AP Biology

The Cell Membrane

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Overview The cell membrane separates the inside of a

living cell from its surroundings Function to maintain the homeostasis of the cell

The cell membrane is selectively permeable. allows some substances to cross more easily

than others, and some not at all.

Made primarily of phospholipids, with proteins & other macromolecules throughout.

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Phospholipids

Fatty acid

Phosphate

Fatty acid tails hydrophobic

Phosphate group head hydrophilic

Arranged as a bilayer

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Phospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

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In and Out Reminder: It is selectively permeable. Only certain things can pass through

the phospholipid bilayer: Pass through easily

Small, non-polar (hydrophobic) substances Ex: CO2 and O2

Do not pass through easily Polar (hydrophilic) substances Ex: Water, Sugar, Ions Large molecules

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More than lipids… Membrane proteins are

inserted into the phospholipid bilayer

Fluid Mosaic Model Fluid

flow Mosaic

made of smaller partsIt’s like a fluid…It’s like a mosaic…

It’s the Fluid Mosaic Model!

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Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer

Extracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

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Membrane Proteins Proteins determine membrane’s specific functions

cell membrane have unique collections of proteins

Membrane proteins: peripheral proteins

loosely bound to surface of membrane cell surface identity marker

integral proteins penetrate lipid bilayer transmembrane protein go all the way through transport proteins

Channels and pumps

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NH2

H+

COOH

Cytoplasm

Retinalchromophore

Nonpolar(hydrophobic)-helices in thecell membrane H+

Porin monomer

-pleated sheets

Bacterialoutermembrane

proton pump channel in photosynthetic bacteria

water channel in bacteria

Examples

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Many Functions of Membrane Proteins

Outside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

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Any Questions??