Membrane transport Flashcards
How is the fluidity of membranes mainly determined?
By fatty acid composition on phospholipids.
Describe molecules which can passively diffuse through a membrane?
Only small, non-polar molecules can passively diffuse.
What are some effects of the blood brain barrier?
Keeps out toxins.
Allows in essential nutrients?
Prevents brain penetration of >98% of small compound drugs (nearly 100% of large molecule therapeutics).
How do ionophores, ion channels and passive transporters affect transmembrane movement of solutes?
Speed up the movement of solutes down their electrochemical gradient.
What is the function of primary active transporters compared to secondary?
Primary:
Can pump solutes against a gradient using ATP.
Secondary:
Use the energy of a second solute gradient.
What do aquaporins allow?
Rapid water passage through membranes.
What is the role of a K+ channel?
The passive transport of K+ ions along its electrochemical gradient
What is the purpose of influx ABC transporters?
Used to transport amino acids and sugars through membranes.
What is the purpose of efflux ABC transporters?
Have multi-drug pumps to drive out antibiotics and toxins.
Secrete enzymes such as proteases and lipids.
What is the general structure of ABC transporters?
Four proteins:
Two hydrophobic proteins forming the membrane channel.
Two peripheral cytoplasmic proteins which have nucleotide binding domains (for binding ATP).
What is the purpose of solute binding proteins in relation to ABC transporters?
They direct solutes to periplasmic phase of the transporter.
How is an ABC transporter affected by solutes in the periplasmic phase?
The solute triggers structural change in the channel protein.
This is telegraphed to the ATP binding sites on nucleotide binding proteins.
How do the nucleotide binding proteins react to structural change of its channel protein in ABC transporters?
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.
What are the three classes of transporters (briefly explain each)?
Uniport:
Moves a single solute.
Cotransport (2 forms):
Symport - moves 2 solutes one way.
Antiport - moves one solute in, one out.
Glucose transport, in erythrocytes, uses a uniporter (GLUT1). Which two conformations can GLUT 1 be found (briefly explain each)?
T1 - Glucose binding site exposed on outer surface of plasma membrane.
T2 - binding site exposed on inner surface.
Glucose importing in myocytes uses GLUT4, what is GLUT 4?
An insulin regulated glucose transporter.
How is GLUT4 (glucose importer for myocytes) affected by type 1 diabetes mellitus?
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.
What is a first messenger and what does it do?
An extracellular signalling molecule.
Binds to cell surface receptors which activates intracellular signalling pathways.
What is the relation between first and second messengers?
second messenger molecules are released by cells in response to exposure to first messengers.
What is a second messenger and what does it do?
A non-protein intracellular signalling molecule.
Relays extracellular signals, received at cell receptors, to target molecules within the cytosol.
Which changes can extracellular signals cause in relation to cell composition and function (3 things)?
Differentiation and antibody production.
Growth in size or strength.
Sexual vs asexual cell division.
Define a receptor?
A membrane-bound or soluble protein or protein complex.
Which exerts a physiological effect (intrinsic effect) after binding to its natural ligand.
Why are G-protein coupled receptors major drug targets?
They are implicated in many common human diseases such as:
Allergies.
Depression.
Blindness.
Diabetes.
Various cardiovascular defects.
G-protein coupled receptors are integral membrane proteins, what are some roles they have?
Detect:
Hormones.
Neurotransmitters.
Ions.
Light.
Odours.
Flavours.
and transmit signals across the cell membrane (this changes cell behaviour).
Calcium is used as a secondary messenger, What is its resting concentration and concentration when signalling?
Resting:
10-100 nM.
Signalling:
500-1000 nM.
What are the effects of calcium ions being released on a regular cell? (not neuron specific)(protein based)
Ca2+ binds to (and activates) calmodulin.
Calmodulin may activate calcium-calmodulin-dependent protein kinases.
OR
May act directly on other effector proteins.
Name some physiological roles of calcium ions (7)?
Muscle contraction.
Neuronal transmission.
Cellular mobility.
Fertilization.
Cell growth/proliferation.
Learning/memory.
Secretion of saliva.
Name some biochemical roles of calcium ions (3)?
Regulates enzyme activity.
Permeability of ion channels.
Activity of ion pumps.
Name some effects of dysregulation of calcium signalling (4)?
Cardiovascular + neurological defects.
Metabolic disorders.
Muscular diseases.
Cancer.
Membranes are electrically polarized, what is the internal resting potential of a cell?
-50mV to -70mV
How is membrane potential established?
Na+K+ ATPase establishes membrane potential by moving 3 Na+ out and 2 K+ in (using ATP).
What is the role of gated ion channels and which 2 stimuli do they respond to?
Role:
To regulate transport of ions across membranes.
Stimuli:
Changes in membrane potential.
Ligands binding to specific receptor sites.
