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History of the Plasma Membrane. 1665: Robert Hooke 1895: Charles Overton - composed of lipids 1900-1920's: must be a phospholipid 1925: E. Gorter and G. Grendel - phospholipid bilayer1935: J.R. Danielli and H. Davson ? proteins also part, proposed the Sandwich Model 1950's: J.D. Robertson ? pro
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1. The Plasma Membranehttp://staff.jccc.edu/aalarabi/memb_related_mov.htm
2. History of the Plasma Membrane 1665: Robert Hooke
1895: Charles Overton - composed of lipids
1900-1920’s: must be a phospholipid
1925: E. Gorter and G. Grendel - phospholipid bilayer
1935: J.R. Danielli and H. Davson – proteins also part, proposed the Sandwich Model
1950’s: J.D. Robertson – proposed the Unit Membrane Model
1972: S.J. Singer and G.L. Nicolson – proposed Fluid Mosaic Model
3. Plasma Membrane is made of Phospholipids Gorter + Grendel
Red Blood Cells analyzed
Enough for Phospholipid bilayer
Polar heads face out and Nonpolar tails face in
Does not explain why some nonlipids are permeable
4. Plasma Membrane Models
Sandwich Model
(Danielli + Davson)
2 layers of globular proteins with phospholipid inside to make a layer and then join 2 layers together to make a channel for molecules to pass
Unit Membrane Model
(Robertson)
Outer layer of protein with phospholipid bilayer inside, believed all cells same composition, does not explain how some molecules pass through or the use of proteins with nonpolar parts, used transmission electron microscopy
Fluid Mosaic Model
(Singer + Nicolson)
Phospholipid bilayer with proteins partially or fully imbedded, electron micrographs of freeze-fractured membrane
5. Which membrane model is correct? 1) Rapidly freeze specimen
2) Use special knife to cut membrane in half
3) Apply a carbon + platinum coating to the surface
4) Use scanning electron microscope to see the surface
According to the electron micrograph which membrane model is correct?
Why?
Fluid-Mosaic Model
6. Fluid-Mosaic Model Fluid – the plasma membrane is the consistency of olive oil at body temperature, due to unsaturated phospholipids. (cells differ in the amount of unsaturated to saturated fatty acid tails)
Most of the lipids and some proteins drift laterally on either side. Phospholipids do not switch from one layer to the next.
Cholesterol affects fluidity: at body temperature it lessens fluidity by restraining the movement of phospholipids, at colder temperatures it adds fluidity by not allowing phospholipids to pack close together.
Mosaic – membrane proteins form a collage that differs on either side of the membrane and from cell to cell (greater than 50 types of proteins), proteins span the membrane with hydrophilic portions facing out and hydrophobic portions facing in. Provides the functions of the membrane
7. Structure of the Plasma Membrane
8. Structure of the Plasma Membrane
Phospholipid bilayer
Phospholipid
Hydrophilic head
Hydrophobic tails
Cholesterol
Proteins
Transmembrane/
Intrinsic/Integral
Peripheral/Extrinsic
Cytoskeletal filaments
Carbohydrate chain
Glycoproteins
Glycolipids
9. Proteins of the Plasma Membrane Provide 6 Membrane Functions:
1) Transport Proteins
2) Receptor Proteins
3) Enzymatic Proteins
4) Cell Recognition Proteins
5) Attachment Proteins
6) Intercellular Junction
Proteins
10. 1) Transport Proteins Channel Proteins – channel for lipid insoluble molecules and ions to pass freely through
Carrier Proteins – bind to a substance and carry it across membrane, change shape in process
11. 2) Receptor Proteins – Bind to chemical messengers (Ex. hormones) which sends a message into the cell causing cellular reaction
12. 3) Enzymatic Proteins – Carry out enzymatic reactions right at the membrane when a substrate binds to the active site
13. 4) Cell Recognition Proteins – Glycoproteins (and glycolipids) on extracellular surface serve as ID tags (which species, type of cell, individual). Carbohydrates are short branched chains of less than 15 sugars
14. 5) Attachment Proteins Attach to cytoskeleton (to maintain cell shape and stabilize proteins) and/or the extracellular matrix (integrins connect to both).
