1. CHAPTER 5 The Working Cell
Modules 5.1 – 5.4

2. Cool “Fires” Attract Mates and Meals
Fireflies use light, instead of chemical signals, to send signals to potential mates
Females can also use light flashes to attract males of other firefly species — as meals, not mates

3. The light comes from a set of chemical reactions, the luciferin-luciferase system
Fireflies make light energy from chemical energy
Life is dependent on energy conversions

4. ENERGY AND THE CELL
Living cells are compartmentalized by membranes
Membranes are sites where chemical reactions can occur in an orderly manner
Living cells process energy by means of enzyme-controlled chemical reactions

5. 5.1 Energy is the capacity to perform work
Energy is defined as the capacity to do work
All organisms require energy to stay alive
Energy makes change possible

6. Kinetic energy is energy that is actually doing work
Figure 5.1A
Potential energy is stored energy
Figure 5.1B

7. 5.2 Two laws govern energy conversion
First law of thermodynamics
Energy can be changed from one form to another
However, energy cannot be created or destroyed
Figure 5.2A

8. 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

9. 5.3 Chemical reactions either store or release energy
Cells carry out thousands of chemical reactions
The sum of these reactions constitutes cellular metabolism

10. Potential energy of molecules
There are two types of chemical reactions:
Endergonic reactions absorb energy and yield products rich in potential energy
Products
Amount of energy INPUT
Potential energy of molecules
Reactants
Figure 5.3A

11. 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

12. 5.4 ATP shuttles chemical energy within the cell
In cellular respiration, some energy is stored in ATP molecules
ATP powers nearly all forms of cellular work
ATP molecules are the key to energy coupling

13. Adenosine triphosphate Adenosine diphosphate (ADP)
When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work
Adenine
Phosphate groups
Hydrolysis
Energy
Ribose
Adenosine triphosphate
Adenosine diphosphate (ADP)
Figure 5.4A

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

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

16. CHAPTER 5 The Working Cell
Modules 5.5 – 5.9

17. For a chemical reaction to begin, reactants must absorb some energy
HOW ENZYMES WORK
5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
For a chemical reaction to begin, reactants must absorb some energy
This energy is called the energy of activation (EA)
This represents the energy barrier that prevents molecules from breaking down spontaneously

18. A protein catalyst called an enzyme can decrease the energy barrier
EA barrier
Enzyme
Reactants 1
Products 2
Figure 5.5A

19. EA without enzyme EA with enzyme Reactants Net change in energy
Products
Figure 5.5B

20. 5.6 A specific enzyme catalyzes each cellular reaction
Enzymes are selective
This selectivity determines which chemical reactions occur in a cell

21. 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

22. 5.7 The cellular environment affects enzyme activity
Enzyme activity is influenced by
temperature
salt concentration pH
Some enzymes require nonprotein cofactors
Some cofactors are organic molecules called coenzymes

23. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with enzymes
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

24. 5.9 Connection: Some pesticides and antibiotics inhibit enzymes
Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system
Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria
Penicillin inhibits an enzyme that bacteria use in making cell walls

25. CHAPTER 5 The Working Cell
Modules 5.10 – 5.21

26. 5.10 Membranes organize the chemical activities of cells
MEMBRANE STRUCTURE AND FUNCTION
5.10 Membranes organize the chemical activities of cells
Membranes organize the chemical reactions making up metabolism  
Cytoplasm
Figure 5.10

27. Membranes are selectively permeable
They control the flow of substances into and out of a cell
Membranes can hold teams of enzymes that function in metabolism

28. 5.11 Membrane phospholipids form a bilayer
Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Head
Symbol
Tails
Figure 5.11A

29. In water, phospholipids form a stable bilayer
The heads face outward and the tails face inward
Water
Hydrophilic heads
Hydrophobic tails
Water
Figure 5.11B

30. 5.12 The membrane is a fluid mosaic of phospholipids and proteins
Phospholipid molecules form a flexible bilayer
Cholesterol and protein molecules are embedded in it
Carbohydrates act as cell identification tags

31. The plasma membrane of an animal cell
Glycoprotein
Carbohydrate (of glycoprotein)
Fibers of the extracellular matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments of the cytoskeleton
Proteins
CYTOPLASM
Figure 5.12

32. 5.13 Proteins make the membrane a mosaic of function
Some membrane proteins form cell junctions
Others transport substances across the membrane
Figure 5.13
Transport

33. Many membrane proteins are enzymes
Some proteins function as receptors for chemical messages from other cells
The binding of a messenger to a receptor may trigger signal transduction
Messenger molecule
Receptor
Activated molecule
Figure 5.13
Enzyme activity
Signal transduction

34. 5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
They spread from areas of high concentration to areas of lower concentration
Molecule of dye
Membrane
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B

35. 5.15 Osmosis is the passive transport of water
Hypotonic solution
Hypertonic solution
In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration
Selectively permeable membrane
Solute molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water molecule
Selectively permeable membrane
Solute molecule with cluster of water molecules
NET FLOW OF WATER
Figure 5.15

36. 5.16 Water balance between cells and their surroundings is crucial to organisms
Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution
The control of water balance (osmoregulation) is essential for organisms
ISOTONIC SOLUTION
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
ANIMAL CELL
(1) Normal
(2) Lysing
(3) Shriveled
Plasma membrane
PLANT CELL
Figure 5.16
(4) Flaccid
(5) Turgid
(6) Shriveled

37. 5.17 Transport proteins facilitate diffusion across membranes
Small nonpolar molecules diffuse freely through the phospholipid bilayer
Many other kinds of molecules pass through selective protein pores by facilitated diffusion
Solute molecule
Transport protein
Figure 5.17

38. 5.18 Cells expend energy for active transport
Transport proteins can move solutes across a membrane against a concentration gradient
This is called active transport
Active transport requires ATP

39. Active transport in two solutes across a membrane
FLUID OUTSIDE CELL
Phosphorylated transport protein
Active transport in two solutes across a membrane
Transport protein
First solute 1
First solute, inside cell, binds to protein 2
ATP transfers phosphate to protein 3
Protein releases solute outside cell
Second solute 4
Second solute binds to protein 5
Phosphate detaches from protein 6
Protein releases second solute into cell
Figure 5.18

40. 5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
a vesicle may fuse with the membrane and expel its contents (exocytosis)
FLUID OUTSIDE CELL
CYTOPLASM
Figure 5.19A

41. or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B

42. Material bound to receptor proteins
Three kinds of endocytosis
Pseudopod of amoeba
Food being ingested
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Figure 5.19C

43. 5.20 Connection: Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Phospholipid outer layer
LDL PARTICLE
Receptor protein
Protein
Cholesterol
Plasma membrane
Vesicle
CYTOPLASM
Figure 5.20

44. 5.21 Chloroplasts and mitochondria make energy available for cellular work
Enzymes and membranes 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

45. Chemicals recycle among living organisms and their environment
Sunlight energy
Nearly all the chemical energy that organisms use comes ultimately from sunlight
Chloroplasts, site of photosynthesis
CO2 + H2O
Glucose + O2
Mitochondria sites of cellular respiration
Chemicals recycle among living organisms and their environment
(for cellular work)
Heat energy
Figure 5.21

46. CHAPTER 5 Extra Photographs

47. Kinetic energy
Figure 5.1x1

48. Potential and kinetic energy
Figure 5.1x2

49. Potential and kinetic energy
Figure 5.1x3

50. Forest fire
Figure 5.3x

51. ATP, molecular model
Figure 5.4Ax