4.1 Plasma Membrane Structure and Function

• Regulates the entrance and exit of molecules into and out of the cell

• Phospholipid bilayer with embedded proteins– Hydrophilic polar heads– Hydrophobic nonpolar tails– Cholesterol (animal cells)

Fluid-mosaic Model of Plasma Membrane Structure

4.1 Plasma Membrane Structure and Function

• Types of Membrane Proteins– Channel Proteins

– Carrier Proteins

– Cell Recognition Proteins

– Receptor Proteins

– Enzymatic

A Proteins

4.2 Permeability of the Plasma Membrane

• Differentially (selectively) Permeable

• Factors that determine how a substance may be transported across a plasma membrane:– Size– Polar or Nonpolar

How Molecules Cross the Plasma Membrane

Passage of Molecules into and out of the CellKnow for test

4.2 Permeability of the Plasma Membrane

• Diffusion and Osmosis– Diffusion is the movement of molecules from

an area of higher to lower concentration

Process of Diffusion

4.2 Permeability of the Plasma Membrane

• Diffusion and Osmosis– Diffusion is the movement of molecules from

an area of higher to lower concentration– Oxygen and Carbon Dioxide are two gases

that can diffuse through the plasma membrane

Gas Exchange in Lungs

4.2 Permeability of the Plasma Membrane

• Osmosis– Osmosis is the diffusion of water across a

differentially permeable membrane.

4.2 Permeability of the Plasma Membrane

• Osmosis– Osmosis is the diffusion of water across a

differentially permeable membrane.– Osmotic pressure is the pressure that

develops in a system due to osmosis.

Osmosis Demonstration

4.2 Permeability of the Plasma Membrane

• Osmosis– Isotonic: the solute concentration is

equal inside and outside of a cell

– Hypotonic: a solution has a lower solute concentration than the inside

of a cell

– Hypertonic: a solution has a higher solute concentration than the

inside of a cell

Osmosis in Animal and Plant Cells

4.2 Permeability of the Plasma Membrane

• Transport by Carrier Proteins – Carrier proteins combine with a molecule or

ion to be transported across the membrane.

– Carrier proteins are required for:• Facilitated Transport• Active Transport

Facilitated Transport

• Small molecules that are not lipid-soluble• Molecules combine with carrier proteins• Molecules follow the concentration gradient• Energy is not required

4.2 Permeability of the Plasma Membrane

• Active Transport– Small molecules

– Molecules combine with carrier proteins

– Molecules move against the concentration gradient

– Energy is required

The Sodium-Potassium Pump

4.2 Permeability of the Plasma Membrane

• Vesicle Formation– Transport of large molecules

– Requires energy

– Keeps the macromolecule contained

4.2 Permeability of the Plasma Membrane

• Vesicle Formation– Exocytosis - Vesicles form as a way to transport

molecules out of a cell

Exocytosis

Vesicle Formation

• Vesicle Formation– Endocytosis - Vesicles form as a way to transport

molecules into a cell• Phagocytosis: Large,particulate matter• Pinocytosis: Liquids and small particles dissolved in liquid• Receptor Mediated Endocytosis: A type of pinocytosis that

involves a coated pit

Three Methods of Endocytosis