Extracellular Matrix – protein fibers and carbohydrates secreted by cells and fills the spaces between cells and supports cells in a tissue.
Extracellular matrix can influence activity inside the cell and coordinate the behavior of all the cells in a tissue.
15. 6) Intercellular Junction Proteins – Bind cells together
Tight junctions
Gap junctions
16. Types of Cell Junctions
Tight Junctions
Desmosomes
Gap Junctions
17. Tight Junctions Transmembrane Proteins of opposite cells attach in a tight zipper-like fashion
No leakage
Ex. Intestine, Kidneys, Epithelium of skin
18. Desmosomes Cytoplasmic plaques of two cells bind with the aid of intermediate filaments of keratin
Allows for stretching
Ex. Stomach, Bladder, Heart
19. Gap Junctions Channel proteins of opposite cells join together providing channels for ions, sugars, amino acids, and other small molecules to pass.
Allows communication between cells.
Ex. Heart muscle, animal embryos
20. Materials must move in and out of the cell through the plasma membrane.
Some materials move between the phospholipids.
Some materials move through the proteins. How do materials move into and out of the cell?
21. Plasma Membrane Transport Molecules move across the plasma membrane by:
22. What are three types of passive transport? Diffusion
Facilitated Diffusion
Osmosis
23. Passive Transport 1: Diffusion Molecules can move directly through the phospholipids of the plasma membrane
This is called …
24. What is Diffusion? Diffusion is the net movement of molecules from a high concentration to a low concentration until equally distributed.
Diffusion rate is related to temperature, pressure, state of matter, size of concentration gradient, and surface area of membrane.
25. What molecules pass through the plasma membrane by diffusion? Gases (oxygen, carbon dioxide)
Water molecules (rate slow due to polarity)
Lipids (steroid hormones)
Lipid soluble molecules (hydrocarbons, alcohols, some vitamins)
Small noncharged molecules (NH3)
26. Why is diffusion important to cells and humans? Cell respiration
Alveoli of lungs
Capillaries
Red Blood Cells
Medications: time-release capsules
27. Passive Transport 2: Facilitated Diffusion Molecules can move through the plasma membrane with the aid of transport proteins
This is called …
28. What is Facilitated Diffusion? Facilitated diffusion is the net movement of molecules from a high concentration to a low concentration with the aid of channel or carrier proteins.
29. What molecules move through the plasma membrane by facilitated diffusion? Ions
(Na+, K+, Cl-)
Sugars (Glucose)
Amino Acids
Small water soluble molecules
Water (faster rate)
30. How do molecules move through the plasma membrane by facilitated diffusion? Channel and Carrier proteins are specific:
Channel Proteins allow ions, small solutes, and water to pass
Carrier Proteins move glucose and amino acids
Facilitated diffusion is rate limited, by the number of proteins channels/carriers present in the membrane.
31. Why is facilitated diffusion important to cells and humans? Cells obtain food for cell respiration
Neurons communicate
Small intestine cells transport food to bloodstream
Muscle cells contract
32. Passive Transport 3: Osmosis Water Molecules can move directly through the phospholipids of the plasma membrane
This is called …
33. What is Osmosis? Osmosis is the diffusion of water through a semipermeable membrane. Water molecules bound to solutes cannot pass due to size, only unbound molecules. Free water molecules collide, bump into the membrane, and pass through.
34. Osmosis in action What will happen in the U-tube if water freely moves through the membrane but glucose can not pass?
Water moves from side with high concentration of water to side with lower concentration of water. Movement stops when osmotic pressure equals hydrostatic pressure.
35. Why is osmosis important to cells and humans? Cells remove water produced by cell respiration.
Large intestine cells transport water to bloodstream
Kidney cells form urine
36. Osmosis and Tonicity Tonicity refers to the total solute concentration of the solution outside the cell.
What are the three types of tonicity?
