1. Honors Biology - Chapter 5
The Working Cell

2. 5.2 Energy Transformations in a Cell
Cell metabolism - uses or makes energy
a) exergonic reaction - make energy:
- release energy stored in molecules
- oxidation (catabolic) ex. cell respiration
b) endergonic reaction - use energy:
- use energy (ATP) to do cell work
- reduction, (anabolic)
ex. move, synthesize
Coupled reactions - energy released in exergonic reactions is used to power endergonic

3. Chemical Reactions either store or release energy

4. 5.5 ATP - energy molecule in a cell
ATP - adenosine triphosphate
adenine, ribose (adenosine) + three phosphates
bonds between phosphates are easily broken
phosphate group transfers energy

5. ATP - ADP ATP ADP + P triphosphate diphosphate phosphate group
P is free energy - powers cellular work
Phosphorylate - add a phosphate group to a molecule
- transfers energy to new molecule

6. ATP is renewable energy
ATP breakdown products (ADP + P) remain in cell
are used again to regenerate more ATP when needed
Energy from exergonic reactions
Energy for endergonicreactions
ATP made in cell respiration
ATP used for cellular work
Very fast!! 10 million ATP/second in a cell; needs help of enzymes

7. 5.4 How ATP powers cellular work
Membrane Transport
P  membrane protein
Protein changes shape
Protein pushes solute through membrane
P released
Biosynthesis
P  reactant
Reactants bond
- Product forms
P released
Mechanical Motion
P onto motor protein  protein changes shape
Pulls on muscle fibers  muscle contracts
P released

8. Enzymes speed up reactions

9. 5.6 Enzymes are biologic catalysts
catalyst - speeds reaction but is not changed or used up
Substrate - molecule the enzyme acts upon
specific - only one kind of molecule
Enzyme names
- for process or for substrate
- end in -ase

10. Enzyme must fit the substrate
Active site – region on enzyme molecule that binds to substrate molecule
Active site
substrate

11. Enzyme control all types of reactions
catabolic – breaking synthesis – building

12. Models of Enzyme Fit Lock-and-key model – perfect fit, no shape change
Induced fit – shape of enzyme changes when substrate attaches

13. 5.7 Factors Affecting Enzyme Action
Enzymes are protein - shape is critical to function
Temperature - heat makes molecules move faster
 more contact - enzyme with substrate  faster reaction rate
BUT - HIGH TEMPS DENATURE PROTEINS!

14. Enzymes and pH Ions - break weak bonds holding molecule shape
electrolyte (salts) or pH change

15. Enzyme activity and concentration
Increase concentration of enzyme or of substrate
- increases reaction rate BUT ONLY TO A POINT
limiting reagent – all molecules being used
Rate does not increase any farther

16. Enzyme Inhibition
1. Competitive inhibitor - another molecule competes for active site - blocks substrate
2. Noncompetitive inhibitor – another molecule binds somewhere else on the enzyme -> enzyme changes shape
- active site no longer fits substrate

17. A molecule made in reaction sequence inhibits the enzyme
Feedback inhibition
A molecule made in reaction sequence inhibits the enzyme

18. Feedback

19. Product from later reaction inhibits an earlier reaction
Feedback inhibition in enzymes
Product from later reaction inhibits an earlier reaction
 Sequence stops

20. Feedback inhibition - examples
Many poisons and drugs act this way
Penicillin (blocks bacterial wall assembly)
Aspirin (blocks pain sensation)
Sarin, malathion (block nerve impulses)
In ALD – Lorenzo’s Oil blocks synthesis of long chain fatty acids

21. When substrate is at saturation: Non-competitive--- active site is still open, so some substrate molecules can still bind to active site  reaction continues but at slower rate

22. Inhibition can be reversed
If enough substrate molecules are present, some will displace inhibitor molecules

23. Coenzymes Many enzymes need the help of COFACTORS
- inorganic, ex. ions
or COENZYMES
- organic, ex. vitamins

24. 5.10: Membranes organize chemical activities in a cell
a) keep structural order
b) compartments have specific enzymes
Plasma membrane
- boundary between cell and its environment

25. Fluid Mosaic Model Describes structure of cell membranes
“mosaic” – sea of lipids with scattered proteins
“fluid” – molecules float and move around within the layer

