Where do we get the energy we need?
 Energy needs a source
How much energy do we need?
It all depends on what we are doing
 The Pathways of Metabolism
 http://www.sigmaaldrich.com/img/assets/4202/
MetabolicPathways_6_17_04_.pdf
ATP: ADENOSINE TRIPHOSPHATE
 Structure
 Three phosphate groups
 Energy is stored in
phosphate bond
ATP: adenosine triphosphate
 When energy is required
• ATP binds to enzyme
• ATP  ADP + Pi +Energy
 release energy to perform a needed function
 ADP gets recycled into ATP repeatedly
 ATP↔ ADP + (Pi) + Energy
NADH/NAD+ REDOX R(X)
Chemical energy
 Energy comes from electrons
 Glucose (and other molecules) store energy in
chemical bonds
• One glucose molecule contains 90 times the
energy produced by 1 ATP
• Remember last chapter….
The first steps are always the hardest…. (except for here)
Movies are always better than the book (?!)
 http://henge.bio.miami.edu/mallery/movies/glyc
olysis.mov
GLYCOLYSIS: series of reactions in which a
molecule of glucose is broken down
 “Sugar breaking”
 If this process shuts down, it cannot restart
 Always the first step to breaking down carbs
 Requires energy to get energy
• Requires 2 ATP to get things started
• Results in 4 ATP being produced
 Takes place in cytosol
GLYCOLYSIS: series of reactions in which a
molecule of glucose is broken down
 The steps
• Two phosphate groups attach to glucose
 Phosphates are supplied by 2 ATP  2ADP
 Form a new 6-carbon compound
• 6-carbon molecule splits
 Forms two 3-carbon molecules of PGAL
GLYCOLYSIS: series of reactions in which a
molecule of glucose is broken down
 The steps (cont.)
• Two PGAL  2 molecules of a 3-carbon
compound
 PGAL gets oxidized (loses an e-)
 Each PGAL gains a phosphate group
 NAD+ reduced to NADH + H+
• Phosphate groups are removed
 Two molecules pyruvic acid are made
 Phosphate groups attach to ADP
 4 ADP + 4 phosphate groups  4 ATP
GLYCOLYSIS: series of reactions in which a
molecule of glucose is broken down
 Net production
• Two molecules pyruvic acid
• Two molecules ATP
• Two pair high energy e- carried by NADH
 Energy from e- is used when O2 is not available
2Pi
C-C-C-C-C-C
Glucose
2 ATP
P-C-C-C-C-C-C-P
6-C
compound
2ADP
P-C-C-C
C-C-C-P
2 PGAL
2NAD+
P-C-C-C-P
P-C-C-C-P
C-C-C
C-C-C
2 molec
3-C
compound
2 molecules
pyruvic acid
2NADH +2H+
4ADP
4 ATP
What is next? It all depends on the air
Fermentation
Glucose
Cellular Respiration
What is next? It all depends on the air
Fermentation
Glucose
Cellular Respiration
What is next? It all depends on the air
Fermentation
Glucose
Cellular Respiration
Or “What to do when you can’t get enough air….”
FERMENTATION:
 regeneration of NAD+ when oxygen is unavailable
 Temporary solution
 Two types (each organism uses only one, but two are
critical to our lives…)
Electron gets passed back from NADH to C atoms
 Allows cell to recycle NAD+
 Allows glycolysis to continue
 Cell accumulates compounds that accept electrons
LACTIC ACID FERMENTATION
 Pyruvic acid  lactic acid
• Transfer of 2 H+ from NADH + H+ to pyruvic acid
• NADH oxidized to NAD+
• NAD+ used in glycolysis
 Regeneration of NAD+ allows continuation of
glycolysis
LACTIC ACID FERMENTATION
 Occurs when you are very active (i.e.: running)
• When there is insufficient oxygen to cells fermentation
occurs
• Lactic acid accumulates in cells decreasing pH of cell
• Increased acidity reduces cell’s ability to contract
 results in muscle fatigue, pain, cramps
 eventually diffuses into blood stream and is processed by liver
 reverts to pyruvic acid when oxygen becomes available
 Used in cheese and yogurt industry
Cheese is produced by lactic acid
fermentation. (So is yogurt!)
C-C-C-C-C-C
Glucose
C-C-C C-C-C
Lactic
acid
C-C-C C-C-C
Glycolysis
NAD+
NADH
Pyruvic
acid
ALCOHOLIC FERMENTATION
 Pyruvic acid – CO2  ethyl alcohol (ethanol)
 Two steps
• Pyruvic acid  2-C compound + CO2
• 2-C compound + 2H+  ethyl alcohol
 H+ comes from NADH + H+  NAD+
ALCOHOLIC FERMENTATION
 Yeast utilizes alcoholic fermentation
• beer and wine industry
• yeast produces ethanol until [ethanol] is too high for
yeast to survive
 wine: CO2 allowed to escape
 champagne & beer: CO2 is retained
• bread
 CO2 that is released causes bread to rise
 Ethyl alcohol evaporates during baking
Yeast undergoes alcoholic
fermentation to produce….
