1. Chapter 5
The Working Cell

2. Cool "Fires" Attract Mates and Meals
Living cells put energy to work by means of enzyme-controlled reactions
The firefly's use of light to signal mates results from a set of such reactions
The reactions occur in light-producing organs at the rear of the insect
Females of some species produce a light pattern that attracts males of other species, which the female eats

4. 5.1 Energy is the capacity to perform work
ENERGY AND THE CELL
5.1 Energy is the capacity to perform work
Energy is defined as the capacity to do work
Life depends on the fact that energy can be converted from one form to another
Kinetic energy is the energy of motion
Heat and light are forms of kinetic energy

5. Animation: Energy Concepts
Potential energy is stored energy that is dependent on an object's location or structure
The most important potential energy for living things is the chemical energy stored in molecules
Potential energy can be converted to kinetic energy
Animation: Energy Concepts

9. 5.2 Two laws govern energy transformations
Thermodynamics is the study of energy transformations
The First Law of Thermodynamics
Energy can be changed from one form to another but cannot be created or destroyed
The Second Law of Thermodynamics
Energy transformations increase disorder, or entropy, and some energy is lost as heat

11. LE 5-2b Heat Chemical reactions Carbon dioxide Glucose Water Oxygen
ATP
ATP
Water
Oxygen
Energy for cellular work

12. 5.3 Chemical reactions either store or release energy
Endergonic reactions
Require an input of energy from the surroundings
Yield products rich in potential energy
Example: photosynthesis

13. Amount of energy required
LE 5-3a
Products
Amount of
energy
required
Energy required
Potential energy of molecules
Reactants

14. Exergonic reactions
Release energy
Yield products that contain less potential energy than their reactants
Examples: cellular respiration, burning

15. Amount of energy released
LE 5-3b
Reactants
Amount of
energy
released
Energy released
Potential energy of molecules
Products

16. Cells carry out thousands of chemical reactions, which constitute cellular metabolism
Energy coupling uses energy released from exergonic reactions to drive endergonic reactions

17. 5.4 ATP shuttles chemical energy and drives cellular work
ATP (adenosine triphosphate) powers nearly all forms of cellular work
ATP is composed of one adenine, one ribose, and three negatively charged phosphates
The energy in an ATP molecule lies in the bonds between its phosphate groups

18. Adenosine diphosphate
LE 5-4a
Adenosine
Triphosphate
Adenosine diphosphate
Phosphate
group
H2O P P P P P + P +
Energy
Hydrolysis
Adenine
Ribose
ATP
ADP

19. ATP powers cellular work through coupled reactions
The bonds connecting the phosphate groups are broken by hydrolysis, an exergonic reaction
Hydrolysis is coupled to an endergonic reaction through phosphorylation
A phosphate group is transferred from ATP to another molecule

20. Chemical work Mechanical work Transport work P P Reactants P P P
LE 5-4b
ATP
Chemical work
Mechanical work
Transport work
Membrane
protein
Solute P
Motor
protein P
Reactants P P P
Product P
Molecule formed
Protein moved
Solute transported
ADP  P

21. Cellular work can be sustained, because ATP is a renewable resource that cells regenerate
The ATP cycle involves continual phosphorylation and hydrolysis

22. LE 5-4c ATP Energy from exergonic reactions Energy for endergonic
Phosphoylation
Hydrolysis
Energy from
exergonic
reactions
Energy for
endergonic
reactions
ADP + P

23. HOW ENZYMES FUNCTION
5.5 Enzymes speed up the cell's chemical reactions by lowering energy barriers
Energy of activation
Amount of energy that must be input before an exergonic reaction will proceed (the energy barrier)

25. Proteins that function as biological catalysts
Enzymes
Proteins that function as biological catalysts
Increase the rate of a reaction without themselves being changed
An enzyme can decrease the energy of activation needed to begin a reaction

