Unit 1: Biochemistry -#8 The Cell Membrane

The Cell Membrane

• Separates the living cell from nonliving surrounding

• Selectively Permeable - Controls which substances can cross the membrane, allows some substances to cross more easily than others

• Keep nutrients in and waste products out

The Fluid Mosiac Model

• Membranes are not rigid, with molecules locked in place

• Instead molecules are in constant motion (Fluid Part)

• Membrane consists of a fluid phospholipid bilayer - proteins embedded into it float freely

• There are many types of proteins, lipids and carbohydrates embedded in the membrane (Mosiac Part)

Phospholipids

• Phosphate Group Head (Hydrophilic Polar Head)

• 2 Fatty Acid Tails (Hydrophobic Non-Polar Tails)

• Forms a lipid bilayer in aqueous (watery environments) that is two lipid molecules thick

• No water inside the lipid bilayer itself - water is present outside and inside the cell

Fluidity - Saturated Fatty Acids

• Saturated hydrocarbons - each carbon is bound to the maximum number of hydrogen atoms

• Single bounds cause the membrane to form a semi solid gel due to linear arrangement

• Have a straight shape - lipids are able to pack together more tightly

Fluidity - Unsaturated Fatty Acids

• Double bonds in an unsaturated fatty acid bend its structure - lipid molecules are less straight and more loosely packed

• Double bonds keep membrane fluid (less viscous)