Why is the cell membrane so important???

Selectively permeable membrane Semi permeable membrane Names! Cell membrane Plasma membrane Selectively permeable membrane Semi permeable membrane

Functions of the Cell Membrane Protects the cell Regulates what goes in and out of cell Helps to communicate with other cells Creates attachments between cells Dynamic! **Maintains HOMEOSTASIS in the cell**

Structure of the Cell Membrane Phospholipid bilayer – double layered sheet Properties of the lipids determine the properties of the membrane: Hydrophobic (“water-fearing”) = tails Hydrophilic (“water-loving”) cluster together = heads Heads DO touch water, tails DO NOT touch water

Fluid Mosaic Model dev. By Singer & Nicolson 1972 Proteins move within layers of lipids w/I viscous fluid Transport Structure Hydrogen bonds can form between water and phospholipid heads inside and outside of cell The more double bonds there are in the tails the more fluid the membrane Incr. in temp. causes membr. To be more fluid (because mol. Move faster) Decr. Temp. (mol. Move slower -> less fluid)

Selectively Permeable Some substances can pass, others cannot pass Most substances can pass Substances that are too big or charged cannot cross the bilayer Therefore, cells need different means of TRANSPORT to move these substances into and out of the cell

Vocabulary Terms Solution- mixture in which one or more substances are UNIFORMLY distributed in another. “homogenous solution” Solute- what gets dissolved. Solvent- what does the dissolving. Ex. salt water: salt is solute water is solvent. Ex. Ice tea Mix is solute Water is solvent

Movement from a high concentration to a low concentration! Passive Transport Requires NO energy!! Movement from a high concentration to a low concentration!

Passive Transport 1. diffusion 2. osmosis 3. facilitated diffusion 4. diffusion through ion channels

Diffusion

Diffusion Molecules moving from a greater concentration to a lower concentration Ex: perfume Simple diffusion – substances pass through the membrane with no outside aid Ex. substances: Oxygen, Carbon Dioxide, water and lipid soluble molecules

Vocabulary Concentration gradient: difference in concentrations (amount of solute) Equilibrium: particles/molecules are equal on both sides of membrane

More diffusion -> “equilibrium”!!

Osmosis

Osmosis Movement of WATER from a high concentration to a low concentration across the cell membrane

Iso – Hyper – Hypotonic Solutions

Vocabulary Isotonic: concentration inside and outside of cell are the same  no net diffusion Hypertonic: when concentration of solute outside of cell is greater, water moves out of cell (shrink) Hypotonic: concentration of solute inside of cell is greater, water moves into cell (burst)

Where is there more water? Which way will it move? Type of Solution? Out of the cell Into the cell Hypotonic Solution

Where is there more water? Which way will it move? Type of Solution? Equal No net movement Isotonic Solution

Where is there more water? Which way will it move? Type of Solution? In the cell Out of the cell Hypertonic Solution

Plasmolysis

Plants! Plasmolysis = cell shrinks away from cell wall due to water loss ex: drought (low rain fall) causing plants to wilt Turgor Pressure = cell wall sustains shape, otherwise would explode

Facilitated Diffusion

Facilitated Diffusion Carrier Protein – -protein recognizes substance->changes shape->delivers substance to inside of the cell Facilitated Diffusion: water soluble molecules (hydrophillic). Ex: ions, amino acids (small proteins), and sugars

Ion Channels

Ion channels -allows ions Ca2+ and Cl- to enter cell Some are open all the time Others are gated and will open when Cell membrane stretches Electrical signals Chemical signals

Movement from a LOW concentration to a HIGH concentation! Active Transport REQUIRES ENERGY! Movement from a LOW concentration to a HIGH concentation!

Active Transport 1. Sodium Potassium Pump 2. Endocytosis 3. Exocytosis

Active Transport

Sodium Potassium Pump -pumps like to keep ions in balance 3 Na+ out for every 2 K+ in This creates a build up of Na+ outside cell and K+ inside cell forming a net electrical charge across the membrane Allows for nerve impulses Contraction of muscles 1/3 of all energy in animal cells goes to running this pump even as we sleep!

Endocytosis

Endocytosis Take in external fluid, macromolecules and other large particles. Forms “vesicle” some fuse with lysosomes (digestion) others fuse with membrane of other organelles. 2 Types: a) pinocytosis – cell drinking fluid b) phagocytosis – cell eats

Exocytosis opposite of endocytosis!!