METABOLISM
 Chapter 8
An Introduction to
Metabolism (Part 1)
Metabolism = total of
an organism’s
chemical reactions
AP Biology
Flow of energy through life
 Life is built on chemical reactions

transforming energy from one form to another (solar to
chemical)

transferring energy (giraffe to lion)
organic molecules  ATP &
organic
molecules
sun
solar energy 
AP
Biology
ATP
& organic molecules
organic molecules 
ATP & organic molecules
http://www.youtube.com/watch?v=JZU82G3_lAk
Metabolism
Circle the correct answer.
 Chemical reactions of life

forming bonds between molecules
synthesis/Hydrolysis
 Dehydration
___________________
 synthesis
anabolic/catabolic reactions
 ___________

breaking bonds between molecules
synthesis/Hydrolysis
 Dehydration
________________
 digestion
 anabolic/catabolic
___________ reactions
AP Biology
That’s why
they’re called
anabolic steroids!
Metabolism
 Chemical reactions of life

forming bonds between molecules
 dehydration synthesis
 synthesis
 anabolic reactions

breaking bonds between molecules
 hydrolysis
 digestion
 catabolic reactions
AP Biology
That’s why
they’re called
anabolic steroids!
Thermodynamics
http://www.scienceanimations.com/support-files/energy.swf
 Energy (E)~ capacity to do work;


Kinetic energy: _______________________
Potential energy: _____________________________
 Thermodynamics~ study of Energy transformations
 1st Law: conservation of energy

Energy is transferred/transformed, not created/destroyed
 2nd Law: transformations affect entropy
(disorder, randomness)
potential
Kinetic
Zoom zoom!
APNote:
quantity of E is constant, quality is not
Biology
Thermodynamics
http://www.scienceanimations.com/support-files/energy.swf
 Energy (E)~ capacity to do work;


Kinetic energy: energy of motion (does work);
Potential energy: stored energy (has the potential to do work)
 Thermodynamics~ study of Energy transformations
 1st Law: conservation of energy

Energy is transferred/transformed, not created/destroyed
 2nd Law: transformations affect entropy
(disorder, randomness)
potential
Kinetic
Zoom zoom!
APNote:
quantity of E is constant, quality is not
Biology
Free energy
How does an increase in ΔS affect ΔG?
How does a decrease in ΔS affect ΔG?
• Free energy: the portion that
can perform work
• ΔG = ΔH – TΔS
• ΔH: change in enthalpy
the quantity of energy of
• T: Temperature in Kelvin motion of the component
particles
• ΔS: change in system entropy
H2O(l) -> 2 H2(g) + O2(g)
AP Biology
Free energy
 Free energy: portion of system’s E that can perform work
(@ cst T)
 Exergonic reaction: ______________________________
 Endergonic reaction: _____________________________
AP Biology
Free energy
 Free energy: portion of system’s E that can perform work
(@ cst T)
 Exergonic reaction: net release of free E to surroundings
(“ex” = out)
 Endergonic reaction: absorbs free E from surroundings
(“en”=in)
AP Biology
Spontaneity
 Spontaneous
processes occur
without energy input
(negative ΔG)

System must give up
energy/enthalpy (ΔH)
or give up order (ΔS)
ΔG = ΔH – TΔS
 Other processes
need energy input
(positive/zero ΔG)
AP Biology
Indicate the sign of DG in the box of each diagram.
Spontaneity
 Spontaneous
processes occur
without energy input
(negative ΔG)

System must give up
energy/enthalpy (ΔH)
or give up order (ΔS)
ΔG = ΔH – TΔS
 Other processes
need energy input
(positive/zero ΔG)
AP Biology
Chemical reactions & energy
 Some chemical reactions release energy
exergonic
 digesting polymers
 hydrolysis = catabolism

digesting molecules=
LESS organization=
lower energy state
& higher entropy
 Some chemical reactions require
input of energy
building molecules=
MORE organization=
higher energy state
& less entropy
endergonic
 building polymers
 dehydration synthesis = anabolism

AP Biology
Endergonic vs. exergonic reactions
exergonic
endergonic
- energy released
- digestion/hydrolysis
- energy invested
- synthesis
+DG
-DG
AP Biology
DG = change in free energy = ability to do work
The energy needs of life
 Organisms are endergonic systems

What do we need energy for?
 synthesis
 building biomolecules
 reproduction
 movement
 active transport
 temperature regulation
AP Biology
Where do we get the energy from?
 Work of life is done by energy coupling

use exergonic (catabolic) reactions to
fuel endergonic (anabolic) reactions
digestion
+
+
synthesis
+
AP Biology
+
energy
Give a biological example of coupling. Hint – plants.
energy
Living economy
 Fueling the body’s economy

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
AP Biology
ATP
 Adenosine TriPhosphate

modified nucleotide
 nucleotide =
adenine + ribose + Pi  AMP
 AMP + Pi  ADP
 ADP + Pi  ATP
 adding phosphates is endergonic
Efficient!
Build once,
use many ways
AP Biology
high energy
bonds
How does ATP store energy?
O–
–O P
ATP
O
O–
–O–P
O
O–
–O–P
How unstable…
O–
O
 Subsequent PO4 s 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
AP
Biology
How
does the instability of the P bonds make ATP an excellent energy donor?
How does ATP transfer energy?
O–
–O P
O
ATP
O–
–O–P
O–
–O–P
O
O–
O–
–O P
O
 ATP  ADP

O–
+
O
Pi
releases energy
 ∆G = -7.3 kcal/mole
 Fuel other reactions
 Phosphorylation

released Pi can transfer to other molecules
 destabilizing the other molecules

AP Biology
enzyme that phosphorylates = “kinase”
7.3
energy
Explain.
An example of Phosphorylation…
 Building polymers from monomers
need to destabilize the monomers
 phosphorylate!

H
C
OH
+
H
C
HO
synthesis
+4.2 kcal/mol
“kinase”
H
C
OH
+
H
C
AP Biology
ATP
enzyme
-7.3 kcal/mol
H
+
P
C
HO
H H
C C
OHHO
enzyme
H H
+
C C
O
H2O
H
+
C
ADP
P
H H
-3.1 kcal/mol
C C
O
+
Pi
Organization of the Chemistry of Life
into Metabolic Pathways
A metabolic pathway:
begins with
a specific
molecule
(reactant) &
ends with a
product.
Enzyme 1
A
Enzyme 2
B
Enzyme 3
C
Starting
molecule
Each step is catalyzed by a specific enzyme.
Enzymes are specific.
AP Biology
D
Product
Enzymes are proteins
 Enzymes interact with substrate
AP Biology
Specificity of Ser-Protease Family
cut at Lys, Arg
Deep and negatively
charged pocket
O
O
–C–N–C–C–N–
C
C
C
C
NH3
+
COOC
Asp
AP Biology
Chymotrypsin
Elastase
cut at Trp, Phe, Tyr
cut at Ala, Gly
O
O
–C–N–C–C–N–
C
O
O
–C–N–C–C–N–
CH3
Shallow and
non-polar
pocket
Non-polar
pocket
Active Site
Enzymes are specific!
Juang RH (2004) BCbasics
Trypsin