BUBBLES!! MUST wear goggles at ALL times! NO taking straw out of the dish! NO drinking/ inhaling bubble fluid THIS IS an EXPERIMENT!!! You can have fun, but ALL usual lab safety RULES APPLY!

Questions to think about: Can anything pass through the bubble without breaking it? Can one bubble divide to become several bubbles? Can several bubbles merge to form one- how? Can a drop of water pass through a bubble without popping it? Does it look like the surface of the bubble moves? How can you tell?

soapy “membranes” 1. How does a bubble model the fluid nature of a membrane? 2. Can anything pass through the membrane without rupturing it? If so what; if no, what did you try? 3. Can one bubble divide to become several bubbles? 4. Can several bubbles merge to become one bubble? 5. Can a drop of water pass through a bubble without popping the bubble? 6. A bubble is a lipid monolayer – draw a diagram of a segment of a bubble using this symbol for a lipid molecule:

Bubble Summary! A bubble is a lipid monolayer!! What is the structure of the membranes of our cells? How does a bubble model the fluid nature of a cell membrane?

L3 Biology Chapter 4 CELL MEMBRANES and TRANSPORT

The Cell

Learning Objectives Describe the fluid mosaic model of membrane structure and explain the underlying reasons for this structure. Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes. Outline the roles of the plasma membrane, and the roles of membranes within cells.

Plasma Membrane (aka Cell Membrane) All living things are surrounded by a membrane. It controls exchange of materials (like nutrients, waste) between cells and the environment. Other important functions include: communicate to other cells respond to hormones. To understand FUNCTION in BIOLOGY, you must first study STRUCTURE!

Cell Membranes from Opposing Neurons (TEM x436,740). Nerve cell Gap between cells Cell membrane { } cell membrane Is 7nm wide Nerve cell

Remember our discussion of our favorite POLAR Molecule? WATER! Due to unequal distribution of electrons (electronegativity of Oxygen), one end of molecule is partially positive while other end is partially negative. The molecule has ‘poles’ WATER is the solvent inside and outside every cell.

Phospholipids are the Primary Building block of the membrane: HYDROPHILIC heads (water loving) -Attracted to the water called POLAR head HYDROPHOBIC tails (water fearing) -Not attracted to the water called NON-POLAR Tails.

PHOSPHOLIPIDs are AMPHIPATHIC molecules with both POLAR AND NONPOLAR regions Which atoms/regions are Polar? Which atoms/regions are nonpolar?

Why does the phospholipid have a Hydrophilic Head? One end of the phospholipid has a phosphate group and several oxygens atoms that are not shared equally. This end of the molecule has a charge and is attracted to water. It is POLAR! 3D model of a Phospholipid

Why does the phospholipid have Hydrophobic tails? Two long chains (tails) at bottom of phospholipid made up of carbon and hydrogen. Both these elements share their electrons evenly, so there is no charge (NON POLAR). They are not attracted to water; water molecules tend to push them out of the way as they are attracted to another H2O. These molecules do NOT dissolve in water. 3D model of a Phospholipid

How does the Plasma Membrane form? Phospholipid tails interact AWAY from the water, and the heads associate with the water of the solution and cytoplasm -The result is 2 layers of phospholipids with hydrophobic tails protected inside the membrane by the hydrophilic heads. Lipid BILAYER, the MAIN structure of the Plasma Membrane

WATER Hydrophilic head Hydrophobic tail WATER Figure 7.2 Figure 7.2 Phospholipid bilayer (cross section). 16

Properties of Cell Membranes Basic structure is Phospholipid Bilayer. Phospholipids move laterally within the membrane. Composition of Phospholipid fatty acid tails can be Saturated (straight) or Unsaturated (bent) depending on the organism & environmental conditions (ie temperature)

Phospholipids move within the membrane: Lateral movement occurs 107 times per second. Flip-flopping across the membrane is rare ( once per month). Figure 7.6 The movement of phospholipids. 18

Unsaturated hydrocarbon tails Saturated hydrocarbon tails Figure 7.8 Fluid Viscous Unsaturated hydrocarbon tails Saturated hydrocarbon tails (a) Unsaturated versus saturated hydrocarbon tails (b) Cholesterol within the animal cell membrane Figure 7.8 Factors that affect membrane fluidity. Cholesterol 19

Animation of membrane formation http://telstar.ote.cmu.edu/biology/MembranePage/index2.html

