Miller & Urey’s Experiment Purpose of Experiment: to observe the behavior of molecules under conditions that mimic Earth’s atmosphere before cells Results of Experiment: confirmed that organic molecules could spontaneously form from inorganic molecules

Pasteur’s Experiment Purpose of Experiment: to investigate whether sterile nutrient broth could spontaneously generate bacteria (life) Results of Experiment: “cells can only come from pre-existing cells” (i.e. life can only come from life)

Overview of the Plasma Membrane: Also called a “phospholipid bilayer” Structure is described by the “Fluid Mosaic Model” or “Singer-Nicolson Model” Membrane is “selectively permeable”; it regulates what enters and exits the cell Selective permeability due to structure of membrane Made up of phospholipids, cholesterol, and proteins.

Structure of Phospholipids & Their Arrangement in Membranes Hydrophillic (polar) heads are made of glycerol and phosphate Hydrophobic (non-polar) tails are made of fatty acid chains Phospholipids are amphipathic b/c they contain both hydrophobic and hydrophilic parts Phospholipids will spontaneously form into a bilayer

Properties of Phospholipid Bilayer Structure of membrane is held together by weak interactions between the hydrophobic tails Weak attraction allows phospholipids to move around, allowing for membrane fluidity and flexibility Fluidity allows for spontaneous breaking and reforming of membranes http://www.stolaf.edu/people/giannini/flashanimat/lipids/membrane%20fluidity.swf

Bubbles & Cell Membranes https://vimeo.com/52263821

Fluid Mosaic Model (Singer-Nicolson Model) of Cell Membranes “Fluid” – phospholipids can move around “Mosaic” – phospholipid bilayer is embedded with proteins and cholesterol

Function of Cholesterol Used for structural AND functional support of plasma membrane Functions to immobilize outer surface of membrane & maintain physical integrity of membrane Makes cell membrane less permeable to small water-soluble molecules Excess or inadequate levels of cholesterol affect permeability of membrane

Types & Function of Proteins (JETRAT!)

What does it mean for a plasma membrane to be semi-permeable What does it mean for a plasma membrane to be semi-permeable? Why is selective permeability important for cells/organisms?

What types of molecules and ions are membranes MOST permeable to?

How do molecules actually cross the membrane. (I. E How do molecules actually cross the membrane? (I.E. How are molecules transported in and out of cells?)

Cellular Transport is Based on Concentration Gradients Concentration Gradient: the presence of a difference in concentration of some material, going from one area to another All forms of matter will move from areas of high concentration to lower concentration

Describing the Relative Concentration of Solutions “hyper” = over “hypo” = below “iso” = same A hypertonic solution is a solution with a HIGHER concentration of solutes OUTSIDE of the cell, compared to inside of the cell. A hypotonic solution is a solution with a LOWER concentration of solutes OUTSIDE the cell. An Isotonic solution is a solution with the same concentration of solutes as the inside of the cell.

2 Categories of Transport Based on Use of Energy ATP (Adenosine Triphosphate) is the form of energy used by most living organisms

Types of Passive Transport: Diffusion & Osmosis

Diffusion & Osmosis: Both involve the movement of substances Diffusion & Osmosis: Both involve the movement of substances. Both involve movement across a concentration gradient.

What is osmosis? Animation : http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

What direction would water move in relation to your cells What direction would water move in relation to your cells? (AKA What direction would osmosis occur in?)

Facilitated diffusion is the passive net movement of particles, facilitated by channel proteins Channel proteins are specific to the molecules they transport.

Active vs. Passive Transport Across Membranes