1. Harvesting stored energy
Energy is stored in organic molecules
carbohydrates, fats, proteins
Heterotrophs eat these organic molecules  food
digest organic molecules to get…
raw materials for synthesis
fuels for energy
controlled release of energy
“burning” fuels in a series of step-by-step enzyme-controlled reactions
We eat to take in the fuels to make ATP which will then be used to help us build biomolecules and grow and move and… live!
heterotrophs = “fed by others”
vs.
autotrophs = “self-feeders”

2. Photosynthesis in chloroplasts Cellular respiration in mitochondria
Figure 9.2
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
 O2
Organic molecules
CO2  H2O
Cellular respiration in mitochondria
Figure 9.2 Energy flow and chemical recycling in ecosystems.
ATP powers most cellular work
ATP
Heat energy

5. ATP Living economy Fueling the body’s economy Need an energy currency
eat high energy organic molecules
food = carbohydrates, lipids, proteins, nucleic acids
break them down
digest = catabolism
capture released energy in a form the cell can use
Need an energy currency
a way to pass energy around
need a short term energy storage molecule
ATP
Whoa! Hot stuff!

6. ATP Adenosine TriPhosphate nucleotide = adenine + ribose + Pi  AMP
modified nucleotide
nucleotide = adenine + ribose + Pi  AMP
AMP + Pi  ADP
ADP + Pi  ATP
adding phosphates is endergonic
Marvel at the efficiency of biological systems!
Build once = re-use over and over again.
Start with a nucleotide and add phosphates to it to make this high energy molecule that drives the work of life.
Let’s look at this molecule closer.
Think about putting that Pi on the adenosine-ribose ==>
EXERGONIC or ENDERGONIC?
How efficient!
Build once, use many ways
high energy bonds

7. How does ATP store energy?
I think he’s a bit unstable… don’t you? P O– O –O P O– O –O P O– O –O
AMP
ADP
ATP
Each negative PO4 more difficult to add
a lot of stored energy in each bond
most energy stored in 3rd Pi
3rd Pi is hardest group to keep bonded to molecule
Bonding of negative Pi groups is unstable
spring-loaded
Pi groups “pop” off easily & release energy
Not a happy molecule
Add 1st Pi  Kerplunk! Big negatively charged functional group
Add 2nd Pi  EASY or DIFFICULT to add? DIFFICULT takes energy to add = same charges repel  Is it STABLE or UNSTABLE? UNSTABLE = 2 negatively charged functional groups not strongly bonded to each other So if it releases Pi  releases ENERGY
Add 3rd Pi  MORE or LESS UNSTABLE? MORE = like an unstable currency • Hot stuff! • Doesn’t stick around • Can’t store it up • Dangerous to store = wants to give its Pi to anything
Instability of its P bonds makes ATP an excellent energy donor

8. How does ATP transfer energy?+
ATP
ADP
ATP  ADP
releases energy
∆G = -7.3 kcal/mole
Fuel other reactions
Phosphorylation
released Pi can transfer to other molecules
destabilizing the other molecules
enzyme that phosphorylates = “kinase”
How does ATP transfer energy?
By phosphorylating
Think of the 3rd Pi as the bad boyfriend ATP tries to dump off on someone else = phosphorylating
How does phosphorylating provide energy?
Pi is very electronegative. Got lots of OXYGEN!! OXYGEN is very electronegative. Steals e’s from other atoms in the molecule it is bonded to. As e’s fall to electronegative atom, they release energy.
Makes the other molecule “unhappy” = unstable. Starts looking for a better partner to bond to. Pi is again the bad boyfriend you want to dump.
You’ve got to find someone else to give him away to. You give him away and then bond with someone new that makes you happier (monomers get together).
Eventually the bad boyfriend gets dumped and goes off alone into the cytoplasm as a free agent = free Pi.

9. ATP / ADP cycle Can’t store ATP ATP
good energy donor, not good energy storage
too reactive
transfers Pi too easily
only short term energy storage
carbohydrates & fats are long term energy storage
ATP
cellular respiration
7.3 kcal/mole
ADP Pi +
A working muscle recycles over 10 million ATPs per second
Whoa! Pass me the glucose
(and O2)!

10. How do we harvest energy from fuels?
Digest large molecules into smaller ones
break bonds & move electrons from one molecule to another
as electrons move they “carry energy” with them
that energy is stored in another bond, released as heat or harvested to make ATP
• They are called oxidation reactions because it reflects the fact that in biological systems oxygen, which attracts electrons strongly, is the most common electron acceptor.
• Oxidation & reduction reactions always occur together therefore they are referred to as “redox reactions”.
• As electrons move from one atom to another they move farther away from the nucleus of the atom and therefore are at a higher potential energy state.
The reduced form of a molecule has a higher level of energy than the oxidized form of a molecule. • The ability to store energy in molecules by transferring electrons to them is called reducing power, and is a basic property of living systems.
loses e-
gains e-
oxidized
reduced + – + e- e- e-
oxidation
reduction
redox

