Lecture 10 - Diffusion, osmosis, crossing membranes lipids and carbohydrates

Compare and contrast the processes of diffusion and osmosis.

Diffusion- molecules want to spread out (as a fas or a liquid) until their spacing is even (solvent migrates across semipermeable membrane, only solvent particles move)

Osmosis - water will move to areas where there are more particles until the ratio of particles to solution is equivalent. (semipermeable membrane is not required and both solute and solvent particle move)

Both result in the solution concentration being equalized.

Describe the components of the fluid mosaic model of the membrane.

• Lipids 

  • Phospholipid- make up the basic structure of the membrane, hydrophilic heads face outwards and hydrophobic tails face inwards

  • Cholesterol- found in the lipid bilayer, this helps to maintain membrane fluidity by preventing the phospholipids from becoming too packed at lower temperatures and too fluid at higher temperatures

• Carbohydrates

  • Glycoproteins- carbohydrates covalently bonded to proteins, located on the outer surface of the plasma membrane

  • Glycolipids- carbohydrates covalently bonded to lipids, also found in the cells exterior

  • Glycocalyx- the term for the layer of glycoproteins and glycolipids on the cell’s surface, which plays roles in cell recognition and protection

• Proteins

  • Integral proteins- embedded within the lipid bilayer and often span across the entire membrane

  • Peripheral proteins- these are located on the surface of the membrane either on the inside or the outside.

• Lipid Rafts -regions of high cholesterol (a special type of lipid) that sequesters specific ‘signaling’ proteins

Explain the important properties of fatty acids that determine their solidity and function.

Saturated versus Unsaturated:

• fats form via condensation reactions

• fats consist of glycerol linked by ester linkages to 3 fatty acids

• Hard fat (saturated): fatty acids with single bonds between all carbon pairs

• Oil (unsaturated): fatty acids that contain double bonds between one or more pairs of carbon atoms

• Fatty acid tail length influences the state of fats

  • saturated lipids (like butter) are relatively soft

  • saturated lipids (like honeycomb) have long hydrocarbon tails

  • unsaturated lipids (like safflower oil) are short and bent

Explain how the lipid bilayer is used to transport material within cells.

• phospholipids enable vesicular transport using coat proteins

  • specific proteins act to make a curvature in the lipid bilayer; others pinch off the vesicle; still others help direct vesicles to their docking site

    • Donor Compartment —→ Acceptor compartment

      • Coat protein complex and proteins and lipids to be transported

      • sorting, budding, uncoating, tethering and docking, fusion

      • arrival at the acceptor compartment

Recognize saccharides (rings and linear forms) - not names but recognize structure.

List 2 cellular functions of saccharides.

Starch

• used for energy storage in plant cells (such as in potatoes)

Glycogen

• used for energy storage in animal cells (such as in liver and muscles)

Cellulose

• used for structural support in cell walls of plants and many algae

Chitin

• used for structural support in the cell walls of fungi and the external skeletons of insects and crustaceans

Peptidoglycan

• used for structural support in bacterial cell walls

______

• The molecular energy stored in starch and glycogen lays within bonds involving the highly electronegative O

• Cell wall strength comes from unbranched polysaccharides like cellulose, chitin, and peptidoglycan