Membrane Structure

Question 1

What are hydrophilic substances?

Answer 1

Substances that are attracted to water

Question 2

What are hydrophobic substances

Answer 2

Substances that are not attracted to water

Question 3

What is a phospholipid?

Answer 3

Integral component of cell membranes, along with membrane proteins

Question 4

What are the two parts of a phospholipid?

Answer 4

1. One phosphate head (polar & hydrophilic)

2. Two fatty-acid tails (non-polar & hydrophobic)

Question 5

Why are phospholipids called amphipathic?

Answer 5

Have a part that is hydrophilic and also have a part that is hydrophobic

Question 6

What are the 3 properties of phospholipids?

Answer 6

1. Bilayer formed through hydrophobic interactions between non-polar tails
2. Hydrophobic/hydrophilic layers restrict entry of many molecules
3. Membrane is fluid and flexible, allowing endocytosis and exocytosis

Question 7

What are the 2 types of membrane proteins?

Answer 7

1. Integral proteins: permanently attached

2. Peripheral proteins: temporarily attached

Question 8

What are the 5 functions of membrane proteins?

Answer 8

1. Hormone receptor
2. Cell-to-cell adhesion
3. Immobilized enzyme
4. Channel proteins for facilitated diffusion
5. Pump proteins for active transport

Question 9

What is cholesterol?

Answer 9

Component of animal cell membranes. Has a hydrophilic end and a hydrophobic end, which allows it to fit within the phospholipid bilayer.

Question 10

What are the 2 main functions of cholesterol?

Answer 10

1. Reduces fluidity and permeability of membrane to hydrophilic particles.
2. Helps membrane to curve, which helps in formation of vesicles

Question 11

What did the first model of membrane structure suggest?

Answer 11

The Davson-Danielli Model proposed in 1935 proposed that there was a bilayer of phospholipids in the center of the membrane with layers of protein on either side

Question 12

What were the 3 ways Davson-Danielli Model was falsified?

Answer 12

1. Freeze-fracturing
2. Analysis of membrane proteins
3. Fluorescent tagging of membrane proteins

Question 13

How did freeze-fracturing prove the Davson-Danielli Model wrong?

Answer 13

Demonstrated that globular proteins were present in the center of the phospholipid bilayer

Question 14

How did analysis of membrane proteins prove the Davson-Danielli Model wrong?

Answer 14

Membrane proteins were discovered to be hydrophobic and varying in size, thereby the assumption of a constant lipid:protein ratio was wrong

Question 15

How did fluorescent tagging of membrane proteins prove the Davson-Danielli Model wrong?

Answer 15

Demonstrated that membrane proteins could move