BIOL 1306: Chapter 5

What factors contribute to the fluidity of the plasma membrane bilayer?

*Amphipathic* polar head (charged) = hydrophilic non polar tail (uncharged) = hydrophobic *Length of fatty acyl tails* Short tails = *more* fluid Long tails = *less fluid* = grouped together and moves as a single unit (cholesterol) *Double Bonds* Unsaturated number of hydrogens = "kinks" = more fluid *Cholesterol* Temperature buffer (good) Tightly packed membrane contributes to viscosity of membrane (bad)

What is the difference between simple diffusion, facilitated diffusion, and active transport?

*Simple Diffusion* - substance (solute) moves from *high* concentration to low concentration *Facilitated diffusion* -transport protein provides passageway for solute to move down the concentration gradient and diffuse across a membrane (transport proteins and carrier proteins) *Active transport* Movement of solute from low to high concentration *against* concentration gradient

What is the function of the plasma membrane?

1. Cell-to-cell recognition & Cell Adhesion 2. Signal transduction (cell signaling) 3. Attachment to the cytoskeleton 4. Adhesion to the ECM 5. Transport

What does active transport require?

ATP and *Transport* protein

Which movement is not energetically favorable?

Flip-flop

What is the optimal solution for a plant cell?

Hypotonic

How do animal cells respond in a hypotonic solution? In an isotonic solution? In a hypertonic solution?

Hypotonic - swells Isotonic - normal Hypertonic - burst

How do plant cells react in an isotonic solution, a hypotonic solution, and a hypertonic solution?

Isotonic - Flaccid (wilt) Hypotonic - Turgid (normal) Hypertonic - Plasmolysis

What is exocytosis?

Material from inside the cell is packaged into vesicles and *excreted* outside of cell

How does cholesterol contribute to the fluidity of the bilayer (either positively or negatively)?

Negatively, tightly packs the membrane = making it thick

What are the mechanisms of endocytosis and how do they differ?

Plasma membrane folds inward to form a vesicle that brigs substances *into* cell

Phospholipids are said to be amphipathic; What does amphipathic mean?

Polar head (water-loving) and a non-polar tai (hydrophobic)

Why is the plasma membrane called a "Fluid-Mosaic" model?

Proteins - mosaic Phospholipid bilayer - fluid Composed of a Phospholipid Bilayer with various protein molecules floating around within it. The 'Fluid' part represents how some parts of the membrane can move around freely, if they are not attached to other parts of the cell

How do phospholipids move in the bilayer and which movements are energetically favorable?

Rotationally (favorable) Laterally (favorable) Flip-flop

Which molecules diffuse easily across the bilayer? (Small-uncharged molecules or Large-charged molecules)

Small-uncharged molecules

What is osmosis?

The movement of water across membranes to balance solute concentrations