Membrane transport

Question 1

How is the fluidity of membranes mainly determined?

Answer 1

By fatty acid composition on phospholipids.

Question 2

Describe molecules which can passively diffuse through a membrane?

Answer 2

Only small, non-polar molecules can passively diffuse.

Question 3

What are some effects of the blood brain barrier?

Answer 3

Keeps out toxins.
Allows in essential nutrients?
Prevents brain penetration of >98% of small compound drugs (nearly 100% of large molecule therapeutics).

Question 4

How do ionophores, ion channels and passive transporters affect transmembrane movement of solutes?

Answer 4

Speed up the movement of solutes down their electrochemical gradient.

Question 5

What is the function of primary active transporters compared to secondary?

Answer 5

Primary:
Can pump solutes against a gradient using ATP.
Secondary:
Use the energy of a second solute gradient.

Question 6

What do aquaporins allow?

Answer 6

Rapid water passage through membranes.

Question 7

What is the role of a K+ channel?

Answer 7

The passive transport of K+ ions along its electrochemical gradient

Question 8

What is the purpose of influx ABC transporters?

Answer 8

Used to transport amino acids and sugars through membranes.

Question 9

What is the purpose of efflux ABC transporters?

Answer 9

Have multi-drug pumps to drive out antibiotics and toxins.
Secrete enzymes such as proteases and lipids.

Question 10

What is the general structure of ABC transporters?

Answer 10

Four proteins:
Two hydrophobic proteins forming the membrane channel.
Two peripheral cytoplasmic proteins which have nucleotide binding domains (for binding ATP).

Question 11

What is the purpose of solute binding proteins in relation to ABC transporters?

Answer 11

They direct solutes to periplasmic phase of the transporter.

Question 12

How is an ABC transporter affected by solutes in the periplasmic phase?

Answer 12

The solute triggers structural change in the channel protein.
This is telegraphed to the ATP binding sites on nucleotide binding proteins.

Question 13

How do the nucleotide binding proteins react to structural change of its channel protein in ABC transporters?

Answer 13

The nucleotide binding proteins hydrolyse ATP and send another conformal change through the channel protein.
Opening the cytoplasmic side of the protein channel, allowing solutes through.
Afterwards ATP and Pi are released and the transporter returns to resting state.

Question 14

What are the three classes of transporters (briefly explain each)?

Answer 14

Uniport:
Moves a single solute.
Cotransport (2 forms):
Symport - moves 2 solutes one way.
Antiport - moves one solute in, one out.

Question 15

Glucose transport, in erythrocytes, uses a uniporter (GLUT1). Which two conformations can GLUT 1 be found (briefly explain each)?

Answer 15

T1 - Glucose binding site exposed on outer surface of plasma membrane.
T2 - binding site exposed on inner surface.

Question 16

Glucose importing in myocytes uses GLUT4, what is GLUT 4?

Answer 16

An insulin regulated glucose transporter.

Question 17

How is GLUT4 (glucose importer for myocytes) affected by type 1 diabetes mellitus?

Answer 17

GLUT 4 is insulin regulated.
No release of insulin means no mobilisation of GLUT 4 transporter.
Low rates of glucose uptake to muscle and adipose tissue occurs.

Question 18

What is a first messenger and what does it do?

Answer 18

An extracellular signalling molecule.
Binds to cell surface receptors which activates intracellular signalling pathways.

Question 19

What is the relation between first and second messengers?

Answer 19

second messenger molecules are released by cells in response to exposure to first messengers.

Question 20

What is a second messenger and what does it do?

Answer 20

A non-protein intracellular signalling molecule.
Relays extracellular signals, received at cell receptors, to target molecules within the cytosol.

Question 21

Which changes can extracellular signals cause in relation to cell composition and function (3 things)?

Answer 21

Differentiation and antibody production.
Growth in size or strength.
Sexual vs asexual cell division.

Question 22

Define a receptor?

Answer 22

A membrane-bound or soluble protein or protein complex.
Which exerts a physiological effect (intrinsic effect) after binding to its natural ligand.

Question 23

Why are G-protein coupled receptors major drug targets?

Answer 23

They are implicated in many common human diseases such as:
Allergies.
Depression.
Blindness.
Diabetes.
Various cardiovascular defects.

Question 24

G-protein coupled receptors are integral membrane proteins, what are some roles they have?

Answer 24

Detect:
Hormones.
Neurotransmitters.
Ions.
Light.
Odours.
Flavours.
and transmit signals across the cell membrane (this changes cell behaviour).

Question 25

Calcium is used as a secondary messenger, What is its resting concentration and concentration when signalling?

Answer 25

Resting:
10-100 nM.
Signalling:
500-1000 nM.

Question 26

What are the effects of calcium ions being released on a regular cell? (not neuron specific)(protein based)

Answer 26

Ca2+ binds to (and activates) calmodulin.

Calmodulin may activate calcium-calmodulin-dependent protein kinases.
OR
May act directly on other effector proteins.

Question 27

Name some physiological roles of calcium ions (7)?

Answer 27

Muscle contraction.
Neuronal transmission.
Cellular mobility.
Fertilization.
Cell growth/proliferation.
Learning/memory.
Secretion of saliva.

Question 28

Name some biochemical roles of calcium ions (3)?

Answer 28

Regulates enzyme activity.
Permeability of ion channels.
Activity of ion pumps.

Question 29

Name some effects of dysregulation of calcium signalling (4)?

Answer 29

Cardiovascular + neurological defects.
Metabolic disorders.
Muscular diseases.
Cancer.

Question 30

Membranes are electrically polarized, what is the internal resting potential of a cell?

Answer 30

-50mV to -70mV

Question 31

How is membrane potential established?

Answer 31

Na+K+ ATPase establishes membrane potential by moving 3 Na+ out and 2 K+ in (using ATP).

Question 32

What is the role of gated ion channels and which 2 stimuli do they respond to?

Answer 32

Role:
To regulate transport of ions across membranes.
Stimuli:
Changes in membrane potential.
Ligands binding to specific receptor sites.