Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish...

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Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectiv es: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure and molecular organization of the cell membrane and list factors determining its selective permeability. 4- Explain and illustrate the following mechanisms of cell transport: diffusion, osmosis, facilitated diffusion, active transport endocytosis, and exocytosis. 3- Explain osmotic pressure and how isotonic, hypertonic, and hypotonic solutions affect cells.

Transcript of Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish...

Page 1: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Lecture # 8: The Cell Surface (Part 2) (Chapter 3)

Objectives:

1- Define a cell and distinguish between cytosol and cytoplasm.

2- Explain the structure and molecular organization of the cell membrane and list factors determining its selective permeability.

4- Explain and illustrate the following mechanisms of cell transport: diffusion, osmosis, facilitated diffusion, active transport endocytosis, and exocytosis.

3- Explain osmotic pressure and how isotonic, hypertonic, and hypotonic solutions affect cells.

Page 2: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

PASSIVE TRANSPORT ACTIVE TRANSPORTIt moves ions or molecules across the plasma membrane with no expenditure of energy by the cell (down gradient)

It requires that the cell expends energy, generally in the form of ATP (up gradient)

Simple Diffusion (down gradient)

Osmosis (a special case of simple diffusion)

Facilitated Diffusion (down gradient, carrier mediated)

The Sodium-Potassium Pump

Secondary Active Transport

Vesicular Transport

1- Endocytosis

2- ExocytosisReceptor-Mediated EndocytosisPinocytosisPhagocytosis

Membrane Transport

Filtration (driven by hydrostatic pressure)

Page 3: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

1- FiltrationIt is the process in which particles are driven through a selectively permeable membrane by hydrostatic pressure (force exerted on a membrane by water)

1- Filtration of nutrients through gaps in blood capillary walls into tissue fluids

Examples:

Blood pressure in capillary forces water and small solutes such as salts through narrow clefts between capillary cells.

2- Filtration of wastes from the blood in the kidneys while holding back blood cells and proteins

Page 4: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

It is the passive net movement of ions or molecules from the region of higher concentration to the region of lower concentration.

It is the difference between the high and low concentration areas

Lower concentration

Higher concentration

Concentration Gradient:

The tendency of ions and molecules in a concentration gradients is to move from the region of higher concen-tration to the region of lower concentration

Diffusion:

Diffusion tends to eliminate the concentration gradient

Brownian Movement: It is the irregular movement of particles suspended in a liquid or gas caused by the kinetic energy of these particles

Page 5: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Concentration Gradient:

The natural tendency of a solute is to move down its concentration gradient, from higher concentration to lower concentration.

It is the difference between the high and low concentration areas of a solute within a given medium

5- Membrane permeability : permeability, rate

Factors affecting diffusion rate through a membrane

3- Temperature: temp., motion of particles

1- Steepness of concentrated gradient: difference, rate

2- Molecular weight: larger molecules move slower

4- Membrane surface area: area, rate

The random molecular motion of particles (Brownian movement) provides the necessary energy

Page 6: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Down gradient

Larger molecules move slower

Diffusion in a Concentration Gradient

Substance A is larger (higher molecular weight) than substance B

A

B

Page 7: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Impermeable Membrane

It is a membrane through which none substance can pass

Page 8: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

It is a membrane through which any substance can pass

Freely Permeable membrane

Page 9: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Selectively Permeable Membrane

It is a membrane that permits the free passage of some materials and restricts the passage of other

The plasma membrane works as a selectively permeable membrane

It allows some things through, such as nutrients and wastes, but usually prevents other things as proteins and phosphates, from entering or leaving the cell.

Page 10: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

It is the passive net diffusion of solvent (water), across a selectively permeable membrane, toward the solution that has the higher concentration of solutes

A B

Osmosis:

OSMOSIS

Osmosis and Tonicity

Page 11: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Osmosis

Reverse osmosis

Side A Side BThe hydrostatic pressure causes a filtration of water from A to B (reverse osmosis) , which produces that net osmosis slows down and stop

At this point, an equilibrium would exist

It is the hydrostatic pressure required to stop osmosis Osmotic Pressure: The higher the concentration of nonpermeating solute in A, the greater the osmotic pressure

Hydrostatic pressure

Page 12: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Osmolarity and Tonicity

It is the total solute concentration (osmole/L) in an aqueous solution

Solution A has a lower osmolarity than solution BSolution B has a higher osmolarity than solution A

OSMOSIS

A BIf two solutions of different osmolarity are separated by a selectively permeable membrane, the solvent (water) will pass the membrane until equilibrium is attained and both solution contain equal concentration of solutes

One osmole: It is one mole of dissolve particles

Osmolarity:

Page 13: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

It is the ability of a solution to affect fluid volume and pressure in a cell

Isotonic solution

It is a solution with the same concentration of non-penetrating solutes as that found in the cells. (Intravenous solutions are isotonic solutions).

