Cellular Respiration
Harvesting Chemical Energy
First Law of Thermodynamics
• Energy is the ability to bring about change or do work.
• The first law of thermodynamics states that: energy can
be changed from one form to another, but it cannot be
created or destroyed.
• For cells this means that the energy from ATP must be
obtained from another energy source such as the organic
molecules derived from photosynthesis. And the energy
to create molecules such as glucose must come from
another energy source (ie-light).
Second Law of Thermodynamics
• In the process of energy
transfer, some energy will
dissipate as heat.
• For cells this means that
during either energy use or
storage there will
inevitably be some energy
lost as heat. These
processes are inefficient.
Cellular Respiration
• Cellular respiration is the
process by which organic
molecules (ie-glucose) in
combination with oxygen
are converted into usable
energy (ie-ATP), carbon
dioxide and water.
• Energy storage in the
biosphere can be viewed as
a balance between
photosynthetic and cellular
respiratory activities.
Metabolism
• Metabolism: the
sum of all chemical
reactions that occur
in the body (ATP
made vs. ATP used)
• There are two types
of metabolism
» anabolism
» catabolism
Photosynthesis as an Anabolic Process
• Anabolism: metabolic pathway that stores
energy by the synthesis of complex
molecules form simple ones
• Sunlight Energy + 6 CO2 + 6 H2O ---> C6H12O6 + 6 O2
+
+
Cellular Respiration as a Catabolic Process
• Catabolism: metabolic pathway that releases
energy by breaking down complex molecules
into simpler compounds
C6H12O6* + 6 O2 ------> 6 CO2 + 6 H2O + Energy (ATP + Heat)
* carbohydrates, fats and proteins could all be processed in
replacement of glucose
+
+
Respiration as Combustion
• You can think of cellular respiration as the combustion of
gases in the car’s engine.
• Main Engine: Mitochondria
• Main Fuel: Glucose
• Main Exhausts: CO2 + H2O
ATP
• The goal of cellular respiration is to generate ATP
• WHAT IS ATP?
•
•
•
•
Universal energy molecule
Makes energy readily available
Continuously being remade
Stands for Adenosine Triphosphate
Adenosine
P
P
+
P
High Energy Bond
Adenosine
ATP Uses
• What is ATP used for?
– Movement: muscle
contraction
– Heat: hypothermia
– Synthesis: hair, blood cells,
fingernails
– Active Transport: nervous
system, kidneys
– Bioluminescence: the
generation of light using
biochemical processes
– Cellular Growth: energy for
regular cellular processes
Site of Cellular Respiration: Mitochondria
• The primary site
of cellular
respiration is the
mitochondria (cell
organelle).
• Glycolysis: occurs
in the cytosol
• Krebs Cycle:
occurs in the
mitochondrial
matrix
• Oxidative
Phosphorylation:
occurs in the inner
membrane of the
mitochondria
Mitochondria
• Components of a mitochondrion.
Evolution of Mitochondria
• Prokaryotes: cells
that are small in size
and have relatively
simple construction.
• Eukaryotes: cells
that are large in size
and have a complex
construction.
• There are many
features that separate
the two
classifications. One
characteristic is that
prokaryotes do not
have mitochondria.
Picture of a eukaryote
Endosymbiotic Theory
• For a long period of Earth’s history only prokaryotes existed.
• As prokaryotes developed they became increasingly
specialized, living in adapted communities.
• It is now theorized that specialized aerobic heterotrophic
prokaryotes (mitochondria) began living inside larger host
cells.
Endosymbiotic Theory
• These early mitochondria probably gained entry as
undigested prey or as internal parasites.
• Eventually this symbiosis became mutually beneficial.
• It is also believed that chloroplasts developed in this
manner. However, because not all eukaryotes have
chloroplasts it is believed that chloroplasts began
symbiotic processes after the development of
mitochondria.
Evidence
• Existing symbiotic relationships.
• Similarities between bacteria and the eukaryotic organelles of
chloroplasts and mitochondria. For example:
–
–
–
–
–
–
size
construction of their membranes
organelles split similar to binary fission in bacteria
have circular DNA
have their own ribosomes
these ribosomes resemble prokaryotic ribosomes.
Leber’s Disease
There are
2 types of respiration
1 Aerobic Respiration – takes place in the
presence of oxygen
2 Anaerobic Respiration– takes place in the
absence of oxygen.
Glycolysis
• Glcolysis occurs in the cytosol of the cell.
1st Step of Cellular Respiration: Glycolysis
• Glycolysis
– Occurs in CYTOPLASM
– Breaks GLUCOSE into two molecules called
PYRUVIC ACID
– Takes place in the ABSENCE OF OXYGEN
1st Step of Cellular Respiration: Glycolysis
1st Step of Cellular Respiration: Glycolysis
• Glycolysis literally means “splitting of sugar”.
• Notice that we have not yet used any oxygen.
• Two ATP molecules are used up in the process, but four are
produced.