26. Fluid-Mosaic Model

27. 5.11 Phospholipids make cell membranes
Phospholipid = lipid molecule with phosphate
glycerol + two fatty acids + phosphate group
phosphate group = polar end
(hydrophilic “head”)
Fatty acids = nonpolar end
(hydrophobic “tails”)

28. Phospholipids form a double layer in water
Polar heads are on the outside ( touch water)
Nonpolar tails are on the inside (away from water)
- Unsaturated – keep membrane flexible

29. Features of the Cell Membrane
Semipermeable = some substances can pass through
- some cannot
- depends on: molecule size, charge, polar or nonpolar, needs of cell, signals from environment
Cholesterol – scattered among the phospholipids
- in animal cells only
- keep membrane flexible in changing temperatures
Carbohydrates – glucose chains on outside of cell
- Identification “tags”
- Receptor sites for messenger molecules

30. Membrane Proteins have many functions
Transport
Allows a specific
molecule to
pass through
the membrane
Enzyme
Catalyzes a
reaction inside
the cell
Receptor
Site for messenger molecule to attach

31. Transport Proteins
Channels, pores, and carriers move particles across the membrane
Specific
May use energy

32. Signal Transduction
Message from outside cell is relayed to a specific molecule inside cell Chemical signal binds to receptor protein - message sent inside cell - 2nd messenger relay - causes response in cell Ex. hormones, neurotransmitters

33. Receptor Proteins – Insulin Receptors
Receptors on cell membrane
Insulin attaches
Signal transduction
Message allows glucose into cell
Transport protein for glucose

34. Example: insulin receptors
- cause a different membrane protein to allow glucose to enter cell

35. Membrane proteins (2) Identification “SELF” – cell belongs
in this organism, Ex. immunity
Junctions
Cells join to
form tissues, communicate
Structure
Attach to extracellular matrix or cytoskeleton; Keeps internal parts organized

36. How do membranes keep homeostasis?
Cell membranes are selectively permeable
The lipid layer blocks most substances
Some molecules can cross the membrane
By passive or active transport
Some are too big to cross at all

37. PASSIVE TRANSPORT USES NO CELL ENERGY
Diffusion: Molecules move randomly – spread out until evenly distributed

38. DIFFUSION
Diffusion: movement of particles from an area of higher concentration to an area of lower concentration
Adjacent areas with different concentrations = concentration gradient
Particles move in all directions (random)
NET movement is from high concentration to low
“Down the concentration gradient”

39. Diffusion Particles spread out until evenly distributed
 equilibrium (homogeneous)
Still move randomly, but
 NO further change in concentration

40. Cell Membranes allow some particles to cross
Particles can diffuse across
the lipid bilayer if they are:
Small
Nonpolar (lipid-soluble)
Examples: CO2 , O2, fatty acids

41. Ex. Gas exchange in lungs
Two or more solutes – each moves down its own gradient
Ex. Gas exchange in lungs

42. Others need help to get through - Facilitated Diffusion
Transport proteins- specific for one substance
Down the gradient - no cell energy needed
Particles can cross by facilitated diffusion if they are:
Small
POLAR (water soluble) or CHARGED
Examples: H2O, glucose, amino acids, ions .

43. Facilitated Diffusion
Diffusion through a membrane protein

44. 5.15: Facilitated Diffusion
Channel (pore)
Carrier

45. Why do particles cross the membrane?
Depends on:
Size
Polar or nonpolar
Charge
Concentration gradient
Chemical signals inside or outside cell
Needs of the cell

46. 5.16: OSMOSIS Diffusion of water across a membrane
Important process in cell homeostasis 
Water crosses the cell membrane easily
- Small enough to pass between lipid molecules
Also pass through special proteins, aquaporins

47. Water diffuses easily across membranes; many solutes don’t

48. Osmotic Pressure – tendency of water to move across a membrane
Which way does water go?
From side with more water (less solutes)
to side with less water (more solutes)
Type of solutes doesn’t matter, only total concentration
- down its gradient

49. Osmotic equilibrium when concentrations are equal
or when force of gravity equals osmotic pressure

50. Why osmosis matters
Water crosses membrane easily, faster than many solutes
Water will try to reach equilibrium
If NET water moves into or out of cell  disrupts homeostasis
Water balance is needed for homeostasis

