1. Chapter 5
The Working Cell

2. Energy Energy is defined as the capacity to do work
Movement against an opposing force
The ability to bring about change
All organisms require energy to stay alive

3. Kinetic energy is energy that is actually doing work
Energy in motion
Figure 5.1A
Potential energy is stored energy
Potential for motion
Figure 5.1B

4. Unstable systems:

5. Types of potential energy found in metabolism
Chemical energy – energy stored in the bonds of molecules.
Energy stored in the position of electron around the nucleus of an atom.

6. Two laws govern energy conversion
First law of thermodynamics
Energy cannot be created or destroyed
However, energy can be changed from one form to another
Figure 5.2A

7. 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

8. ENERGY AND THE CELL
All living things need energy
Cells use energy for chemical work, mechanical work, and electrochemical work
Living cells process energy by means of enzyme-controlled chemical reactions
Membranes are one of the primary sites where chemical reactions occur
Membranes compartmentalize the cell

9. What Can Cells Do with Energy?
Cells use energy to carry out thousands of chemical reactions
The sum of these reactions constitutes cellular metabolism
Reactions use energy coupling – run in a sequence of two reactions: one requires energy, one releases energy
endergonic - store energy
exergonic - release energy

10. Endergonic Reactions Energy input required
Product has more energy than starting substances
product with
more energy
(plus by-products
602 and 6H2O)
ENERGY IN 6 12

11. Potential energy of molecules
Endergonic reactions absorb energy and yield products rich in potential energy
Products
Amount of energy INPUT
Potential energy of molecules
Reactants
Figure 5.3A

12. Exergonic Reactions Energy is released
Products have less energy than starting substance
energy-rich
starting
substance
ENERGY
OUT +
602 6 6
products with less energy

13. Amount of energy OUTPUT Potential energy of molecules
Exergonic reactions release energy and yield products that contain less potential energy than their reactants
Reactants
Amount of energy OUTPUT
Potential energy of molecules
Products
Figure 5.3B

14. Cells survive by coupling energy inputs to energy outputs
Combine endergonic reactions with exergonic reactions
Help make these endergonic reactions possible
ATP is the main coupling agent

15. ATP the cell’s chemical energy
ATP molecules are the key to energy coupling
ATP molecules store energy during the process of cellular respiration
ATP power nearly all forms of cellular work

16. The Role of ATP Cellular money Cells “earn” ATP in exergonic reactions
Cells “spend” ATP in endergonic reactions
adenine P P P
ribose

17. Adenosine triphosphate Adenosine diphosphate (ADP)
Energy Coupling
Hydrolysis breaks a phosphate group bond from the ATP molecules releasing energy
The exergonic reaction supplies energy for cellular work
Adenine
Phosphate groups
Hydrolysis
Energy
Ribose
Adenosine triphosphate
Adenosine diphosphate (ADP)
Figure 5.4A

18. Potential energy of molecules
Phosphorylation
How ATP powers cellular work
Reactants
Products
Potential energy of molecules
Protein
Work
Figure 5.4B

19. Dehydration synthesis
The ATP cycle
Hydrolysis
Dehydration synthesis
Energy from exergonic reactions
Energy for endergonic reactions
Figure 5.4C

20. ENZYMES AND CELLULAR REACTIONS
All molecules have energy barriers to prevent spontaneous breakdown
Enzymes speed up the cell’s chemical reactions by lowering energy barriers
The amount of energy needed to overcome the energy barrier is the energy of activation (EA)
Enzymes lower the EA for chemical reactions to begin; decreases the amount of energy the reactants must absorb

21. Energy of Activation (EA)
For a reaction to occur, an energy barrier must be overcome
Enzymes make the energy barrier smaller
activation energy
without enzyme
starting
substance
activation energy
with enzyme
energy
released
by the
reaction
products

22. Four Features of Enzymes
Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster.
Enzymes cannot make a nonspontaneous reaction spontaneous
2) Reactions do not alter or use up enzyme molecules

23. Four Features of Enzymes, cont.
3) The same enzyme usually works for both the forward and reverse reactions
4) Each type of enzyme recognizes and binds to only a certain molecule called the substrate

24. Enzymes are selective
Each cellular reaction is catalyzed by a specific enzyme
Active site - a pocket with specific shape for a certain substrate
The enzyme fits around the substrate when iit enters the active site - induced fit

25. The enzyme is unchanged and can repeat the process
How an enzyme works
Active site
Enzyme (sucrase)
Substrate (sucrose)
Glucose
Fructose 1 4
Enzyme available with empty active site
Products are released 3 2
Substrate is converted to products
Substrate binds to enzyme with induced fit
Figure 5.6
The enzyme is unchanged and can repeat the process

26. Enzyme Helpers Some enzymes require nonprotein cofactors
Some are inorganic metal ions of zinc, iron, and other trace elements
Some are organic molecules called coenzymes
Includes vitamins or altered vitamin components

27. NORMAL BINDING OF SUBSTRATE
Enzyme Inhibitors
Inhibitors block enzyme action
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

28. Negative Feedback
Inhibition usually caused by the product of the enzyme + substrate reaction
Product binds to site other than active site and alters enzyme shape
Essential process to regulate cellular metabolism
Often the last products in an enzymatic pathway inhibits one of the first enzymes in the pathway

29. Environmental Effects
Enzyme activity is influenced by the cellular environment
temperature
salt concentration pH

30. Connection: Some pesticides and antibiotics inhibit enzymes
Certain pesticides inhibit key enzymes in the nervous system
Noncompetitive inhibitors may permanently damage the enzyme
Many antibiotics inhibit enzymes that are essential to disease-causing bacteria
Penicillin inhibits an enzyme that bacteria use in making cell walls