Unit 1: Lipids and Membranes

Question 1

What are the main functions of cell membranes (5) ?

Answer 1

• Form a barrier against pathogens
• Be physically separated from external environment
• Take in nutrients, minerals and ions
• Excrete waste products from the cell
• Receive and act on signals from outside and send signals to other cells

Question 2

What are the components of the bilayer (3) ?

Answer 2

• Lipids
• Proteins
• Carbohydrates

Question 3

What is the job of lipids in the bilayer ?

Answer 3

They are responsible for forming the basic structure that seals each cell from its external environment

Question 4

What are lipids made up from ?

Answer 4

Phospholipids and cholesterol

Question 5

What is the job of proteins in the bilayer ?

Answer 5

They are responsible for communication with the external environment

Question 6

How do proteins communicate with their environments ?

Answer 6

By compromising receptors, channels and pumps

Question 7

What is the most abundant membrane lipid ?

Answer 7

Phospholipids

Question 8

What is the main phospholipid ?

Answer 8

Phosphoglycerides

Question 9

What are the components of a phospholipid ?

Answer 9

Head - Phosphate and glycerol
Tail- Two long chain fatty acid tails

Question 10

What are the 4 main phospholipids present in the plasma membrane ?

Answer 10

• Phosphatidylcholine
• Phosphatidylethanolamine
• Phosphatidylserine
• Sphingomyelin

Question 11

What phospholipids are present in the outer membrane ?

Answer 11

Phosphatidylcholine & Sphingomyelin

Question 12

What phospholipids are present in the inner membrane ?

Answer 12

Phosphatidylethanolamine & Phosphatidylserine
& Phosphatidylinositol (an important cell signallng molecule)

Question 13

What does fluidity of the plasma membrane depend on ?

Answer 13

• Temperature
• Composition of fatty acid tails

Question 14

What is the job of cholesterol in lipid bilayers ?

Answer 14

To provide structure and rigidity

Question 15

How can cholesterol influence membrane fluidity at cold temps ?

Answer 15

At cold temperatures cholesterol prevents phospholipids packing together and maintains fluidity

Question 16

What is a lipid raft ?

Answer 16

Lipids that are restricted within specialised membrane micro domains

Question 17

What are the components of a lipid raft ?

Answer 17

• Cholesterol
• Sphingomylein
• Glycolipids

Question 18

How do lipid rafts move within the membrane ?

Answer 18

Laterally (side to side)

Question 19

What are the functions of membrane proteins (5)?

Answer 19

• Transport specific molecules
• Provide channels for ion passage
• Receptors for external cues (chemical, physical)
• Structural links to other cells
• Enzyme activity

Question 20

Are carbohydrates found on the interior or exterior side of the membrane ?

Answer 20

Exterior

Question 21

What are the 2 types of protein- carbohydrate molecules ?

Answer 21

• Glycoproteins
• Proteoglycans

Question 22

Carbohydrate chains that form a net around cells are known as what ?

Answer 22

The glycocalyx

Question 23

What is endocytosis ?

Answer 23

Mechanism by which cells internalise substances from the external environment

Question 24

Give 3 reasons why endocytosis is important

Answer 24

• Nutrient uptake
• Entry of pathogens
• Phagocytosis

Question 25

What is Clathrin-mediated endocytosis ?

Answer 25

The major endocytic pathway in mammalian cells

Question 26

What are the 6 steps of Clathrin mediated endocytosis ?

Answer 26

1) Macromolecules bind to specific cell surface receptors e.g. Low-density lipoprotein binds to LDL receptor 2) Receptors cluster and recruit clathrin which builds a coat around the membrane forming a clathrin-coated pit 3)An actin network forms around clathrin and helps bend membrane inward 4) The neck of mature pits is cleaved from the membrane by dynamin to form small clathrin-coated vesicles containing receptors and bound cargo 5) Vesicles fuse with early endosomes for sorting of cargo 6) Clathrin is recycled back to membrane

Question 27

Give one type of lipid raft

Answer 27

Caveolae

Question 28

What are extracellular vesicles ?

Answer 28

Nano sized lipid bilayer decimated particles that are released from almost all cells

Question 29

Give 3 examples of extracellular vesicles

Answer 29

- Exosomes - Microvesicles - Apoptotic bodies

Question 30

Where can extracellular vesicles be found ?

Answer 30

In plasma, urine, breast milk and saliva

Question 31

What is neurotransmission an example of ?

Answer 31

Exocytosis

Question 32

What is a SNARE complex ?

Answer 32

SNARE complexes mediate the docking of vesicles across a synapse

Question 33

Where is a V-SNARE located ?

Answer 33

Attached to the vesicle

Question 34

Where is a T-SNARE located ?

Answer 34

On the target membrane

Question 34

Neurotoxins cleave SNARE proteins, what does this mean ?

Answer 34

Prevents vesicles docking with the membrane

Question 35

What does PLA stand for ?

Answer 35

Phospholipases

Question 36

What does PLA do ?

Answer 36

Hydrolyses phospholipids- cleave (separate) fatty acid tails from glycerol backbone