Lecture 5 Outline (Ch. 8)
I.
Energy and Metabolism
II.
Thermodynamics
A. 1st Law – conservation of energy
B. 2nd Law - entropy
III. Free Energy
IV. Chemical Reactions
V.
Cellular Energy - ATP
VI. Enzymes
A. Function
B. Regulation
VII. Lecture Concepts
Energy
What is Energy?
The capacity to
cause change
Types of Energy:
- Kinetic Energy = energy of movement - thermal
- Potential = stored energy - chemical
Metabolism
Metabolism – all the chemical conversions in an organism
Thermodynamics
Thermodynamics – study of energy transformation in a system
Potential energy can be converted to kinetic energy (& vice versa)
Potential Energy
Kinetic Energy
Thermodynamics
Laws of Thermodynamics: Explain the characteristics of energy
1st Law:
• Energy is conserved
• Energy is not created or destroyed
• Energy can be converted (Chemical  Heat)
2nd Law:
• During conversions, amount of useful energy decreases
• No process is 100% efficient
• Entropy (measure of disorder) is increased
Energy is converted from more useful to less useful forms
Metabolism
Metabolic reactions:
• Chemical reactions in organism
Two Types of Metabolic Reactions:
Catabolic = breaks
down molecules
Anabolic = builds
up molecules
Free Energy
Chemical Reaction:
• Process that makes and breaks chemical bonds
+
+
Reactants
Products
Two Types of Chemical Reactions:
1) Exergonic = releases energy
2) Endergonic = requires energy
Free Energy
Energy of a system
• Gibb’s free energy = energy available to cause change
• difference in free energy (ΔG) - predict if rxn will occur
• system – moves to more stable (lower energy)
• If ΔG (-),
-release energy
-process spontaneous
• If ΔG (+) or 0,
-consume energy
-process non-spontaneous
Chemical Reactions
Glucose  CO2 + H20
CO2 + H20  Glucose
-ΔG
+ΔG (or 0)
release free energy
intake free energy
spontaneous
non-spontaneous
• Exergonic reaction
• Endergonic reaction
Chemical Reactions
Chemical Reactions:
• Like home offices – tend toward disorder
Chemical Reactions
Chemical Reactions:
• Endergonic – energy required to complete reaction
• Exergonic – energy given off
Exergonic
Endergonic
Chemical Reactions
1. Exergonic reactions: “Energy out”
• Reactants have more energy than products
• Reaction releases energy
2. Endergonic reactions: “Energy in”
•Products have more energy than reactants
•Requires influx of energy »
Chemical Reactions
Activation Energy: Energy required to “jumpstart” a chemical
reaction
• Must overcome repulsion of molecules due to negative
charged electrons
Nucleus
Repel
Nucleus
Activation
Energy
Nucleus
Repel
Activation
Energy
Nucleus
Chemical Reactions
Exergonic Reaction:
–
“Downhill” reactions
Reactants have more energy than products
But will sugar spontaneously burst into flames?
Activation energy:
Make sugar and O2
molecules collide
sugar + O2
water + CO2
Cellular Energy - ATP
• ATP = adenosine
triphosphate
• ribose, adenine, 3 phosphates
• last (terminal) phosphate
- removable
Cellular Energy - ATP
• ATP hydrolyzed to ADP
• Exergonic
• ΔG = -7.3 kcal/mol
ATP + H2O
ADP + Pi
• Energy released, coupled to another rxn (endergonic)
Cellular Energy - ATP
endergonic
exergonic
• by coupling, overall rxn still exergonic
Cellular Energy - ATP
• ATP regenerated
• ΔG = +7.3 kcal/mol
• cells power ATP generation by coupling to exergonic rxns
- cellular respiration
Enzymes
• Enzymes – rate of chemical rxn
• sucrase – enzyme sucrose breakdown
• sucrase – catalyst
• break bonds
reactants
“-ase” enzyme
-speed up rxn, not consumed
-contort molecule
• form bonds products
-unstable
-energy given off
-need energy input
Enzymes
• energy input
Energy of activation (EA)
• reactants – absorb
energy - EA
• EA from heat
• rxn proceeds
Exergonic – energy given off
• rxn rate – due to reaching EA
• EA from ambient heat? - usually insufficient
• This is GOOD!
Enzymes
Enzymes
• lower EA
• only for specific rxns
• cell chooses which
rxns go forward
• This is GOOD!
enzymes: -don’t change ΔG
-don’t make endergonic
exergonic
-do speed up rxn would occur anyway
Enzymes
• enzyme – specific to substrate
• active site – part of enzyme -substrate
• binding tightens fit – induced fit
• form enzyme-substrate complex
• catalytic part of enzyme:
converts reactant(s) to product(s)
Enzymes
• Enzymes lowers EA by:
-template orientation
• substrate(s) enter
-stress bonds
-microenvironment
• enzyme reused
• products formed
• Enzyme activity affected by: substrate conc., temp., pH
Enzymes
• inhibitors:
normal
competitive – bind active site
non-competitive – binds other
site – alters conformation
competitive
inhibition
• Drug – blocks HIV enzyme
- competitive
inhibition
non-competitive
inhibition
Enzymes
Feedback Inhibition:
Like your furnace:
Room
is cold
warmer
Detector
activated
warmer
Heat
kicks on
Heat
stays on
Room
is warm
Self-Check
Endergonic
Exergonic
energy used/given off
catabolic/anabolic
spontaneous/not
ΔG (+)/ (-)
ATP made/hydrolyzed
downhill/uphill
Enzyme regulation
Competitive inhibition
Non-competitive inhibition
Feedback inhibition
Description
Lecture 5 concepts
-
Define metabolism, thermodynamics, free energy
Describe the 1st and 2nd laws of thermodynamics and how
they relate to chemical reactions
Explain the terms exergonic and endergonic in terms of free
energy and chemical reactions
Draw a graph of free energy for exothermic and endothermic
chemical reactions; label products, reactants, & EA
Discuss the structure and purpose of ATP
Draw and describe how enzymes affect chemical reactions
List factors that affect enzyme activity
Write out a list of new terminology and provide descriptions