– A net gain of 2 ATP/glucose
• Two molecules of NAD+ are reduced to NADH therefore
– 2 NADH are produced/glucose
Krebs Cycle
• The Krebs cycle occurs in the mitochondrial
matrix
2nd Step of Cellular Respiration: Krebs Cycle
• Krebs Cycle
– Occurs in mitochondrial
matrix (inside the
mitochondrion)
– Completely
decomposes pyruvic
acid into CO2
– Needs oxygen to occur
Krebs Cycle
Krebs Cycle
• 8 steps to produce
–
–
–
–
8 NADH/glucose
2 FADH/glucose
2 ATP/glucose
6 CO2/glucose
• 2 Pyruvic acid molecules are changed into 6
CO2 molecules
Electron Transport Chain
• The electron transport chain is located on the
inner membrane of the mitochondria
3rd Step of Cellular Respiration: Electron
Transport Chain
• Very small amounts of ATP have been generated so far,
most will come from the electron transport chain.
• Electron Transport Chain
– Occurs on the inner membrane of the mitochondrion
– Involves a group of molecules built into the inner
membrane of the mitochondrion
– Electrons (from NADH, FADH) pulled off of food by
glycolysis and Krebs are passed between these
molecules
• This will ultimately result in the production of ATP
– Oxygen is required for this step
– Water is an end product
– Lots of ATP is made (32)
Electron Transport Chain
• NADH transfers electrons to
the first molecule in the
electron transport chain.
• These high energy electrons
pass to successive molecules
lowering their energy levels.
• Reduction: occurs when the
electrons are transported to
successive electron carriers.
• Oxidation: the state of
electron carriers after an
electron has been passed to
the next carrier.
Electron Transport Chain
• Chemiosmosis: How the mitochondrial membrane
couples electron transport to oxidative phosphorylation.
Electron Transport Chain
• At the same time H+ ions from the mitochondrial matrix are pumped
across the inner membrane into the intermembrane space.
• The result is a H+ gradient.
Electron Transport Chain
• Throughout the inner membrane of the mitochondrion there are
proteins called ATP synthase.
• ATP synthase creates ATP by using the hydrogen ion gradient. When
ions cross the membrane the process is called chemiosmosis.
• This gradient powers the process of oxidative phosphorylation.
• Oxidative Phosphorylation: The production of ATP using energy
derived from the redox reactions of an electron transport chain.
Electron Transport Chain
• The result is 3 ATP produced for every NADH molecule
and 2 ATP produced for every molecule of FADH. Or, in
total around 32 ATP are produced per glucose molecule in
oxidative phosphorylation.
Electron Transport Chain
• The final step in the electron transport chain is the transfer of H+
ions to oxygen in the formation of water.
• In other words, oxygen is the final electron acceptor during
aerobic respiration.
Big Picture: Why Electron Transport Chain?
• The object of the ETC is to turn high energy electrons into
low energy electrons.
• If all this energy is released in one step, it would be lost as
heat.
• When it is released in many steps, it is converted into ATP.
Anaerobic Respiration
• The production of energy
without oxygen.
• Takes place in the cytoplasm.
• Very inefficient -- only 6% of
glucose energy is made
available.
• Only 2 ATP are produced per
glucose molecule (vs. 36 in
aerobic respiration)
• Oxygen is required for pyruvic
acid to enter Krebs where it
can be broken down.
Anaerobic Respiration
• Pyruvic acid is toxic to the cell. When it does not enter the
Krebs cycle it must be converted into a safer form.
– In animals -- LACTIC ACID*
• causes muscle cramps
• process is called Lactic Acid Fermentation
– In bacteria and yeast -- ETHYL ALCOHOL & CO2*
• process is called Alcohol Fermentation
* also denotes the final electron acceptors in anaerobic respiration
Anaerobic Respiration
• Notice how the NADH passes the electrons to the
organic molecules.
Versatility of Catabolism
• Glycolysis can accept a wide range of carbohydrates for
catabolism. This process begins when carbohydrates are
hydrolyzed to glucose.
• Proteins can be used but must be broken down into their
constituent amino acids. They then loose their amino groups and
become intermediates of glycolysis and the Krebs cycle.
• Energy can also be harvested from fats. The glycerol of fats can
be converted to an intermediate of glycolysis. Larger fatty acids
can also be broken down into acetyl CoA. A gram of fat can
generate twice as much ATP as a gram of carbohydrates.
Versatility of Catabolism
Pollutants effect on Respiration
• Cyanide (CN-) blocks electron transport and therefore halts oxygen
consumption.
• Rotenone (Amazonian Aboriginals), comes from plants and is used as
a toxin.
Pollutants Effects on Cellular Respiration
• Carbon monoxide is
produced as a by-product in
the combustion of organic
molecules.
• Carbon monoxide prevents
cellular respiration when it
binds to hemoglobin
preventing the binding of
oxygen.
Effects of Pollutants on Cellular Respiration
• Fluoride: Sodium fluoroacetate and fluoroacetamide are readily
absorbed by the gut, but only to a limited extent across skin.
• Three molecules of fluoroacetate or fluoroacetamide are combined in
the liver to form a molecule of fluorocitrate.
• This blocks the Krebs cycle inhibiting aerobic cellular respiration.
• Fluorocitrate was found in the effluent of a factory and killed cows
downstream.