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
 Overall Reaction:
 C6H12O6
+ 6O2 → 6CO2 + 6H2O
How much energy is actually present
in food?
g of sugar glucose (C6H12O6) when burned in
the presence of O2 releases 3811 calories of heat
How many calories do you burn a
How many calories do you burn a
 Male
 150
 5’9”
 Somewhat active
 Burns 3023 kcal a day or 3023 Calories or
3,023,000 calories
g of glucose produces 3811 calories
 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
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
 The
process in which one molecule of glucose is
broken in half, producing two molecules of
pyruvic acid
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
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 then adds the 2-carbon acetyl group
to a 4-carbon compound (oxaloacetate), forming
Citric Acid
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
more molecules of CO2
 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
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
 Each pair of high-energy electrons that moves
down the electron transport chain provides enough
energy to produce three molecules of ATP

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