Introductory Questions #6
1)
Explain how potential energy is different from kinetic
energy. What are some ways we can measure energy?
2) Define each variable in the equation:
∆G = ∆H – T ∆S
3) How much energy expenditure will Trent Samaha have to
exert to ask Ema Armstrong to Homecoming? (Ema
please go outside to answer the question…NOW!)♥
3.5)What is the difference between an exergonic reaction and
an endergonic reaction?
4) How is ATP associated with coupled reactions? What
purpose does it serve?
5) How is an electron carried from one molecule to the next?
Name a molecule that can carry an electron.
Chapter 8
An Introduction to Energy & Metabolism
(Pages 141-159)
Topics:
•Thermodynamic Laws
•Catabolism & Anabolism (metabolism)
•Exergonic vs. Endergonic Reactions
•Free Energy
•ATP Cycle & Energy Coupling
•Enzyme (structure & function)
Main Topics to Cover-Ch. 8
•
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Potential vs. Kinetic Energy
First Two Laws of Thermodynamics
Entropy, Enthalpy, and Free Energy
Endergonic vs. Exergonic Reactions
Anabolism & Catabolism = Metabolism
Energy Coupling: Oxidation/Reduction
ATP; Structure & Function
Enzymes Structure & Function (Lab #6)
-allosteric, feedback mechanisms, inhibitory sit.
Energy is the capacity to perform
work
• Energy is defined as the capacity to do work
• All organisms require energy to stay alive
• Energy makes change possible
ENERGY AND THE CELL
• Living cells are compartmentalized by
membranes
• Membranes are sites where chemical
reactions can occur in an orderly manner
• Living cells process energy by means of
enzyme-controlled chemical reactions
• Kinetic energy is
energy that is actually
doing work
Figure 5.1A
• Potential energy is
stored energy
Figure 5.1B
Thermodynamics
• Energy (E)~ capacity to do work; Kinetic energy~ energy of
motion; Potential energy~ stored energy
• Thermodynamics~ study of E transformations
• 1st Law: conservation of energy; E transferred/transformed,
not created/destroyed
• 2nd Law: transformations increase entropy (disorder,
randomness)
• Combo: quantity of E is constant, quality is not
Two laws govern energy conversion
• First law of thermodynamics
• Energy can be changed from one form to
another
– However, energy cannot be created or
destroyed
Figure 5.2A
• Second law of thermodynamics
• Energy changes are not 100% efficient
– Energy conversions increase disorder, or
entropy
– Some energy is always lost as heat
Figure 5.2B
Metabolism/Bioenergetics
• Metabolism: The totality of an organism’s
chemical processes; managing the
material and energy resources of the cell
• Catabolic pathways: degradative process
such as cellular respiration; releases
energy
• Anabolic pathways: building process such
as protein synthesis; photosynthesis;
consumes energy
Equation Used to Determine Free
Energy of a System
G = H - T S
G: Quantity of Free Energy
H: Enthalpy = System’s Total Energy
(chemical Bond energy)
T: Temperature (absolute temp. in Kelvin units)
S: Entropy = Disorder of the system
Spontaneous Reaction = G will be negative
(energy is released ie. Exergonic.)
Non spontaneous Reaction (Endergonic) G will be positive.
What happens when G
is ZERO ???
Free Energy
• Free energy: portion of system’s E that can perform work
(at a constant T)
• Exergonic reaction: net release of free E to surroundings
• Endergonic reaction: absorbs free E from surroundings
ATP & Energy Coupling
See Pgs.
ATP shuttles chemical energy within
the cell
• ATP is thought as the energy “currency” of a
cell
• In cellular respiration, some energy is stored
in ATP molecules
• ATP powers nearly all forms of cellular work
• ATP molecules are the key to energy
coupling
General Facts about ATP
• Human use about 99 lbs of ATP each day
@rest
• Every second 10 million ATP’s are made
from ADP
• Bacteria has about a one-second supply of
ATP
Energy Coupling & ATP
• Energy coupling: use of exergonic process
to drive an endergonic one (ATP)
• Adenosine triphosphate (nucleotide w/3 PO4’s)
• ATP tail: high negative charge
• ATP hydrolysis: release of free Energy
• Phosphorylation: binding of the released
phosphate to another molecule
Introductory Video for Chapter 8
“Metabolism”
1) Name the American Olympiad profiled in this video.
What condition did she have?
2) What are the two major reasons why cells use
energy?
3) What unique metabolic process does Dr. Margo
Haygood discuss in the video? Name the enzyme
used for this process.
4) Which two laws of thermodynamics are summarized
by Dr. Saltman & Dr. Haygood?
5) Briefly explain how enzymes are able to speed up
reactions based on the information from the video.
Describe the mechanisms that regulate enzyme
activity.