51. TONICITY = osmotic pressure in cells
ISOTONIC
Equal concentrations of solutes inside and outside cell
Equal concentrations of water
Water goes in and out of cell at equal rates

52. Isotonic pressure in cells
No NET movement of water into or out of cell
Normal water pressure in animal cells
Wilted (“flaccid”) water pressure in plant cells

53. When solute concentration is different on two sides of a membrane
lower solute concentration = hypotonic
Higher solute concentration = hypertonic
Solutes will move down their gradient IF THEY CAN CROSS THE MEMBRANE

54. Water concentration is OPPOSITE of solutes
Low solutes  HIGH WATER concentration
High solutes  LOW WATER concentration
Water WILL diffuse down its gradient and crosses the cell membrane easily
Goes TO whichever side has more solutes

55. Cells in hypertonic solutions
Solutes are higher outside cell, water is lower
Water leaves cell by osmosis
Cytoplasm shrinks - “plasmolysis”
- animal cells: shrivel
- plant cells: low turgor pressure
- cytoplasm pulls away from cell wall
- but cell wall does not shrink

56. Cells in hypotonic solutions
Solutes are lower outside cell, water is higher
Water enters cell by osmosis
Cytoplasm swells
- animal cells: swell, may burst (“lyse”)
- plant cells: high osmotic pressure “turgor”
- won’t burst (have a cell wall)
- “Turgid” – stiff and firm, upright stem

57. Isotonic Hypotonic Hypertonic

58. Osmosis in Animal Cells
Animal cells like ISOTONIC conditions best

59. Plant cells like HYPOTONIC conditions best
Osmosis in Plant Cells
Plant cells like HYPOTONIC conditions best

60. Plant cells in hypotonic solution Plant cells in hypertonic solution
Red blood cells - in isotonic in hypotonic in hypertonic
Plant cells in hypotonic solution
Plant cells in hypertonic solution

61. Contractile Vacuoles
Fresh-water protists (like Paramecia or Amoeba) must constantly remove water that comes into the cell by osmosis

62. Cells can maintain a concentration that is NOT at equilibrium
5.18 Active transport uses cell energy
Protein pumps move particles against the gradient
- from LOW concentration to HIGH
Cells can maintain a concentration that is NOT at equilibrium

63. Why would cells use active transport?
1) To concentrate substances:
Examples: kidneys : wastes in urine
- intestine : nutrients in blood
2) To maintain an ion concentration
- sodium-potassium pump for nerve impulses

65. Na+ - K+ pump

66. in photosynthesis and cell respiration
Proton (H+) pump
in photosynthesis and cell respiration

67. Bulk Transport – uses energy
For particles too big to pass through membrane Endocytosis = brings material into cell - fold cell membrane around it form a vacuole a. Phagocytosis = “cell eating” - large particles or whole cells - examples: amoeba white blood cells
pseudopods

68. Endocytosis
– substance pulled INTO CELL

69. Pinocytosis – “cell drinking”
Small folds of membrane take in liquids
Example: small intestine absorbs some water this way

70. 5.19: Exocytosis – substance goes OUT OF cell
- enclosed in membrane vesicle vesicle fuses with plasma membrane releases contents outside cell

71. Exocytosis For secretory cells
ex. Hormones from endocrine glands: pancreas - insulin  bloodstream
digestive juices from pancreas, intestine  food cavity

72. “coated pit” on membrane
Receptor-mediated endocytosis
Receptors on plasma membrane for a specific molecule
Membrane encloses molecule  forms a vesicle
“coated pit” on membrane

73. LDL Cholesterol
cholesterol: essential for normal cell functioning and for making other lipids
a) carried in the blood by low-density lipoproteins (LDL)
b) LDL has a surface protein that fits a receptor on cell membranes
- cells remove it from the blood by receptor-mediated endocytosis

74. 5.20: Hypercholesterolemia
If receptors are faulty or missing, cholesterol remains in the blood  collects inside blood vessels (high risk for heart disease) and in pockets under the skin
Cholesterol in pockets under skin
cholesterol inside blood vessel