Why is the Plasma Membrane necessary? Provide containment for the cell structures Phospholipids are PRIMARY component that forms the membrane Phospholipids protect the cell from environmental hazards by acting as a barrier to most water soluble substances BUT, Phospholipids are only PART of the story of the plasma membrane…………

Diagram (model) representing the cell membrane Remember the membrane is 7nm wide

Models in Biological Systems: A Model is a HYPOTHESIS: A visual representation of an abstract concept or minute molecules A way to manipulate and perform a biological process

What are 2 important points of Models: Accuracy in representing the concept, molecules or process Precision in the details of the representation

Models to represent Biological Systems: Replacing 1 model for another does NOT imply first was worthless Acceptance or rejection of model depends on how well it Fits observations Explains experimental results New findings may result in revision of model or development of NEW model New model MAY incorporate some properties of old model

Their model was named the Fluid Mosaic Model. In 1972, S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water Their model was named the Fluid Mosaic Model. © 2011 Pearson Education, Inc.

Phospholipid bilayer Hydrophobic regions of protein Figure 7.3 Phospholipid bilayer Figure 7.3 The original fluid mosaic model for membranes. Hydrophobic regions of protein Hydrophilic regions of protein 27

Current Model of the Cell Membrane Fibers of extra- cellular matrix (ECM) Glyco- protein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Figure 7.5 Updated model of an animal cell’s plasma membrane (cutaway view). Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE 28

Fluid mosaic model!! Cell membranes also contain cholesterol and proteins within the phospholipid bilayer. This ‘model’ for the structure of the membrane is called the: FLUID MOSAIC MODEL

Why call it a Fluid Mosaic Model? FLUID- because phospholipids and proteins move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by scattered protein molecules in the membrane when viewed from above.

Animation of membrane formation http://telstar.ote.cmu.edu/biology/MembranePage/index2.html

Remember Cholesterol (Lipids)

What is the function of cholesterol? Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.

Cholesterol between the phospholipid tails

Proteins determine most of the membrane’s specific functions Where are the proteins? Integral membrane proteins: Integrated in the membrane with access to both cytoplasm and outside cell Peripheral membrane proteins: Facing only the cytoplasm OR outside the cell as part of one side of the membrane Proteins can float or be fixed: - Like phospholipids, many of them have hydrophobic and hydrophilic regions Proteins determine most of the membrane’s specific functions

Individual Proteins serve different functions: 1. Proteins act as channels for substances to move in or out of cell. 2. Proteins act Pumps to move molecules across the membrane. 3. Proteins act as membrane enzymes in chemical reactions. 4. Proteins help to stabilize the membrane

Some proteins have sugars attached These are called Glycoproteins What is their function? Glycoproteins act as markers for cell communication, antigens for other cells to recognise them, or receptors that hormones & other proteins can bind.

Membrane with protein http://telstar.ote.cmu.edu/biology/MembranePage/index2.html

Summary Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER. Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads. The best model of the cell membrane is called the FLUID MOSAIC MODEL The average thickness of the membrane is 7nm.

Summary, cont. The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent) Phospholipids form the bilayer, act as barrier to most water soluble substances Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.

Summary, cont. Proteins determine specific properties of the membrane (Key to Cell differentiation!) Proteins are integrated or peripheral: float or fixed in the membrane also have hydrophobic and hydrophilic portions. Proteins function in: Transport- channels for substances to move in or out of cell Enzymes Pumps Membrane stabilizers

Summary, cont. Some proteins have carbohydrates attached to them to form GLYCOPROTEINS . Glycoproteins act as receptor molecules (eg for hormones and neurotransmitters), as antigens for cell recognition, as markers for cell communication.

Visualizing structure and function http://multimedia.mcb.harvard.edu/anim_innerlife.html

Do it yourself- build a membrane! https://www.wisc-online.com/learn/natural-science/life-science/ap1101/construction-of-the-cell-membrane Go to this website on the notepads, and follow directions to build a membrane!

(Hint-Is it ever the same??) Wrap-up! How is the cell’s membrane structured (chemically) to ensure efficiency, survival, & differentiation? (Hint-Is it ever the same??)

Preview of coming attractions! Membrane structure allows for the movement of substances into and out of the cell Living organisms demonstrate many adaptations to their membranes allowing them to survive in their environments!

Movement of selected molecules across the cell membrane

Moving amoeba Contractile vacuole

Functions of Cell Membrane Components: Use the following headings to produce a table summarizing the functions of the different types of molecules found in the cell membrane. Use your notes to find the information. Component Structure Functions Phospholipids Cholesterol Proteins Glycoproteins