The Plasma Membrane

Question 1

What is the biologic membrane composed of?

Answer 1

Lipids and proteins

Question 2

What type of lipids are found in the membrane?

Answer 2

1. Phospholipids
2. Glycolipids
3. Cholesterol

Question 3

What are two choline-containing phospholipids that are abundant in cell membranes?

Answer 3

1. Phosphatidylcholine (Lecithin)

2. Sphingomyelin

Question 4

What are two amine phospholipids present in some cell membranes?

Answer 4

1. Phosphatidylethanolamine (Kephalin)

2. Phosphatidylserine

Question 5

What is phosphatidylinositol (a type of phospholipid) important for, in the cell?

Answer 5

Cell to cell signaling

Question 6

Where in the plasma membrane is glycolipids present and what is their function?

Answer 6

Found in the outer layer of the bilayer.
Participate in the formation of the glycocalyx.
(Has sugar residues)

Question 7

Where in the plasma membrane is cholesterol present and what is their function?

Answer 7

Between phospholipid tails.

Increase the stability and rigidity of the cell membranes.

Question 8

What are the two classes of membrane transporting proteins?

Answer 8

Peripheral and transmembrane (integral).

Question 9

What does peripheral proteins bind to?

Answer 9

Phospholipids or transmembrane proteins.

Question 10

What are the two classes of transmembrane proteins?

Answer 10

Single-pass proteins

Multi-pass proteins

Question 11

What protein classifications can we find in/at the cell membrane?

Answer 11

Transporters, linkers, receptors, enzymes. (One protein can perform more than one function)

Question 12

What can freely diffuse through the plasma membrane?

Answer 12

Gasses and hydrophobic molecules. (Hydrophilic molecules are transported across via specific transport proteins)

Question 13

Give 3 examples of Ion channels.

Answer 13

1. Sodium channels
2. Calcium Channels
3. Proton (hydrogen) Channels

Question 14

How does ions get transported passively across the membrane?

Answer 14

Via ion channels acording to concentration gradient.

Question 15

What are the different types of channels?

Answer 15

1. Voltage-gated channels (open due to electrical potential change) Ex: Nerve cells.
2. Ligand-gated (open due to signaling molecule) Ex: Postsynaptic membrane.
3. Mechanically-gated channels (stress-activated) Ex: Inner ear, striated muscle cells.

(Some channels are constantly open. Withdrawed and inserted into membrane when needed) Ex: Potassium leak channel, water channels (aquaporins).

Question 16

In what structures are aquaporins(water channels) especially important?

Answer 16

Renal tubules. Responsible for the final concentration of urine.

Question 17

What does carrier proteins do?

Answer 17

Transports small molecules passively according to the concentration gradient. Changes conformation. No energy required.

Question 18

How does pump proteins work?

Answer 18

Transports molecules across the plasma membrane by changing conformation. Use ATP to pump against the concentration gradient.

Ex:
Sodium potassium pump.
Calcium pump.
Proton pump.

Question 19

Define antiport, symport and uniport. (Carriers and pumps)

Answer 19

Antiport: Transports molecules in different directions.
Symport: Transports more than one molecule in the same direction simultaneously.
Uniport: Transports only one molecule in any direction.

Question 20

What is the function of translocons?

Answer 20

Allow for large proteins to cross the membrane.

Question 21

What does the abbreviation ABC transporters stand for?

Answer 21

ATP-binding cassette transporters.

Transports large molecules across membranes: drugs and peptides

Question 22

What is meant by the term membrane trafficking?

Answer 22

All the pathways of vesicular transport.

Question 23

What is vesicular transport?

Answer 23

The predominant mechanism for transport of large molecules like lipids and peptides across the membrane.

Question 24

What are the steps of the anterograde pathway?

Answer 24

ER –> Golgi –> Cell Membrane

Question 25

What are the steps of the retrograde pathway`?

Answer 25

Cell Membrane –> Endosomes –> Lysosomes

Question 26

How thick is the cell membrane?

Answer 26

7.5 nm (trilaminar structure in microscope)

Question 27

What is the outer sugar coat of the cell membrane called? And what is its function?

Answer 27

Glycocalyx.

Strands of proteins and sugars bound together. Up to 50 nm thick. Cell recognition, endocytosis, protects cells, aids in attachment of cells to matric components.

Question 28

What are 4 adhesion molecules?

Answer 28

1. Cadherins - cell to cell (same type cell).
2. Selectins - cell to cell (different type cell)
3. Immunoglobulin superfamily - cell to cell adhesion (different type cell)
4. Integrins - cell to extracellular matrix adhesion. Some times cell to cell (same type).

Question 29

What is lipid rafts?

Answer 29

Subdomains of the membrane that contains high amounts of cholesterol and glycolipids.

Question 30

What is Caveolae?

Answer 30

Formed by attachment of protein caveolin and are invagination in the membrane. It contains receptors and transporters (transports Ca2+). Participate in pinocytosis.

Question 31

What are coated pits?

Answer 31

Surrounded by protein clathrin. Participate in receptor-mediated endocytosis.

Question 32

What is meant by saying that the phospholipid bilayer is asymmetric?

Answer 32

The phospholipid bilayer is asymmetric because there is an unsymmetric distribution of phospholipids in the bilayer.

Question 33

What is spectrin?

Answer 33

Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane.

Question 34

How does the cell membrane grow?

Answer 34

The cell membrane grows only by the incorporation of new components. It cannot be produced de novo.

Question 35

The membranes of which organelles does NOT participate in membrane trafficking?

Answer 35

The membranes of mitochondria and peroxisomes do not participate in membrane trafficking.