Hypertonic solution

It is a solution with a higher concentration non-penetrating solutes than that found in the cells.

Hypotonic solution

It is a solution with a lower concentration of non-penetrating solutes than that found in the cells.

water waterwater

water

Tonicity:

Page 14: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Osmotic Flow across a Plasma Membrane

Page 15: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Effects of Tonicity on RBCs

Hypotonic, isotonic and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a) Hypotonic (b) Isotonic (c) Hypertonic© Dr. David M. Phillips/Visuals Unlimited

Swollen cell

Normal cell

Crenated cell

Page 16: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Carrier-Mediated Transport

It is a process that employs transport proteins (carriers) in the plasma membrane that carry solutes from one side of the membrane to the other.

Carrier-Mediated Transport:

1- Facilitated Diffusion: It is the carried-mediated transport of a solute through the membrane down its concentration gradient. It is a passive transport process; that is, does not consume ATP (energy)

2- Active Transport: It is the carried-mediated transport of a solute through the membrane up its concentration gradient, using energy provided by the ATP.

Carriers:

1- Uniport: It carries one solute at a time

2- Symport: It carries two or more solutes through the membrane simultaneously in the same direction (cotransport)

3- Antiport: It carries two or more solutes through the membrane in opposite directions (countertransport)

Page 17: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

1- Facilitated Diffusion: It is the carried-mediated transport of a solute through the membrane down its concentration gradient. It is a passive transport process; that is, does not consume ATP (energy)

Uniport: It carries one solute at a time

Page 18: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

2- Active Transport: It is the carried-mediated transport of a solute through the membrane up its concentration gradient, using energy provided by the ATP.

Sodium-Potassium Pump

2- Each pump cycle consumes one ATP and exchanges three Na+ for two K+ against (up) the gradient

1- Na+ and K+ are constantly leaking through membrane down the gradient

3- The pump keeps the K+ concentration higher and the Na+ concentration lower with in the cell than in the extracellular fluid (ECF)

4- Half of daily calories is used for the Na+ - K+ pump

Page 19: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Vesicular TransportIt is when materials move into or out of the cell in vesicles, small membranous sacs that form at, or fuse with, the plasma membrane

1- Endocytosis

2- Exocytosis

Receptor-Mediated EndocytosisPinocytosis

Phagocytosis

Page 20: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Phagocytosis (cell eating)It is a process of bringing large materials (bacteria, dust, cellular debris) into the cell by means of pseudopodia that surround the material

Page 21: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Phagocytosis or “Cell-Eating”

Keeps tissues free of debris and infectious microorganisms.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Particle

Pseudopod

Nucleus

Residue

Phagosome

LysosomeVesicle fusingwith membrane

Phagolysosome

1

2

3

45

6

7

A phagocytic cell encounters aparticle of foreign matter.

The cell surroundsthe particle with itspseudopods.

The particle is phagocytizedand contained in aphagosome.

The phagosome fuseswith a lysosome andbecomes a phagolysosome.

The indigestibleresidue is voided byexocytosis.

The phagolysosomefuses with theplasma membrane.

Enzymes from thelysosome digest theforeign matter.

Page 22: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Pinocytosis (cell drinking)

It is a form of endocytosis that brings into the cell a small volume of extracellular fluid (ECF)

Page 23: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

Receptor-Mediated EndocytosisIt involves the formation of vesicles at the surface of the plasma membrane, which contain specific receptors (ligand receptors) for the substance that will be interiorized (ligand)

Lipoproteins (cholesterol), iron ions (Fe 2+)

Page 24: Lecture # 8: The Cell Surface (Part 2) (Chapter 3) Objectives: 1- Define a cell and distinguish between cytosol and cytoplasm. 2- Explain the structure.

ExocytosisIt is the movement of materials out of the cell through the fusion of a vesicle with the plasma membrane