Isotonic
Hypotonic
Hypertonic
37. Isotonic Solutions that have the same concentration of solutes as the suspended cell.
What will happen to a cell placed in an Isotonic solution?
The cell will have no net movement of water and will stay the same size.
Ex. Blood plasma has high concentration of albumin molecules to make it isotonic to tissues.
38. Hypotonic Solutions that have a lower solute concentration than the suspended cell.
What will happen to a cell placed in a Hypotonic solution?
The cell will gain water and swell.
If the cell bursts, then we call this lysis. (Red blood cells = hemolysis)
In plant cells with rigid cell walls, this creates turgor pressure.
39. Hypertonic Solutions that have a higher solute concentration than a suspended cell.
What will happen to a cell placed in a Hypertonic solution?
The cell will lose water and shrink. (Red blood cells = crenation)
In plant cells, the central vacuole will shrink and the plasma membrane will pull away from the cell wall causing the cytoplasm to shrink called plasmolysis.
40. Review: Passive Transport Diffusion – O2 moves in and CO2 moves out during cell respiration
Facilitated Diffusion – glucose and amino acids enter cell for cell respiration
Osmosis – cell removal or addition of water
41. Review Tonicity What will happen to a red blood cell in a hypertonic solution?
What will happen to a red blood cell in an isotonic solution?
What will happen to a red blood cell in a hypotonic solution?
42.
Active Transport
Primary
Secondary (no ATP)
Bulk Transport
Exocytosis
Endocytosis
Phagocytosis
Pinocytosis
Receptor-Mediated endocytosis What are three types of Active transport?
43. Active Transport Molecules move from areas of low concentration to areas of high concentration with the aid of ATP energy.
Requires protein carriers called Pumps.
44. The Importance of Active Transport Bring in essential molecules: ions, amino acids, glucose, nucleotides
Rid cell of unwanted molecules (Ex. sodium from urine in kidneys)
Maintain internal conditions different from the environment
Regulate the volume of cells by controlling osmotic potential
Control cellular pH
Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium-Potassium pump and Proton pumps)
45. The Sodium-Potassium Pump 3 Sodium ions move out of the cell and then 2 Potassium ions move into the cell.
Driven by the splitting of ATP to provide energy and conformational change to proteins by adding and then taking away a phosphate group.
Used to establish an electrochemical gradient across neuron cell membranes.
46. Secondary Active TransportVia Facilitated Diffusion of Na Counter Transport – the transport of two substances at the same time in opposite directions, without ATP. Protein carriers are called Antiports.
Co-transport – the transport of two substances at the same time in the same direction, without ATP. Protein carriers are called Symports.
Gated Channels – receptors combined with channel proteins. When a chemical messenger binds to a receptor, a gate opens to allow ions to flow through the channel.
47. Bulk Transport: Exocytosis Movement of large molecules bound in vesicles out of the cell with the aid of ATP energy. Vesicle fuses with the plasma membrane to eject macromolecules.
Ex. Proteins, polysaccharides, polynucleotides, whole cells, hormones, mucus, neurotransmitters, waste
48. Bulk Transport: Endocytosis Movement of large molecules into the cell by engulfing them in vesicles, using ATP energy.
Three types of Endocytosis:
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
49. Phagocytosis “Cellular Eating” – engulfing large molecules, whole cells, bacteria
Ex. Macrophages ingesting bacteria or worn out red blood cells.
Ex. Unicellular organisms engulfing food particles.
50. Pinocytosis “Cellular Drinking” – engulfing liquids and small molecules dissolved in liquids; unspecific what enters.
Ex. Intestinal cells, Kidney cells, Plant root cells
51. Receptor-Mediated Endocytosis Movement of very specific molecules into the cell with the use of vesicles coated with the protein clathrin.
Coated pits are specific locations coated with clathrin and receptors. When specific molecules (ligands) bind to the receptors, then this stimulates the molecules to be engulfed into a coated vesicle.
Ex. Uptake of cholesterol (LDL) by animal cells
52. Review Types of Endocytosis What is phagocytosis?
What is pinocytosis?
What is receptor-mediated endocytosis?