Chapter 7: How Cells Harvest
Energy
• How our food becomes energy for our cells (ATP)
How to make ATP
from glucose
Can be aerobic
(with oxygen) or
anaerobic (without
oxygen
ATP Review
Requires coenzymes NADH and
FADH2
Need to collect electrons from
the food and use them to drive
the machine that synthesizes
ATP
Redox Reactions
Redox with NAD and FAD
Aerobic Respiration
How cells harvest energy from glucose
Glucose + 6O2  6CO2 + 6H2O + Energy
ATP + Heat
4 Steps of Aerobic respiration
1. Glycolysis
2. Oxidation of pyruvate
3. Kreb’s cycle (aka Citric Acid Cycle)
4. Electron transport chain
Glycolysis: 6 carbon glucose to
two 3 carbon pyruvates
Occurs in Cytoplasm
Glycolysis
• 6 carbon molecule broken into two 3 carbon molecules
• Glucose has to be activated. This uses up 2 ATP
molecules, but kick-starts the whole thing off.
• 4 ATPs are made during glycolysis, so a net gain of 2
ATPs
Glycolysis
• Uses an electron carrier called NADH
• Each NADH molecule carries 2 electrons that it
has removed from glucose
• These electrons will be very important later!!!!!
Over-all Glycolysis
• End products are 2 pyruvates (2 carbon
molecules), 2 ATPs, and 4 electrons stored on 2
NADH’s
Oxidation of Pyruvate
(Breaking 3 carbon pyruvate into a 2
carbon molecule and CO2)
Oxidation of Pyruvate
• Pyruvate is
transported into
the
mitochondrial
matrix
Oxidation of Pyruvate
• The 3 carbon pyruvate is
broken down into a 2 carbon
molecule called AcetylCoA
and a CO2
• The CO2 bubbles out of the
mitochondria, then the cell
• The AcetylCoA will be
further broken down in the
next step
• 2 NADH’s are made in this
step (stealing electrons from
the organic pyruvate)
Summary: Oxidation of Pyruvate
• Carbon backbone has been broken from 3 to 2
carbons
• CO2 has been made and released
• 2 NADH’s made (one per pyruvate)
• No ATP made
Stage 3: Kreb’s Cycle
(aka Citric Acid Cycle)
• Occurs in the matrix
• AcetylCoA is broken apart into CO2
• Final breakdown of the carbon backbone
Kreb’s Cycle
(In mitochondrial matrix)
• The last electrons are removed from the organic
molecules and put on electron carriers.
• FADH2 is an electron carrier like NADH. It can
carry 2 electrons on each molecule.
Summary Kreb’s Cycle
• No more carbon-carbon bonds or electrons from
glucose
• 6 NADH’s and 2 FADH2 created (16 electrons
stored and carried)
• CO2 given off
• 2 ATPs made
Summary so far:
• Glucose carbon-backbone is totally
demolished. Carbons have been released
in CO2 molecules.
• All available electrons have been stripped
from glucose and are now carried on 10
NADH’s and 2 FADH2’s
• Only net gain of 4 ATP’s
What to do with the electrons?
Electron Transport Chain
• NADH and FADH2 drop off electrons on
the inner membrane proteins
– This results in recycling NAD+ and FAD,
which will go back and participate in earlier
events
– The electrons jump from one protein to the
next creating something like an electric
current
– This “electricity” runs something called the H+
pump. This protein moves H+ from the matrix
into the inter-membrane space.
Electron Transport Chain
The H+ build up in the inter-membrane space and create a
big potential energy called the proton motive force
Electron Transport Chain
• The H+ can move back into the matrix, but only through
a channel attached to an enzyme called ATP Synthase,
This is called chemiosmosis.
• Like water running over a water-wheel, the H+ moving
across the membrane powers the ATP Synthase to build
ATP
• Approximately 32 ATPs are made in the ETC for every
glucose
ATP Synthesis via
Chemiosmosis
Summary: Electron Transport
Chain
•NADH and FADH are
2
used to power the
proton pump
•Protons (H+) are
pumped from
mitochondrial matrix
into intermembrane
space
•These protons push
through the ATP
synthase making its
“motor work”
•ADP and Phosphate
are put together to
make ATP in the matrix
One last thing about the
Electron Transport Chain
• The electrons moving through the ETC will finally bind to
a oxygen with 2 H+, making water
• THIS IS THE REASON YOU BREATHE IN OXYGEN! To
keep the electron chain moving
• If no oxygen, no ATP, and you die
• Cyanide blocks the last step of the electron
transport chain, so electrons are blocked from
oxygen
• The whole thing gets backed up and no
electrons move through.
• Without “electric current”, the H+ pumps don’t
build up the concentration gradient.
• The ATP synthase has no H+ to drive it.
• You die within minutes without the new ATP!
Summary of Glycolysis and
Aerobic Respiration
Aerobic –vs- Anaerobic Respiration
If no oxygen available, the
glucose molecule can’t be
broken down all the way.
The results are 2 ATPs and
either:
• 2 Lactic acids
(3 carbon molecules)
Or
• 2 Ethanosl (2 carbon
molecule) and 2 CO2
(Fermentation)
Lactate Fermentation
• Uses glycolysis
• Makes 2 ATPs
• Recycles 2 NAD+
Occurs in the muscles when not enough oxygen available to make ATP needed
Hurts!
Alcohol Fermentation
•
•
•
•
Uses glycolysis
Makes 2 ATPs
Recycles 2 NAD+
Makes carbonated
ethanol (beer?)
We use yeast to do this when making alcohol.
Lots of money & research goes done on this metabolic pathway.
Anaerobic vs Aerobic
Anaerobic fermentation
Aerobic respiration
No oxygen
No mitochondria needed
Only net gain of 2 ATPs
Begins with glucose
Uses glycolysis
In cytoplasm
Uses coenzymes
FAD and NAD
Oxygen is required
Occurs in cytoplasm and
inside mitochondria
Makes about 36 ATPs