All living systems require constant
input of free energy.
Metabolism and Energy
AP Biology
The First Law of Thermodynamics
Energy cannot be created or destroyed,
only transformed.
Living systems need to continually acquire
and transform energy
in order to remain
alive.
“Free energy”: The
energy available in a
system to do work.
AP Biology
Flow of energy through life
 Life is built on chemical reactions

transforming energy from one form to
organic molecules  ATP
another
& organic molecules
sun
solar energy 
AP
Biology
ATP
& organic molecules
organic molecules 
ATP & organic molecules
The 2nd Law of Thermodynamics
Every time energy is transformed, the
entropy (“disorder”) of the universe
increases.
In order to increase/
maintain their internal
order, living systems
must process more
ordered forms of
matter in to less
ordered ones
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Living Systems are “Open” Systems
Matter and energy move in to living systems
from the environment. Living systems
transform matter and energy and return it to
the environment
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Multi-Step Metabolism
To increase control, living systems produce free energy
in multiple-step pathways, mediated by enzyme catalysts.
AP Biology
Metabolic Reactions
 Can form bonds between molecules
dehydration synthesis
 synthesis
 anabolic reactions
 ENDERGONIC

building molecules=
more organization=
higher energy state
 Can break bonds between molecules
hydrolysis
 digestion
 catabolic reactions
 EXERGONIC

AP Biology
breaking down molecules=
less organization=
lower energy state
Endergonic vs. exergonic reactions
exergonic
endergonic
- energy released
- digestion
- energy input
- synthesis
+G
-G
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G = change in free energy = ability to do work
What drives reactions?
 If some reactions are “downhill”, why
don’t they just happen spontaneously?

because covalent bonds are stable bonds
Stable polymers
don’t spontaneously
digest into their
monomers
AP Biology
Getting the reaction started…
 Breaking down large molecules
requires an initial input of energy
activation energy
 large biomolecules are stable
 must absorb energy to break bonds

Can cells
use heat to
break the
bonds?
AP Biology
cellulose
energy
CO2 + H2O + heat
Too much activation energy for life
 The amount of energy needed to
destabilize the bonds of a molecule

moves the reaction over an “energy hill”
Not a match!
That’s too much
energy to expose
living cells to!
AP Biology
Catalysts
 So what’s a cell got to do to reduce
activation energy?

get help! … chemical help… ENZYMES
Call in the
ENZYMES!
G
AP Biology
Energy needs of life
 Organisms are endergonic systems

What do we need energy for?
 synthesis (biomolecules)
 reproduction
 active transport
 movement
 temperature regulation
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2005-2006
Metabolic pathways
 Work of life is done by energy coupling

use exergonic (catabolic) reactions to
fuel endergonic (anabolic) reactions
+
+
AP Biology
+
energy
+
energy
Metabolic Strategies
 Temperature must be maintained for
metabolic reactions.
Ectotherms vs. endotherms
 Body size vs. metabolic rate

 Reproductive strategies optimized
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Insufficient Free Energy Production
 Individual = disease or death
 Population = decline of a population
 Ecosystem = decrease in complexity
Less productivity
 Less energy moving
through system

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Living economy
 Fueling the body’s economy

eat high energy organic molecules
 food = carbohydrates, lipids, proteins, nucleic acids

break them down
 catabolism = digest

capture released energy in a form the cell can use
 Uses an energy currency


a way to pass energy around
need a short term energy
storage molecule
Whoa!
Hot stuff!
AP Biology
ATP
ATP
 Adenosine Triphosphate

modified nucleotide
 nucleotide =
adenine + ribose + Pi  AMP
 AMP + Pi  ADP
 ADP + Pi  ATP
 adding phosphates is endergonic
How efficient!
Build once,
use many ways
AP Biology
high energy bonds
How does ATP store energy?
O–
ADP
AMP
ATP
I think
he’s a bit
unstable…
don’t you?
O–
O– O –
O–
–O P
–O–P
–O–P–O PO– –O–P
O–
O
O
O O
O
 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


Pi groups “pop” off easily & release energy
Spring Loaded!
AP Biology
Instability of its P bonds makes ATP an excellent energy donor
How does ATP transfer energy?
O–
–O P
O
ATP
ADP
O–
–O–P
O
O–
–O–P
O–
O–
–O P
O
O–
+
O
 ATP  ADP

releases energy (exergonic)
 Phosphorylation (adding phosphates!)

released Pi can transfer to other molecules
 destabilizing the other molecules

AP Biology
enzyme that phosphorylates = kinase
7.3
energy
An example of Phosphorylation…
 Building polymers from monomers
need to destabilize the monomers
 phosphorylate!

H
C
OH
+
H
C
HO
H
It’s
C
never that
OH
simple!
+
H
C
AP Biology
+
P
H
C
HO
+4.2 kcal/mol
“kinase”
ATP
enzyme
-7.3 kcal/mol
-3.1 kcal/mol
enzyme
H H
C C
O
H
C
H H
C C
OHHO
+
+
H2O
ADP
P
H H
C C
O
+
Pi
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
AP Biology
A working muscle recycles over
10 million ATPs per second
2005-2006
What’s the point?
 Cells spend a lot of time making ATP!
“WHY?”
For chemical, mechanical,
and transport work
Make ATP!
That’s all I
do all day.
And no one
even notices!
AP Biology
3.1: All living systems require constant input of free energy.
2. MATH SKILLS: GIBBS FREE ENERGY
AP Biology
What You Have To Do
Be able to use and interpret the Gibbs Free Energy
Equation to determine if a particular process will occur
spontaneously or non-spontaneously.
ΔG= change in free energy
(- = exergonic, + = endergonic)
ΔH= change in enthalpy for the reaction
(- = exothermic, + = endothermic)
T = kelvin temperature
ΔS = change in entropy
(+ = entropy increase, - = entropy decrease)
Spontaneity
Spontaneous reactions continue once they
are initiated. Non-spontaneous reactions
require continual input of energy to continue.
Using the Equation
To use the equation, you’ll need to be given values.
Exothermic reactions that increase entropy are
always spontaneous/exergonic
Endothermic reactions that decrease entropy are
always non-spontaneous/endergonic.
Other reactions will be spontaneous or not depending
on the temperature at which they occur.
Sample Problem
Determine which of the following reactions will
occur spontaneously at a temperature of 298K,
justify your answer mathematically:
Reaction 1:
A + B → AB
Δ H: +245 KJ/mol
Δ S: -.02 KJ / K
Reaction 2:
BC → B + C
Δ H: -334 KJ/mol
Δ S: +.12 KJ/K
3.1: All living systems require constant input of free energy.
4. MATH SKILLS: COEFFICIENT Q10
What You Have To Do
Be able to use and interpret the Coefficient Q10 equation:
t2 = higher temperature
t1 = lower temperature
k2= metabolic rate at higher temperature
k1= metabolic rate at lower temperature
Q10 = the factor by which the reaction rate increases
when the temperature is raised by ten degrees.
What It Means
Q10 tells us how a particular process will be
affected by a 10 degree change in
temperature.
Most biological processes have a Q10 value
between 2 and 3
Sample Problem
Data taken to determine the effect of
temperature on the rate of respiration in
a goldfish is given in the table below.
Calculate the Q10 value for this data.
Temperature (°C)
Heartbeats per minute
20
18
25
42