eLFH - Cell Membrane characteristics and Receptors Flashcards
Structure of cell membrane
Fluid mosaic model
made up of phospholipids and proteins
Thickness of cell membrane
7.5 nm thick
Functions of the cell membrane
Separation of interior cell from external environment
Maintenance of concentration gradients and membrane potentials
Control movement in and out of cell
Maintenance of cell shape
Cell signalling
Phospholipid components
Hydrophilic polar phosphate head - water soluble
Hydrophobic non-polar insoluble tails
What holds phospholipids together
Van der Waals forces
Hydrogen bonds
Non-covalent interactions
Types of membrane proteins
Integral
Surface
Transport
Enzymes
Receptors
How are membrane surface proteins anchored
Glycosylphosphatidylinositol
Forms basis for antigens and cell adhesion molecules
Modes of transport across cell membrane
Diffusion
Osmosis
Active transport
Endocytosis
Exocytosis
Diffusion across cell membrane
Particles move down concentration gradient
Can be simple diffusion or facilitated diffusion
Active transport across cell membrane
Movement of particles against concentration gradient
Requires energy
Primary active transport
uses chemical energy of ATP (adenosine triphosphate)
Secondary active transport
Uses an electrochemical gradient
Endocytosis across cell membrane
Cells absorb molecules by engulfing them
Usually for large or polar molecules that cannot cross cell membrane in other ways
Exocytosis across cell membrane
Method cells direct contents of excretory vesicles out of the cell
Receptor definition
Molecules on surface of cells
Receive specific chemical signals from environment via ligands
When ligand binds to receptor, it induces or halts an intracellular activity
Ligand definition
Peptides, neurotransmitters, hormones, drugs or toxins which bind to specific receptors to bring about a cellular response
Types of receptor
Transmembrane proteins
Intracellular receptors
Peripheral membrane proteins - rare
Example of transmembrane protein receptors
G protein or ligand-gated ion channels
Example of intracellular receptors
Hormone receptors
Example of peripheral membrane proteins
Elastin
G protein coupled receptors
Seven transmembrane domains
Enzyme linked receptors
Effects are on Guanosine triphosphate (GTP) proteins
Two main signal transduction pathways for G protein coupled receptors
cAMP
Phosphatidylinositol
Examples of G protein coupled receptors
Muscarinic acetylcholine receptors
Adrenoreceptors
Histamine receptors
Activation of G protein coupled receptors
Ligand binding to extracellular portion of receptor
Conformational change allows GDP to exchange for GTP on the G-alpha subunit
This causes dissociation of the subunits into a G-alpha-GTP complex and a G-beta-gamma complex
G-alpha-GTP complex acts on effector organs or ion channels to modulate cellular processes
Deactivation of G protein coupled receptors
GTPase exchanges GTP back for GDP on G-alpha subunit
This deactivates it and causes re-association of all receptor subunits (G-alpha-beta-gamma-GDP complex)
Subunit complex re-binds to seven transmembrane receptor on intracellular portion
Tyrosine kinase receptors
Receptor for many polypeptides including hormones and growth factors
E.g Insulin and Erythropoietin
Structure of tyrosine kinase receptors
Extracellular N terminal with ligand biding site
Intracellular C terminal which is responsible for kinase activity
Kinase enzymes function
Phosphorylation
Tyrosine kinase receptor pathway
Receptor binding leads to phosphorylation of tyrosine
Activates signal transduction pathways
Alters cellular activity
Ionotropic receptors definition
Ligand gated ion channels
Open and close in response to ligand binding
Allosteric binding definition
Binding site for ligand is on a different part of the protein to the ion channel
Examples of ionotropic receptors
Nicotinic acetylcholine receptors
NMDA glutamate receptor (N-Methyl-D-Aspartic acid)
GABA receptor (Gamma-aminobutyric acid)
Nicotinic acetylcholine receptor structure in adults
Ligand gated ion channel
5 subunits:
- 2x alpha units
- beta unit
- delta unit
- epsilon unit
Foetal nicotinic acetylcholine receptor structure
5 subunits:
- 2x alpha units
- beta unit
- 2x delta unit
(I.e extra delta instead of epsilon subunit that adults have)
Nicotinic acetylcholine receptor activation
2 acetylcholine molecules binds to both alpha subunits
Conformational change opens the ion channel
Na+ moves into cell down concentration gradient
K+ moves out of cell down concentration gradient
Intracellular receptors ligand binding
Receptors are intracellular
Ligands that bind them either secondary messengers or lipophilic hormones that can pass through cell membrane
Examples of ligands which use intracellular receptors
Nuclear receptors that bind oestrogen and thyroid hormones
Vitamin D receptors
IP3 receptor on endoplasmic reticulum
Types of drug receptor interaction
Full agonist
Partial agonist
Inverse agonist
Competitive antagonist
Non-competitive antagonist
Full agonist definition
Drug induces a receptor’s maximal response
Partial agonist definition
Drug induces a submaximal receptor response
Inverse agonist definition
Drug induces opposite effect than the intrinsic agonist
Competitive antagonist definition
Drug competes with the intrinsic agonist for the receptor and blocks its activity
Non-competitive antagonist
Drug binds to a different site to the intrinsic agonist and prevents receptor activation
