Cellular
Respiration
Harvesting Chemical Energy
 So
we see how energy enters food chains (via
autotrophs) we can look at how organisms use that
energy to fuel their bodies.
 Plants and animals both use products of
photosynthesis (glucose) for metabolic fuel
 Heterotrophs: must take in energy from outside
sources, cannot make their own e.g. animals
 When we take in glucose (or other carbs), proteins,
and fats-these foods don’t come to us the way
our cells can use them
When we take in glucose (or other carbs),
proteins, and fats-these foods don’t come to us
the way our cells can use them
 Animals
use cellular respiration to transform
chemical energy in food into chemical energy cells
can use: ATP
 These reactions proceed the same way in plants and
animals.
 Overall Reaction:
 C6H12O6
+ 6O2 → 6CO2 + 6H2O
How much energy is actually present
in food?
1
g of sugar glucose (C6H12O6) when burned in
the presence of O2 releases 3811 calories of heat
energy
How many calories do you burn a
day?
How many calories do you burn a
day?
 Male
 150
lb
 5’9”
 Somewhat active
 Burns 3023 kcal a day or 3023 Calories or
3,023,000 calories
1
g of glucose produces 3811 calories
Calorie
 calorie: The
amount of energy needed to raise the
temperature of 1 gram of water 1 degree Celsius
 Calorie:



food labels
1000 calories
Cells don’t burn glucose – cells gradually release
energy from glucose and other food compounds
Cells release energy from glucose by performing
cellular respiration
Cellular Respiration Overview
 Breakdown
of glucose begins in the cytoplasm:
the liquid matrix inside the cell
 At this point life diverges into two forms and two
pathways


Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration
Cellular Respiration
 Cellular
respiration is the process that releases
energy by breaking down glucose and other food
molecules in the presence of oxygen
 C6H12O6 + 6O2 → 6CO2 + 6H2O
Cellular Respiration
 Glycolysis
 The
Krebs Cycle
 Electron Transport
Glycolysis
 The
process in which one molecule of glucose is
broken in half, producing two molecules of
pyruvic acid
http://upload.wikimedia.org/wiki
pedia/commons/1/17/Glycolysis
2.svg
Glycolysis – ATP Production
 2 ATP used
 4 ATP produced

Net gain of 2 ATP
Glycolysis – NADH Production
 NAD+
accepts a pair of high-energy electrons until
they are transferred to other molecules
Anaerobic Respiration
 When
oxygen is not present, glycolysis is followed
by a different pathway – FERMENTATION
 Alcoholic fermentation (yeast)


Pyruvic acid + NADH  alcohol + CO2 + NAD+
Causes bread to rise – CO2 forms the air spaces that
you see in bread
 Lactic

acid fermentation (muscles)
Pyruvic acid + NADH  lactic acid + NAD+
Substrate Level Phosphorylation
Glycolysis
Krebs Cycle
Citric Acid Production
 Pyruvic
acid enters the mitochondrion
 A carbon is removed, forming CO2
 Electrons are removed: NAD+  NADH
 Coenzyme A joins the 2-carbon molecule, forming
Acetyl-Co-A
 Acetyl-Co-A then adds the 2-carbon acetyl group
to a 4-carbon compound (oxaloacetate), forming
Citric Acid
Cytoplasm
Inner
Mitochondrial
Space
Krebs Cycle
Acetyl Co A  Citric Acid
Energy Extraction
 Citric
acid is broken down into a 5-carbon
compound, then into a 4 carbon compound

Produces
2
more molecules of CO2
 NAD+  NADH
 FAD+  FADH2
 1 ATP
Electron Transport
 Electrons
from NADH and FADH2 are used in the
electron transport chain to convert ADP to ATP
Electron Transport Chain



Composed of carrier proteins located in the inner
membrane of the mitochondrion
High-energy electrons are passed from one carrier
protein to the next
An enzyme combines these electrons with hydrogen
ions and oxygen  H2O


Oxygen is the final electron acceptor of the electron
transport chain
Oxygen is essential for getting rid of low-energy electrons
and hydrogen ions

Low-energy electron and hydrogen ions are waste
products of cellular respiration
Hydrogen Ion Movement
 Every
time 2 high-energy electrons transport down
the electron transport chain, their energy is used to
transport hydrogen ions (H+) across the membrane
 H+ build up in the intermembrane space, making it
positively charged
 The other side of the membrane is negatively
charge
ATP Production
 The
cell uses the build up of charge differences
 As H+ escape through the ion channels, the ATP
synthase (a protein enzyme) spins
 Each time the ATP synthase spins, the enzyme
grabs an ADP and attaches a phosphate, forming
ATP
 Each pair of high-energy electrons that moves
down the electron transport chain provides enough
energy to produce three molecules of ATP