Chapter 7: Membranes (Exam 2)

Fluid Mosaic Model

Describes the structure of cell membranes as a dynamic mosaic of phospholipids, proteins, cholesterol, and carbohydrates. These components can move laterally, giving the membrane a fluid and flexible nature

Phospholipid Bilayer

Proteins can travers the membrane; Hydrophobic tail, hydrophillic head

How do things move in the plasma membrane?

Most laterally; Once a month flip flop (switch)

What happens when membrane temps cool off?

Fluid state turns to a solid state

What determines temperature function fo membranes?

Depends on the types of lipids present in membrane

What restrains movement of phospholipids?

Cholesterol

Diffusionq

The natural tendency of particles to move

Proteins:

Determine most of the membranes specific functions

Peripheral proteins

Proteins that are not embedded

Integral proteins

Penetrate the hydrophobic core; span across the membrane.

What are Transmembrane proteins?

Integral proteins that span the membrane

Hydrophobic regions of integral proteins:

Consist of one or more stretches of nonpolar a-acids; coiled into alpha helices

Functions of membrane proteins:

1. Transport

2. Enzymatic Activity

3. Signal Transduction

4. Cell-cell recognition

5. Interstellar joining

6. Attachment to cytoskeleton and extracellular matrix (ECM)

How do cells recognize each other?

Binding to surface molecules, often carbs, on plasma membrane

Inside Membrane face:

Intracellular

Outside Membrane face

Extracellular

Selective Permeability

regulates what leaves and enters the cell membrane

Hydrophobic Molecules:

Dissolve in the lipid bilayer and pass through the membrane rapidly

Polar Molecules (Sugars):

Do not cross the membrane easily

Transport Proteins

Allow passage of hydrophilic, polar substances across the membrane

Channel Proteins

Hydrophilic channel that certain molecules or ions can use as a tunnel

Carrier Proteins

Bind to molecules and change shape to shuttle them across membrane

Dynamic Equilibrium

As many molecules cross one way cross in the other direction

Which way do substances diffuse?

Down their concentration gradient

Passive Transport

Requires no energy from cell to make it happen

Osmosis

Diffusion of water across a selectively permeable membrane

Direction of osmosis is determined by:

Difference in total solute concentration; goes from lower solute to higher solute.

Tonicity

Ability of a solution to cause a cell to gain or lose weight

Isotonic Solution

Solute concentration is the same as that inside the cell

Hypertonic Solution

Solute concetration is greater thatn that inside the cell; cell loses water

Hypotonic Solution

Solute concentration is less than that inside the cell; cell gains water

Osmoregulation

The control of water balance

Turgid

Plant cell in hypotonic solution until the wall opposes uptake

Flaccid

Plant cell with 0 net movement

Plasmolysis

contraction of the protoplast of a plant cell as a result of loss of water from the cell.

Facilitated diffusion

Passive transport aided by proteins; Transport proteins speed movement of molecules across membranes