26. LE 5-5b enzyme enzyme EA without EA with Reactants Energy Net change
in energy
Products
Progress of the reaction

27. 5.6 A specific enzyme catalyzes each cellular reaction
Each enzyme has a unique three-dimensional shape that determines which chemical reaction it catalyzes
Substrate: a specific reactant that an enzyme acts on
Active site: A pocket on the enzyme surface that the substrate fits into

28. Animation: How Enzymes Work
Induced fit: The way the active site changes shape to "embrace" the substrate
A single enzyme may act on thousands or millions of substrate molecules per second
Animation: How Enzymes Work

29. LE 5-6 Enzyme available with empty active site Active site Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
Glucose
Fructose
H2O
Products are
released
Substrate is
converted to
products

30. 5.7 The cellular environment affects enzyme activity
Physical factors influence enzyme activity
Temperature, salt concentration, pH
Some enzymes require nonprotein cofactors
Metal ions, organic molecules called coenzymes

31. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme's activity
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
In feedback inhibition, enzyme activity is blocked by a product of the reaction catalyzed by the enzyme

32. Normal binding of substrate
LE 5-8
Substrate
Active site
Enzyme
Normal binding of substrate
Competitive
inhibitor
Noncompetitive
inhibitor
Enzyme inhibition

33. 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors
CONNECTION
5.9 Many poisons, pesticides, and drugs are enzyme inhibitors
Cyanide inhibits an enzyme involved with ATP production during cellular respiration
Some pesticides irreversibly inhibit an enzyme crucial for insect muscle function
Many antibiotics inhibit enzymes essential for disease-causing bacteria
Ibuprofen and aspirin inhibit enzymes involved in inducing pain

34. MEMBRANE STRUCTURE AND FUNCTION
5.10 Membranes organize the chemical activities of cells
Membranes provide structural order for metabolism
Form most of the cell's organelles
Compartmentalize chemical reactions
The plasma membrane forms a boundary between a living cell and its surroundings
Exhibits selective permeability
Controls traffic of molecules in and out

35. LE 5-10
Outside
of cell
Cytoplasm

36. 5.11 Membrane phospholipids form a bilayer
Phospholipids are the main structural components of membranes
Two nonpolar hydrophobic fatty acid "tails"
One phosphate group attached to the hydrophilic glycerol "head"

37. LE 5-11a
Hydrophilic head
Phosphate
group
Symbol
Hydrophobic tails

38. In membranes, phospholipids form a bilayer Two-layer sheet
Phospholipid heads facing outward and tails facing inward
Selectively permeable
Polar lipid-soluble molecules pass through
Nonpolar molecules not soluble in lipids do not pass through

39. LE 5-11b
Water
Hydrophilic
heads
Hydrophobic
tails
Water

40. 5.12 The membrane is a fluid mosaic of phospholipids and proteins
A membrane is a mosaic
Proteins and other molecules are embedded in a framework of phospholipids
A membrane is fluid
Most protein and phospholipid molecules can move laterally
Membrane glycoproteins and glycolipids function in cell identification

41. LE 5-12 Extracellular matrix Glycoprotein Carbohydrate Glycolipid
Plasma
membrane
Phospholipid
Proteins
Microfilaments
of cytoskeleton
Cholesterol
Cytoplasm

42. 5.13 Proteins make the membrane a mosaic of function
Proteins perform most membrane functions
Identification tags
Junctions between adjacent cells
Enzymes
Receptors of chemical messages from other cells (signal transduction)
Transporters of substances across the membrane

43. LE 5-13a
Enzyme activity

44. Messenger molecule Receptor Activated molecule Signal transduction
LE 5-13b
Messenger molecule
Receptor
Activated
molecule
Signal transduction

45. LE 5-13c
ATP
Transport

46. Animation: Membrane Selectivity

47. 5.14 Passive transport is diffusion across a membrane
Diffusion is the tendency for particles to spread out evenly in an available space
From an area of high concentration to an area of low concentration
Passive transport across membranes occurs when a molecule diffuses down a concentration gradient
Small nonpolar molecules such as O2 and CO2 diffuse easily across the phospholipid bilayer of a membrane

