W5 Plasma membranes

Question 1

What does a cell membrane do?

Answer 1

It is a boundary that separates the cell from its surroundings.
A barrier to prevent the contents of the cell from escaping and mixing with the surrounding environment

Question 2

How are lipids arranged in a cell membrane?

Answer 2

A bilayer (of phospholipids)
(two-layer sheets)

Question 3

Phospholipids are amphipathic. What does this mean?

Answer 3

They contain hydrophobic and hydrophilic regions
Hydrophobic Fatty acid tail
Hydrophilic Phosphate head

Question 4

What is the fluid mosaic model?

Answer 4

It is a dynamic and complex structure of the plasma membrane
Fluid= viscosity of lipid bilayer
Mosaic=Besides phospholipids, Glycolipids, sterols (cholesterol
in mammalian cells) and various proteins and glycoproteins are contained

Question 5

Phospholipids can lead to..

Answer 5

Rapid lateral diffusion
Spin in place
Flexion (contraction movement)

Question 6

What does cholesterol do?

Answer 6

Modulates the membrane fluidity and improves its stability. Stiffens the membrane, reducing molecules passage
Maintains rigidity

Question 7

What are glycolipids

Answer 7

Lipids containing sugars representing their hydrophilic head

Question 8

Are cholesterol and Glycolipids amphipathic?

Answer 8

YES

Question 9

Where are membrane proteins synthesised?

Answer 9

Rough ER

Question 10

What are the functions of membrane proteins?

Answer 10

Transport of molecules
Enzymatic activity
Cell communication
Structural support

Question 11

What are glycoproteins?

Answer 11

Short chains of sugars linked to amino acids/protein

Question 12

What is passive transport?

Answer 12

Movement of molecules or ions across membranes without energy expenditure
Movement DOWN the concentration (or electrical) gradient
Movement from areas with high concentrations to a low concentration of the molecule, with the aim to reach an equilibrium

Question 13

What are the 3 types of passive transport?

Answer 13

Simple diffusion, Osmosis, Facilitated diffusion

Question 14

What is diffusion?

Answer 14

FREE movement of molecules across the lipid bilayer
* No energy (ATP) cost (passive)
* Down their gradient concentrations (until an
equilibrium is reached)

Question 15

Which molecules can diffuse through the membrane?

Answer 15

Gases e.g. O2 and CO2
Small, uncharged polar molecules e.g. Urea and Ethanol

Question 16

What is osmosis?

Answer 16

The spontaneous movement
(passive transport) of water/solvent across a
semipermeable membrane from a solution with higher water potential (lower solute concentration) to a solution with lower water potential (higher solute concentration)

• Water potential of a solution is inversely proportional to the solutes concentration

Question 17

What is osmotic pressure?

Answer 17

Hydrostatic pressure required to stop the net Flow of water across a membrane separating solution of different water potentials

Question 18

What is an:
isotonic solution
hypertonic solution
hypotonic solution

Answer 18

Isotonic Solution – a solution with the same concentration of solutes both inside and outside the cell.
Hypertonic Solution – a solution that has a higher solute concentration (water moves out)
outside the cell than inside.
Hypotonic Solution – a solution that has a higher solute concentration inside the cell than outside (water moves in)

Question 19

What is facilitated diffusion

Answer 19

The passive movement of molecules down a
concentration gradient (or electric potential) via a
transport protein (transmembrane proteins):
Protein channel (ions or water)
Protein carrier/transporters (of specific small
molecules or ions)
* Highly specific (glucose vs. fructose)
* Reversible
* No energy (ATP) cost

Question 20

Symporters and anti porters are associated with..?

Answer 20

Active transport

Question 21

What are protein channels?

Answer 21

• Channels (pore membrane forming) form a hydrophilic
  “tube” across the membrane through which specific
  molecules/ions diffuse (down a concentration gradient)
• Do not interact with the molecules, although specific
• Move at a very rapid rate
• Passive transport (no energy cost)

Question 22

What are symporters and antiporters?

Answer 22

Symporters moving 2 different molecules across the cell membrane (same direction)
Antiporter moving 2 distinct molecules across the membrane (opposite directions)
E.g. Na+-K+ pump uses the energy of one ATP to pump 3 Na+ out and 2 K+ in.

Question 23

What is active transport?

Answer 23

• Moves substances against their concentration or electrochemical gradients
• Requires energy, usually in the form of ATP
• Performed by specific proteins embedded in the membranes
• Allows for stockpiling

Question 24

What are the 2 types of bulk transport?

Answer 24

Exocytosis and Endocytosis.

Question 25

What happens during exocytosis?

Answer 25

• Secretion or excretion (from inside
  to outside) e.g. insulin (protein hormone) by
  pancreatic cells
• Transport vesicles (from Golgi) migrate to
  the plasma membrane, fuse with it, and
  release their contents

Question 26

What happened during endocytosis?

Answer 26

Uptake (from outside to inside) of macromolecules and large particles
*Invagination of the cell surface to form an intracellular membrane-bounded vesicle
containing extracellular fluid

Question 27

What are the 3 types of endocytosis?

Answer 27

Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

Question 29

What is an inactive enzyme called in the absence of its essential cofactor?

Answer 29

Apoenzyme