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Ground Rules of Metabolism
Chapter 6 Part 1
Impacts, Issues:
A Toast to Alcohol Dehydrogenase
 In the liver, alcohol dehydrogenase helps break down
toxic alcohols, but at the expense of liver function and
energy metabolism( 12oz beer, 5oz wine, 1oz of vodka
all have the same effects on the liver)
Energy Disperses
 First law of thermodynamics
• Energy is neither created nor destroyed (goes back
into the evnrionment as heat), but can be transferred
from one form to another
 Second law of thermodynamics
• Entropy (a measure of dispersal of energy in a
system) increases spontaneously ( Ex.Heat/pan)
• Energy is converted from a more concentrated
form to a less concentrated form when energy is
transferred.
One Way Flow of Energy
 The total amount of energy available in the
universe to do work is always decreasing
• Each time energy is transferred, some energy
escapes as heat; thermal energy decreased (not
useful for doing work)
• Potential energy can be converted to kinetic
energy, ATP in muscle cells (mechanical energy)
gives up potential energy to contractile units,
chemical energy is converted to kinetic energy.
Energy In, Energy Out
 Reaction
• A chemical change that occurs when atoms, ions,
or molecules interact
 Reactant
• Atoms, ions, or molecules that enter a reaction
 Product
• Atoms, ions, or molecules remaining at the end of
a reaction
Reactants
2 H2
O2
+
(hydrogen)
(oxygen)
4 hydrogen
atoms
Products
2 H2O
(water)
2 oxygen
atoms
Fig. 6-6, p. 96
Reactions Require or Release Energy
 We can predict whether a reaction requires or
releases energy by comparing the bond
energies of reactants with those of products
 Endergonic (“energy in”)
• Reactions that require a net input of energy (Ex.
Photosynthesis)
 Exergonic (“energy out”)
• Reactions that end with a net release of energy
(Ex. Cellular Respiration)
Why the World Doesn’t Go Up in Flames
 Activation energy
• The minimum amount of energy needed to get a
reaction started or to proceed on its own.
ATP – The Cell’s Energy Currency
 ATP (adenosine triphosphate)
• A nucleotide with three phosphate groups
• Gives up a phosphate group and energy to other
molecules
• Primes stable molecules to react (Ex. PGA gives
up a P group to ADP
• Made by all cells
 Phosphorylation
• A phosphate-group transfer
adenine
ribose
AMP
P
ADP
P
ATP
P
B The molecule is called ATP when it has three phosphate groups.
After it loses one phosphate group, the molecule is called ADP
(adenosine diphosphate); after losing two phosphate groups it is
called AMP (adenosine monophosphate).
Fig. 6-9b, p. 97
Animation: Mitochondrial chemiosmosis
6.3 How Enzymes
Make Substances React
 Enzyme
• A catalyst that makes a reaction occur much faster
than it would on its own
• Enzymes are not consumed or changed by
participating in a reaction
• Most are proteins (organic molecules, some are RNA
• Are very specific and have special shapes
 Substrate
• The specific reactant acted upon by an enzyme
How Enzymes Work
 Enzymes lower the activation energy required to
bring on the transition state, when substrate
bonds break
 Active sites
• A groove in the structure of the enzyme where
substrates bind and reactions proceed
Transition state
Free energy
Activation energy
without enzyme
Activation energy
with enzyme
Reactants
Products
Time
Fig. 6-11, p. 98
Transition state
Free energy
Activation energy
without enzyme
Activation energy
with enzyme
Reactants
Products
Time
Stepped Art
Fig. 6-11, p. 98
Animation: Activation energy
Mechanisms of
Enzyme-Mediated Reactions
 Binding at enzyme active sites may bring on the
transition state by four mechanisms
• Helping substrates get together they will react
• Orienting substrates in positions that favor
reaction
• Inducing a fit between enzyme and substrate
(induced fit model- enzyme sqeezes the
substrate)
Effects of Temperature, pH, and Salinity
 Raising the temperature boosts reaction rates by
increasing a substrate’s energy
• But very high temperatures denature enzymes
• Optimum temperature (37-40°celcius)
 Each enzyme has an optimum pH range (6-8)
Help from Cofactors
 Cofactors
• Atoms or molecules (other than proteins) that are
necessary for enzyme function
 Coenzymes
• Organic cofactors such as vitamins
• Examples: NAD and FAD