CELLULAR
RESPIRATION
NOTES
Cellular Respiration Overview
• The transformation of chemical
energy in food into chemical energy
cells can use: ATP, adenosine
triphosphate.
• These reactions proceed the same
way in plants and animals. Process is
called cellular respiration.
• Overall Reaction:
• C6H12O6 + 6O2 → 6CO2 + 6H2O
• FLIP THE REACTANTS & PRODUCTS TO
GET THE EQUATION FOR
PHOTOSYNTHESIS!
Cellular Respiration Overview
• Breakdown of glucose begins in the cytoplasm.
• At this point life diverges into two forms and two pathways
• Anaerobic cellular respiration (aka fermentation)
• Aerobic cellular respiration
STEPS OF CELLULAR RESPIRATION
1. Glycolysis
• Series of reactions which break
the 6-carbon glucose molecule
down into two 3-carbon
molecules called “pyruvate”
• This process is an “ancient one”
because all organisms from
simple bacteria to humans
perform it the same way
• Yields 2 ATP molecules for
every one glucose molecule
broken down
Anaerobic Cellular Respiration
• Some organisms thrive in
environments with little or no
oxygen
• Marshes, bogs, gut of animals,
sewage treatment ponds
• No oxygen used= ‘an’aerobic
• Results in no more ATP, final steps
in these pathways serve ONLY to
regenerate NAD+ so it can return
to pick up more electrons and
hydrogens in glycolysis.
• End products such as ethanol and
CO2 (single cell fungi (yeast) in
beer/bread) or lactic acid (muscle
cells)
Aerobic Cellular Respiration
• Oxygen required=aerobic
• Steps 2 & 3 of cell respiration will occur in succession in the presence
of oxygen. This set of reactions will occur in a specialized structure
within the cell called the mitochondria
• 2. Kreb’s Cycle
• 3. Electron Transport Chain
KREB’s Cycle &
The ETC
A Little Krebs Cycle History
Discovered by Hans
Krebs in 1937
He received the Nobel
Prize in physiology &
medicine in 1953 for
his discovery
Forced to leave
Germany prior to
WWII because he was
Jewish
2. Kreb’s Cycle / Citric Acid Cycle
• Completes the breakdown of glucose
• Takes both pyruvates and simultaneously
completes the reaction needed to break down
the each pyruvic acid into CO2 and H2O
• Hydrogens and electrons are stripped and
loaded onto NAD+ and FAD to produce NADH
and FADH2
• Yields only 2 more ATP but loads up the
coenzymes with H+ and electrons which
move to Step 3.
What is NAD or NADH?
 NAD+ (nicotinadenine
dinucleotide) acts as the
energy carrier by carrying
electrons
 NAD+ is a “coenzyme”
 It’s Reduced to NADH when
it picks up two electrons and
one hydrogen atom (hence
the name, NAD+H)
Coenzymes
INACTIVE
STATE
ACTIVE
STATE
Other Electron Carriers
FAD+ (Flavin adenine dinucleotide)
Also a coenzyme!
Reduced to FADH2
• Both NAD & FAD are election carriers. The main difference seen between in
the two is in accepting the excess Hydrogen Atoms.
• NAD is reduced when it accepts a single hydrogen whereas FAD is reduced by
a two Hydrogen atoms, hence their names NADH and FADH2.
KREB’s
Cycle
Cytoplasm
Net Gain = 2 ATP
Net Gain = 2 ATP
In Depth Look
Cytoplasm
3. Electron Transport Chain
• Electron carriers loaded
with electrons and protons
from the Kreb’s cycle move
to this chain-like a series of
steps (staircase).
• As electrons drop down
stairs, energy released to
form a total of 34 ATP
• Oxygen waits at bottom of
staircase, picks up electrons
and protons and in doing so
becomes water
• HAPPENS IN THE CRISTAE of
the MITOCHONDRIA
Diagram of the Process
Occurs
across
Cristae
Cytoplasm
Occurs in
Cytoplasm
Occurs in
Matrix
Energy Tally
• 36 ATP for aerobic vs. 2 ATP for anaerobic
• Glycolysis
2 ATP
• Kreb’s
2 ATP
• Electron Transport
34 ATP
38 ATP
- 2ATP to get Glycolysis started!
- “TOTAL” ATP produced – 38 ATP
- “Net Gain” ATP produced – 36 ATP
• Anaerobic organisms can’t be too energetic but are important for global recycling
of carbon