Cell Membrane structure and transport

Cell membrane of cheek cells, 400X magnification

Cell membrane (

Cell membrane at 240,000 X magnification (

Cell Membrane (plasma membrane) Separates living cell from nonliving surroundings Selectively permeable (semi-permeable)

Membrane Structure Phospholipid bilayer Proteins – Integral protein – Peripheral protein Cholesterol Carbohydrates

Phospholipid bilayer Phosphate group ( PO 4 -3 ) – Polar, Hydrophilic Lipid tail – Non-polar, hydrophobic Unsaturated fat: kink, don’t pack tight Saturated fat: lie straight, pack tight

Cholesterol Breaks up phospholipid tails More of them in cold- weather cells, fewer in tropical cells Makes the cell membrane – More fluid in colder temperatures – More rigid in warmer temperatures

Proteins Two main kinds – Integral Lie within the membrane Transmembrane proteins span the entire core – Peripheral Attach to external surface by weak bonds Two main functions – Transporters – Receptors

Carbohydrates Short sugar chains = oligosaccharides. covalently bonded to lipids or proteins – Glycolipid – Glycoprotein Function – Cell to Cell recognition

The Cell Membrane The parts are dynamic…they move around and change positions (the membrane is FLUID) The cell membrane is NOT a single, solid structure—it is made up of many smaller parts (it is a MOSAIC) hence, the name… FLUID MOSAIC MODEL OF THE CELL MEMBRANE

Transport Diffusion – Osmosis – Facilitated Diffusion Active Transport Endocytosis – Phagocytosis – Pinocytosis Exocytosis

Diffusion Movement of molecules from areas of high concentration to areas of low concentration. Passive, requires no extra energy Small, non polar molecules – O 2 – CO 2

Osmosis Diffusion of water through a membrane from an area of high concentration to an area of low concentration – Isotonic – Hypertonic – Hypotonic No extra energy required iso- = equal hyper- = above/over hypo- = below/under

Plasmolysis and Turgor Plasmolysis – The shrinking of a plant cell when placed in a hypertonic environment. Cell membrane pulls away from the cell wall. Turgor pressure – When a cell is full of water. The water vacuole exerts pressure against the walls Helps hold the plant up.

Facilitated Diffusion Molecules moving from high to low concentration with help. Use Channel or Carrier protein – Aquaporins Requires no energy Large, polar or ionic molecules. – Na + – Ca +2 – Glucose

Active Transport Movement of molecules against a concentration gradient. Requires energy – Na + /K + pump – Ca +2 pump in muscle cells – H + pump (plants, fungi,bacteria) – Builds electrochemical gradient

CoTransport A substance that has been actively pumped to one side, builds a gradient. This gradient, potential energy, can do work as it leaks back across. Escorts, in this case, glucose – Na + with glucose Why should you drink gatorade or powerade when dehydrated or pedialyte when you have the flu?

A Represents? B.Represents? C.Represents?

Endocytosis Cell takes in macromolecules or large particles by forming new vesicles from the plasma membrane. – Three kinds Phagocytosis Pinocytosis Receptor-mediated endocytosis

Endocytosis Phagocytosis – Cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane enclosed sac. Amoeba White Blood Cell –Macrophage

Endocytosis Pinocytosis – “Cell drinking” – Unspecific as it takes in any solute along with the solvent

Endocytosis Receptor mediated endocytosis – Specific substances “ligands” bind to receptors on cells. – Receptors are in areas called “pits”.

Exocytosis The opposite of endocytosis. Cell gets rid of substances by forming a membrane around the substance. The bubble of material moves to the cell membrane and is released.