The Cell Membrane

A structure that functions to maintain homeostasis at the cellular level

Big Idea #2

Cellular Engineering

• Design a “screen” according to the guidelines below:– Steroids can dissolve and pass though.– Large proteins can interact with the surface but

cannot penetrate.– Allows small, nonpolar molecules to pass through.– Glucose goes through slower than a smaller

molecule like oxygen gas– Ions cannot pass directly through

How did you do?

• Did you come up with the cell membrane?

• Complete Campbell’s Activity 8A, sketch and label the membrane

Campbells Picture

Let’s Discuss the following:• Structure of a phosopholipid bilayer• Evidence for the fluid mosaic model of the cell

membrane• Properties of proteins embedded in cell membrane

and freeze fracture• How does winter wheat avoid cell membrane

solidification?• Role of emergence in the functionality of the

membrane (sidedness)• How cells attach together through an extracellular

matrix• Functions of proteins in membrane

Phospholipid Bilayer

Why???• Hydrophilic • Hydrophobic

Term: Amphipathic

How are phospholipids different than triglycerides?

• What is the difference between the two?

• Where might the phosphate group come from?

• Where do the fatty acids come from?

Site of Lipid Biosynthesis

• The organ where everything happens!

Fluid Mosaic Model

• Proteins are embedded in cell membrane rather than sandwiched.

• Evidence: freeze fracture technique

Freeze Fracture Technique

Structure of Integral proteins

• Amphipathic

• Aquaporin is an example of an amphipathic protein that spans the cell membrane and has a hollow core to allow water to pass through

Aquaporin

• Where might the hydrophobic parts be?

• Hydrophilic?

• How might influx of water be controlled?

Role of substances within the lipid bilayer

• What keeps membranes flexible?

• Unsaturated vs. Saturated fats

• Role of cholesterol– Depends on

temperature• High Temperatures

• Low Temperatures

Winter Wheat…eh?

• Why is this such an important crop in Canada?

• How might he composition of the cell membranes be different than wheat in more temperate climates?

Sidedness of Membranes

• Proteins are part of a fluid mosaic and they can disperse in cell membrane.

• How is the above experiment evidence of this concept?

Cell with sidedness?

• How would a nerve cell display sidedness?

• Would a cell in the intestine need to display sidedness?

• What cell might not have a sidedness?

How does this tissue show sidedness?

• Where are these tissues found?

Extracellular Matrix 6.7

• Collagen

• Elastin

• Proteoglycans

• Integrins

• Fibronectins

Cellular Junctions

• Plants– Plasmodesmata

• Allow ions to pass from cell to cell.

• Animals– Junctions are

specialized for certain functions

Animal Junctions

• Tight Junction: Prevents movement of fluid between cells.

• Desmosome: Adheres two cells, very common in epidermis

• Gap Junction: Allows ions to pass directly from cell to cell

Interaction Between Membrane and Outside of Cell 6.6

Adhesion to ECM can alter tension on cytoskeleton.

Plastic on petri dishes mimics an ECM. Why do cells usually grow in a single layer?

??Cancer cells??

Comparing Cytoskeletal Components

Motor Proteins

• Myosin can bind and walk along actin.– Muscle conractions– Ameoboid movement– Movement of

organelles around cytoplasm (plant and animal cells)

Functions of Membrane Proteins

Getting Across!

• Campbell’s Activities B, C, D

We will begin an investigation of cell tissues. It will be important to recognize how these tissues are organized and connected through the ECM.