The Cell Membrane

Cell Membrane Properties

In or Out?

• How is a window screen similar to a cell membrane?– What are some things that can pass through a

window screen?– What are some things that can not pass through a

window screen? Why is it important to keep these things from moving through the screen?

– Why is it important to regulate what moves into and out of the cell?

Main part of the cell membrane

Phospholipid mainly lipid molecule that contains phosphate

Composition (make-up) of cell membrane

hydrophobic lipid tail

Hydrophilic phosphate head

Lipid

bilayer

Protein channel

Carbohydrate chain

glycoprotein

Properties and Composition Vocabulary

• Selectively permeable: allows only certain things to enter• Lipid Bilayer: Double layered structure composed of lipids,

proteins, and carbohydrates• Hydrophobic lipid tails: Fatty acid tails stay away (inside) from

cytoplasm “water fearing”• Hydrophilic phosphate heads: face the cytoplasm “ water

loving”• Integral Protein Channel: passageway for large molecules to

enter and leave cell• Peripheral Glycoproteins: proteins that act as receptors to

receive chemical messages from the outside of the membrane• Carbohydrate Chains: can receive certain molecules into cell

by means of a receptor

Complete Cell Membrane

Main Function of the Cell Membrane

• Regulates what molecules enter in and out of the cell to help maintain the HOMEOSTASIS of the cell

How Do Molecules Pass Through the Membrane?

• Passive Transport

• Active Transport

Diffusion- A type of passive transport

DIFFUSION

• Does NOT require energy • Occurs when there is a concentration GRADIENT

– Gradient: a difference in amounts. Gradients move from high to low

DIFFUSION GOES WITH THE GRADIENT

HIGH CONCENTRATION LOW CONC.• Molecules will stop diffusing when they are equal on both sides of

the membrane• Oxygen and carbon dioxide use this method of transport through the

membrane•  http://highered.mcgraw-hill.com/sites/0072495855/student_view0/

chapter2/animation__how_diffusion_works.html

Facilitated Diffusion

• Facilitate= help

• No energy is required

• helped by a protein channel

• Proteins channels have larger openings so that larger molecules diffuse through the membrane

• Moves with the gradient HIGH LOW CONCENTRATION

Click to view the animation about facilitated diffusion

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

Passive Transport

Active Transport

– Requires ATP (cellular energy)– Movement of molecules AGAINST the

concentration gradient– Movement of molecules from

Low concentration High concentration

Sodium and Potassium pump is an example of how nerve cells maintain a high concentration of sodium on one side

Click to view the animation of active transport

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

HIGH

LOW

ENERGY FROM ATP PUSHES MOLECULES ACROSS THE MEMBRANE

WATCH ACTIVE TRANSPORTLOW TO HIGH ENERGY NEEDED

Active Transport

TYPES OF ACTIVE TRANSPORT

• Endocytosis: molecules moving INTO the cell. – Phagocytosis: large particles are ingested

into the cell– Pinocytosis: When solutes are taken into the

cell

• Exocytosis: molecules moving OUT of the cell

THESE ALL REQUIRE ENERGY (ATP)

Phagocytosis Animation

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html

Endocytosis

Exocytosis

How Do Certain Factors Affect How Molecules Move Through the Membrane?

• Molecule size smaller molecules move faster through than larger through membrane

• Charge on molecule outside of membrane is attracted to polar molecules inside to nonpolar molecules

• Concentration of molecules more molecules on one side of the membrane will affect rate which movement happens

• Temperature of Cellular Environment: molecules move quicker in warmer temps slower in cooler temp

The Tea Bag Demo

• Imagine the tea bag is the cell. The contents inside are the organelles. The bag itself is the membrane.

• Place the tea bag in room temp water. Notice the rate at which the water changes color which is an indication of molecule movement.

• Place the second tea bag in the warm/hot water. Notice the difference that it makes