1.3 MEMBRANE STRUCTURE

Understandings Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.

Membrane proteins are diverse in terms of structure, position in the membrane, and function.

Cholesterol is a component of animal cell membranes.

Applications and Skills A: Cholesterol in mammalian membranes reduces fluidity a permeability to some solutes.

S: Drawing of the fluid mosaic model. S: Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.

S: Analysis of the falsification of the Danson-Danielli model that led to the Singer-Nicolson model.

Guidance- Amphipathic phospholipids have hydrophilic and hydrophobic properties.- Drawings of the fluid mosaic model of membrane structure can be two-dimensional

rather than three-dimensional. Individual phospholipid molecules should be shown using the symbol of a circle with two parallel lines attached. A range of membrane proteins should be shown including glycoproteins.

THE DAVSON-DANIELLI MODEL

Proposed in 1935 Lipid bilayer model that was covered on both sides by a layer of globular protein

Intended to explain the surface tension of observations about surface tension of membranes (actually caused by phospholipid heads)

http://2.bp.blogspot.com/-91coQJNOvo8/UQWgQ42TRCI/AAAAAAAASzw/daixktrs9tc/s640/davson+danielli+membrana.jpg

SINGER-NICOLSON MODEL Proposed that proteins are inserted into the phospholipid layer in a mosaic pattern Evidence includes:Not all membranes are identical/symmetrical

Electron microscopes can detect membranes with different structures and functions

A protein layer would be largely nonpolar and would interface with the aqueous extracellular fluid

http://publishing.cdlib.org/ucpressebooks/data/13030/n2/ft796nb4n2/figures/ft796nb4n2_00146.gif

FLUID MOSAIC MODEL Current model Relatively the same for plasma membranes and organelle membranes

Membranes composed of a bilayer of phospholipids with integral proteins, peripheral proteins, glycoproteins, and cholesterol

http://www.factmonster.com/images/cig/biology/02fig01.png

PHOSPHOLIPIDS

http://upload.wikimedia.org/wikipedia/commons/3/3c/0301_Phospholipid_Structure.jpg

Soap Molecule

https://tse1.mm.bing.net/th?id=OIP.M249d88827275758d92bd781aa3842054H0&pid=15.1&P=0&w=256&h=158

CHOLESTEROL Embedded in the hydrophobic tails of the bilayer Reduces membrane fluidity of animal cells by allowing membranes to function in a broader range of temperatures Plant cells lack cholesterol

https://s.yimg.com/fz/api/res/1.2/aLBIjabupDBLJoGx4udA7A--/YXBwaWQ9c3JjaGRkO2g9MzU5O3E9OTU7dz01MDk-/http://www.uic.edu/classes/bios/bios100/lectf03am/cholesterol.jpg

PROTEINS Two major typesIntegralPeripheral

http://unexpurgatedme.files.wordpress.com/2011/11/phospholipid-bilayer22.jpg

INTEGRAL PROTEINS Amphipathic Hydrophobic region in the midsection of the bilayer Hydrophilic region exposed to aqueous solutions on outside and inside of cell

http://classconnection.s3.amazonaws.com/410/flashcards/2392410/jpg/picture21354924380156.jpg

PERIPHERAL PROTEINS Bound to the surface of the membrane Often anchored to an integral protein

http://classconnection.s3.amazonaws.com/410/flashcards/2392410/jpg/picture21354924380156.jpg

GLYCOPROTEINS Composed of carbohydrate chains attached to peripheral protein Involved in cell to cell recognition and immune response

http://isite.lps.org/sputnam/Biology/U3Cell/glycoprotein_1.png

MEMBRANE FUNCTIONS Hormone binding: Proteins that are exposed to the exterior that have a specific shape to fit the shape of specific hormones; interaction relays message to interior

Enzymatic action: for chemical reaction on inside or outside of cell; can be grouped together for a metabolic pathway

Cell adhesion: proteins on exterior that can hook together in form permanent or temporary connections

Cell-to-cell communication: performed by glycoproteins that have specific identification labels

Passive transport: material moves through a channel from an area of high concentration to low concentration

Active transport: protein pump moves material (generally against a concentration gradient) from one side to the other by changing shape; requires ATP

HOMEWORKVocab

Hydrophobic Hydrophilic Endocytosis Integral proteins

Peripheral proteins

Glycoproteins

Amphipathic

Other TOK: pg 27 Exercises 12-15: pg 30

Metabolic pathwayJunctionsGap junctionsTight junctionsActive transportPassive transport