1. Chapter 5
The Working Cell

2. Fireflies use light to send signals to potential mates
Intro: Cool “Fires” Attract Mates and Meals
Fireflies use light to send signals to potential mates
Instead of using chemical signals like most other insects
The light comes from a set of chemical reactions, that occur in light-producing organs at the rear of the insect.

3. Energy is the capacity to perform work
ENERGY AND THE CELL
Energy is the capacity to perform work
All organisms require energy!
(“ability to obtain and use energy” was a defining characteristic of living things!)
What is Energy?

4. Kinetic energy is the energy of motion
Potential energy is stored energy, which can be converted to kinetic energy.
Rollercoaster animation
Figure 5.1A–C

5. 5.2 Two laws govern energy transformations
Thermodynamics- the study of energy transformations
The First Law of Thermodynamics
Energy can be changed from one form to another, but energy cannot be created or destroyed.
Figure 5.2A

6. Energy for cellular work
The Second Law of Thermodynamics
energy transformations increase disorder or entropy, and some energy is lost as heat.
Heat
Chemical reactions
Carbon dioxide
Glucose + +
ATP
ATP
water
Oxygen
Figure 5.2B
Energy for cellular work

7. Chemical reactions either store or release energy

8. Endergonic reactions - absorb energy and yield products rich in potential energy.
Potential energy of molecules
Reactants
Energy required
Products
Amount of energy required
Figure 5.3A

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

10. Energy coupling- Uses exergonic reactions to fuel endergonic reactions
Energy coupling- Uses exergonic reactions to fuel endergonic reactions. This is how cells carry out thousands of chemical reactions! (cellular metabolism)
Endergonic and exergonic

11. Currency of the cells
Energy is like a bank account, with ATP being the “currency” for the cells.
You either save $ or you withdraw $!
You cells can either store (save $) energy by forming bonds OR release (withdraw $) energy by breaking bonds!
Can only do one or the other
at any given time!

12. ATP (adenosine triphosphate) powers nearly all forms of cellular work
The energy in an ATP molecule lies in the bonds between its phosphate groups.
Phosphate groups
ATP
Energy P
Hydrolysis
Adenine
Ribose
H2O
Adenosine diphosphate
Adenosine Triphosphate +
ADP
Figure 5.4A

13. Take off a phosphate; breaks the bond = release of energy.
Phosphorylation = adding a phosphate group to make molecules more reactive by storing energy.
ATP
Chemical work
Mechanical work
Transport work P
Molecule formed
Protein moved
Solute transported
ADP +
Product
Reactants
Motor protein
Membrane protein
Solute
Take off a phosphate; breaks the bond = release of energy.
Add a phosphate; builds a bond = stores/absorbs energy.
Animation
Figure 5.4B

14. Cellular work can be sustained because ATP is a renewable resource that cells constantly regenerate!
ADP + P
Energy for endergonic reactions
Energy from exergonic reactions
Phosphorylation
Hydrolysis
Figure 5.4C

15. HOW ENZYMES FUNCTION
For a chemical reaction to begin reactants must absorb some energy, called the energy of activation (energy needed to get the reaction going)
Enzymes speed up the cell’s chemical reactions by lowering energy barriers.
EA barrier
Reactants
Products 1 2
Enzyme
Figure 5.5A

16. Progress of the reaction
A catalyst speeds up a reaction, by decreasing the energy of activation needed to begin a reaction.
Reactants
EA without enzyme
EA with enzyme
Net change in energy
Products
Energy
Progress of the reaction
Figure 5.5B

17. THEREFORE, ALL ENZYMES are catalysts!

18. An enzymes specific shape determines which chemical reactions it will catalyze.1
Enzyme available with empty active site
Active site
Substrate (sucrose) 2
Substrate binds to enzyme with induced fit
Enzyme (sucrase)
Glucose
Fructose
H2O 4
Products are released 3
Substrate is converted to products
Animation 1
Figure 5.6

19. What affects enzyme activity??
Temperature, salt concentration, and pH influence enzyme activity and can affect its function.
How??
Some enzymes require nonprotein cofactors such as metal ions or organic molecules called coenzymes.
Ex. Coenzyme Q 10

