1. Energy and Metabolism
Chapter 8

2. Outline Flow of Energy in Living Things Laws of Thermodynamics
Free Energy
Activation Energy
Enzymes
Forms
Activity
ATP
Biochemical Pathways

3. Flow of Energy in Living Things
Energy - the capacity to do work
kinetic - energy of motion
potential - stored energy
Thermodynamics - changes in heat
calorie - heat required to raise the temperature of one gram of water one degree Celsius
kilocalorie = 1000 calories

4. Flow of Energy in Living Things
Oxidation - Reduction
Oxidation occurs when an atom or molecule loses an electron.
Reduction occurs when an atom or molecule gains an electron.
Redox reactions occur because every electron that is lost by an atom through oxidation is gained by some other atom through reduction.

5. Fig. 8.3 (TEArt) Energy-rich molecule Enzyme H H NAD+ H Product NAD+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 8.3 (TEArt)
Energy-rich molecule
Enzyme H H
NAD+ H
Product
NAD+
NAD+
NAD H
1. Enzymes that harvest
hydrogen atoms have a
binding site for NAD+
located near another
binding site. NAD+ and
an energy-rich
molecule bind to
the enzyme.
2. In an oxidation-
reduction reaction,
a hydrogen atom
is transferred to
NAD+, forming
NADH.
NAD H
3. NADH then
diffuses away and
is available to
other molecules.

6. Laws of Thermodynamics
First Law of Thermodynamics
Energy cannot be created or destroyed, but only change form.
During each conversion, some of the energy dissipates into the environment as heat.
Heat is defined as the measure of the random motion of molecules.

7. Laws of Thermodynamics
Second Law of Thermodynamics
The disorder (entropy) in the universe is continuously increasing.
Energy transformations proceed spontaneously to convert matter from a more ordered, less stable form, to a less ordered, more stable form.

9. Free Energy
Free energy refers to the amount of energy actually available to break and subsequently form other chemical bonds.
Gibbs’ free energy (G)
change in free energy
endergonic - any reaction that requires an input of energy
exergonic - any reaction that releases free energy
Important Note: All reactions require an Activation Energy

10. Activation Energy
Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.
catalyst - substance that lowers the activation energy
cannot violate laws of thermodynamics.
direction of a chemical reaction is determined solely by the difference in free energy between the reactants and the products

11. Activation Energy and Catalysis

12. Enzymes Are Biological Catalysts
Enzymes are proteins that carry out most catalysis in living organisms.
Unique three-dimensional shape enables an enzyme to stabilize a temporary association between substrates.
Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and can then be reused.

13. Enzymes
Most enzymes are globular proteins with one or more active sites.
Substrates bind to the enzyme at these active sites, forming an enzyme-substrate complex.
Often end in suffix ase but not always.

15. Enzyme Forms
A multienzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another.
subunits work in concert, providing significant advantages in catalytic efficiency
RNA catalysts “ribozymes”

16. CARBONIC ANHYDRASE Read about Carbonic Anhydrase Page 149
How much does C.A increase the rate of reaction?
What is the “knife” in this enzyme?

17. Pyruvate Dehydrogenase What does it do?
60 protein subunits, a very COMPLEX COMPLEX

18. Factors Affecting Enzyme Activity
Temperature
Rate of an enzyme-catalyzed reaction increases with temperature, but only up to an optimum temperature. pH
Ionic interactions also hold enzymes together.

19. Factors Affecting Enzyme Activity
Inhibitors and activators
inhibitor - substance that binds to an enzyme and decreases its activity
competitive inhibitors - compete with the substrate for the same active site
noncompetitive inhibitors - bind to the enzyme in a location other than the active site
allosteric sites - specific binding sites acting as on/off switches

20. Factors Affecting Enzyme Activity
activator - substances that bind to allosteric sites and keep the enzymes in their active configurations
increase enzyme activity
cofactors - chemical components that facilitate enzyme activity (minerals)
Coenzyme (vitamins)

21. ATP
Adenosine triphosphate (ATP) is the chief energy currency of the cell.
Each molecule is a nucleotide composed of ribose, adenine, and a triphosphate group.
energy stored in the triphosphate group
cell uses ATP to drive endergonic reactions

22. Biochemical Pathways
Biochemical pathways are the organizational units of metabolism.
Metabolism is the total of all chemical reactions carried out by an organism.
anabolism- reactions that expend energy to make bonds
catabolism - reactions that harvest energy when bonds are broken

23. Regulation of Biochemical Pathways
Biochemical pathways must be coordinated and regulated to operate efficiently.
advantageous for cell to temporarily shut down biochemical pathways when their products are not needed
feedback inhibition - When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more.

24. Feedback Inhibition
The Concept of REGULATION is a KEY CONCEPT in Biology

25. Feedback Mechanisms
Negative Feedback- Brings the amount of final product back to a baseline
Positive Feedback- Brings the amount of product away from a baseline.

26. Summary Flow of Energy in Living Things Laws of Thermodynamics
Free Energy
Activation Energy
Enzymes
Forms
Activity
ATP
Biochemical Pathways

27. See Chapter 8 Animation “Feedback Inhibition of Biochemical Pathways