folds of the mitochondria (called cristae)
The cristae contain the enzymes needed for aerobic respiration to take place
Aerobic Respiration yields a great deal of energy and is much more efficient
than anaerobic respiration
III.
Overview of Aerobic Cellular Respiration – 3 Steps total
1. Glycolysis – this is the first step in both aerobic and anaerobic cellular
respiration [remember: if no oxygen is present, fermentation is next (anaerobic
respiration)]
2. Krebs Cycle – during the Krebs Cycle, pyruvic acid is broken down into *citric
acid* and then into **carbon dioxide** in a series of energy-extracting reactions.
A large amount of high-energy electrons are produced and released in carriers
(the carriers are NADH and FADH2).
*Because of this, sometimes this is referred to as the Citric Acid Cycle*
**This is where all the carbon dioxide we breathe out comes from**
3. Electron Transport Chain – uses the high-energy electrons from the Krebs
Cycle to convert ADP back into ATP. Occurs within the inner membrane of the
mitochondria (the cristae)
IV.
ADENOSINE TRIPHOSPHATE (A.T.P.)
1. This is the “currency” used by cells as the actual energy source to carry out daily
life activities.
2. Made up of three things:
A. Adenine
B. Ribose (a 5-carbon sugar)
C. 3 Phosphate groups
3. The feature of ATP that makes it so special is the extremely high-energy bond
that attaches the 3rd phosphate group, and the fact that ATP is easily regenerated.
4. Once broken, that 3rd phosphate group’s bond releases tremendous amounts of
energy that will be used to carry out daily life activities (like growth,
development, reproduction, repair, response, etc.)
This is what a molecule of ATP looks like: