Fluid Mosaic Model

Membrane Structure &Processes

http://www.wisc-online.com/objects/ViewObject.aspx?ID=ap1101

Cell Membrane Structure – Current ModelFluid Mosaic Model

•Contains a double layer of phospholipids•Phospholipids arranged with tails pointing in•Globular proteins are scattered throughout•Proteins have a variety of functions

EnzymesReceptor SitesCarriersCell Recognition

Fluid Mosaic Model

Membranes can be one of four types-

•permeable•impermeable

•Permeable – allows everything in & out•Impermeable - allows nothing in or out•Semi-permeable – allows substance in & out

based on size•Selectively permeable – allows substances in & out

based on size and chooses between substances of equal size

•semi-permeable•selectively permeable

Definitions:

Which sidewalk is permeable and which sidewalk is impermeable to water?

Gortex raincoats allow air in and keep water out. Use the words in the box at the right to

describe how a gortex coat is affected by rain and air.

• permeable• impermeable• semi-permeable• selectively

permeable

Using the definitions of the words below, what type of permeability does cell membranes have?

• permeable• impermeable• semi-permeable• selectively

permeable

Movement Processes: 1. Diffusion -movement of a substance from an area

of high concentration to an area of low concentration -passive process – no energy required -used to move respiratory gases

oxygen & carbon dioxide

2. Osmosis: -diffusion of water across a cell membrane -movement of water from an area of high

concentration (of water) to an area of lowconcentration (of water)

-passive process – no energy required

0.7%salt

0.7%salt

Isotonic cell &Bathing Solution

-no net movement of water

1%salt

15% salt

Hypertonic bathing-more concentrated

Hypotonic cell-more water

Water moves outCrenation-animal cell shrinksPlasmolysis-plant vacuole shrinks

15%salt

1%salt

Hypertonic cell-more concentrated

Hypotonic bathing-more water

Water moves inLysis-animal swells to burstTurgor- plant vacuole fills to capacity

Red Blood Cell

Plant Cell

Turgor –vacuole fills with water -cell is in a hypotonic solution-chloroplasts move to the edges

Plasmolysis -vacuole shrinks-cells in a hypertonic solution-chloroplasts move to the center

3. Facilitated Diffusion• movement with the concentration gradient

(from high to low)• passive process – no energy required• requires a protein carrier

• protein carrier is actually a channel protein(creates a pathwayfor the substance)

• used to moves simple sugars (glucose) and

amino acids

4. Active Transport• requires a protein carrier (channel protein)• moves AGAINST the concentration gradient

(from low to high)• requires energy (ATP)• used to conserve and move ions

Ex. Calcium, sodium & potassium

5. Exocytosis• used to export (release) large molecule• requires energy• vacuole merges with cell membrane to

release a cell productEx. Goblet cell releases mucus

6. Endocytosis• used to bring larger molecules/substances

into the cell• requires energy• form a vacuole from the cell membrane• two types

a. pinocytosis – “cell drinking”b. phagocytosis – “cell eating”