IB Topic 2 4 Membranes Cell Membranes A

IB Topic 2. 4 Membranes

Cell Membranes A. B. The Fluid Mosaic Model-model of the plasma membrane The model is a mosaic of proteins embedded in a phospholipid bilayer

C. Amphipathic- has a polar head and a non-polar tail D. Hydrophilic= water loving (polar) -found on inner and outer edges of cell membrane E. Hydrophobic= water fearing (non-polar) -found inside the cell membrane Diagram of cell membrane Hydrophilic heads Hydrophobic tails Cytoplasm

F. Lipids can move laterally through the cell membrane G. Cholesterol: may reduce fluidity (moderate temperatures, but prevent crystallization at low temperatures) H. Membranes must be fluid to work

I. Proteins make up the mosaic part of the membrane (3 main types) 1. Integral proteins - embedded in the membrane (partially or completely (transport proteins) 2. Peripheral proteins - found in hydrophilic areas only 3. Glycoproteins - proteins within the membrane that have carbohydrates attached to them

J. Protein functions -antibody recognition -cell to cell recognition -channels for passive transport -pumps for active transport -hormone binding sites -enzymes -electron carriers

Types of Cellular Transport PASSIVE TRANSPORT: (no energy) 1. Diffusion: passive movement of solute from and area of high concentration to an area of low concentration (move down concentration gradient) 2. Osmosis: movement of water from an area of low solute (high water) concentration to an area of high solute (low water) concentration 3. Facilitated diffusion: same as diffusion but with the help of transport proteins

Diffusion:

OSMOREGULATION: Hypertonic solution- high solute/low solvent (shrivel) Hypotonic solutions- low solute/high solvent (swell) Isotonic solution- equal solute/solvent (equal) http: //www. tvdsb. on. ca/westmin/science/sbi 3 a 1/Cells/Osmosis. htm Look at the red blood cells, not the black circles.

Facilitated diffusion - involves transport of charged molecules (ions) - does not require energy - charged molecules must diffuse through special proteins (they cannot diffuse through the cell membrane on their own)

ACTIVE TRANSPORT: - requires energy - used when diffusion cannot occur - substances move up the concentration gradient (move from low to high concentrations)

The Sodium Potassium Pump - An example of active transport - Pumps ions against the gradient - Translocates three sodium ions out of the cell for every two potassium ions pumped in - ATP powers the changes in protein structure to transport the ions

-ATP phosphorylation = a phosphate group from the ATP is added to the protein -When ATP is broken energy is released -ATP ADP (adenosine triphosphate adenosine diphosphate) Sodium Potassium Pump 2

Other forms of cellular transport 1. Endocytosis- when a cell extends its membrane around a substance in order to engulf it 2. There are two types: -Phagocytosis- when the cell engulfs a solid (‘cell eating’) -Pinocytosis- when the cell engulfs a fluid (‘cell drinking’) 3. Exocytosis- the excretion of macromolecules by vesicles fusing to the plasma membrane

L. Membrane fluidity A. The cell membrane is highly fluid allowing it to creating vesicles for endocytosis and exocytosis B. In endocytosis the membrane becomes slightly smaller C. In exocytosis the membrane becomes slightly larger D. Animation for endocytosis and exocytosis