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oTODAYTODAY: Is bigger : Is bigger better? Does better? Does size matter?size matter?

oPlasma Plasma Membrane Membrane Homework due Homework due NOW.NOW.

oCells Quiz on Cells Quiz on Friday.Friday.

oQuick KAHOOTS Quick KAHOOTS on tomorrow.on tomorrow.

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CYTOPLASMIC CYTOPLASMIC STREAMINGSTREAMING

• the directed flow of cytosol and organelles around cells

• mediated by “motor” proteins and use ATP

• aids in the delivery of organelles, nutrients, metabolites, genetic information, and other materials to all parts of the cell.

• also called protoplasmic protoplasmic streamingstreaming

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The PLASMA Membrane The PLASMA Membrane

2007-2008

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The membrane is a collage of proteins & other The membrane is a collage of proteins & other

molecules embedded in the fluid matrix of the molecules embedded in the fluid matrix of the

lipid bilayer.lipid bilayer.Extracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

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More than lipids… More than lipids… • In 1972, S.J. Singer & G. Nicolson proposed that

membrane proteins are inserted into the phospholipid bilayer

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• Cell membrane separates living cell from nonliving surroundingso thin barrier = 8 nanometers thick

• Controls traffic in & out of the celloselectively permeable: allows some

substances to cross more easily than others• hydrophobic vs hydrophilic

• Made of phospholipids, proteins, & other macromolecules

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• Fatty acid tails ohydrophobic

• Phosphate group head ohydrophilic

• Arranged as a bilayerFatty acid

Phosphate

PhospholipidsPhospholipids

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Phospholipid bilayerPhospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

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Membrane Membrane Carbohydrates Carbohydrates

• Play a key role in cell-cell recognitionoability of a cell to distinguish one

cell from another• antigens

o important in organ & tissue development

obasis for rejection of foreign cells by immune system

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• CholesterolCholesterol = reduces membrane fluidity reduces membrane fluidity at moderate temperatures but hinders at moderate temperatures but hinders solidification of phospholipids at low solidification of phospholipids at low temperaturestemperatures; animal cells do not need cell walls; maintains membrane integrity.maintains membrane integrity.

• Integral proteins Integral proteins = penetrate the hydrophobic core of the lipid bilayer; transport, enzymes, cell identificationtransport, enzymes, cell identification

• Peripheral proteins Peripheral proteins = appendages bound to the membrane surface; signal transduction signal transduction or intercellular joining (gap junctions/tight or intercellular joining (gap junctions/tight junctions)junctions)

• GlycolipidGlycolipid = molecules that are formed by a covalent bond between carbohydrates and lipids; cellular recognitioncellular recognition

• GlycoproteinGlycoprotein = molecules formed by a covalent bond between carbohydrates and proteins; cellular recognitioncellular recognition

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Proteins domains Proteins domains anchor moleculeanchor molecule

• Within membraneo nonpolar amino acids • hydrophobic • anchors protein

into membrane• On outer surfaces of

membraneo polar amino acids • hydrophilic• extend into

extracellular fluid & into cytosol

Polar areasof protein

Nonpolar areas of protein

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• Fibers of extracellular matrix Fibers of extracellular matrix (ECM) (ECM) = attached to certain membrane proteins on the exterior of the cell; provides structure and provides structure and supportsupport

• Microfilaments of cytoskeleton Microfilaments of cytoskeleton = may be bonded to membrane proteins; maintains cell shape; stabilizes the location of certain membrane proteins; aids in cell movement (cytoplasmic streaming, cell division, etc.)

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membrane fat composition membrane fat composition

variesvaries• Fat composition affects flexibility

omembrane must be fluid & flexible• about as fluid as thick salad oil

o% unsaturated fatty acids in phospholipids• keep membrane less viscous• cold-adapted organisms, like winter wheat

oincrease % in autumnoFish?

ocholesterol in membrane

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Membrane ProteinsMembrane Proteins• Proteins determine membrane’s specific functions

• Membrane proteins:o peripheral proteins

• loosely bound to surface of membrane• cell surface identity marker (antigens)

o integral proteins • penetrate lipid bilayer, usually across whole

membrane

• aka: transmembrane protein

• transport proteins

ochannels, permeases (pumps)

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Classes of amino Classes of amino acidsacids

What do these amino acids have in common?What do these amino acids have in common?

nonpolar & hydrophobicnonpolar & hydrophobic

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Classes of amino Classes of amino acidsacids

What do these amino acids have in common?What do these amino acids have in common?

polar & hydrophilicpolar & hydrophilic

I like thepolar onesthe best!

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Many Functions of Membrane ProteinsMany Functions of Membrane ProteinsOutside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion