An Introduction to Metabolism A.P. Biology Chapter 8 Mr. Knowles Liberty High School.
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Transcript of An Introduction to Metabolism A.P. Biology Chapter 8 Mr. Knowles Liberty High School.
An Introduction to Metabolism
A.P. Biology
Chapter 8
Mr. Knowles
Liberty High School
Why do you eat?What is the purpose of a
food chain?
Answer: Energy and Organic Building Blocks
Bioenergetics• Bioenergetics- how energy
behaves and changes in living systems (food chains).
• Metabolism = Anabolism (require energy to make new bonds) + Catabolism (release energy from bonds)
Energy-The Stuff of Life!• Energy – the capacity to do work.
• Two States of Energy:
–Kinetic Energy- energy of motion.
–Potential Energy- stored energy.
Potential Kinetic Potential
Forms of energy?• Chemical• Mechanical• Electrical• Light• HEAT• Nuclear• Biology – mostly potential chemical and kinetic
chemical; light; heat (from chemical bonds)
• Some organisms – Convert chemical energy to light, as in
bioluminescence
Figure 8.1
Measuring Energy in Biology• In terms of heat changes
(thermodynamics).• Unit of heat in biology – calorie.• 1.0 calorie = amount of heat req’d to
raise 1.0g of H20, 1° C.• In biology, 1.0 kilocalorie (kcal) =
1,000.0 calories (cal)• 1,000 cal = 1.0 kcal. = 1.0 Calorie
• Energy can be converted from one form to anotherOn the platform, a diverhas more potential energy.
Diving converts potentialenergy to kinetic energy.
Climbing up converts kinetic
energy of muscle movement
to potential energy.
In the water, a diver has less potential energy.
Figure 8.2
Photosynthesis • Conversion of unusable light energy
into usable chemical energy.
C6H12O6
Redox Reactions
PhotosynthesisLight
6 CO2 + 12 H2O 6 O2 + 6 H2O
C6H12O6
Stores 686 kcal/mol
Photosynthesis is a Redox Reaction
6 CO2 + 12 H2O 6 O2 + 6 H2O
C6H12O6
H
Cellular Respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O +
ENERGY (ATP)
686 kcal/mole glucose
Cellular Respiration is a Redox Reaction
C6H12O6 + 6 O2 6 CO2 + 6 H2O +
ENERGY (ATP) 686 kcal/mole glucoseH
First Law of Thermodynamics• Energy cannot be created nor
destroyed, but it can be converted from one form to another.
• Ex. Food chains
An example of energy conversion
Figure 8.3
First law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b).
(a)
Chemicalenergy
First Law of ThermodynamicsProducers (Light Energy Potential
Chemical)
1st Order Consumer or Herbivore (Potential Chemical Potential, Kinetic Chemical)
2nd Order Consumer or Carnivore (Potential Chemical Potential, Kinetic Chemical)
HEAT
HEAT
The Second Law of Thermodynamics• According to the second law of thermodynamics
– Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe
Figure 8.3
Second law of thermodynamics: Every energy transfer or transformation increasesthe disorder (entropy) of the universe. For example, disorder is added to the cheetah’ssurroundings in the form of heat and the small molecules that are the by-productsof metabolism.
(b)
Heat co2
H2O
+
Biological Order and Disorder• Living systems
– Increase the entropy of the universe– Use energy to maintain order
50µm
Figure 8.4
2nd Law of Thermodynamics• As energy is transformed from one
state to another, some of the energy is lost as heat (random molecular motion) and the ability to do work decreases.
• Disorder (Entropy) in the universe is increasing.
• Order Disorder
Show me the 2nd Law of Thermodynamics in
Action
Video: Predators: How They Hunt, Cheetahs
Free-Energy Change, G
• A living system’s free energy
– Is energy that can do work under cellular conditions
• At maximum stability– The system is at equilibrium
Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules.
.
Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed.
Gravitational motion. Objectsmove spontaneously from ahigher altitude to a lower one.
• More free energy (higher G)• Less stable• Greater work capacity
• Less free energy (lower G)• More stable• Less work capacity
In a spontaneous change • The free energy of the system decreases (∆G<0) • The system becomes more stable• The released free energy can be harnessed to do work
(a) (b) (c)
Figure 8.5
Chemical Bonds have Potential Energy
• When bonds are broken, some of the energy is lost as heat and is not available to do work (form new chemical bonds).
• Free Energy (G) – the amt. of energy in a bond available to do work.
• In a molecule, the amt. of Free Energy (G) = the amt. of energy in chemical bond (Enthalpy, H) – the energy lost as disorder (Entropy, S). G = H - TS
Free Energy of Chemical Rxns.
