1: Membrane Structure

Question 1

What does the fluid mosaic model show?

Answer 1

cell membrane structure

of animal cell because it includes cholesterol, more on that later

Question 2

In the fluid mosaic model diagram, how are phospholipids shown?

Answer 2

phospholipids:

• oval (phosphate head)
• two parallel lines attached (fatty acid tails)

Question 3

Give the names of types of proteins based on their position in the membrane.

Answer 3

• integral protein

- peripheral protein

Question 4

Where are integral proteins positioned in relation to the phospholipid bilayer in the membrane?

Answer 4

integral proteins = embedded in the phospholipid bilayer

Question 5

Where are peripheral proteins in relation to the phospholipid bilayer in the membrane?

Answer 5

peripheral proteins = attached to an outer surface of the membrane

Question 6

What do glycoproteins have attached to them? Where are they attached? What is the function of a glycoprotein?

Answer 6

• sugar units
• attached to to glycoprotein (duh) on the outer surface of the membrane
• cell-to-cell communication

Question 7

Draw a diagram of the fluid mosaic model. (p9)

Answer 7

• hydrophilic phosphate head
• hydrophobic hydrocarbon tail
• integral proteins embedded in phospholipid bilayer
• peripheral protein on surface of membrane
• glycoprotein (with sugar units)
• pump or channel protein
• cholesterol

Question 8

What is the basic component of all biological membranes?

Answer 8

phospholipids

Question 9

Which part of a phospholipid is attracted to water? Which part is not attracted to water?

Answer 9

• head

- tail

Question 10

What is the biological term for ‘not attracted to water’? What is the biological term for ‘attracted to water’?

Answer 10

• hydrophobic

- hydrophilic

Question 11

What is the term that describes a molecule which has one part attracted to water, and one part not attracted to water?

Answer 11

amphipathic

Question 12

What happens when phospholipids are mixed with water?

Answer 12

they naturally become arranged into bilayers

Question 13

When in contact with water, which part of the phospholipids will face out? Which part will face in?

Answer 13

• head will face out making contact with the water

- hydrocarbon tail will face away from water

Question 14

Why is the phospholipid bilayer so stable in water?

Answer 14

attraction between:

• hydrophobic tails in centre of bilayer
• and between hydrophilic heads and surrounding water

= stable membrane

Question 15

Other than phospholipids and proteins, what is also a component of animal cell membranes?

Answer 15

cholesterol

Question 16

Is the cholesterol molecule mostly hydrophobic or hydrophilic?

Answer 16

mostly hydrophobic

Question 17

How is cholesterol structurally similar to a phospholipid? Hence, how is cholesterol positioned in the phospholipid bilayer?

Answer 17

• cholesterol has one hydrophilic end (like phospholipid), but is mostly hydrophobic
• cholesterol fits between phospholipids in the membrane

Question 18

What is the effect of cholesterol in the membrane? What is the significance of this effect?

Answer 18

• restricts the movement of phospholipid molecules

- therefore reduces the fluidity of the membrane

Question 19

Cholesterol reduces the fluidity of the membrane. What other effect does cholesterol have on the membrane? Why is this important?

Answer 19

• also reduces the permeability of the membrane to hydrophilic particles such as sodium ions and hydrogen ions
• diffusion across membrane must be restricted because animal cells need to maintain concentration differences of these ions across their membranes

Question 20

“Membrane proteins are diverse in … , … and … in the membrane.” Fill the gaps.

Answer 20

• structure
• function
• position

Question 21

Give 6 examples of membrane proteins (other than glycoprotein).

Answer 21

1. insulin receptor
2. cadherin
3. cytochrome c
4. cytochrome oxidase
5. nicotinic acetylcholine receptor
6. calcium pump

Question 22

Outline the position and function of an insulin receptor in the cell membrane.

Answer 22

• integral protein

- is a hormone receptor

Question 23

Outline the position and function of cadherin in the cell membrane.

Answer 23

• integral protein

- used for cell-to-cell adhesion

Question 24

Outline the position and function of cytochrome c and cytochrome oxidase in the cell membrane.

Answer 24

cytochrome c:

• peripheral protein
• used for electron transport

cytochrome oxidase:

• integral protein
• immobilized enzyme

Question 25

Outline the position and function of a nicotinic acetylcholine receptor in the cell membrane.

Answer 25

• integral protein

- is both a receptor for a neurotransmitter AND a channel for facilitate diffusion of sodium ions

Question 26

Outline the position and function of a calcium pump in the cell membrane.

Answer 26

• integral protein

- active transport of calcium ions

Question 27

Draw and label 6 different membrane proteins (not glycoprotein) in the phospholipid bilayer*. (p9)

*phospholipid bilayer can be represented by two parallel lines.

Answer 27

these are the proteins:

1. insulin receptor
2. cadherin
3. cytochrome c
4. cytochrome oxidase
5. nicotinic acetylcholine receptor
6. calcium pump