3.2.3 (membrane structure)

Question 1

Describe the structure of a triglyceride

Answer 1

One glycerol molecule bonded to 3 fatty acids

Question 2

Describe the structure of a phospholipid

Answer 2

One glycerol molecule bonded to 2 fatty acids and a phosphate group

Question 3

How are bilipid layers formed and where are they found?

Answer 3

Found in cell membranes
In a phospholipid the phosphate group is hydrophilic and the fatty acid tail is hydrophobic
The hydrophilic heads point to the inside and outside of cell as they are attracted to water, the hydrophobic non polar tails point towards each other as they are repelled by the water on both sides

Question 4

Why is the arrangement of phospholipids in the cell membrane useful?

Answer 4

Lipid soluble molecules can move through the membrane
Warer soluble substances are prevented from entering and exiting the cell
Also allows for membrane flexibility

Question 5

Describe the proteins found in cell membranes

Answer 5

Intrinsic/integral proteins- embedded in surface of bilayer, don’t extend across it
- mechanical support
-join with glycolipids to act as cell surface receptors
Extrinsic/ peripheral proteins- span across phospholipid bilayer
-protein channels (water filled tubes allowing water soluble substances to diffuse across)
- carrier proteins which bind to a substance then change shape to move molecule from one side of membrane to other

Question 6

Describe the function of cholesterol in membranes

Answer 6

Adds strength
Extremely hydrophobic- prevents loss of water and dissolved ions
Pull together fatty acid tails- reduces lateral movement of other molecules
Makes membrane less fluid at higher temps

Question 7

What are glycolipids and what do they do in the cell membrane?

Answer 7

Carbohydrate covalently bonded to a lipid
Carbohydrate extends from lipid bilayer into aqueous solution outside cell
Act as recognition sites
Maintain membrane stability
Helps cells attach to each other to form tissues

Question 8

What are glycoproteins and what do they do in the cell membrane?

Answer 8

Carbohydrates attached to many intrinsic proteins on outer surface of cell membrane
Act as recognition sites for hormones and chemicals
Help cells attach to each other to form tissues
Allow cells to recognise each other

Question 9

What model name is given to the cell membrane and why?

Answer 9

Fluid mosaic model
Fluid- phospholipids can move, allows membrane to be flexible
Mosaic- components eg proteins vary in shape and size, not evenly distributed throughout phospholipids