1. Unit 3: Cells and Cellular Communication
Chapters 6-7,11

2. “I’m talking to you!...You’re so…so…so thick-membraned sometimes.”

3. CHAPTER 8 Cell Membrane Structure and Function Cell Memranes are…
Selectively permeable
Fluid

4. Discovering Membrane Sructure
Memorizing this timeline is unnecessary- Important concept is that each researcher worked from previous ideas, up to the currently accepted theory.
Discovering Membrane Sructure
Made of lipids and proteins
Evidence:
1895 substances that dissolve in lipids enter cells fastest (Overton)
1917 man-made membrane of phospholipids created (Langmuir)
1925 proposal that memranes are phospholipid bilayers (Gorter + Grendel)

5. Discovering Membrane Structure
1935 theory that proteins surround both sides of the phospholipid bilayer (Davson +Danielli)
1950’s + 60’s Questions about this model because membrane proteins have large hydrophobic sections, not all membranes are the same
1972 fluid mosaic model proposed- and still in use in 2008 (Singer + Nicolson)

6. Fluid Mosaic Model of Membranes
Insert pic of model

7. Chemistry: phospholipids
Insert pic
Amphipathic molecules = has a hydrophobic region and a hydrophilic region

8. Fluidity within the membrane
Movement of lipids
2 µm/s
Same size as bacterial cell

9. Movement of Phospholipids is controlled by
Cytoskeleton- some are immobile because of it
Temp- as temp ↓ movement ↓ until it solidifies
Cholesterol- at 37C it limits fluidity, but it allows the membrane to be fluid at lower than normal temp b/c it blocks the packing of lipids
Cells- can change lipid composition to adjust to temp
Temp for solid memb depends on types of ipids. More unsaturated = fluid longer

10. Cholesterol in membranes
Insert pic of cholesterol blocking movement

11. Mosaic= huge variety of molecules
50+ types of proteins in membranes of RBC’s!
Integral proteins- cross into the hydrophobic core
Transmembrane proteins- span entire memb
Peripheral proteins- stuck to the surface

12. A Transmembrane Protein with 7 passes through the membrane

13. Inside ≠ Outside of Membrane
Membrane showing all types labeled

14. Carbs in the Membrane cell-cell recognition “Name Tags”
Branched oligosaccharides (less than 15 monosaccharides)
Uses:
Correct placement of cells as embryo develops
Immune system defenses

15. Glycolipids and Glycoproteins
Insert image of glycolipid and label parts

16. Structure + Function = moving things across the cell membrane
Sugar
Amino acids
water
Oxygen
Na+ K+
Ca2+
Cl-
OUT
Carbon Dioxide
Water
Other waste products
Na+ K+
Ca2+
Cl-

17. How to Cross a Membrane Hydrophobics:
Dissolve in the lipid bilayer and pass through
Hydrocarbons
Carbon dioxide
Oxygen

18. What if you are hydrophilic??
Transport proteins
Let water, ions, and polar molecules through
“toll gate”
Some are just tunnels, others carry a molecule through

19. Passive Transport Diffusion – [high]  [low]
Concentration gradient- the natural direction of flow (different for each molecule)

20. Passive Transport for Life: Cellular Respiration
Oxygen diffuses INTO a cell as long as C.R. is happening
Water diffuses in/out of cells freely through transport proteins
No energy needed!

21. OSMOSIS
DIFFUSION OF WATER
Pic of hypo, hyper, isotonic solns

22. What type of solution is this cell sitting in?

23. Osmoregulation
Control of water balance in organisms without cell walls
Paramecium live in ponds that are hypotonic compared to their cell.
Adaptation- Contractile Vacuole collects water and forces it out.
Pic Of contractile vacuole in para.

24. Water Balance With Cell Walls
When surrounded by incoming rain water, it is in a hypotonic solution.
Turgid- cell membrane pushed up against cell wall- normal for plants
Flaccid- cell membrane pulls in from cell wall- plant wilts
Plasmolysis- water leaves cell, cell shrivels, fatal to cell

25. Facilitated Diffusion
Passive transport
Hydrophilic molec. diffuse via transport proteins

26. Transport Proteins are Like Enzymes
Specific match to molecules they transport
Some have specific active sites
Rate of transport slows down when it becomes saturated
Inhibited by “imitation” molecules
Catalyze movement of molecules instead of reactions

27. Gated Channels
Example: Neurotransmitter arrives at a nerve cell, causes Na+ to enter the cell
Channel Protein
Example: Aquaporins

28. Some proteins have “induced fit” like an enzyme
Triggered by binding/release of the molecule to be moved

29. How can transport proteins affect your health?
Cystinuria
Body is unable to make memb. Proteins that transport cystine and other A.A. out of the kidney cells
Affect: chronic kidney stones

30. Active Transport Movement AGAINST the concentration gradient
Requires Energy!
ATP is the key
Allows cells to have a different internal environment than surroundings
More K+ and less Na+ inside than outside

