Plasma Membrane Transport

Cells

Fluid Mosaic Model

Phospholipid

Cholesterol -immobilizes phospholipids (makes membranes less fluid and stronger)

Membrane Protein Functions

Passive Transport

• Requires no energy• Occurs due to natural concentration gradient• Molecules move from high concentration to low

concentration (DOWN the gradient)

3 Types Diffusion Osmosis Faciliated Diffusion

Diffusion

Diffusion

• A.K.A. simple diffusion

• Movement of small molecules across a selectively permeable membrane from an area of HIGH concentration to an area of LOW concentration w/o the use of energy (DOWN the concentration gradient)

e.g. O2, CO2, urea, & alcohol

Osmosis The diffusion of WATER across a selectively

permeable membrane

OSMOTIC PRESSURE

The pressure exerted on plasma membranes in solution• Isotonic solution• Hypertonic solution• Hypotonic solution

Water Potential

• The physical property predicting the direction in which water will flow, controlled by the solute concentration

Water potentials (ψ) are a way of measuring the free-energy of water. Water will flow spontaneously from a high potential to a low potential, like a ball rolling down a hill.

(ψ) = Greek letter psi

Physical pressure due to air & the container

How So l ute Concentr a t ion Aff ects Water Po tent ia l

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Solute Concentr ation

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Cells in Isotonic Solution

Isotonic Solutions

• If the concentration of solute (salt) is = on both sides, there will be no net movement of water

• "ISO" means the same

Cells in Hypertonic Solution

Hypertonic Solutions• More solute (salt) molecules outside the cell, which causes

water to be sucked out of the cell.

• In plant cells, the central vacuole loses water and the cells shrink, causing plasmolysis resulting in the plant wilting.

• In animal cells, the cells also shrink.

• In both cases, the cell may die.

• This is why it is dangerous to drink sea water

Plasmolysis

A phenomenon in plant cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.

Cells in Hypotonic Solution

Hypotonic Solutions• There are less solute (salt) molecules outside the cell,

since salt sucks, water will move into the cell.

• The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting

• In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this.

Osmotic Potential

The tendency of water to move across a selectively permeable membrane into a solution

Determined by measuring the pressure required to stop the osmotic movement of water into the solution.

Osmosis Review

Facilitated DiffusionProtein Channel or Pore

Facilitated DiffusionProtein Carrier

Active Transport

• Requires cell energy (ATP) to move molecules AGAINST the concentration gradient; from an area of LOW concentration to an area of HIGH concentration

• Sodium–Potassium pump (Exchange 3 sodium ions for 2 potassium ions)

• Hydrogen ion, or proton pump (Pump hydrogen ion against the concentration gradient)

Phosphorylation

The addition of a phosphate (PO4) group

(From ATP) to a protein or a small molecule

This changes the protein shape

Active Transport (Uniport)

Active Transport Na-K Pump

Na-K Pump Antiport

Glucose-Sodium Symport

Proton (Hydrogen Ion) Pump

Bulk Media Transport

• Endocytosis – Vesicle is created from the invagination of the plasma membrane, which pinches off, bringing large molecules into the cell

• Pinocytosis – Cell drinking (endocytosis)

• Phagocytosis – Cell eating (endocytosis)

• Receptor Mediated Endocytosis – Substrate binds to receptor found on the plasma membrane to be brought into the cell

• Exocytosis – Vesicle binds to the plasma membrane releasing the contents outside of the cell

Endocytosis

Pinocytosis

Phagocytosis

Receptor Mediated Endocytosis

Exocytosis