Chapter 7: Cellular Respiration
Cellular (aerobic) respiration (red arrows) is the main
means by which both fungi and plants utilize energy in
the form of organic compounds that were previously
created through photosynthesis (green arrow). ( wikipedia)
Cellular respiration is
• the process by which
cells break down
organic compounds to
produce ATP.
• Products of cellular
respiration are the
reactants in
photosynthesis;
they are opposites!
Plants & Animals:
• Both autotrophs
and heterotrophs
use cellular
respiration to get
energy from
organic compounds
and O2 & produce
waste products CO2
and water
Cellular Respiration
• Refers to the biochemical pathway by which
cells release energy from the chemical bonds
of food molecules and provide that energy for
the essential processes of life.
Cellular respiration can be
divided into 2 stages:
• glycolysis
• aerobic respiration.
During glycolysis
• One six-carbon glucose molecule is
oxidized to form two three-carbon
pyruvic acid molecules.
• A net yield of two ATP molecules
is produced for every molecule of glucose
that undergoes glycolysis
Glycolysis takes a 6-carbon sugar &
breaks it into 2 3-carbon sugars
http://terravivida.com/vivida/glyintro/page01.htm
Remember: Lysis means to break up
• Breaking up the
glucose molecule into
2 smaller sugars
(pyruvic acid)
provides energy to
make ATP which is
the principle energy
'currency' in the cell
http://terravivida.com/vivida/glyintro/page05.htm
Glycolysis
• occurs in the
• There are 10
cytoplasm
steps in
(cytosol) and
glycolysis and
does not require
each one is
oxygen.
catalyzed by a
specific enzyme
In more detail ( you do not need to know this:
Glycolysis is a definite sequence of ten reactions
involving ten intermediate compounds (one of the steps
involves two intermediates). The intermediates provide
entry points to glycolysis. For example, most
monosaccharides, such as fructose, glucose, and galactose,
can be converted to one of these intermediates.
http://en.wikipedia.org/wiki/Glycolysis
• Steps in
glycolysis
(you do not need
to memorize
these.)
http://library.thinkquest.org/C004535/glycolysis.html
So- What happens after glycolysis?
• (Anaerobic) - If no oxygen is
available- fermentation occurs
• (Aerobic) If oxygen is availablethe krebs cycle
Glycolysis - in the cytoplasm.
The next step is aerobic Respiration in the
Krebs (TCA) cycle. Unless there is no
Oxygen, in which case Anaerobic
Fermentation occurs.
hyperphysics.phy-astr.gsu.edu
1. Fermentation (anaerobic).
• Occurs if oxygen is not present
• convert pyruvic acid into other compounds
• For example:
1. Lactic Acid Fermentation
– an enzyme converts pyruvic acid into another
three-carbon compound, called lactic acid.
2. Alcoholic Fermentation
– Some plants and unicellular organisms, (like yeast)
convert pyruvic acid to ethyl alcohol & CO2.
2. Aerobic Respiration
• occurs in the mitochondria.
• occurs only if oxygen is present in
the cell.
• Called the Krebs cycle
The Krebs cycle
• Also known as the:
tricarboxylic acid cycle (TCA)
• was first recognized in 1937 by the man for
whom it is named,
German biochemist Hans Adolph Krebs
Krebs happens in the mitochondria
• After the glycolysis takes place in
the cell's cytoplasm,
• the pyruvic acid molecules travel
into the interior of the
mitochondria.
The Krebs Cycle:
In this simplified cycle
diagram you can see that
Each turn produces
1 ATP
2 CO2
3 NADH
1 FADH2
http://ncam.wgbh.org/publications/stemdx/images/krebs.jpg
The Krebs Cycle.
• First, pyruvic acid (produced in glycolysis)
reacts with coenzyme A to form acetyl CoA.
Then, acetyl CoA enters the Krebs cycle.
• The original glucose becomes completely
broken down after 2 turns of the Krebs cycle.
• 2 turns produce:
– four CO2 molecules,
– two ATP molecules,
– and hydrogen atoms that are used to make
six NADH and two FADH2 molecules.
The Krebs or Citric Acid (TCA) Cycle
Note that there
are 8 steps
acccn.net
Finally: Electron Transport
Chain
• High-energy electrons in hydrogen atoms
from NADH and FADH2 are then passed
from molecule to molecule in the
electron transport chain along the
inner mitochondrial membrane
Electron Transport Chain
• In eukaryotes, oxidative phosphorylation occurs
in the mitochondrial cristae. It comprises the
electron transport chain that establishes a proton
gradient (chemiosmotic potential) across the
inner membrane by oxidizing the NADH
produced from the Krebs cycle.
• A by-product of oxidative phosphorylation is
hydrogen peroxide. (a toxin)
• Remember the liver lab. What enzyme in liver
broke down the H2O2? What were the products?
Catalase, O2, H2O
Electron Transport Chain
kirksville.k12.mo.us
Efficiency of Cellular
Respiration
• Cellular respiration can produce up to 38
ATP molecules from the oxidation of a
single molecule of glucose.
• Most eukaryotic cells produce about 36
ATP molecules per molecule of glucose.
• Thus, cellular respiration is nearly 20
times more efficient than glycolysis alone.
Summary of Cellular Respiration
• Providing cells with energy : ATP
is an important function of cellular respiration.
• Also: Molecules formed at different steps in
glycolysis and the Krebs cycle are often used by
cells to make compounds that are missing in food.
Summary of Glycolysis and
Cellular Respiration
Remember Homeostasis?
• Cellular respiration produces CO2 as a
metabolic waste.
• This CO2 binds with water to form carbonic
acid, helping to maintain the blood's pH.
• Since too much CO2 would lower the
blood's pH too much, the removal of the
excess CO2 must be accomplished on an
ongoing basis- or homeostasis is disturbed.
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/celres.html
Usefulness of FermentationAnaerobic exercise
• During vigorous exercise, oxygen is consumed
faster than breathed in.
• Additional ATP energy is provided to the muscles
by glycolysis and the result is a buildup of lactate in
the muscles.
• When lactate builds up, the blood pH drops and the
muscles fatigue.
• At rest, lactate is converted back to pyruvate (the
oxygen debt is repaid). This is why you continue to breathe
hard after you have finished running or rapid stair climbing.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files
faculty.clintoncc.suny.edu
Summary diagram- cellular respiration:
http://www.chem.uwec.edu/Webpapers2005/mintermm/pages/Intro_media/intro.gi