Transport mechanisms

Question 1

To which molecules is the cell membrane highly permeable to?

Answer 1

H20
Lipid-soluble substances
Dissolved gases (O2,CO2)
Small uncharged molecules

Question 2

To which molecules is the cell membrane less permeable to?

Answer 2

Larger molecules
Charged particles

Question 3

To which molecules is the cell membrane impermeable to?

Answer 3

Very large molecules

Question 4

where does the hydrophilic head point toward

Answer 4

outward ( toward the extracellular fluid and the cytoplasm)

Question 5

where does the hydrophobic tails point toward

Answer 5

inward (towards one another)

Question 6

What is the function of cholesterol in the phospholipid bilayer?

Answer 6

It reduces the packing of fatty acid tails and increase the membrane fluidity by keeping fatty acid tails apart

Question 7

Which proteins of the cell membrane correspond to this description:

Closely associated with phospholipids, mostly cross the membrane (transmembrane amphipathic) , hard to isolate

Answer 7

Integralproteins

Question 8

Which proteins of the cell membrane correspond to this description:

More loosely associated, mostly on the cytoplasmic side and easy to isolate

Answer 8

Peripheral proteins

Question 9

What is Glycocalyx and what does it do?

Answer 9

A layer of carbohydrates formed by a chain of monosaccharides that extend from the extracellular surface of the cell membrane bound to proteins .

It provides protection from infection and enable cells to identify each other and interact

Question 10

What are the passive transport mechanisms?

Answer 10

They are energy independent

Diffusion, Carrier-mediated facilitated diffusion and osmosis

Question 11

What are the active transport mechanisms?

Answer 11

They are energy dependent

Carrier-mediated active transport ( primary and secondary), Pino/Phagocytosis

Question 12

How do we calculate the rate of diffusion?

Answer 12

Using Fick’s law of diffusion

J=PA (C0-Ci)

J= Net flux, P= Permeability coefficient , A= Surface area of the membrane, (C0-Ci)= concentration gradient of the diffusing molecule

Question 13

What factors affect diffusion across the cell membrane?

Answer 13

1. Mass of the molecule
2. Concentration gradient across the cell membrane
3. Lipid Solubility
4. Electrical charge
5. Availability of selective ion channels or membrane carriers

Question 14

What is an Electrochemical gradient?

Answer 14

It is the simultaneous existence of an electrical and a concentration gradient for a particular ion

Question 15

What are the 3 ways that Ion Channels can be gated (undergo s conformational changes)?

Answer 15

a. Ligand-gated
b. Voltage-gated
c. Mechanically-gated

Question 16

What are the characteristics of Mediated-Transport Systems ?

Answer 16

a. Specificity – system usually transports one particular type of molecule only
b. Saturation – rate of transport reaches a maximum when all binding sites on all transporters are occupied. Thus, a limit – the transport maximum (Tm) – exists for a given substance across a given membrane
c. Competition – occurs when structurally similar substances compete for the same binding site on a membrane carrier

Question 17

What is cotransport/symport?

Answer 17

When a solute X is transported in the same direction as Na+

Question 18

What is counter transport/Antiport ?

Answer 18

When solute X is transported in the opposite direction to Na+

Question 19

What type of exocytosis is this: Not regulated, functions to replace plasma membrane, deliver membrane proteins to the cell membrane and to get rid of substances from cell?

Answer 19

Constitutive Exocytosis

Question 20

What type of exocytosis is this: Tend to be triggered by extracellular signals and the increase of cytosolic Ca2+. Responsible for the secretion of hormones, digestive enzymes, and neurotransmitters ?

Answer 20

Regulated Exocytosis

Question 21

How does water diffuse freely across most cell membranes?

Answer 21

By using groups of proteins called aquaporins that form water permeable channels

Question 22

What is the Osmotic pressure?

Answer 22

The pressure required to prevent the movement of water across a semi-permeable membrane. It is proportional to the number of particles in solution/unit volume.

Using Van’t Hoff equation for osmotic pressure