Chapter 7 and 11 Membrane “Strunction”

Fluid Mosaic Model

Fluidity:

• P.Membrane (PM) held together by weak hydrophobic interactions

• Lateral drifting ability– Lipids– Proteins: some stable/attached to

cytoskeleton

• Temperature Dependent

“Mosaic”

• Protein collage: >50 proteins• Classes:

– Integral Proteins: • Transmembrane proteins• Penetrate hydrophobic core of membrane

– Peripheral• Loosely bound to surface• Attached to cyto-skeleton or ECM (Extracellular

matrix)

Review: What organelles are responsible for creating membrane proteins?

Selective PermeabilityGeneral rule: like dissolves like

– Non-polar/hydrophobic solutes dissolve in lipid– Ions and hydrophillic solutes dissolve in water

Selective Permeability: some substances can pass more easily than others– CO2 , hydrocarbons, lipids, and O2 are nonpolar

(can pass lipid membrane core easily)– Water, glucose, sugars, charged ions (cannot

pass lipid core easily) so must use hydrophillic transport proteins to pass (ex. Aquaporins)

– Small molecules are more permeable than larger ones

Passive Transport

• Mvmt down [gradient]

• Spontaneous process –ΔG

• Types of Passive Transport: – Diffusion– Osmosis– Facilitated Diffusion

Diffusion

• Diffusion – molecules of any substance moves down [gradient]

Osmosis

– Osmosis (tonicity dependent)

• Isotonic vs. hypotonic vs. hypertonic conditions

• Water always moves from hypotonic to hypertonic side

Balancing Water Uptake

• Animals: cannot tolerate change in tonicity– Ex. Salt water fish

vs. fresh water fish, vice versa

– Some Freshwater protists prevent lysing due to contractile vacuoles

Balancing Water Uptake

• Plants: Cell walls help maintain water balance– Turgid Conditions Good!– Flacid Conditions cause plasmolysis– (lab 1E review)

Function of Membrane Proteins

• protein channels for passive transport• protein pumps for active transport

• Catalysis of Chemical Reactions at the Membrane Surface

• substrates bind to protein surface sends a signal within the cell to start a chemical chain reaction or cell response

• oligosaccharides on proteins or lipids act as “name tags” for cells.

• Ex. Gap Junctions, Tight Junctions, etc.

• Maintenance of Cell Shape

End of Slide Show

Facilitated Diffusion

• diffusion of solutes (ions) with help from channel proteins in the plasma membrane

Active Transport

• Movement against [gradient]• Nonspontaneous, + ΔG, Requires ATP• Types:

– Protein pumps– Cotransport– Exocytosis: Phagocytosis and Pinocytosis– Endocytosis– Receptor Mediated Endocytosis

Active Transport generates an electrochemical gradient: charge difference (disequilibrium) between both sides of the membrane

Protein Pumps

Ex 1: Sodium-Potassium Pump

(take notes about the function of Na/K pump from the video)

Sodium-Potassium Pump 3-D overview

Ex 2: Pumping H+ ions into lysosome to create acidic env’t

Co-transport• Involves the

transport of a substance against a concentration gradient powered indirectly by an ATP powered pump

H+

ATP

H+

H+

H+

H+

H+

ADP + Pi

Exocytosis

Fusing of vesicles to the plama membrane, thus releasing its contents

Endocytosis

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• The engulfing of substances by pseudopods extensions of the plasma membrane

• Three types:– Phagocytosis (cell eating – lg. particles

engulfed)– Pinocytosis (cell drinking – sm. ions and

liquids engulfed)– Receptor Mediated Endocytosis (use of

surface proteins to engulf a specific substrate)

Signal Transduction

3 Stages of Signal Transduction 1) Reception: A ligand (analogous to a

substrate) binds to receptor protein. Receptor proteins can be on the cell surface, but not always. Receptor protein changes shape

2) Transduction: Amplifies and sends the signal through chemical relay

3) Cell Response: Specific response is triggered

Examples of Signal Transduction

Why is this hormone-receptor protein not found on the surface of the plasma membrane?

Steroids and Hormones are types of lipids, which can pass through phospholipid membranes easily.

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