48. LE 5-14a
Molecules of dye
Membrane
Equilibrium

49. LE 5-14b
Equilibrium
Animation: Diffusion

50. 5.15 Transport proteins may facilitate diffusion across membranes
In facilitated diffusion
Transport proteins that span the membrane bilayer help substances diffuse down a concentration gradient
To transport the substance, a transport protein may
Provide a pore for passage
Bind the substance, change shape, and then release the substance

51. LE 5-15
Solute
molecule
Transport
protein

52. 5.16 Osmosis is the diffusion of water across a membrane
In osmosis water, molecules diffuse across a selectively permeable membrane
From an area of low solute concentration
To an area of high solute concentration
Until the solution is equally concentrated on both sides of the membrane
The direction of movement is determined by the difference in total solute concentration
Not by the nature of the solutes
Animation: Osmosis

53. cluster of water molecules
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

54. 5.17 Water balance between cells and their surroundings is crucial to organisms
Osmoregulation is the control of water balance
Tonicity is the tendency of a cell to lose or gain water in solution
Isotonic solution: solute concentration is the same in the cell and in the solution
No osmosis occurs
Animal cell volume remains constant; plant cell becomes flaccid

55. Hypotonic solution: solute concentration is greater in the cell than in the solution
Cell gains water through osmosis
Animal cell lyses; plant cell becomes turgid
Hypertonic solution: solute concentration is lower in the cell than in the solution
Cell loses water through osmosis
Animal cell shrivels; plant cell plasmolyzes

56. LE 5-17 Isotonic solution Hypotonic solution Hypertonic solution H2O
Animal
cell
(1) Normal
(2) Lysed
(3) Shriveled
H2O
H2O
H2O
Plasma
membrane
H2O
Plant
cell
(4) Flaccid
(5) Turgid
(6) Shriveled
(plasmolyzed)
Video: Plasmolysis
Video: Turgid Elodea

57. Animation: Active Transport
5.18 Cells expend energy for active transport
Active transport requires energy to move solutes against a concentration gradient
ATP supplies the energy
Transport proteins move solute molecules across the membrane
Animation: Active Transport

58. LE 5-18 Transport protein P P Protein changes shape Phosphate detaches
ATP
Solute
ADP
Solute binding
Phosphorylation
Transport
Protein reversion

59. 5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a cell membrane
A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis)
Membranes may fold inward, enclosing material from the outside (endocytosis)

60. LE 5-19a
Fluid outside cell
Vesicle
Protein
Cytoplasm

61. LE 5-19b
Vesicle forming

62. Endocytosis can occur in three ways
Phagocytosis ("cell eating")
Pinocytosis ("cell drinking")
Receptor-mediated endocytosis

63. Receptor-mediated endocytosis
LE 5-19c
Pseudopodium of amoeba
Food being ingested
LM 230
Phagocytosis
Plasma membrane
Material bound to receptor proteins
PIT
TEM 54,000
TEM 96,500
Cytoplasm
Pinocytosis
Receptor-mediated endocytosis

64. Animation: Receptor-Mediated Endocytosis
Animation: Exocytosis and Endocytosis Introduction
Animation: Exocytosis
Animation: Pinocytosis
Animation: Phagocytosis

65. 5.20 Faulty membranes can overload the blood with cholesterol
CONNECTION
5.20 Faulty membranes can overload the blood with cholesterol
Cholesterol is carried in the blood by low-density lipoprotein (LDL) particles
Normally, body cells take up LDLs by receptor-mediated endocytosis
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
People with hypercholesterolemia have more than twice the normal level of blood cholesterol

66. LE 5-20 Phospholipid outer layer LDL particle Vesicle Cholesterol
Protein
Plasma
membrane
Receptor
protein
Cytoplasm