Dynamic Cells Chapter 8 p  Membrane Properties  Transport Across Cell Membranes  Cell Size and Functions

Membrane Properties pg  Membrane Structure  Membrane Function

Phospholipid Bilayer pg Cell membranes are composed of a phospholipid bilayer 2 layers of phospholipids with embedded proteins

Each layer has: ◦ a hydrophilic phosphate end (hydro = water, philic = loving) ◦ and a hydrophobic lipid tail (phobic = fears, repels)

Membrane Proteins can be peripheral (on surface) or integral (spans the membrane) pg. 293

Fluid Mosaic Model Cell membranes are constantly MOVING and CHANGING. Gives cell flexibility, movement Changes the positions of the proteins embedded in the membrane, changing the “mosaic”

3 Functions of the Cell Membrane pg Barrier – keeps wastes, toxins, etc. out - allows needed substances in 2. Organization – membranes surround and package materials in vessicles i.e. lysosomes, endoplasmic reticulum

3 Functions of the Cell Membrane pg Selective Filter – SEMI-PERMEABLE – only allows certain substances in or out Regulated by particle size and by selective transport by membrane proteins

The Plasma Membrane

Transport Across Cell Membranes pg Types 1. Passive Transport - high concentration to low concentration - no energy (ATP) is required - usually gases (CO 2, O 2, water) because they are very small particles

2. Active transport - low concentration to high concentration - energy (ATP) is required - carrier proteins are usually needed as well

3. Endocytosis/exocytosis - Larger particles are involved - The cell membrane is used to create vessicles (endocytosis) or release particles from vessicles (exocytosis)

Brownian Motion and Concentration Gradients p  Brownian Motion: matter is made up of tiny particles that are in constant motion laser scanparticle movement

PASSIVE TRANSPORT Molecules always move 1) randomly 2) from areas of high concentration to areas of low concentration This is called DIFFUSION

Concentration Gradient The difference in concentration between the high and low concentration areas. The greater the difference in concentration – the faster the particles move Eventually equilibrium is reached

Why does this happen? At high concentrations the molecules ricochet off of each other and move towards the area of low concentration

Equilibrium Remember: at equilibrium the particles DO NOT stop moving, they continue to move back and forth across the concentration gradient.

Transport Across Cell Membranes pg Types 1. Passive Transport 2. Active Transport 3. Endocytosis/Exocytosis

Passive Transport pg NO ENERGY REQUIRED Small molecules move by diffusion (water, oxygen, carbon dioxide) When WATER molecules move by diffusion across a membrane we call it OSMOSIS

Tonicity pg. 299 Hypotonic more water than in the cell Hypertonic less water than in the cell Isotonic Same amount of water

Should you drink salt water if you are lost at sea??? Potato Experiment

Should you drink salt water if you are lost at sea???

Red blood cells in an ISOTONIC solution

Red blood cells in a HYPOTONIC solution

Red blood cells in a HYPERTONIC solution

Plasmolysis in Onion cells Observe the tonicity of the onion cells as a hypertonic saline solution is added to the microscope slide – what happens to the cells?

Facilitated Transport (also called facilitated diffusion) Another form of passive transport Used for molecules that are too large to cross the membrane by diffusion (i.e. glucose)

Facilitated Diffusion p. 303 Carrier proteins bind to larger molecules, and change their shape so molecules can diffuse through. Channel proteins provide water filled pores for charged ions to pass through

Transport Across Cell Membranes pg Types 1. Passive Transport 2. Active Transport 3. Endocytosis/Exocytosis

Active Transport pg Molecules move against the concentration gradient (low to high) Energy must be provided (even when we are resting, 40% of our energy is spent on active transport!)

Active Transport Uses specialized transport proteins and protein pumps

Why spend so much energy on active transport? Maintains internal cell environments (i.e. cell’s electrical gradient, roots pull in minerals from soil, filtering blood in your kidneys)

Passive and Active Transport Animations ology1111/animations/transport1.html ology1111/animations/transport1.html

Endocytosis/Exocytosis For substances the cell needs to take in (endo = in) or expel (exo = out) that are too large for passive or active transport

Two Types of Endocytosis 1. phagocytosis (solids) 2. pinocytosis (liquids)

Dialysis, Reverse Osmosis and the Transdermal Patch Dialysis HDanim.php danim.php Reverse Osmosis erse_osmosis_flash.asp Nicotine patch