Today: Membrane Function Structure & Function Biology Homework due Monday; Lab 5 on Monday!

The Fluid Mosaic Model

Origins of Membrane Proteins Result: Membranes have an “inside” and an “outside”

Types of Membrane Proteins Most common: Integral proteins penetrate the hydrophobic core and may also be… Transmembrane proteins completely span the membrane Peripheral proteins aren’t embedded in the membrane at all

Role of Carbohydrates On the Cell Membrane Typically branched oligosaccharides bonded to lipids (=glycolipid) or proteins (=glycoproteins)

Functions of Membrane Proteins:

What types of things does a cell need to get across its membrane? Brainstorm What types of things does a cell need to get across its membrane? Of those things, which can cross freely?? Why?? What about everything else??

X Cell membranes are SELECTIVELY PERMEABLE O2, CO2, and other small, nonpolar molecules;and H2O large, polar molecules; ions such as H+, Na+, CI-, Ca++; X

Transport Proteins Transport proteins provide a hydrophillic channel (doorway?) through the membrane Transport proteins may also bind to molecules or ions and move them across the membrane

Passive transport is diffusion across a membrane Substances diffuse down their concentration gradients in a spontaneous process

Passive Transport of Water = Osmosis The direction of osmosis is determined by the total solute concentration, or tonicity Solutions may be hypertonic, hypotonic, or isotonic to each other.

What will happen if I separate these two solutions with a selectively permeable membrane? ??

Osmosis in Cells Without Walls Organisms with cells without walls have adaptations for osmoregulation Possible mechanisms??

POP QUIZ! Normal Red Blood Cells Shriveled Red Blood Cells

Net Movement of Water in Isotonic, Hypotonic, and Hypertonic Solutions

Osmosis in Cells with Walls Osmosis helps a plant cell maintain turgor pressure in a hypotonic environment When cells lose their turgor pressure, they become flaccid as the membrane pulls away from the cell wall (plasmolysis)

Facilitated Diffusion Passive diffusion aided by a transport protein (ex. Aquaporins) Gated Channel Channel Protein

Active Transport What happens to the charge inside and outside the cell when this pump runs?

Membrane Potential All cells have voltage (separation of charges) across their membranes Cytoplasm is negative (-50 to -200 millivolts) Thus molecules can be driven across membrane by both a chemical force (concentration gradient) and an electrical force. This combination = electrochemical gradient

Transport proteins that generate voltage are called electrogenic pumps Membrane Potential Transport proteins that generate voltage are called electrogenic pumps

Review:

Active Transport: Cotransport An ATP-powered pump can indirectly drive the transport of other molecules

EXOCYTOSIS OF A VESSICLE TRANSPORT PROTEINS work well for individual molecules, but… LARGE ITEMS (or molecules) must be transported by EXOCYTOSIS or ENDOCTOSIS PLASMA MEMBRANE EXOCYTOSIS OF A VESSICLE

ENDOCYTOSIS PLASMA MEMBRANE

Three Types of Endocytosis Phagocytosis (“cellular eating”) Pinocytosis (“cellular drinking”) Receptor-mediated endocytosis