Cell membranes and transport through membranes

Question 1

What does micelle mean?

Answer 1

• a micelle is a spherical structure formed by fatty acids when they are dissolved in water
• the hydrophilic heads of the fatty acid molecules are turned toward the water, while the hydrophobic tails are sheltered in the interior

Question 2

What does the term aqueous refer to?

Answer 2

the term aqueous refers to a system that involves water

Question 3

How is a bilayer formed?

Answer 3

• a bilayer is formed when phospholipid molecules are completely surrounded by water

Question 4

Explain how phospholipids form a cell surface membrane?

Answer 4

• hydrophilic parts (phosphate group) associate with water
• hydrophobic parts (fatty acids) repel water
• a bilayer forms with hydrophobic parts pointing in towards the centre of the bilayer

Question 5

What are the properties of cell membranes? (think about what the cell membrane does)

Answer 5

• it is a selectively permeable membranes
  (regulating what materials enter and exit the cell)
• it consists of a lipid bilayer that is soft, flexible, and self-repairing
• protects the integrity and shape of the cell
• contains proteins and phospholipids as the major components
• found in all cells

Question 6

What does permeable mean?

Answer 6

A material which allows water or liquids to flow through

Question 7

What is a phospholipid made up of? What are their R groups?

Answer 7

• phosphate group (polar, hydrophilic, negatively charged)
• glycerol (molecule) group
• 2 fatty acid tails (non-polar, hydrophobic, uncharged)

Question 8

What is the structure of a cell membrane?

Answer 8

• the cell membrane is a thin and flexible barrier
• protects interior of a cell
• made up of a lipid bilayer
• cell membrane is impermeable to ions and most water-soluble molecules

Question 9

What is a lipid bilayer?

Answer 9

• consists of two layers of phospholipid molecules, and proteins embedded in it

Question 10

What certain substances cannot pass through the phospholipid bilayer? Why?

Answer 10

• the cell membrane is selectively permeable and therefore only allows small polar molecules to pass through, but ions and large polar molecules cannot
• this is due to the hydrophobic fatty acid tails of the phospholipid
• hydrophobic substances (carbon dioxide and oxygen) can easily pass through the lipid bilayer

Question 11

What are the proteins in the lipid bilayer?

Answer 11

• integral protein
• peripheral protein (does not enter into the hydrophobic space)
• channel protein

Question 12

What does a glycoprotein and a glycolipid look like?

Answer 12

• glycoprotein has a ‘Y’ shape (carbohydrate chain), is attached to a ball (globular protein)
• glycolipid has a single line ‘I’ shape

Question 13

What do glycoproteins and glycolipids do?

Answer 13

• help recognise cell shapes so they can fit together/ bind
• they recognise and bind to carbohydrate receptors

Question 14

What does cholesterol do?

Answer 14

• pivotal role in maintaining the structural integrity
• and regulating the fluidity of the cell membranes

Question 15

How does temperature effect membrane permeability?

Answer 15

• as the temperature increases, the membrane permeability also increases
• at high temps the proteins denature because the heat damages the bonds in the tertiary structure
• makes it easier for molecules to pass through because it creates gaps in the membrane

Question 16

How does alcohol concentration effect membrane permeability?

Answer 16

• as alcohol concentration increases, the membrane permeability increases
• alcohol is lipophilic and therefore reacts with the phospholipids in the cell membrane
• at higher concentrations, the alcohol breaks down the lipid bilayer and can cause it to dissolve
  -ethanol dissolves lipids