Cell MembraneCell Membrane

Function of Cell MembraneFunction of Cell Membrane

Separates the cell’s contents from Separates the cell’s contents from materials outside the cellmaterials outside the cell

Regulates what moves in and out of a cellRegulates what moves in and out of a cell *without the cell membrane to contain the *without the cell membrane to contain the

substances the cell needs for life, the substances the cell needs for life, the cell would die.cell would die.

Structure of Cell MembraneStructure of Cell Membrane --composed of groups of organic composed of groups of organic

compounds (glycolipids, compounds (glycolipids, glycoproteins, proteins, cholesterol, glycoproteins, proteins, cholesterol, and phospholipids)and phospholipids)

Phospholipid – shaped like a head Phospholipid – shaped like a head with 2 tailswith 2 tails

-made from a phosphate group -made from a phosphate group connected to 2 fatty acid tails (forms a connected to 2 fatty acid tails (forms a double layer called a lipid bilayer)double layer called a lipid bilayer)

Structure of PhospholipidStructure of Phospholipid

Why are the phospholipids Why are the phospholipids arranged tail to tail?arranged tail to tail?

--b/c water is inside and outside the b/c water is inside and outside the cell cell

phosphate group is hydrophilic (polar) phosphate group is hydrophilic (polar) endend

-attracts water-attracts water fatty acid tail end is hydrophobic fatty acid tail end is hydrophobic

(nonpolar) (nonpolar) -repels water-repels water

Arrangement of phospholipids Arrangement of phospholipids “tail to tail”“tail to tail”

Polar vs. NonpolarPolar vs. Nonpolar

Polar- positive and negative ends (b/c Polar- positive and negative ends (b/c electrons are not shared equally)electrons are not shared equally)

Ex. WaterEx. Water Nonpolar- does not have oppositely Nonpolar- does not have oppositely

charged ends (atoms share electrons charged ends (atoms share electrons equally)equally)

Arrangement of phospholipids Arrangement of phospholipids “tail to tail” due to water inside & “tail to tail” due to water inside &

outside the celloutside the cell

Fluid Mosaic Model of Cell Fluid Mosaic Model of Cell MembraneMembrane

-lipid bilayer is not strong & firm like a -lipid bilayer is not strong & firm like a hard shell, but it is fluid like a soap hard shell, but it is fluid like a soap bubble (often called a bubble (often called a fluid mosaic fluid mosaic modelmodel))

-individual phospholipids, arranged -individual phospholipids, arranged side by side, float within the bilayer side by side, float within the bilayer (cholesterol prevents phospholipids (cholesterol prevents phospholipids from sticking together)from sticking together)

Structure of Cell MembraneStructure of Cell Membrane

--nonpolar interior zone-nonpolar interior zone- true barrier true barrier that separates the cell from its that separates the cell from its surroundingssurroundings

many polar particles like sugars, many polar particles like sugars, proteins, ions, & most cell wastes proteins, ions, & most cell wastes cannot cross this zone b/c they are cannot cross this zone b/c they are repelled by the nonpolar regionrepelled by the nonpolar region

What’s in the cell membrane?What’s in the cell membrane? Solution?Solution? -passageways through the barrier that -passageways through the barrier that

enable the cell to regulate what enable the cell to regulate what substances go in and out.substances go in and out.

Cell Surface ProteinsCell Surface Proteins- proteins - proteins embedded within the plasma membrane embedded within the plasma membrane of cells of cells

Proteins- 50% to 70% of cell membraneProteins- 50% to 70% of cell membrane

Types of Cell Surface ProteinsTypes of Cell Surface Proteins Channel ProteinsChannel Proteins- act as “gates” to - act as “gates” to

the cell interior, transporting food & the cell interior, transporting food & other molecules (sugar, proteins, other molecules (sugar, proteins, ions) in & wastes outions) in & wastes out

Types of Cell Surface ProteinsTypes of Cell Surface Proteins

Receptor proteinsReceptor proteins- information receivers - information receivers they are the informers of the cell, gathering they are the informers of the cell, gathering information about the cell’s surroundingsinformation about the cell’s surroundings

*many hormones act by binding to specific *many hormones act by binding to specific receptor proteinsreceptor proteins

Ex. Glycoproteins- combination of protein Ex. Glycoproteins- combination of protein and carbohydratesand carbohydrates

Ex. Integral proteins- span entire range of Ex. Integral proteins- span entire range of cell membranecell membrane

Types of Cell Surface ProteinsTypes of Cell Surface Proteins

Marker proteinsMarker proteins- “name tags of the cell” - “name tags of the cell” identifies what kind of cell it is (ex. Liver identifies what kind of cell it is (ex. Liver cell, heart cell, or brain cell)cell, heart cell, or brain cell)

marker proteins have long exterior arms marker proteins have long exterior arms that often have carbohydrates attached to that often have carbohydrates attached to them them

Ex. Glycoproteins or glycolipidsEx. Glycoproteins or glycolipids

Arrangement of cell surface Arrangement of cell surface proteinsproteins

Cell Membrane StructureCell Membrane Structure