1. Metabolism and Energy

2. Metabolic reactions & energy
Some chemical reactions release energy
exergonic
breaking polymers
hydrolysis = catabolism
Some chemical reactions require input of energy
endergonic
building polymers
dehydration synthesis = anabolism
digesting molecules= less organization= lower energy state
building molecules= more organization= higher energy state

3. Examples
dehydration synthesis
hydrolysis

4. Endergonic vs. exergonic reactions
energy released
energy invested G
G = change in free energy = ability to do work

5. Energy & life Organisms require energy to live
where does that energy come from?
coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy)
energy + +
An exergonic reaction is coupled (paired) with an endergonic reaction so that the energy from the first can be supplied to the second. Ex: cell respiration making ATP for muscle contraction
energy + +

6. Spontaneous reactions?
If reactions are “downhill”, why don’t they just happen spontaneously?
because covalent bonds are stable
Why don’t polymers (carbohydrates, proteins & fats) just spontaneously digest into their monomers

7. Activation energy
Breaking down large molecules requires an initial input of energy
activation energy
large biomolecules are stable
must absorb energy to break bonds
Need a spark to start a fire
energy
cellulose
CO2 + H2O + heat

8. Activation energy the amount of energy needed to start the reaction.
moves the reaction over an “energy hill”
2nd Law of thermodynamics
Universe tends to disorder
so why don’t proteins, carbohydrates & other biomolecules breakdown?
at temperatures typical of the cell, molecules don’t make it over the hump of activation energy
but, a cell must be metabolically active
heat would speed reactions, but… would denature proteins & kill cells

9. Catalysts So what’s a cell to do to reduce activation energy? ENZYMES
get help! … chemical help…
ENZYMES
Call in the... ENZYMES! G

10. Energy needs of life Organisms are endergonic systems
synthesis (biomolecules)
reproduction
active transport
movement
temperature regulation
Organisms are endergonic systems
What do we need energy for?
Which is to say… if you don’t eat, you die… because you run out of energy.
The 2nd Law of Thermodynamics takes over!

11. ATP Living economy Fueling the economy Need an energy currency
eat high energy organic molecules (food)
break them down = catabolism (digest)
capture energy in form cell can use
Need an energy currency
a way to pass energy around
ATP
Whoa! Hot stuff!

12. Build once, use many ways
ATP
Adenosine Triphosphate
modified nucleotide
adenine + ribose + Pi  AMP
AMP + Pi  ADP
ADP + Pi  ATP
How efficient!
Build once, use many ways
an RNA nucleotide
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?

13. Why does ATP store energy?
Why is the 3rd phosphate like a bad boyfriend? P O– O –O P O– O –O P O– O –O P O– O –O P O– O –O
Each Pi group more difficult to add
a lot of stored energy in each bond
most stored in 3rd Pi
Phosphorylation...
Storing energy with ATP
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
spring-loaded
instability of its P bonds makes ATP an excellent energy donor

14. An example of Phosphorylation…
Building polymers from monomers
need ATP for energy & to take the water out C H OH O +
H2O
+4.2 kcal/mol C H OH + P
ATP
ADP
-7.3 kcal/mol
“kinase” enzyme
Monomers  polymers
Not that simple!
H2O doesn’t just come off on its own
You have to pull it off by phosphorylating monomers.
Polymerization reactions (dehydration synthesis) involve a phosphorylation step!
Where does the Pi come from? ATP H OH C O + P Pi
-3.1 kcal/mol

15. A working muscle recycles over 10 million ATPs per second
ATP / ADP cycle
Can’t store ATP
too reactive
transfers Pi too easily
only short term energy storage
carbs & fats are long term energy storage
Coupling of exergonic and endergonic reactions.
A working muscle recycles over 10 million ATPs per second

16. “The point is to make ATP!”
What’s the point?
Cells spend a lot of time making ATP!
“The point is to make ATP!”
For chemical, mechanical, and transport work
Make ATP! That’s all I do all day. And no one even notices!
I didn’t HEAR you!