20. Normal binding of substrate
Enzyme inhibitors can block enzyme action
Competitive inhibitors- take the place of a substrate in the active site
Noncompetitive inhibitors alters an enzyme’s function by changing its shape
Substrate
Enzyme
Active site
Normal binding of substrate
Enzyme inhibition
Noncompetitive inhibitor
Competitive inhibitor
Many poisons, pesticides, and drugs are enzyme inhibitors.
Figure 5.8

21. Phospholipids have a hydrophilic head and 2 hydrophobic tails.
The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell
Phospholipids have a hydrophilic head and 2 hydrophobic tails.
Phospholipid bilayer, with the heads facing
outward and the tails facing inward
CH2
CH3 CH N + O O– P C
Phosphate group
Symbol
Hydrophilic head
Hydrophobic tails
Water
Hydrophilic heads
Hydrophobic tails
Figure 5.11A

22. A membrane is a fluid mosaic with proteins, lipids and carbohydrate embedded in a phospholipid bilayer or along each side.
Fibers of the extracellular matrix
Carbohydrate (of glycoprotein)
Glycoprotein
Microfilaments
Phospholipid
Cholesterol
Proteins
Plasma membrane
Glycolipid
Cytoplasm
Figure 5.12

23. Membrane proteins can function as:
Enzymes - they help speed up chemical reactions for the cell.
Receptors – bind and transmit chemical messages from other cells
Transport- moving substances across the membrane
ATP
Messenger molecule
Receptor
Activated molecule
Receptor site animation
Figure 5.13A

24. TYPES OF TRANSPORT ACROSS A MEMBRANE

25. NO ENERGY REQUIRED!
1) Passive transport- substances diffuse through membranes without work by the cell; spread from areas of high concentration to areas of low concentration
Small nonpolar molecules such as O2 and CO2
Diffuse easily across the phospholipid bilayer of a membrane (Diffusion animation)
Equilibrium
Membrane
Molecules of dye
Figure 5.14A
Figure 5.14B

26. Many kinds of molecules DO NOT diffuse freely across membranes
NO ENERGY REQUIRED!
Many kinds of molecules DO NOT diffuse freely across membranes
For these molecules, transport proteins MUST provide passage across membranes through a process called facilitated diffusion.
Solute molecule
Transport protein
Facilitated diffusion
animation
Figure 5.15

27. NO ENERGY REQUIRED!
Osmosis is the diffusion of water across a membrane
In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration (higher water conc. to lower water conc.)
Lower concentration of solute
Higher concentration of solute
Equal concentration of solute
H2O
Solute molecule
Selectively permeable membrane
Water molecule
Solute molecule with
cluster of water molecules
Net flow of water
Osmosis animation
Figure 5.16

28. Shrink in hypertonic solutions Swell in hypotonic solutions
The control of water balance is called Osmoregulation.
Shrink in hypertonic solutions
Swell in hypotonic solutions
Equal movement of particles in isotonic solutions
(Animal cells are normal, but plant cells are limp)
Plant cell
H2O
Plasma membrane
(1) Normal
(2) Lysed
(3) Shriveled
(4) Flaccid
(5) Turgid
(6) Shriveled (plasmolyzed)
Isotonic solution
Hypotonic solution
Hypertonic solution
Animal cell
Figure 5.17

29. Active transport- ENERGY REQUIRED!
Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP (One example of active transport is the sodium-potassium pump used in nerve impulses) P
Protein changes shape
Phosphate detaches
ATP
ADP
Solute
Transport protein
Solute binding 1
Phosphorylation 2
Transport 3
Protein reversion 4
Figure 5.18

30. ENERGY REQUIRED!
To move large molecules or particles through a membrane, a vesicle may fuse with the membrane and expel its contents (exocytosis)
Membranes may fold inward enclosing material from the outside (endocytosis)
Fluid outside cell
Cytoplasm
Protein
Vesicle
Vesicle forming
Figure 5.19A

31. Endocytosis can occur in 3 ways:
Phagocytosis – cellular eating (animation)
Pinocytosis – cellular drinking
Receptor-mediated endocytosis
Pseudopodium of amoeba
Food being ingested
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Material bound to receptor proteins
PIT
Cytoplasm
Plasma membrane
TEM 54,000
TEM 96,500 
LM 230
Figure 5.19C

32. Enzymes are central to the processes that make energy available to the cell
Chloroplasts carry out photosynthesis using solar energy to produce glucose and oxygen from carbon dioxide and water
Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP.
Overview animation
(We’ll go. into more detail on each process in the upcoming chapters!)