Lecture 5

Question 1

Explain how the structure of the carbohydrates, cellulose and starch are related to their functions

Answer 1

Carbohydrate - monomers and dimers are available fuel and carbon source in cells
Carbohydrate - polymers serve as energy storage and structural roles
The rigid structure of cellulose is what allows plants to stand upright. The bonds between each cellulose molecule are very strong, which makes cellulose very hard to break down
Starch - formed from alpha glucose. Can be straight or branched and is used as energy storage for plants because it can form compact structures and is easily broken down

Question 2

Explain why lipids are not polymers and describe how the structure of a phospholipid is related to its function in membrane

Answer 2

Lipids are not true macromolecules because the monomers are not covalently bonded together. Simple lipids are composed of subunits made of fatty acids covalently bonded to a triose sugar – glycerol
Phospholipids form the basic structure of a cell membrane, called the lipid bilayer.
Scattered in the lipid bilayer are cholesterol molecules, which help to keep the membrane fluid consistent. Membrane proteins are important for transporting substances across the cell membrane.

Question 3

Distinguish between saturated and unsaturated fats and explain the factors that affect membrane fluidity

Answer 3

Saturated fats - lack double bonds between the individual carbon atoms (tend to be solid at room temperature)
Hydrocarbon tails prevent packing enhancing membrane fluidity
Unsaturated - there is at least one double bond in the fatty acid chain (are usually liquid and from plant sources)
Hydrocarbons tails pack together, increasing membrane viscosity

Question 4

Describe functions of the plasma membrane and membrane proteins

Answer 4

Protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells
Membrane proteins - Transport proteins move molecules and ions across the membrane.

Question 5

Explain the meaning of ‘fluid’ and ‘mosaic’

Answer 5

Fluid - means that the molecules cannot pass each other vertically, only horizontally
Mosaic - proteins are embedded in the phospholipid bilayer