• ΔG = difference in bond energies between reactants and products of a chemical reaction.
• Δ G = ΔH – TΔS• If ΔG is negative (products contain less
energy than reactants) = Exergonic Reactions. Ex. Cellular Respiration
• If ΔG is positive (products contain more energy than reactants) = Endergonic Reactions. Ex. Photosynthesis
C6H12O6 + O2
CO2 + H2OFre
e E
ner
gy
G
Rxn Time
Cellular Respiration
HEAT
CO2 + H2OFre
e E
ner
gy
G
Rxn Time
Photosynthesis
C6H12O6 + O2
Light Energy Supplied
Exergonic and Endergonic Reactions in Metabolism
• An exergonic reaction– Proceeds with a net release of free energy and is
spontaneous
Figure 8.6
Reactants
Products
Energy
Progress of the reaction
Amount ofenergyreleased (∆G <0)
Fre
e e
ne
rgy
(a) Exergonic reaction: energy released
An endergonic reaction:
– Is one that absorbs free energy from its surroundings and is nonspontaneous
Figure 8.6
Energy
Products
Amount ofenergyreleased (∆G>0)
Reactants
Progress of the reaction
Fre
e e
ne
rgy
(b) Endergonic reaction: energy required
Equilibrium and Metabolism• Reactions in a closed system
– Eventually reach equilibrium
Figure 8.7 A
(a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.
∆G < 0 ∆G = 0
• Cells in our body– Experience a constant flow of materials in and
out, preventing metabolic pathways from reaching equilibrium
Figure 8.7
(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium.
∆G < 0
An analogy for cellular respiration
Figure 8.7 (c) A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucoce is brocken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium.
∆G < 0
∆G < 0
∆G < 0
Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
• A cell does three main kinds of work:
– Mechanical
– Transport
– Chemical
• Energy coupling
– Is a key feature in the way cells manage their energy resources to do this work
The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate)
– Is the cell’s energy shuttle– Provides energy for cellular functions
Figure 8.8
O O O O CH2
H
OH OH
H
N
H H
O
NC
HC
NC
C
N
NH2Adenine
RibosePhosphate groups
O
O O
O
O
O
-
- - -
CH
• Energy is released from ATP– When the terminal phosphate bond is broken
Figure 8.9
P
Adenosine triphosphate (ATP)
H2O
+ Energy
Inorganic phosphate Adenosine diphosphate (ADP)
PP
P PP i
ATP hydrolysis:
Can be coupled to other reactionsEndergonic reaction: ∆G is positive, reaction is not spontaneous
∆G = +3.4 kcal/molGlu Glu
∆G = + 7.3 kcal/molATP H2O+
+ NH3
ADP +
NH2
Glutamicacid
Ammonia Glutamine
Exergonic reaction: ∆ G is negative, reaction is spontaneous
P
Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/molFigure 8.10
How ATP Performs Work
• ATP drives endergonic reactions:– By phosphorylation, transferring a phosphate to
other molecules
The three types of cellular work– Are powered by the hydrolysis of ATP
(c) Chemical work: ATP phosphorylates key reactants
P
Membraneprotein
Motor protein
P i
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
ATP
(b) Transport work: ATP phosphorylates transport proteins
Solute
P P i
transportedSolute
GluGlu
NH3
NH2
P i
P i
+ +
Reactants: Glutamic acid and ammonia
Product (glutamine)made
ADP+
P
Figure 8.11
The Regeneration of ATP• Catabolic pathways
– Drive the regeneration of ATP from ADP and phosphate
ATP synthesis from ADP + P i requires energy
ATP
ADP + P i
Energy for cellular work(endergonic, energy-consuming processes)
Energy from catabolism(exergonic, energy yieldingprocesses)
ATP hydrolysis to ADP + P i yields energy
Figure 8.12
If all Exergonic Reactions happen spontaneously…
…then how come all of them haven’t already
happened?
Activation Energy!
We need catalysts!
Biological Catalysts Are Enzymes
Activation EnergyE
ner
gy
C6H12O6 +O2
CO2 + H20
Reaction Time
EnergyActivation
Energy
Enzymes are Proteins• Organic catalysts - increase the
rate of chemical reactions in cells.
• Hold reactant molecules close together for reaction to occur- uses an active site.
• The active site is used to bind the reactant molecules-substrate.
The Lock and Key Model
Enzyme Binding
The active site:
– Is the region on the enzyme where the substrate binds.
