Cell Membrane and Function Chapter 7 Big Idea #2: Biological systems use energy to grow, reproduce, and maintain dynamic homeostasis.

Essential Knowledge 2B1:Cell membranes are selectively permeable due to their structure 2B2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes 2B3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regions

Separates internal environment of cell from external environment. Is selectively permeable: some substances can cross more easily than others (small, nonpolar, not charged particles)

Semi-Permeability Is due to structure of membrane Contains phosholipids, embedded proteins, cholesterol, glycoproteins, and glycolipids

Fig. 7-2 Hydrophilic head WATER Hydrophobic tail WATER Made of a double phospholipid layer that has amphipathic molecules (hydrophobic and hydrophilic areas)

Fig. 7-3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein

Can be hydrophilic w/ charged and polar side groups. Can be hydrophobic with nonpolar side groups Embedded Proteins

Fig. 7-8 N-terminus C-terminus  Helix CYTOPLASMIC SIDE EXTRACELLULAR SIDE Hydrophobic regions of an integral protein: made of 1 or more stretches of nonpolar amino acids, often coiled into alpha helices

Cholesterol Steroid found in b/t phospholipids. Affects membrane fluidity High temps  Less fluid membrane. Low temps  Hinders solidification of membrane by disrupting phospholipid packing

Fig. 7-5a (a) Movement of phospholipids Lateral movement (  10 7 times per second) Flip-flop (  once per month) Membrane is fluid  Moves When Cold, Moves Less!!

Cell to Cell Recognition Cells recognize each other by binding to surface molecules, often carbs, on membrane Membrane carbs may be covalently bonded to lipids (forming glycolipids) or to proteins (forming glycoproteins)

Permeability of the Lipid Bilayer Pass: Small, uncharged molecules and small nonpolar molecules (N 2 ) Large hydrophilic, polar molecules (sugars) can cross w/ help of embedded channel or transport proteins

Aquaporins Channel protein that allows water to move across

Binds to molecules and changes shape to shuttle them across membrane…extremely specific Transport Proteins

Cell Walls Provides a structural boundary and an internal permeability boundary. Cell Wall

Bacteria Cell Wall: Made of peptidoglycan

Plant Cell Wall: Made of Cellulose

Fungi Cell Wall: Made of Chitin

Movement of molecules in and out of cell w/out using energy. AKA Diffusion Passive Transport

High to low concentrations! Often used for import of resources/ export of wastes Concentration Gradient

Osmosis Passive transport process: movement of water across cell membrane. Again, it follows the magic rule!

Lower concentration of solute (sugar) Fig H2OH2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis Osmosis Video Clip!

Tonicity Ability of a solution to cause a cell to gain or lose water  osmoregulation Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater out of cell; cell loses water Hypotonic solution: Solute concentration is high inside cell; cell gains water

Fig Hypotonic solution (a ) Animal cell (b ) Plant cell H2OH2O Lysed H2OH2O Turgid (normal) H2OH2O H2OH2O H2OH2O H2OH2O Normal Isotonic solution Flaccid H2OH2O H2OH2O Shriveled Plasmolyzed Hypertonic solution

Facilitated Diffusion A channel/carrier protein carries molecules across (area of high to low conc.) Often charged and polar molecules cross here

Fig EXTRACELLULAR FLUID Channel protein (a) A channel protein Solute CYTOPLASM Solute Carrier protein (b) A carrier protein Facilitated Diffusion

Active Transport Energy- requiring: materials move across cell membrane from low to high conc. Uses ATP Done by embedded proteins

Allows cells to maintain concentration gradients that differ from their surrounding Ex: Sodium-Potassium Pump hered.mcg raw- hill.com/si tes/ /stud ent_view0 /chapter2/ animation __how_th e_sodium _potassiu m_pump_ works.ht ml

Fig Passive transport Diffusion Facilitated diffusion Active transport ATP

Exocytosis Internal vesicles fuse w/ plasma mebrane to secrete large macromolecules out of cell. Requires ATP!

Cell takes in macromolecules by forming new vesicles derived from plasma membrane. Endocytosis

Eukaryotes Compartmentalize… Minimizes competing interactions and increases surface area. Keep reactions and enzymes localized Bacteria and Archaea (ancient) can’t do this