2. 5.1 The Flow of Energy in Living Things
Energy is defined as the ability to do work
It exists in two states: kinetic and potential
Fig. 5.1
Potential Energy = stored energy
Kinetic Energy = energy of motion

3. 5.1 The Flow of Energy in Living Things
Energy exists in many forms
Mechanical, sound, light, electric, heat, etc.
All other forms can be converted into heat
Thermodynamics is the study of energy
Or heat changes

4. 5.1 The Flow of Energy in Living Things
Energy flows from the sun into the earth
Photosynthetic organisms capture part of it
They then use it to generate sugars
These sugars have potential energy due to the arrangement of their atoms into bonds
A chemical reaction is the making or breaking of chemical bonds

5. 5.2 The Laws of Thermodynamics
A set of universal laws governing all energy changes in the universe
The First Law
Energy cannot be created or destroyed
However, it can change forms
During each conversion, some energy is lost into the environment as heat energy
The energy of random molecular motion

6. The Second Law of Thermodynamics
Disorder in closed systems is continuously increasing
Entropy is a measure of the disorder of a system
Fig. 5.3
Simply put, the Second Law states:
“entropy increases”

7. 5.3 Chemical Reactions
Chemical reactions begin with reactants (substrates) which are converted to products
Exergonic reactions
Products contain less energy than the reactants
Endergonic reactions
Products contain more energy than the reactants

8. Fig. 5.4
Energy of Activation
Extra energy required to destabilize chemical bonds and so initiate a chemical reaction

9. However, they cannot make an endergonic reaction exergonic
Fig. 5.4
Catalysts lower the activation energy of a reaction, and thus increase its rate
However, they cannot make an endergonic reaction exergonic

10. 5.4 How Enzymes Work Enzymes are proteins that serve as catalysts
They speed up chemical reactions within cells
Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely
Active site
Site on enzyme surface where reactant fits
Binding site
Site on reactant where enzyme binds

11. Fig. 5.5 Enzyme shapes determines its activity
Lysozyme
Changes upon binding of the substrate
The substrate is now bound more intimately

12. Fig How enzymes work

13. Fig. 5.7 The catalytic cycle of an enzyme1
The substrate, sucrose, consists
of glucose and fructose bonded together.
Bond
Enzyme
Active site
Glucose
Fructose
Products are released, and the enzyme is free to bind other substrates. 4
The substrate binds to the enzyme, forming an enzyme-substrate complex. 2
H2O
The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. 3

14. 5.5 Factors Affecting Enzyme Activity
Enzyme activity is affected by any change in condition that alters the enzyme’s 3-D shape
The structural bonds of enzymes are sensitive to changes in temperature and pH
Therefore, a temperature or pH beyond the optimal range will cause the enzyme to denature

15. Fig. 5.8 Enzymes are sensitive to their environment
Digests proteins in the stomach
Digests proteins in the intestine

16. 5.6 How Cells Regulate Enzymes
A cell can control the activity of an enzyme by altering its shape
Allosteric enzymes have shapes that can be altered by the binding of signal molecules
These molecules bind to the allosteric site
Repressors bind and repress enzyme activity
Activators bind and restore or increase enzyme activity

17. Fig. 5.9 How cells control enzymes

18. Enzyme inhibition occurs in two ways:
Competitive inhibition
- Inhibitor binds at the enzyme’s active site
Noncompetitive inhibition
- Inhibitor binds at the enzyme’s allosteric site
Fig. 5.10

19. 5.7 ATP: The Energy Currency of the Cell
Fig. 5.11
Due to electrostatic repulsion between phosphate groups
Adenosine triphosphate (ATP) is the main energy currency of the cell
Each ATP molecule is composed of three parts:

20. 5.7 ATP: The Energy Currency of the Cell
Most energy exchanges in the cell involve cleavage of only the outermost bond in ATP
Fig. 5.12
Used to power many of the cell’s activities
Provided through photosynthesis or aerobic respiration

24. Oxidation reduction reactions always take place together
Many reactions involve the passage of electrons from one atom/molecule to another
Oxidation is the loss of electrons
Reduction is the gain of electrons
Oxidation reduction reactions always take place together
Note that the transfer of electrons through these redox reactions also transfers energy

25. Loss of electron (oxidation)
Fig Redox reactions
Loss of electron (oxidation) A* + A B o + B* _
Gain of electron (reduction) e– B A
Low energy
High energy