Forces acting across membranes 2

Question 1

What are the 4 mechanisms of movement?

Answer 1

Osmosis, Active transport, Diffusion, Filtration

Question 2

Which mechanisms are passive?

Answer 2

Osmosis, Diffusion

Question 3

How do macromolecules diffuse across a cell?

Answer 3

Through transporters

Question 4

What are carrier-mediated transport proteins?

Answer 4

Another word for transporter proteins. Act as a valve for larger molecules, too big for carrier proteins. Change shape when a molecule passes through.

Question 5

Passive diffusion vs Facilitated diffusion

Answer 5

Passive involves gas. Lipophillic gasses (o2, n2,) pass faster than lipophobic ones (co2)

Question 6

What causes protein channels to open?

Answer 6

Chemical or electrical charge change

Question 7

How do voltage-gated channels work?

Answer 7

Open/close due to a change in the electrical gradient across a membrane

Question 8

Where are voltage-gated channels mostly found?

Answer 8

Muscle and nerve cells

Question 9

What is a ligand-gated channel?

Answer 9

These cause a conformational change in the channel protein when a chemical/hormone binds to a receptor on the membrane, opening or closing its gate accordingly.

Question 10

What factors drive ions to cross a membrane?

Answer 10

Electrical gradient and concentration gradient

Question 11

What is the electrochemical gradient?

Answer 11

The gradient for which ions will flow.

Question 12

What is electrochemical equilibrium?

Answer 12

When both electrical and chemical gradients are in balance. This ‘rarely’ happens

Question 13

What is active transport?

Answer 13

Uses ATP to drive movement of ions/molecules against a concentration gradient

Question 14

How does Na+K+ ATPase work

Answer 14

Pumps 3 Na+ out of the cell and 2 K+ in the cell. 40% of body’s resting energy is used for this process.

Question 15

What is an electrogenic pump

Answer 15

One which generates current by pushing ions across a membrane, leading to translocation of net charge

Question 16

How is osmotic equilibrium achieved?

Answer 16

Body has no barriers to water so conc. all over is equal, despite different volumed.

Question 17

How are osmosis and diffusion co-dependent?

Answer 17

Where we have diffusion, we always have osmosis (solute and water move in opposite directions). Where we have osmosis, we may or may not have diffusion (depending on permeability of membrane)

Question 18

Define Osmolarity

Answer 18

The conc. of a solution based on no. of solute particles per litre, in osmoles

Question 19

What is the osmolarity of normal human plasma?

Answer 19

285mOsmol/L (300 to remember)

Question 20

What does the volume of a cell depend on?

Answer 20

The number of non-penetrating particles on either side of a membrane

Question 21

Define Hypo-osmotic, Isosmotic and Hyperosmotic

Answer 21

Hypo - a cell containing fewer solute particles per litre of solution, relative to another cell. Iso - same no. of solute particles per litre between 2 cells. Hyper - opposite to hypo

Question 22

What is Tonicity?

Answer 22

The ability of an extra-cellular solution to move water into or out of a cell by osmosis. Takes into account relative solute conc. of solution and cell, and the cells permeability.

Question 23

What do the terms Hypertonic, Isotonic and Hypotonic refer to?

Answer 23

The state of a solution depending on how it affects the volume of a cell when places in said solution.

Question 24

Isosmotic vs Isotonic?

Answer 24

Isotonic solution - different osmotic pressure in and out a cell. Isotonic - 2 solutions have the same osmotic pressure.
Isotonic involves only non-pen particles, isosmotic involves pen and non-pen.
Isotonic tells us volume of solution, while Isosmotic tells only conc.

Question 25

What happens when you transfuse a patient with pure water?

Answer 25

Solutions in the body become hypotonic and cells increase in volume, eventually bursting. Can cause death

Question 26

What solution should we use to transfuse most patients?

Answer 26

0.9g 150mOsmol/L saline (NaCl). Contains 300 particles which is the same as our plasma’s normal mOsmol/L. It is isotonic.