Saccharomyces cerevisiae
…a little beer,…
…a lot of beer,…
…Champagne,…
… and wine.
Released CO2 makes bread rise
Alcoholic Fermentation
C-C-C-C-C-C
Glucose
C-C-C C-C-C
Glycolysis
Pyruvic acid
NAD+
2 CO2
NADH
C-C C-C
Ethyl alcohol
C-C C-C
2-C compounds
Which is which?
In what organisms do each occur?
AEROBIC
RESPIRATION
Pyruvate
Glucose
ATP
ATPATP
ATP
ATP
ATP
7-2: AEROBIC RESPIRATION:
 release of energy from breakdown of food when
oxygen is present
CONVERSION TO ACETYLCOA:
The beginning
 Occurs in mitochondria
 Pyruvic acid diffuses into mitochondria crossing
both membranes
 Reactions occur within the mitochondrial matrix
 Space inside the inner mitochondrial membrane
 Contains enzymes needed for the Krebs Cycle
 Pyruvic acid + Coenzyme A  AcetylCoA
Conversion to Acetyl-CoA
CO2
CoA
C-C-C
Pyruvic Acid
C-C
AcetylCoA
NAD+
NADH
KREBS CYCLE
 AcetylCoA  CO2 + H+ + ATP
 Occurs in the matrix
 The steps
• Step 1:AcetylCoA + oxaloacetic acid  citric acid
 2C + 4C = 6C
• Step 2: Citric acid  CO2 + H+ + a 5-C compound
 regenerates CoA
 citric acid is oxidized
 H+ atom transferred to NAD+ reducing it to NADH
KREBS CYCLE
 AcetylCoA  CO2 + H+ + ATP
 The steps (cont.)
• Step 3: 5-C compound  CO2 + H+ + 4-C
compound (succinyl-CoA)
 NAD+ reduced to NADH
 ADP + phosphate  ATP
KREBS CYCLE
 AcetylCoA  CO2 + H+ + ATP.
 The steps (cont.)
• Step 4: 4-C compound  different 4-C compound + H+
(maleate)
 FAD reduced to FADH2
 FAD is similar to NAD+ - it accepts e- during redox reactions
• Step 5: (new) 4-C compound  H+ + oxaloacetic acid
 Regenerates oxaloacetic acid
 NAD+ reduced
THE KREBS CYCLE
Step 1
CoA
Acetyl
CoA
Step 2
Citric
Acid
CO2
NAD+
Oxaloacetic acid
NADH + H+
5-C compound
NADH +
NAD+
NAD+
NADH + H+
ADP + Phosphate
H+
4-C compound
ATP
4-C compound
Step 5
FADH2
Step 4
FAD
CO2
Step 3
KREBS CYCLE
 Because 1 glucose  2 pyruvic acid then 1 glucose
 2 turns of Krebs cycle
 Final production of Krebs cycle
• Six NADH
continue on
• Two FADH2
• Two ATP – used for energy
• Four CO2 – given off by organism as waste
KREBS CYCLE
 Totals so far from 1 glucose
• NADH –10
 (2 from glycolysis; 2 from AcetylCoA conversion)
• FADH2 – 2
• ATP – 4
 (2 from glycolysis; 2 from Krebs cycle)
• CO2 – 6
 (2 from AcetylCoA conversion; 4 from Krebs cycle)
 http://henge.bio.miami.edu/mallery/movies/krebs.mov
ELECTRON TRANSPORT CHAIN (ETC)
 Occurs in cristae
• H+ atoms contain high energy e-
• e- transported from molecule to molecule along
•
•
•
•
cristae losing energy each time
Energy used to pump p+ of H atoms across matrix
membrane
[H+] increases between inner and outer membranes
concentration gradient is created
concentration gradient drives ATP production
(chemiosmosis)
Electron Transport Chain (ETC)
 Role of oxygen
• e- produced above must be removed
• O2 is final acceptor of e• O2 also accepts H+ protons
• Result: O2 + 4e- + 4 H+  2 H2O
• http://www.johnkyrk.com/mitochondrion.swf
Movie for your viewing pleasure…
 Electron Transport System and ATP Synthesis
 Harvard Cell Krebs Cycle
From trucks to energy….
NADH + H+ + 3 ADP + 3 Pi + 1/2 O2  NAD+ + H2O + 3 ATP
FADH2 + 2 ADP + 2 Pi + 1/2 O2  FAD+ + H2O + 2 ATP
To sum it all up…
 The Final Yield: the complete oxidation of glucose in
aerobic respiration can be summarized as:
The end is near…
Glucose
2 ATP produced directly
Glycolysis
Pyruvic
Acid
2 NADH
+
2 NADH
6 ATP through ETC
+
Acetyl CoA
Krebs
Cycle
+
6 ATP through ETC*
2 ATP produced directly
6 NADH
2 FADH2
+
18 ATP through ETC
+
4 ATP through ETC
38 ATP
To really sum it up succinctly…
What about everything else that we eat?