forces acting across membranes

Question 1

what are the water-filled channels called in the cell membrane? What’s their role?

Answer 1

aquaporin - allows water to move freely between the two compartments ICF AND ECF

Question 2

describe the movement of gases, nutrients and ions :

Answer 2

Gases can pass freely between all compartments.

Nutrients and waste also pass easily but require assistance crossing the cell membrane.

Ions pass freely across the capillary wall to exchange readily between Plasma and ISF, but they do not penetrate the cell membrane.

Question 3

What would happen if ions like Na+ and Cl- could pass through the cell membrane readily in an unregulated manner?

Answer 3

It would disrupt the concentration gradients and cause nerve and muscle functions to go wrong, leading to serious illnesses.

Question 4

Describe the distribution of solutes (Na+, K+, Cl-, HCO3-, Proteins) in Plasma and Interstitial fluid, and Intracellular fluid.

Answer 4

plasma and ISF are identical in everything except plasma protein concentration

Question 5

why are membranes very flexible?

Answer 5

because of the fatty acids composing them, they behave like an oil.

Question 6

why are membranes excellent insulators?

Answer 6

They prevent the passage of electrons and are good insulators against the movement of electrical charge.

Question 7

what are the proteins and phospholipids that are associated with carbohydrates in the membrane called?

Answer 7

glycoproteins and glycolipids

Question 8

what do glycoproteins d?

Answer 8

they have a carbonhydrate molecule attached that act as markers that tell the immune system whether a cell is one of our own or a foreign cell.

Question 9

what are integral proteins?

Answer 9

penetrates the hydrophobic core of the lipid bilayer

allow movement of ions and large molecules since they can’t directly diffuse through the membrane.

Question 10

what are peripheral proteins?

Answer 10

only associated with the hydrophilic phosphate head of the lipid bilayer and do not penetrate the hydrophobic core.

relay a signal between receptor and effector

Question 11

what are membrane receptors?

Answer 11

integral proteins that allow communication of an extracellular signal (Ligand) e.g. neurotransmitter or hormone, to the intracellular space to create a cellular response.

When a Ligand binds to a Membrane Receptor it causes a conformational change in that protein which is transmitted to the intracellular compartment to create a response.

Question 12

give an example of membrane receptors (insulin):

Answer 12

when insulin binds to its receptor it generates a signal that tells the cell to insert glucose transporters in the cell membrane to uptake glucose.

Question 13

what receptors are present inside cells called?

Answer 13

Some receptors are present inside cells, they are called Intracellular Receptors.

Question 14

what are membrane transporters?

Answer 14

integral proteins that allow movement of ions or molecules across the membrane.

Question 15

what are 2 types of membrane transporters?

Answer 15

Channel Proteins - are transporter proteins that create a pore through the membrane so that molecules, such as water and ions, can flow through.

They can be either open (for water - Aquaporins) or gated (for ions)

Carrier Proteins - are transporter proteins that never create a continuous pore that spans from ECF to ICF, rather they open to a single side andthen switch to the other.

They typically move larger molecules e.g. glucose

Question 16

what are membrane enzymes?

Answer 16

they catalyze chemical reactions on the cell membrane.

Question 17

what 2 sides of the membrane can the membrane enzymes be on?

Answer 17

They can be either on the external side of the membrane.

e.g. Membrane enzymes found in the small intestine which break down nutrients into smaller units to aid digestion.

Or the internal side of the membrane.

e.g. Membrane enzymes that convert signals carried from receptors into an intracellular response.

Question 18

what are structural proteins?

Answer 18

they anchor the cell membrane to the intracellular skeleton, the extracellular matrix (collagen)…

Question 19

what are g proteins?

Answer 19

they are peripheral proteins that relay a signal along the membrane from an integral receptor protein to an integral enzyme protein.

Question 20

Give an example of a debility caused by a lack of structural protein.

Answer 20

Lack of dystrophin protein causes Duchenne’s Muscular Dystrophy

Question 21

why is Myelin ideal for function as an insulator around myelinated nerve fibres?

Answer 21

it has a low content of protein at 18% and a high content of lipids.

Question 22

what is the protein content of plasma membranes and membranes involved in other reactions?

Answer 22

Plasma membranes have much greater activity and protein content is typically around 50%

Membranes involved in energy transduction e.g. the inner membranes of mitochondria, have the highest protein content, around 75%

The more function/activity a membrane does, the more protein content it has.

Question 23

what is an electrochemical gradient?

Answer 23

it’s the net effect of two forces:

The electrical gradient - a difference in charge across a membrane.

The chemical gradient - a difference in solute concentration across a membrane.

Question 24

what are the 4 mechanisms of movement across membranes?

Answer 24

Diffusion, which is either:

Passive diffusion - directly through the lipid bilayer.

Facilitated diffusion requires assistance via either:
i) protein channels
ii) protein carriers ‘transporters’

Active Transport requires energy because it moves against the electrochemical gradient.

Osmosis describes the diffusion of water.

Filtration describes movement between Plasma and ISF.

Question 25

what’s the difference between endocytosis and exocytosis?

Answer 25

Endocytosis

• Invagination of the cell membrane to form a vesicle which disintegrates on the cytoplasmic surface of the membrane, releasing contents into the ICF.

Exocytosis

• Membrane-bound vesicles are carried to the cell membrane, and their contents are secreted into the ECF.