Structure and Function Membranes Structure and Function

Membrane Structure Phospholipid Bi-layer Contains Different Types of Proteins Channel proteins Protein Pumps proteins Adhesion proteins Cell-to-Cell Communication proteins Hormone Receptor proteins Immobilized Enzymes Fluid Mosaic Model

Phospholipid Bi-layer Contains Glycoproteins Integral Proteins Peripheral Proteins Cholesterol

Channel proteins Integral protein: embedded across bi-layer Allows for movement of molecules across cell membrane

Protein Pumps Integral protein Transports molecules across membranes by changing shape

Adhesion proteins Connects internal cytoskeleton to external points of attachment Secures cells of multi-cellular organisms in place

Cell-to-Cell Communication proteins Cells within the same organism use membrane proteins to recognize each other Often use glycoproteins Major importance to immune system

Hormone Receptor proteins Hormones bind to cell surface proteins Initiates a series of reactions within cell Results in cellular response such gene expression (making more or less of a protein)

Immobilized Enzymes Many enzymes used by cells are embedded within membranes Useful in keeping certain reactions in specific parts of the cell

Membrane Function Boundary Separates Two Environments Selectively Permeable Passive Transport Simple Diffusion Facilitated Diffusion Active Transport Protein Pumps Endocytosis / Exocytosis

Selectively Permeable Membranes and their proteins allow only certain molecules to cross Diffusion: movement of a substance from an area of high concentration to low concentration Osmosis: movement of water from an area of low solute concentration to high

Diffusion

Osmosis

Passive Transport The movement of a molecule across a membrane from high to low concentration Molecules move with the concentration gradient Simple Diffusion No proteins needed Facilitated Diffusion Membrane proteins required

Simple Diffusion Small, uncharged molecules can move directly across membrane Includes gases (CO2 and 02 ) and water

Facilitated Diffusion Uses either protein channels or transporters (change shape) Channel Transporter

Passive Transport

Active Transport Movement of molecules across a membrane from low concentrations to high Molecules move against the concentration gradient Requires a protein transporter (pump) and energy supplied by ATP Ex. sodium/potassium pump

Active Transport

Active Transport

Passive Vs. Active Transport

Endocytosis Cell membrane surrounds and engulfs food particle or extra-cellular fluid Results in vesicle inside cell Phagocytosis: engulfing large particles like bacteria Pinocytosis: engulfing extra-cellular fluid and whatever it might contain

Exocytosis Opposite of endocytosis Vesicle containing secretory proteins or wastes joins with plasma membrane Molecules inside vesicle are then released outside of the cell

Summary

Review Questions Name 5 types of membrane proteins and describe their functions What is the most significant difference between passive and active transport? Why are transport proteins necessary in facilitated diffusion? Why does active transport require energy?

Problems #1 The internal cell concentration of sucrose is 1M, the external concentration is .1M, how might a cell raise the internal concentration to 2M without using a metabolic pathway? #2 What might happen if a cell continually secreted enzymes, but never participated in endocytosis?