Topic 2: Molecular Biology (Student)
2.8
Essential Idea: Cell Respiration supplies energy for the functions of life.
 2.8 Cell Respiration
i.
Cell respiration is the controlled release of energy from organic compounds to produce
ATP.
o All living cells perform cell respiration in which they break down organic compounds
(ex. Glucose) to release energy. The energy is stored in the covalent bonds of the
compounds.
o Carbohydrates and lipids are the main source of energy in animals. Plants can make
their own carbohydrates and lipids by photosynthesis.
o Cell respiration uses enzymes to control the release of the energy. The energy is then
stored in the usable from of ATP.
Label the
ATP
molecule:
ii.
ATP from cell respiration is immediately available as a source of energy in the cell.
o ATP, adenosine triphosphate, is the energy supplier for the cell.
o Cells need energy for: 1. Making large molecules (DNA, RNA, Proteins). 2. Moving large
substances across membranes by active transport. 3. Moving substances like
chromosomes, and vesicles inside the cell.
o Energy is released from ATP by splitting a phosphate off to make ADP. This breaks a
bond and releases the energy. Energy is released as heat.
o ADP can then be recharged back to and ATP molecule.
 Two types of respiration: Anaerobic and aerobic
1. In anaerobic respiration, glucose is converted (in the absence of oxygen) to either lactate or
ethanol. The ATP yield is low.
- C6H12O6  2 C2H5OH + 2 CO2 + 2 ATP + ethanol
- C6H12O6  2 C3H6O3 + 2 ATP + lactate
2. During aerobic respiration, a respiratory substrate, e.g. glucose, is split in the presence of
oxygen to release carbon dioxide and water. A large number of ATP molecules are produced,
releasing the energy from the glucose.
- C6H12O6 + 6 O2  6 CO2 + 6 H2O + 36 ATP
iii.
Anaerobic cell respiration gives a small yield of ATP from glucose.
o Glucose(C6H12O6) is broken down into 2 pyruvate (pyruvic acid C3H4O3) in the
cytoplasm by the process of glycolysis. There is a net gain of 2 ATP molecules during
this. This step does not require oxygen.
o
o
o
When oxygen is not available the cell carries out anaerobic respiration and the ATP that
is made is small, but can be produced quickly.
Anaerobic respiration is useful during: 1. When short but rapid burst of ATP production is
needed; 2. When oxygen supplies run out in respiring cells; 3. In environments that are
deficient in oxygen.
The products of anaerobic respiration are not the same in all organisms.
Organism
Humans and animals
Product
Equation
Lactic acid (dissolved form lactate)
Glucose -> lactate + 2ATP
causes pain and fatigue in muscles
Yeast and plants
Ethanol and CO2 , helps make
Glucose -> ethanol + carbon dioxide +
alcohol and bread.
2ATP
**** both products are toxic in excess so must be removed from cell or produced in limited quantities.
Label the
boxes:
Label the
boxes:
Net ATP for
Anaerobic
respiration is:
___________
___
APPLICATION: Use of anaerobic cell respiration in yeast to produce ethanol and carbon dioxide in
baking.
APPLICATION: Lactate production in humans when anaerobic respiration is used to maximize the
power of muscle contractions
iv.
o
o
o
o
o
Aerobic respiration requires oxygen and gives a large yield of ATP from glucose.
If oxygen is present glucose can be fully broken down to release a greater quantity of
energy.
Anaerobic respiration produces a yield of 2ATP but in aerobic respiration a yield of more
than 30 ATP can be reached.
Aerobic involves a series of chemical reactions with carbon dioxide and water are
produced as by-products.
In eukaryotic cells most of these reactions happen inside the mitochondria.
After glycolysis, the pyruvate produced moves into the mitochondria and enters into the
Kreb’s cycle and the Electron transport chain.
Label
the
boxes.