The Hydrolysis of ATP
• When the bond joining a phosphate group to
the rest of an ATP molecule is broken by
hydrolysis, the reaction supplies energy for
cellular work. G = -32 KJ/mol (-7.6 Kcal/mol)
Adenine
Phosphate
groups
Hydrolysis
Energy
Ribose
Adenosine triphosphate
Adenosine diphosphate
(ADP)
Figure 5.4A
Figure 5.4C
Hydrolysis
Energy from
exergonic
reactions
Dehydration synthesis
• The ATP
cycle
Energy for
endergonic
reactions
Example of Energy Coupling w/ATP
• Forming the Disaccharide Sucrose involves:
glucose + fructose → sucrose (G = +27 KJ/mol)
ENDERGONIC Reaction
Couple w/hydrolysis of ATP (G = - 32KJ/mol)
Occurs in a couple of reaction steps:
Reaction#1: Glucose + ATP → glucose-P + ADP
**glucose has been phosphorylated
**ATP has been hydolyzed
Reaction #2: Glucose-P + fructose → Sucrose + Pi
(Pi is a low energy inorganic phosphate)
• How ATP powers cellular work
Reactants
Potential energy of molecules
Products
Work
Protein
Figure 5.4B
Three Functions of ATP
Enzymes: Structure & Function
See Pgs. 150-157
Lab #3- Enzyme Catalysis w/Catalase
Three Parts to the lab:
• Establish Baseline Amount of H2O2
• Uncatalyzed Decomposition of H2O2
• Time Trials w/Catalase to determine Rxn rate
• Procedure:
–
–
–
–
–
–
–
10 ml H2O2 in a beaker
1.0 ml (H2O or Catalase)
10 ml 1 M H2SO4
Mix well
Take a 5 ml sample and titrate in KMnO4
Read Initial and final measurements on buret
Record Data
Enzymes speed up the cell’s chemical
reactions by lowering energy barriers
• For a chemical reaction to begin, reactants
must absorb some energy
– This energy is called the energy of activation
(EA)
– This represents the energy barrier that prevents
molecules from breaking down spontaneously
Enzymes
• Catalytic proteins: change
the rate of reactions w/o
being consumed
• Free E of activation
(activation E): the E
required to break bonds
• Substrate: enzyme reactant
• Active site: pocket or
groove on enzyme that
binds to substrate
• Induced fit model
• A protein catalyst called an enzyme can
decrease the energy barrier
Enzyme
EA
barrier
Reactants
1
Figure 5.5A
Products
2
A Specific Enzyme Catalyzes
each Cellular Reaction
• Enzymes are selective
– This selectivity determines which chemical
reactions occur in a cell
How an Enzyme Works-Sucrase
How Enzymes Work
• http://www.ekcsk12.org/science/aplabrevie
w/lab02.htm
**Description of Enzyme Lab
• Lab Simulation:
http://bioweb.wku.edu/courses/Biol114/enzy
me/enzyme1.asp
Effects on Enzyme Activity
• Temperature
• pH
• Cofactors:
inorganic, nonprotein
helpers; ex.: zinc, iron,
copper
• Coenzymes:
organic helpers
ex. vitamins
Enzyme Inhibitors
• Irreversible (covalent); reversible (weak bonds)
• Competitive: competes for active site (reversible); mimics
the substrate
• Noncompetitive: bind to another part of enzyme (allosteric
site) altering its conformation (shape); poisons, antibiotics
Enzyme inhibitors block enzyme
action
• Inhibitors interfere with enzymes
– A competitive
inhibitor takes
the place of a
substrate in the
active site
– A noncompetitive
inhibitor alters an
enzyme’s function
by changing its shape
Substrate
Active
site
Enzyme
NORMAL BINDING OF SUBSTRATE
Competitive
inhibitor
Noncompetitive
inhibitor
ENZYME INHIBITION
Figure 5.8
Competitive & Noncompetitive Inhibitors
The Cellular environment affects
enzyme activity
• Enzyme activity is influenced by
– temperature
– salt concentration
– pH
• Some enzymes require non-protein
cofactors such as: Fe, Zn, Cu, etc.
Some Pesticides and Antibiotics
inhibit Enzymes
• Certain pesticides are toxic to insects
because they inhibit key enzymes in the
nervous system
• Many antibiotics inhibit enzymes that are
essential to the survival of disease-causing
bacteria
– Penicillin inhibits an enzyme that bacteria use in
making cell walls
Allosteric Enzymes-How they Work
Feedback Inhibition
Introductory Questions #6
1) Explain how potential energy is different from
kinetic energy. What are some ways we can
measure energy?
2) Define each variable in the equation:
∆G = ∆H – T ∆S
3) What is the difference between an exergonic
reaction and an endergonic reaction?
4) How is ATP associated with coupled reactions?
What purpose does it serve?
5) How is an electron carried from one molecule to
the next? Name a molecule that can carry an
electron.
Introductory Questions #7
1) Name three ways that enzyme activity can be
measured as mentioned in your lab guidesheet.
2) Explain how the reactivity of pepsin is different
from trypsin. (see pg. 154)
3) Give an two examples of a cofactor and two
examples of a conenzyme. How are they
different?
4) How is a competitive inhibitor different from a
non-competitive inhibitor?
5) What is an allosteric enzyme?
Energy Transfer in Redox
Reactions
See Pgs. 161-162
Redox-Defining Terms
• Oxidation = Electrons are lost
• Reduction = Electrons are gained
• These two reactions are complementary and
occur simultaneously (they must go together)
• Electrons cannot exist in a free state, they must
be associated with a molecule
• This process allows electrons to be transferred
from one molecule to another
• Often occur in a series
• Essential for cellular respiration & Photosynthesis
Electrons are transferred by a
carrier molecule by the hydrogen
atom
• Common electron carrier: NAD+
• NAD+ is Nicotinamide adenine dinucleotide
• When NAD+ is reduced it gains an electron
and becomes reduced.
• The electron losses some of its free energy
during the transfer
• Expressed as: X-H2 + NAD+  X+ NADH + H+
(oxidized)
(reduced)
Other Electron Carriers (hydrogen acceptors)
• NADP+
(see in photosynthesis)
• FAD +
(see in the Kreb cycle for cellular respiration)
• Cytochromes – embedded in membranes
**Remember that:
Reduced state more free energy vs.
Oxidized state which has less free energy
Cool “Fires” Attract Mates and Meals
• Fireflies use light,
instead of chemical
signals, to send signals
to potential mates
• Females can also use
light flashes to attract
males of other firefly
species — as meals,
not mates
• The light comes
from a set of
chemical reactions,
the luciferinluciferase system
• Fireflies make light
energy from
chemical energy
• Life is dependent on
energy conversions