Lecture #3 Date ______

Chapter 8~Membrane Structure & Function

Voyage through a cell

http://www.youtube.com/watch?v=GW0lqf4Fqpg

Golgi http://www.youtube.com/watch?v=K7yku3

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Choroplast and Mitochondrion

Cell Junctions

Contractile vacuole: http://www.youtube.com/watch?v=iG6Dd3

COug4&NR=1 Cilia and flagellates http://www.youtube.com/watch?v=E1L27s

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Membrane structure, I Selective permeability Amphipathic~

hydrophobic & hydrophilic regions

Singer-Nicolson: fluid mosaic model

Membrane structure, II Phospholipids~ membrane fluidity Cholesterol~ membrane stabilization “Mosaic” Structure~ Integral proteins~ transmembrane

proteins Peripheral proteins~ surface of

membrane Membrane carbohydrates ~ cell to

cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

Membrane structure, III Membrane protein

function: •transport•enzymatic activity•signal transduction•intercellular joining•cell-cell

recognition •ECM attachment

Marker proteins are also membrane proteins

Questions

Describe the polarity of an integral protein.Why does a protein for cell recognition never

flip sides by going “inside-out”?Why can phopholipids switch places with

their neighbor to the left and right, but not across from each other?

Why is cholesterol located where it is in the plasma membrane?

Membrane traffic Diffusion~ tendency of any

molecule to spread out into available space

Concentration gradient: High to low

Passive transport~ diffusion of a substance across a biological membrane

Osmosis~ the diffusion of water across a selectively permeable membrane

Water balance Osmoregulation~ control of

water balance Hypertonic~ higher

concentration of solutes Hypotonic~ lower

concentration of solutes Isotonic~ equal

concentrations of solutes Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis~ plasma

membrane pulls away from cell wall

Questions Why do grocery stores spray their vegetables with

water? Why does your skin “prune” when you swim all

day at the pool? Why does your skin crack when you spend all day

at the ocean? Why do trees in the tropics have big leaves

compared to dessert trees? When a plant “wilts”, are its cells turgid or

flaccid?

Specialized Transport Transport proteins Facilitated diffusion~

passage of molecules and ions with transport proteins across a membrane down the concentration gradient

Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

Types of Active Transport Sodium-potassium pump Exocytosis~ secretion of

macromolecules by the fusion of vesicles with the plasma membrane

Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane•phagocytosis (eating)•pinocytosis (drinking)•receptor-mediated endocytosis

Video of the cell working

http://www.youtube.com/watch?v=5ukPD4G5eSw&NR=1

Receptor mediated endocytosis using coated pits

Multiple receptors

Concentrates molecules for endocytosis