Unit 8: Cell Membrane

1.3.S1 Fluid Mosaic Model

-Phospholipid bilayer -Integral proteins -Peripheral proteins -Protein channels with a pore -Glycoproteins with a carbohydrates side chain -Cholesterol between phospholipids in the hydrophobic region -An indication of thickness (10nm)

1.3.U1 Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails

-There is water both OUTSIDE the cell and INSIDE the cell. -Phospholipids will arrange themselves in a bilayer (hydrophilic head associated with water & hydrophobic tails face each other away from water)

Membrane proteins of hamster cells were marked with a blue dye and membrane proteins of human cells were marked with a green dye. What would be seen after the fusion of the cells?

Blue and green marker dyes fully integral

1.3.U2 Primary function of the cell membrane

Cell membrane is semi-permeable and controls the movement of substances in and out of cells

1.3.U2 Contrast the two types of transport proteins

Channel proteins -used for passive transport of molecules -often shaped like pores/tunness -from [high] to [low] Pump proteins -used for active transport of molecules -uses ATP -from [low] to [high] *Picture Explanation* -Channel protein on left, pump protein on right

1.3.A1 Describe the function of cholesterol molecules in the cell membrane

Cholesterol acts as a regulator of membrane fluidity -At high temps, it stabilizes the membrane & raises the melting point -At low temps, it prevents phospholipids from packing too close together which would lead to stiffening Membrane fluidity effects how permeable the structure is to solutes -Too fluid --> too much permeability -Too stiff --> not enough permeability

1.3.U3 Describe the structural placement of cholesterol within the cell membrane

Cholesterol fits between phospholipids int he cell membrane, with its hydroxyl (OH) group by the heads and the hydrophobic rings by the fatty acid tails

1.3.U3 Identify the structure of cholesterol in molecular diagrams

Cholesterol is a lipid that can be distinguished by its characteristic four-ring structure

1.3.S2 Describe the observations and conclusions drawn by Davson and Danielli in discovering the structure of cell membranes

Davson and Danielli proposed the "protein-lipid sandwich" of the cell membrane. In electron micrographs, they observed two dark parallel lines with a light region in between Since proteins appear dark and lipids appear light in micrographs, Davson and Danielli proposed that the phospholipid bilayer was embedded between two laters of proteins

What types of cells have cholesterol?

Eukaryotes, mostly cold blooded animals

1.3.U1 Define amphipathic and outline amphipathic properties of phospholipids

Having hydrophilic and hydrophobic regions

What does cholesterol do in the cell membrane?

Modulates membrane fluidity (more fluid at a lower temp, less fluid at a higher temp)

1.3.U2 Contrast the structure of integral and peripheral proteins

Peripheral proteins -sit on the surface or have small parts that dip into the bilayer Integral proteins -have large sections embedded in the hydrophobic middle of the membrane -Some are "transmembrane" meaning they cross the membrane

1.3.U2 Four functions (with examples) of membrane bound proteins

Receptor Proteins -comunicate signals between the cell's internal and external environments -EX: insulin receptor protein Enzyme Proteins -Promote chemical reactions that synthesize or break apart biological molecules -EX: ATP synthase Adhesion Proteins -Anchors cell membrane to the inner cytoskeleton or proteins outside the cell swell as to other cells -EX: Cadherins Recognition Proteins -Serve as ID tags on the surface of a cell -Often times these are glycoproteins -EX: Major histocompatibility complex proteins Channel Proteins -pores/tunnels for large or hydrophilic molecules to be PASSIVELY transported -EX: Glucose channel protein (high-->low) Pump Proteins -Serves as pres/tunnels for hydrophilic molecules to be ACTIVELY transported in & out of membrane -EX: Sodium Potassium pump (low -->high)

What is cholesterol?

a fat molecule

Name the property of cholesterol which allows it to insert itself into cell membranes.

amphipathic

Glycoproteins

proteins with an attached sugar molecule

1.3.U1 Define hydrophobic

water fearing, tails inside bilayer

1.3.U1 Define hydrophilic

water loving, heads are exposed to water