Figure 8.16
Substate
Active site
Enzyme
(a)
• Induced fit of a substrate:– Brings chemical groups of the active site into
positions that enhance their ability to catalyze the chemical reaction
Figure 8.16 (b)
Enzyme- substratecomplex
The catalytic cycle of an enzyme
Substrates
Products
Enzyme
Enzyme-substratecomplex
1 Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit).
2 Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.
3 Active site (and R groups ofits amino acids) can lower EA
and speed up a reaction by• acting as a template for substrate orientation,• stressing the substrates and stabilizing the transition state,• providing a favorable microenvironment,• participating directly in the catalytic reaction.
4 Substrates are Converted intoProducts.
5 Products areReleased.
6 Active siteIs available fortwo new substrateMole.
Figure 8.17
Conditions that Affect Protein ShapeCan disrupt H bonds by:
• High Temperature
• pH Changes (Acidic or Basic)
• Salt (or Ion) Concentration
• Binding of Regulatory Molecules
Disrupting the 2°, 3°, 4° structure is called denaturation.
Enzymes• Enzymes have a temperature
optimum.• Too Cold - H bonds and van der
Waals forces aren’t flexible enough to allow the induced fit for catalysis.
• Too Hot - they are too weak to maintain the enzymes shape and break apart.
Rat
e of
Rea
ctio
n
Rxn Temperature, °C
3735 3933 434131
Most Human Enzyme Temp. Optimums
Male Reprod. Enzymes
Siamese Cats and Pigment Enzymes
3 wks old
4 yrs. old
Show me a harp seal!
Video: Discovery-Blue Planet: Frozen Seas
Pigment Enzymes in Harp Seal Pups
Show me an application!
Video: Discovery-The Science of the Sexes
Rat
e of
Rea
ctio
n
Rxn pH
54 63 72
Most Human Enzyme pH Optimums
8
TrypsinPepsin
Who cares about optimum conditions for enzymes?
Inhibitors and Activators• Inhibitors – are molecules (usually proteins)
that bind to an enzyme and decrease its activity.
• Two Kinds:– A. Competitive Inhibitors – compete for
the same active site as the substrate; displaces some of the substrate.
– B. Noncompetitive Inhibitors – bind to the enzyme in some other location other than its active site., changing its shape.
Enzyme Inhibitors• Competitive inhibitors
– Bind to the active site of an enzyme, competing with the substrate
Figure 8.19 (b) Competitive inhibition
A competitiveinhibitor mimics the
substrate, competingfor the active site.
Competitiveinhibitor
A substrate canbind normally to the
active site of anenzyme.
Substrate
Active site
Enzyme
(a) Normal binding
Competitive Inhibition
Competitive Inhibition
Noncompetitive inhibitors– Bind to another part of an enzyme, changing the
function
Figure 8.19
A noncompetitiveinhibitor binds to the
enzyme away fromthe active site, altering
the conformation ofthe enzyme so that its
active site no longerfunctions.
Noncompetitive inhibitor
(c) Noncompetitive inhibition
Noncompetitive Inhibition
Noncompetitive Inhibitors• These inhibitors bind to a site other
than the active site called the allosteric site (“other form”).
• Chemical “on/off” switches.• Called Allosteric Inhibitor.• If a molecule binds to an allosteric site
and keeps the enzyme in its active shape – Allosteric Activator.
Enzymes change shape when regulatory molecules bind to specific sites, affecting function
Stabilized inactiveform
Allosteric activaterstabilizes active fromAllosteric enyzme
with four subunitsActive site
(one of four)
Regulatorysite (oneof four)
Active formActivator
Stabilized active form
Allosteric activaterstabilizes active form
InhibitorInactive formNon-functionalactivesite
(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again.
Oscillation
Figure 8.20
Another Look at Allosteric Inhibitors
Allosteric Activation
Things that help Enyzmes• Molecules that bind to the active site and HELP
the enzyme’s function – Cofactor.• Often metal ions, vitamins, etc.• If cofactor is a nonprotein organic molecule-
Coenzyme.• Coenzymes often serve as electron acceptors to
help break bonds.• Coenzymes then transfer the electrons to other
compounds. (Remember NAD+ and FAD+?
Enzymes Work with Co-Enzymes
Captures H+
An Example of a Biochemical Pathway
Feedback Inhibition
E1
E1
Substrate A Substrate B
E2
E2
Substrate C
Substrate CAllosteric Inhibitor
Feedback inhibitionActive siteavailable
Isoleucineused up bycell
Feedbackinhibition
Isoleucine binds to allosteric site
Active site of enzyme 1 no longer binds threonine;pathway is switched off
Initial substrate(threonine)
Threoninein active site
Enzyme 1(threoninedeaminase)
Intermediate A
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
End product(isoleucine)
Figure 8.21