Transport Diffusion Active Transport Osmosis Endo- & Exocytosis.
-
Upload
loren-porter -
Category
Documents
-
view
227 -
download
2
Transcript of Transport Diffusion Active Transport Osmosis Endo- & Exocytosis.
Receptors & Cellular Transport
MechanismsJames Peerless
May 2011
Objectives Cellular Transport Mechanisms
Types Mechanisms
Receptors What are receptors for? Types
Messenger systems
Membrane Transport Mechanisms
Membrane Transport of Substances
Membranes control movement of many types of particle between intra- and extracellular compartments
Phospholipid bilayer allows diffusion of water, small molecules and lipid-soluble substances
Passive and active mechanisms
Simple Diffusion Random movement of molecules
Passive process
Net movement occurs down a concentration gradient
kp dependent upon: Temperature, membrane permeability molecular properties (lipophilicity, charge, MW)
Q = kpA(C1-C2)/T
Facilitated Diffusion
Molecule moves down concentration gradient
Rate determined by carrier and solute concentration
Rate of transport is ‘facilitated’ by a carrier molecule Carrier Channel
Active Transport Specialized facilitated
diffusion
Mediated by membrane carrier proteins & requires energy
Transport of substances against their concentration gradient
Affecting transport: Carrier saturation and
density of carriers Speed of carrier
conformational change
Primary Active Transport
Secondary Active Transport
Transport of a substance and an ion together
No direct energy input
Exo- & Endocytosis
No transport of substances through membrane
Vesicles formed by invagination of the membrane
Pinocytosis is the specialized uptake of water
Summary
Receptors
Receptors
“A molecule that recognises specifically a second molecule whose binding brings about the regulation of a cellular process.”
Lambert DG (2004). Drugs & Receptors. Continuing Education in Anaesthesia, Critical Care & Pain; 4 (6): 181-4
Role of Receptors Cell communication
Chemical messengers can be local or widespread
Regulation, mediation and amplification of signals
Allows homeostatic control
PropertiesLigands
Affinity
Competition
Activity (agonist/antagonist)
Half-life
Lipid solubility
Receptors
Specificity
Sensitivity
Saturation
Down- & Up-regulation
Signal Transduction
Membrane permeability
Membrane potential
Membrane transport
Contractile activity
Secretory activity
Protein synthesis
Clinically important
Receptor Types Ligand-gated ion channels
Acetylcholine receptors
G-protein coupled receptors Adrenergic receptors
Tyrosine kinase coupled receptors Insulin
Intracellular receptors Steroids
Ligand-gated Ion Channels
The Ach Receptor Pentameric,
transmembrane structure
2 α and β, γ, δ subunits
Ion channel opens when 2x Ach binds to α-subunits
G-protein Coupled Receptors
Extensive and important Adrenergic Muscarinic Opioid
Act via second messengers cAMP increased or decreased Activation of protein kinases
Protein phosphorylation Inactivated by phosphodiestereases
Key G-protein Subunits
Subunit Acts on Second Messenger
Example
Gs Adenyl cyclase
Increases cAMP
β-adrenergic receptors
Gi Adenyl cyclase
Decreases cAMP
Opioid receptors
Gq Phospholipase C
DAG & IP3 α-adrenergic receptors
Tyrosine Kinase Coupled
Receptors
Intracellular Receptors
Questions
MCQ 1 The rate of diffusion of a gas (Fick’s Law)
across a membrane:
(a) is directly proportional to the area
(b) is directly proportional to the partial pressure gradient
(c) is inversely proportional to thickness of the membrane
(d) is directly proportional to the molecular weight
(e) is inversely proportional to the density of the gas
T
T
T
F
F
MCQ 2
The following receptors are part of a ligand-gated ion channel:
A) opioid mu receptor
B) muscarinic cholinergic receptors
C) nicotinic cholinergic receptors
D) GABAA receptors
E) GABAB receptors
F
F
T
T
F
Summary Cells have passive and active mechanisms
for controlling passage of molecules across boundaries
Intercellular communication allows homeostatic control via the specific use of chemical messengers and cellular receptors