Cellular Respiration
Cellular Respiration
A.
In cells, the chemical energy from food is broken down into other forms of energy
through a process called Cellular Respiration which occurs as a series of reactions.
B.
The energy in food is measured in calorie. This is the amount of energy needed to raise
the temperature of 1 gram of water by 1degree Celsius.
C.
The first step in respiration is Glycolysis (takes place in cytoplasm) in which one
molecule of glucose is broken into 2 molecules pyruvic acid (3-carbon compound), an
electron carrier called NADH and ATP. It does not require O2.
All living things carry out Glycolysis – It does not need O2, takes place in cytoplasm.
Net gain = 2 ATP
Advantage
1) Fast process
1000 ATP/millisecond
2) No Oxygen required
Disadvantage
When large amount of
ATP is produced, all
NAD+ are filled up with
electrons & ATP
production stops
D.
E.
The reactions then continue as aerobic or anaerobic respiration.

Aerobic pathway - requires the presence of O2.
Glycolysis is followed by Kreb cycle and and Oxidative phosphorylation (Electron
transport chain + Chemiosmosis) .

Anaerobic pathway – does not require O2.
Glycolysis is followed by Fermentation.
Aerobic Respiration – Glycolysis, Kreb cycle (citric acid cycle), and Oxidative
phosphorylation (Electron transport chain + Chemiosmosis) together make up
cellular respiration.

Cellular respiration is a process that releases energy by breaking down food in
presence of O2 (electron acceptor).

The purpose of cellular respiration is to capture the energy from food (glucose) a
little at a time and hold it in the chemical bonds of ATP.

C6H12O6 + 6O2 ---------- 6CO2 + 6H2O + Energy

Glucose is broken down in the process and recombines with oxygen to form new
substances. Energy is released.




Glycolysis takes place in cytoplasm
Kreb’s cycle takes place in mitochondrial matrix
Oxidative phosphorylation (Electron transport chain + Chemiosmosis) takes place in
cristae (inner mitochondrial membrane).
Glycolysis supplies pyruvic acid to Kreb’s cycle and high energy electrons via NADH
to electron transport chain which converts ADP into ATP.
Summary Aerobic Respiration
1.
requires the presence of oxygen, takes place in the mitochondria of the cell
2.
Glycolysis followed by Krebs cycle and Oxidative phosphorylation (Electron
transport chain + chemiosmosis)
3.
Krebs cycle converts pyruvate to ATP, CO2, NADH (carrying high energy e-)
4.
Electron transport chain and chemiosmosis produce H2O, ATP (energy).
5.
produces 36 ATP molecules and heat energy
When O2 is NOT present:
F.
Anaerobic Respiration - Glycolysis is followed by different pathway, combined
together they are known as Fermentation.



During Fermentation, cells convert NADH to NAD+ by passing high energy electrons
back to pyruvic acid allowing glycolysis to continue producing a steady supply of
ATP
The purpose of Fermentation is to replenish NAD+ so glycolysis can continue.
Anaerobic Respiration
1. does not require oxygen
2. occurs in the cytoplasm of the cell
3. energy is produced from glycolysis
4. produces only 2 ATP molecules
G.
Two types of Fermentations
1.
Alcoholic Fermentation
a.
occurs in unicellular fungi
and yeasts
b.
produces carbon dioxide
and ethanol
c.
the alcohol molecule
contains
much
unused energy
2. Lactic acid Fermentation
a. occurs in animal cells
b. pyruvate from glycolysis is converted to lactic acid
c. occurs during strenuous exercise when muscles run out of oxygen
d. only 2 ATP are produced