chpt 2 movement of substances

Question 1

What does the fluid mosaic model contain ?

Answer 1

1. phospholipid bilayer than are arranged so the hydrophobic tails face inwards and the hydrophilic heads fact outwards
2. phospholipids move in bilayer
3. there are various immobile proteins embedded in or attached to the layer of phospholipids

Question 2

Function of membranes in phospholipid bilayer ?

Answer 2

1. selectively permeable so it controls substances going in and out of cell
2. forms a boundary between inside of cell and external envts -> ensures a constant internal envt is maintained
3. responsible for cell to cell communication
   cell membranes equipped with receptor proteins that receive chemical passenger molecules from other cells -> allows for cell to sense changes in external envt and respond to said changes

Question 3

What are the two types of proteins embedded in / attached to the membrane of the phospholipid bilayer ?

Answer 3

1. integral proteins (tightly bound within bilayer)
   hydrophobic amino acid heads in contact with hydrophobic lipid bilayer
   hydrophilic portions exposed to aqueous mediums on either side of protein
2. peripheral proteins (loosely attached to surface of membrane)
   often attached to exposed areas of integral proteins

Question 4

What are the functions of proteins in the membrane ?

Answer 4

1. transport
   carrier and channel proteins
2. enzymatic reactions
   some proteins have enzymes with their active sites exposed to substances outside the membrane
3. signal transduction
   receptors to receive chemical messengers
   relays message to inside of cell
4. cell to cell recognition
   identifies other cells
5. intercellular joining
   proteins join to other proteins on adjacent cells