12. Oxidation & reduction Oxidation Reduction  adding O removing H
loss of electrons
releases energy
exergonic
Reduction
removing O
adding H
gain of electrons
stores energy
endergonic
C6H12O6
6O2
6CO2
6H2O
ATP  +
oxidation
reduction

13. Moving electrons in respiration
Electron carriers move electrons by shuttling H atoms around
NAD+  NADH (reduced)
FAD+2  FADH2 (reduced) P O– O –O C
NH2 N+ H
adenine
ribose sugar
phosphates
NAD+
nicotinamide
Vitamin B3
niacin
NADH P O– O –O C
NH2 N+ H H
How efficient!
Build once, use many ways + H
reduction
Nicotinamide adenine dinucleotide (NAD) — and its relative nicotinamide adenine dinucleotide phosphate (NADP) which you will meet in photosynthesis — are two of the most important coenzymes in the cell.
In cells, most oxidations are accomplished by the removal of hydrogen atoms. Both of these coenzymes play crucial roles in this.
Nicotinamide is also known as Vitamin B3 is believed to cause improvements in energy production due to its role as a precursor of NAD (nicotinamide adenosine dinucleotide), an important molecule involved in energy metabolism. Increasing nicotinamide concentrations increase the available NAD molecules that can take part in energy metabolism, thus increasing the amount of energy available in the cell.
Vitamin B3 can be found in various meats, peanuts, and sunflower seeds. Nicotinamide is the biologically active form of niacin (also known as nicotinic acid).
FAD is built from riboflavin — also known as Vitamin B2. Riboflavin is a water-soluble vitamin that is found naturally in organ meats (liver, kidney, and heart) and certain plants such as almonds, mushrooms, whole grain, soybeans, and green leafy vegetables. FAD is a coenzyme critical for the metabolism of carbohydrates, fats, and proteins into energy.
oxidation
carries electrons as a reduced molecule

14. Overview of cellular respiration
4 metabolic stages
Anaerobic respiration
1. Glycolysis
respiration without O2
in cytosol
Aerobic respiration
respiration using O2
in mitochondria
2. Pyruvate oxidation
3. Citric Acid (Krebs) cycle
4. Electron transport chain
C6H12O6
6O2
ATP
6H2O
6CO2  +
(+ heat)

16. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration (Energy stored in NADH and FADH2 is used to produce ATP)
© 2011 Pearson Education, Inc.

17. A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP
© 2011 Pearson Education, Inc.

18. Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate
Glycolysis occurs in the cytoplasm and has two major phases
Energy investment phase
Energy payoff phase
Glycolysis occurs whether or not O2 is present
© 2011 Pearson Education, Inc.

19. Glycolysis 6C 3C Breaking down glucose glucose      pyruvate 2x
“glyco – lysis” (splitting sugar)
ancient pathway which harvests energy
where energy transfer first evolved
transfer energy from organic molecules to ATP
still is starting point for ALL cellular respiration
but it’s inefficient
generate only 2 ATP for every 1 glucose
occurs in cytosol
In the cytosol? Why does that make evolutionary sense?
glucose      pyruvate 2x 6C 3C
Why does it make sense that this happens in the cytosol?
Who evolved first?
That’s not enough ATP for me!

20. Evolutionary perspective
Enzymes of glycolysis are “well-conserved”
Prokaryotes
first cells had no organelles
Anaerobic atmosphere
life on Earth first evolved without free oxygen (O2) in atmosphere
energy had to be captured from organic molecules in absence of O2
Prokaryotes that evolved glycolysis are ancestors of all modern life
ALL cells still utilize glycolysis
The enzymes of glycolysis are very similar among all organisms. The genes that code for them are highly conserved.
They are a good measure for evolutionary studies. Compare eukaryotes, bacteria & archaea using glycolysis enzymes.
Bacteria = 3.5 billion years ago
glycolysis in cytosol = doesn’t require a membrane-bound organelle
O2 = 2.7 billion years ago
photosynthetic bacteria / proto-blue-green algae
Eukaryotes = 1.5 billion years ago
membrane-bound organelles!
Processes that all life/organisms share:
Protein synthesis
Glycolysis
DNA replication
You mean we’re related? Do I have to invite them over for the holidays?

21. endergonic
invest some ATP
exergonic
harvest a little ATP & a little NADH
net yield
2 ATP
2 NADH

22. If you get bored……but you don’t need to know this!!!

23. Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules
In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed
© 2011 Pearson Education, Inc.

24. The Citric Acid Cycle
The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn
© 2011 Pearson Education, Inc.

25. Citric acid cycle Acetyl CoA Oxaloacetate Malate Citrate Isocitrate
Figure
Acetyl CoA
CoA-SH
NADH 1
H2O
+ H
NAD
Oxaloacetate 8 2
Malate
Citrate
Isocitrate
NAD
Citric acid cycle
NADH 3 7
+ H
H2O
CO2
Fumarate
CoA-SH
-Ketoglutarate 4
Figure 9.12 A closer look at the citric acid cycle. 6
CoA-SH 5
FADH2
CO2
NAD
FAD
Succinate
P i
NADH
GTP
GDP
Succinyl CoA
+ H
ADP
ATP