Cells: Cell membrane structure

Question 1

What is the fluid mosaic model

Answer 1

It is a model describing the structure of the plasma membrane as a mosaic of phospholipids, cholesterol protein and carbohydrates

Question 2

The plasma membrane of a cell is semi-permeable, what does this mean

Answer 2

This means that the membrane only allows some materials through

Question 3

What materials can pass through the plasma membrane

Answer 3

Small, non-polar molecules

Question 4

State the function of a cell surface membrane

Answer 4

• Acts as a barrier between the cell and its environment
• They control which substances enter and leave the cell
• Cell signalling

Question 5

Name the three ways in which substances move across the cell surface membrane

Answer 5

• Diffusion
• Active transport
• Osmosis

Question 6

What does the fluid mosaic model explain

Answer 6

• Passive and active movement between cells and their surroundings
• Cell-to-cell interactions
• Cell signalling

Question 7

What is the structure of a phospholipid bilayer

Answer 7

• Two layers of phospholipid monolayers - consisting of hydrophobic tails (fatty acid chains) and hydrophilic heads (phosphate group)

Question 8

Which part of the phospholipid is polar

Answer 8

• Phosphate head

Question 9

Which part of the phospholipid is non-polar

Answer 9

• Fatty acid tail

Question 10

What forms when phospholipids are mixed/shaken with water

Answer 10

• Micelle
• Phospholipid bilayer

Question 11

Name the features of a cell membrane

Answer 11

• Phospholipid bilayer
• Intrinsic proteins (protein channels, carrier proteins)
• Extrinsic proteins
• Glycoproteins
• Glycolipids
• Cholesterol

Question 12

What are intrinsic proteins

Answer 12

Proteins that are fully embedded in the membrane from one side to the other

Question 13

How are intrinsic proteins adapted to carry out their functions

Answer 13

• They have hydrophobic amino acids on the outside which interacts with the hydrophobic fatty acid ails in the phospholipid bilayer

Question 14

What are extrinsic proteins

Answer 14

Proteins found on one side of the membrane proteins

Question 15

Can extrinsic proteins attach to intrinsic proteins

Answer 15

Yes

Question 16

State the role of extrinsic proteins

Answer 16

• Act as receptors for other molecules - allowing the cell to detect chemicals released from other cells so they can respond (e.g hormones)
• Structural role

Question 17

What are glycoproteins

Answer 17

Proteins with a carbohydrate attached

Question 18

State the functions of a glycoprotein

Answer 18

• They can allow cells to attach to each other to form tissue
• They can present antigens to T cells
• They can act as receptors for hormones

Question 19

What are glycolipids

Answer 19

Lipids with carbohydrate attached (carbohydrate attached to the phosphate head of the phospholipid bilayer)

Question 20

State the functions of a glyolipid

Answer 20

• They can acts as antigens
• They can be used when cells come in contact with each other - each recognising the glycolipid of another cell

Question 21

State what carrier proteins are and how they work

Answer 21

A transport protein that carries ions or molecules across the plasma membrane by changing shape after binding to it

Question 21

State what channel proteins are and how they work

Answer 21

A transport protein that acts like a pore in the plasma membrane letting small ions or water molecules through

Question 22

What is cholesterol

Answer 22

A lipid that slots between the phospholipid tail

Question 23

What is the function of cholesterol

Answer 23

• It binds to the hydrophobic tail of the phospholipid causing them to pack more closely together
• This restricts the movement of the phospholipid making the membrane more rigid

Question 24

Why is cholesterol beneficial to the plasma membrane

Answer 24

It helps to maintain the shape of animal cells (which don’t have cell walls)