Lecture 3

Question 1

What are 4 solutions adopted by membranes to increase diffusional permeability of many vital biological solutes?

Answer 1

Increase area (A) Lower thickness (x) Increase concentration gradient through regulation of cell metabolism (Δcm) Increase diffusion coefficient (D) by altering membrane composition or introducing a pore.

Question 2

What are the two types of possible pores?

Answer 2

Water filled channels or facilitative transporter.

Question 3

What are 4 important channels characteristics?

Answer 3

Solute flux Substrate specific Saturable Specific inhibitor/inactivators

Question 4

List the two properties of gated channels:

Answer 4

Large and fast solute flux when open (10°7-10°8 ions per second) Selectivity depends on size and charge of hydrated ion

Question 5

List the two properties of transporters:

Answer 5

Relatively small / slow solute flux ​(10°2-10°4) Selectivity related to molecular interaction between solute “substrate” and binding-site on carrier protein

Question 6

What are the two types of antiport?

Answer 6

Homoexchance and Heteroexchange

Question 7

What are the two cis effects that affects transporter kinetic?

Answer 7

Saturability: substrate molecules competer for transporter binding sites. Stereospecificity: certain stereoisomers are better fit to binding sites.

Question 8

What are the two trans effects that affect transporter kinetic?

Answer 8

Exchange diffusion: trans-substrate accellerate exchange Countertransport: trans-accelleration by a different substrate in heteroexchange.

Question 9

Describe competitive inhibitors and their effects on transporter kinematics:

Answer 9

Competitive inhibitor binds to the enzyme active site preventing the molecules to bind, consequently Km increases but Vmax remains unchanged.

Question 10

Describe non-competitive inhibitors and their effects on transporter kinematics:

Answer 10

Non-competitive inhibitors binds to another allosteric site of the enzyme, consequently Vmax decreases but Km remains unchanged.

Question 11

What are the characteristics of transport in real cells

Answer 11

-Multiple transport components -Nature of dependence of any ‘co-substrate’ -Binding of multiple substrate may be ordered -Diffusional component of flux

Question 12

Describe the three features of endocytosis:

Answer 12

-May involve saturable receptors binding -Transmembrane movement -No trans effect

Question 13

What is the problem of plasma membrane in respect to inorganic ions, sugars and amino acids?

Answer 13

Cell membrane have low diffusional permeability to many vital biological solutes such as inorganic ions, sugars and amino acids.

Question 14

Describe the SLC (solute carrier) gene superfamily:

Answer 14

It includes 43 families and 298 transporter genes.

Question 15

How are transporters also termed?

Answer 15

Carriers or permeases

Question 16

What do pumps represent?

Answer 16

A special type of transporter

Question 17

What is the peculiarity of substrate-loaded transporter?

Answer 17

It changes conformation quicker.

Question 18

List the values in the michaelis mente equation

Answer 18

v= velocity of reaction (rate of transport, flux) [S]= substrate concentration on cis face of the membrane Vmax= maximum velocity (mol/min), all binding sites are occupied Km= Michaelis constant (mol/l), where 50% of the sites are occupied.

Question 19

What does the relationship given by the MM equation represent if plotted?

Answer 19

This relationship gives a single rectangular hyperbola.