Cell Membrane Cell Membrane Location Surrounding the cell

Cell Membrane

Cell Membrane? Location? Surrounding the cell Function? 1. Protection and support for the cell 2. Regulation of what enters and exits the cell WHY? -Essential in order to maintain *homeostasis within the cell *maintaining normal internal conditions

Composition of Cell Membrane Phospholipid Bilayer 1. Phospholipid: § § Hydrophilic Head; “water-loving” Hydrophobic Tail; “water-fearing” 2. Bilayer § Two-layers (of phospholipids)

Composition of Cell Membrane Proteins embedded throughout phospholipid bilayer Integral Proteins: Span the width of the cell membrane Peripheral Proteins: Located on one side of the cell membrane (or on the ‘periphery’) A variety of different types of proteins within the cell membrane, each with different functions

Composition Cholesterol: another lipid that maintains the structural stability of the cell membrane Carbohydrates: allow for cell-tocell recognition; a “fingerprint” for each cell Allows for the immune system to recognize ‘foreign’ cells and attack them Attached to proteins or phospholipids on outside layer of cell membrane

Fluid Mosaic Model Break it down: FLUID: The cell membrane is constantly moving due to the lipid “tails” on its interior; they “wiggle” This means that the cell membrane is pliable The cell membrane has the consistency of olive oil at body temp. MOSAIC: Proteins of different types, randomly positioned throughout the membrane create a “mosaic” appearance The cell membrane is a constantly moving assemblage of parts.

Cell Membrane Function Transport of molecules from one side of the membrane to the other in order to maintain homeostasis within the cell. Selectively Permeable: Only certain substances can move across the membrane while others cannot. Small, non-charged molecules (H 20, CO 2, etc. ) can freely cross the cell membrane. This is referred to as Passive Transport: molecules are ‘freely’ or ‘passively’ traveling through the cell membrane This occurs through one of two ways: Diffusion or facilitated diffusion

Passive Transport: Diffusion No Energy is required Diffusion: the movement of molecules from a higher concentration to a lower concentration until equilibrium is reached Concentration: the amount of solute in the solvent Solute: dissolved substance (in the solvent) solvent: the liquid containing the dissolved substance Equilibrium: occurs when the solute concentration is the same throughout the system; equal on both sides of the membrane

Passive Transport: Facilitated Diffusion A form of Passive Transport (so no energy required) Facilitated Diffusion: Larger molecules (that are unable to passively cross the cell membrane) are “carried” through via a channel protein. Specific protein channels carry specific types of molecules For example: glucose is transported across the cell membrane via facilitated diffusion