31. Na-K Pump Well studied example of active transport
Exchanges Na+ for K+ across plasma membrane of animal cells

33. Very important concept that will be used in examples all year long.
Membrane Potential
Electrical voltage formed when there is an unequal distribution of ions across a membrane
Inside is negative compared to outside
-50mV to -200mV

34. Electrochemical Gradient
Combination of concentration gradient and electrical force
Inside a cell more negative than outside THEREFORE
Passive transport will move cations IN and anions OUT

35. How this works in a Neuron
Stimulated by trigger
Resting nerve cell
Gated channels open
Na+ enters following electrochemical gradient

36. Electrogenic Pumps Na-K pump does not give equal trade of ions
3Na+ OUT and 2K+ IN
Result: storing energy every time the pump cycles for other jobs
ANIMALS use Na-K pumps
PLANTS, BACTERIA, FUNGI use Proton pumps

37. Proton Pump is the main electrogenic pump in plants, fungi, and bacteria

38. Contransport
A single ATP pump works, and then diffusion of the same substance assists in moving a molecule AGAINST the concentration gradient

39. Moving Very Large Molecules that don’t fit through transport proteins
OUT exocytosis
Insulin created in pancreatic cells is secreted into the blood
Carbs finished in Golgi Apparatus moved outside plant cells to make a new cell wall
IN endocytosis
Process: Vesicles containing molecules fuse with the membrane and release contents

40. Ligand- extracellular substances that bind to receptors

41. Why should you care? Receptor Mediated Endocytosis
Cholesterol carried in blood in Low Density Lipoproteins (LDL’s)
Receptors on cell membranes bind to LDL’s
Vesicle brings cholesterol into cell
If LDL receptor proteins are defective cholesterol accumulates in blood- atherosclerosis…VERY BAD

42. CHAPTER 7 A TOUR OF THE CELL
We will do this very quickly as 95% is review!
If you need extra time see me ASAP! I am happy to help you catch up!

44. Differential Centrifugation

45. Prokaryotes= small + simple

46. E.coli- many different variations exist

47. Cell Membrane- FLASHBACK!!

48. Animal Cells

49. Plant Cell

50. Prokaryotic Cells vs.
Eukaryotic Cells

51. Peroxisomes
FUNCTION IN THE CELL:

52. Centrosomes
FUNCTION IN THE CELL:

53. Microvilli
FUNCTION IN THE CELL:

54. PLANT CELL VS.
ANIMAL CELL

56. Cell Motility: animals, protists + plants

58. CHAPTER 11 CELL COMMUNICATION
This is likely to be 100% new information for you. Be patient and focused, and you will see that it is not as scary as you may think.
CHAPTER 11
CELL COMMUNICATION

59. Sex in Saccharomyces cerevisiae

60. Signal transduction pathway
Process of a signal converted to cellular response
yeast + animal cells similar process
Plant + bacterial cells similar process
THEREFORE…APPROXIMATELY WHEN DID THIS EVOLVE???

61. Communication between starving bacteria

62. Messages over short distances
Local regulators
Paracrine signaling
Growth factors sent out to all nearby cells
Benefits of this method?
Neurotransmitters
Electrical signal  secretion of neurotransmitter into synapse  message to one immediate neighbor only

63. Long Distance Communication: Hormones
Endocrine signaling
Travel in blood in animals
Travel in by diffusion, or through cells in plants
Less known about these mechanisms
Ethylene- causes fruit to ripen is a gas C2H4

65. Direct Contact Communication
Pass signal molecules directly from cytoplasm cell 1 cytoplasm cell 2
Receptor molecules on cell membranes

66. 3 general steps to cell signaling
11.5

67. 1971 Nobel Prize Work: Earl W. Sutherland
Hormone epinephrine stimulates depolymerization of glycogen in liver and skeletal muscles cells
Depolymerization relases glucose-1-phosphate
Cell converts it to glucose-6-phosphate
Cell uses it for glycolysis (make energy)

68. Conclusion 1
1 effect of epinephrine secreted from adrenal gland in times of stress is to quickly mobilize fuel for cells

69. Mechanism Shown by Sutherland
Epinephrine activates enzyme glycogen phosphorylase that starts depolymerization of glycogen
Experiment
Epinephrine + enzyme + substrate = no reaction
Only worked in living cells

70. Conclusion 2 Epinephrine does not directly work with the enzyme
Plasma membrane must be involved in the process

71. Step 1 Reception
Pic 11.6

72. Induced fit of Membrane Receptor Proteins
Each cell has ID tags so the message doesn’t get to the wrong cell.
Ligand- a small molecule that specifically binds to a larger molecule
The induced fit is the trigger to cause another molecular interaction

73. Signal molecues do not need to enter the cell to start the chain reaction of events!!
Epinephrine is HUGE, it will never get into the cell!

