Module 1 Lecture 4: Plasma Membrane

Question 1

What is the plasma membrane also called?

Answer 1

Cell membrane

Question 2

What does the plasma membrane separate the cell into?

Answer 2

Separates the extracellular and intracellular compartments/fluids

Question 3

What is the plasma membrane composed of?

Answer 3

Mainly thin lipid bilayer with proteins and lipids (some carbohydrates)

Question 4

How is the membrane a bilayer? What does that look like?

Answer 4

Two polar heads on each side facing the intracellular and extracellular side; tails face each other away from the water

Question 5

Why are phospholipids so unique?

Answer 5

They have a polar head and non-polar tail

Question 6

What is special about the polar head of the phospholipid?

Answer 6

Choline and **phosphate group along with glycerol backbone = polar and charged => **hydrophilic

Question 7

What is special about the tail of the phospholipid?

Answer 7

Made of aliphatic hydrocarbons = non-polar, uncharged => Hydrophobic

Question 8

How does the membrane have an active role in determining the composition of the cell?

Answer 8

Because it selectively permits the movement of various molecules (ions, nutrients, secretory and waste products)

Question 9

What is the plasma membrane other than a physical barrier?

Answer 9

It controls movement of molecules in and out of the cell

Question 10

Cell to cell communication and cell to environment communication is a role of?

Answer 10

Plasma membrane

Question 11

Where is cholesterol found with respect to the plasma membrane?

Answer 11

Anchored within hydrophobic part of the membrane

Question 12

Why is the plasma membrane both fluid and rigid?

Answer 12

It’s fluid so that it allows for the passage of the molecules but it’s rigid so that a cell doesn’t fall apart entirely

Question 13

How are the phospholipids in the bilayer adding fluidity?

Answer 13

They are constantly twirling, spinning and vibrating; moving around and exchanging places with other phospholipids

Question 14

How can you tell if a cell is dying?

Answer 14

1) If it lets anything through
2) If there’s a lot of phospholipid exchange going on within the membrane

Question 15

What does cholesterol contribute to the plasma membrane?

Answer 15

Contributes to fluidity and stability of the membrane

Question 16

What are proteins in the plasma membrane similar to? and why?

Answer 16

Proteins are like icebergs in a “sea” of lipids; they float on the plasma membrane and move along the membrane

Question 17

Are proteins anchored to the cell?

Answer 17

Not unless something is holding it in place

Question 18

Do proteins span the membrane?

Answer 18

Some proteins span the membrane going from the intracellular fluid to the extracellular fluid - helps with shuttling molecules in and out.

Question 19

Structural characteristics of channel proteins?

Answer 19

Very narrow; only allows one molecule to go at a time - needs to fit criteria to go through

Question 20

How was the Fluid Mosaic Model given its name?

Answer 20

Fluid because it is not rigid & Mosaic because there’s a bunch of things floating around spanning the membrane

Question 21

Some proteins have sugar molecules called glycolipids and glycoproteins? What role do they play?

Answer 21

They play a role in the function, stability and shape of those proteins and lipids; overall acting as self-recognition molecules for cell to cell interactions

Question 22

How many more lipid molecules are there compared to protein molecules?

Answer 22

50x more lipid molecules than protein molecules

Question 23

What molecule accounts for most of the weight of the membrane?

Answer 23

Proteins account for half the mass; much larger than lipids

Question 24

How do channel proteins work?

Answer 24

They fit small enough water-soluble molecules, such as small ions

Question 25

Would charged ions be able to pass through the lipid bilayer without the channel proteins?

Answer 25

No; they would get repelled by the hydrocarbons

Question 26

How can you have a channel protein where some of it interacts with the non-polar tails and then the other interact with the fluid?

Answer 26

Some proteins are hydrophobic and hydrophilic; the channel protein or protein that transports molecules is made and arranged in the membrane based on those characteristics

Question 27

What are carrier molecules?

Answer 27

Another type of membrane protein; transfers larger specific substances - i.e. glucose

Question 28

What are docking-marker acceptors

Answer 28

Membrane protein; specific to secretory vesicles and exocytosis process; accepts and binds the vesicles (lock and key process)

Question 29

How do the secretory vesicles interact with the docking-marker acceptors?

Answer 29

Fuses to the protein and releases the contents

Question 30

What are membrane-bound enzymes?

Answer 30

Membrane protein; important for signalling

Question 31

What are receptors?

Answer 31

Membrane protein; span the membrane - go in and out the cell; recognize and bind with molecules in the environment

Question 32

What are cell adhesion molecules?

Answer 32

Membrane protein; important for cell adhesion so that the cell is apart of the tissue - doesn’t wander off

Question 33

What are peripheral proteins?

Answer 33

Do not cross the entire membrane; either on intracellular or extracellular

Question 34

What do peripheral proteins do?

Answer 34

They act like enzymes and sends signals or act like a scaffold (connecting two proteins together)