Ch. 7 Cellular Respiration
7-1 Glycolysis and Fermentation
7-2 Aerobic Respiration
Glycolysis and Fermentation
• All cells break down complex organic
compounds into simpler molecules.
• Cells use some of the energy that is released
in this process to make ATP.
Harvesting Chemical Energy
• Autotrophs use photosynthesis to convert light
energy from the sun into chemical energy, which
is stored in carbohydrates and other organic
compounds for the energy to power cellular
activities.
• By breaking down these compounds into simpler
molecules, cells release energy.
• Energy is used to make ATP from ADP and
phosphate.
• ATP is the main currency of energy in our cells.
• Cellular Respiration – complex process in
which cells make ATP by breaking down
organic compounds.
Steps to Cellular Respiration
Glycolysis
• Biochemical pathway that starts cellular
respiration
• Products of glycolysis can follow one of
two different pathways.
• 1st if oxygen is present can go to pyruvic
acid conversion.
• 2nd if oxygen is not present it will go to
Fermentation.
• Anaerobic pathways – pathway that operates in
the absence of oxygen.
• Many of the reactions in cellular respiration are
redox reactions.
• Redox reaction is where one reactant is oxidized
while another is reduced.
• Although many kinds of organic compounds can
be oxidized in cellular respiration, it is customary
to focus on the simple sugar glucose, whose
oxidation begins with glycolysis
Glycolysis
• First step to cellular respiration
• Glucose is broken down into two three
carbon molecules called pyruvic acid
• ATP is produced.
• Occurs in the cytosol of the cell.
Fermentation
• In the absence of oxygen, some cells can
convert pyruvic acid into other compounds
through additional biochemical pathways
that occur in the cytosol.
• The combination of glycolysis and these
additional pathways is called fermentation.
• Two common fermentation pathways.
• No ATP is made in fermentation
Lactic Acid Fermentation
• Glycolysis – Glucose is broken down into two
three carbon molecules called pyruvic acid.
• Pyruvic acid is then converted into lactic acid
• Lactic acid fermentation plays a vital role in the
manufacture of food products such as yogurt and
cheese.
• Lactic Acid Fermentation also occurs in your
muscle cells during very strenuous exercise.
• During this exercise muscle cells use up oxygen
more rapidly than it can be delivered to them.
• As oxygen becomes depleted, the muscle cells
begin to switch from aerobic respiration to lactic
acid fermentation.
• Lactic acid accumulates in the muscle cells,
making the cells cytosol more acidic.
• The increased acidity may reduce the capacity of
the cells to contract resulting in muscle fatigue,
pain and even cramps.
• Eventually the lactic acid diffuses into the blood
and is transported to the liver where it is converted
back into pyruvic acid when oxygen becomes
available.
Alcoholic Fermentation
•
•
•
•
Convert pyruvic acid into ethyl alcohol.
Ex. Yeast
Basis of beer and wine industry.
Yeast cells are added to the fermentation mixture
to provide the enzymes needed for alcoholic
fermentation.
• As fermentation proceeds, ethyl alcohol
accumulates in the mixture until it reaches a
concentration that inhibits fermentation. Wine
12%
• Bread making also depends on alcoholic
fermentation performed by yeast cells. The CO2
that is produced by fermentation makes the bread
rise by forming bubbles inside the dough.
Aerobic Respiration
• Occurs after glycolysis if Oxygen is present
• Aerobic Respiration consists of the Krebs
cycle (citric acid cycle) and the electron
transport chain.
• Krebs cycle – finish the breakdown of
glucose.
• Electron transport chain – create ATP
• Krebs cycle and
electron transport
chain in prokaryotes
take place in the
cytosol.
• Krebs cycle and
electron transport
chain in eukaryotes
take place in the
mitochondria
Equation for Cellular Respiration
• C6H12O6 + 6O2
6CO2+ 6H20 + ENERGY
• Glucose + oxygen yields carbon dioxide + water + energy
CH2O + 02
CO2 + H20 + ENERGY
Carbohydrate + oxygen yields carbon dioxide + water + energy