74. Review of Friday’s main idea
Video clip on CD

75. G-protein Linked Receptors
Require the help of a G protein
Yeast mating factor
Epinephrine
Many neurotransmitters and hormones
G proteins are…
On/off swtiches
GDP bound = off
GTP bound =on

76. Diagram of a G Protein linked receptor

77. G Protein act can as GTPase
Enzyme that hydrolizes GTP GDP
Function= shut down reaction when the extracellular signal is gone

78. WHY do we care????
Studies of some G proteins show that if a mouse is conceived and lacks a certain G- protein, blood vessels form incorrectly, mouse is never born.
Human vision and smell depend on G proteins
Cholera bacteria form toxins that interfere with G proteins

79. FYI from the CDC What is cholera?
Cholera is an acute, diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae. The infection is often mild or without symptoms, but sometimes it can be severe. Approximately one in 20 infected persons has severe disease characterized by profuse watery diarrhea, vomiting, and leg cramps. In these persons, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours.

80. Tyrosine-Kinase receptors
Used for growth factors
Cytoplasmic side= enzyme tyrosine kinase.
Catalyzes transfer of phosphate group from ATP to tyrosine (AA) on a substrate protein
Extra cellular side = tyrosine kinase receptor
Attach phosphates to tyrosines on proteins

81. Tyrosine Kinase Receptor model

82. 2 steps to the T-K Receptor reaction
1. ligan binding causes 2 receptor polypeptides to aggregate (dimer)
2. activates the T-K parts of polypeptides , which adds phosphates to the tyrosine on the tail of the 2nd polypeptide
AP exam word: phosphorylation

83. T-K receptors vs. G protein receptors
T-K receptors can trigger many different reaction pathways
G protein receptors are more specific
Some cancers form when the T-K receptors aggregate w/o the ligand

84. Ligand gated ion channels
Protein pores in membrane that open/close in response to signals from ions (Ca+, Na+)
Important for the nervous system cell to cell communication

85. When a specific ligand binds to the protein, the channel opens for ions to pass through.

86. Intracellular receptors
Some receptors are inside the cell
Steroiods, ex testosterone works this way.
Activated testosterone receptor is a transcription factor to regulate specific genes.

87. Steroid hormone goes through membrane
Hormone binds to receptor
Hormone+ receptor enter nucleus binds to specific genes
Starts transcription of the gene
Translation of mRNA completed

88. Signal Transduction Pathway
Once the chain reaction has started there are multiple intermediate steps
Can amplify the message being sent
Better regulation of chemical
processes

89. Relay molecules are usually proteins
Phosphorylation is often the way that a message is passed from one molecule to the next
(Add a phosphate group from ATP to the next molecule in line)
Enzymes that do this are protein kinases

90. THIS IS A HYPOTHETICAL MECHANISM!!!! NOT A REAL ONE!!

91. Importance of Protein Kinases
1% of your genes are for protein kinases
1 cell can have hundreds of different protein kinases
Abnormal activity of those regulating cell division contributes to cancer

92. Turning OFF a signal transduction pathway
Protein phosphatease- enzyme that remove phosphate groups from proteins

93. Second Messengers
Ions, or water soluble molecules that help carry on the chain reaction
Move by diffusion through the cell
Used in G protein linked receptors and T-K receptors
Ca2+ and cAMP most common

94. cyclic AMP

95. Links back to epinephrine
Sutherland observed that the binding of epinephrine caused and increase in the production of cAMP.
Converted back to inactive AMP almost immediately after the epinephrine leaves the receptor

97. Application: Cholera Infections
Vibrio cholerae enters body in water
Bacteria colonize in small intestine
Bacteria form a toxin, that modifies a G protein that regulates salt and water secretion
GTP never made into GDP
Adenylyl cyclase never stops making cAMP
Intestinal cells continue to excrete water and salt
diarrhea

98. Ca2+ as second messenger
Always in cells, BUT there is more than 10,000X more in the blood and extracellular fluid
Protein pumps move it out of the cell or into the ER
A signal molecule tells the cell to release Ca2+ from the ER

99. Ca2+ and inositol triphosphate signal pathway

100. Regulation of cell processes
Pathways may regulate
Activity of enzymes
Synthesis of enzymes
Transcription of DNA
Transcription factors can regulate the on/off of several genes

101. Signal amplification

102. Epinephrine sends different signals to different cells
Liver cells- break down glycogen
Heart cells- contraction, rapid heartbeat
The combination of proteins in each type of cell determine the message

103. Same signal molecule, different messages

104. Scaffolding proteins
Large proteins that “hold” other proteins in the correct order so they are ready for a chain reaction.
In the brain, there are permanent scaffolding proteins that keep synapse proteins in place

105. Signal molecules are only present for a short time
BIG problems if the molecule stays too long!
Go back to cholera example!

106. THE END!!!

107. Practice Essay Question
Cell to cell communication is vital for a multicellular organism.
A. Discuss the ways that cells communicate locally and over long distances.
B. Describe the importance of multistep pathways using one of the following:
Tyrosine kinase receptors
G protein linked receptors