How do we get energy from food?
• Glucose + O2 >> CO2 + H2O + ATP
• We breathe O2 and eat food (glucose), and
convert that to CO2, water and ATP (energy
for our cells to function)
The Big Picture*
• Glycolysis and Cell Respiration are both part of a larger CYCLE
• Plants (and other autotrophs) take sunlight and water and
CO2 and make glucose from it via photosynthesis. Oxygen is a
byproduct of this reaction.
• Humans (and other animals-heterotrophs) take the glucose in
(by eating plant material and other foods) and break it down.
Water and CO2 are by products.
• In this way, plants give us what we need (O2 and glucose) and
we supply the plants with water and CO2.
Photosynthesis Provides the Energy
Released by Glycolysis and Cellular Respiration
energy from sunlight
What do we use energy for?*
• Most cellular energy in the body is stored in
the chemical bonds of ATP
• Cells require a continuous supply of energy to
– Run chemical reactions
– Move the body
More big picture*
• This lecture describes the reactions that move the energy from energy
STORAGE molecules (like glucose and fat) to energy CARRYING molecules
(like ATP, NADH and FADH2)
• About 40% of the energy in glucose can be transferred to ATP, the rest is
released as heat.
• Cells break down glucose (the most common energy storage molecule)
and give it to energy carrying molecules (ATP) via 2 separate reactions:
– Glycolysis (2 steps)
• Glucose activation
• Energy Harvest
– Cellular Respiration (3 steps)
• Creation of Acetyl CoA
• Krebs Cycle
• Oxidative Phosphorylation
A Summary of Glucose Breakdown
If no O2 is availableIf O2 is available
Glycolysis: 2 parts
• Takes place in cytoplasm
• Starts with a molecule of glucose, ends with PYRUVATE
• Is an anaerobic reaction: can happen even in the absence of oxygen
• 2 parts
– Glucose activation: a glucose molecule is energized by the addition of
TWO high energy phosphates FROM TWO ATP molecules, leaving
ADP. (Yes, you have to spend ATP to make it!)
– Energy Harvest: The products of these reactions give high energy
phosphates back to 4 ADP molecules, resulting in the creation of 4
ATP molecules (but only a NET production of 2 ATPs.) Also, 2 high
energy electrons and a hydrogen ion are added to “empty” electron
carrier NAD+ to make NADH. Pyruvate is the end product of glycolysis.
The Essentials of Glycolysis
Energy harvestGlucose activation
CC CCCC CC CC C CC C CCCC
• One molecule of glucose is transformed into 2
molecules of pyruvate
• Pyruvate then moves into the mitochondrial
Anatomy of a mitochondrion*
• Outer membrane: most small molecules can freely diffuse
• Intermembrane Space: space between inner and outer
• Inner Membrane: high ratio of proteins to lipids-most
molecules must pass through protein channels
• Cristae: internal compartments formed by the inner
• Matrix: space inside inner membrane
Cell Respiration: Big Picture*
• Pyruvate (from glycolysis) is broken down (for every molecule
of glucose entering glycolysis, keep in mind TWO pyruvates
• Energy is extracted (given to energy carrying molecules)
• CO2 and H2O are released
• Happens in mitochondria
• 3 reactions make up cellular respiration:
– Creation of Acetyl CoA (matrix)
– Kreb’s Cycle (AKA TCA Cycle, Citric Acid Cycle) (matrix)
– Oxidative Phosphorylation (across inner mito membrane from matrix to
Creation of Acetyl CoA & Kreb’s Cycle
• Pyruvate >> Acetyl CoA (intermediate) + CO2
• Acetyl CoA >> H2O + 2 ATP + more CO2 + NADH +
FADH2 + H ions
• CO2 LEAVES THE MITOCHONDRIA
• 2 ATP are made
• **High energy electrons and hydrogen ions are
transferred to energy carrying molecules NAD+ (10)
and FAD (2), turning them into 10 NADH and 2
FADH2. **follow the NADH, FADH2 and H ions!
• 4 high energy electrons are transferred from NADH and
FADH2 to the ELECTRON TRANSPORT CHAIN, embedded in
the inner mito membrane.
• The electrons “jump” from molecule to molecule along the
chain, losing small amounts of energy each time. SOME OF
THIS ENERGY is used to pump H atoms across inner
membrane and into intermembrane space.
• Result is HIGH H+ concentration inside the intermembrane
• Electrons reach the “end” of the transport chain and are
transferred to oxygen.
• H atoms and oxygen combine to form WATER.
• FINALLY, H atoms flow DOWN their gradient
from intermembrane space BACK to the
• ADP and free phosphate are waiting there,
and they combine to form ATP.
• ATP leaves matrix and mitochondria and enter
cytoplasm to fuel cell’s processes. (and more
ADP moves into matrix to make more ATP.
• One molecule of glucose going through
glycolysis can generate TWO molecules of
ATP. If the material continues through cell
respiration, another 34-36 molecules of ATP
can be generated.
Aerobic vs anaerobic reactions
• Glycolysis is an anaerobic reaction: it can
happen even in the absence of oxygen
• Cellular Respiration requires oxygen to
happen: it is an aerobic reaction.
• (If there is no oxygen available, a cell cannot
do cell respiration, and instead performs a
fermentation reaction. Lactate-lactic acid- is a
byproduct of fermentation.)
If no O2 is availableIf O2 is available
Can we get energy from other
molecules besides glucose?
• Keep in mind that most animals can harvest
ATP from a number of different molecules
(like glycogen-storage form of glucose- and
fats and proteins), but glucose is the PRIMARY
source of our ATP.
• (We would have to break down these other
molecules and they can enter the cell
respiration pathway at different points.)