Key Area 4 Flashcards
Multicellular organisms:
Signal between cells using extracellular signalling molecules.
Different cell types produce signals that can only be detected by cells with the specific receptor.
Different cell types may show a tissue-specific response to the same signal.
Extracellular signalling molecules examples:
Steroid hormones
Peptide hormones
Neurotransmitters
Receptor molecules:
Proteins with a binding site for a specific signal molecule.
Binding changes the conformation of the receptor, which initiates a response within the cell.
Signalling molecules:
Have different effects on different target cell types.
Caused by differences in the intracellular signalling molecules and pathways.
Hydrophobic signalling molecules:
Diffuse directly through the phospholipid bilayers of membranes.
Bind to intracellular receptors.
Receptors are transcription factors.
Examples:
- Oestrogen
- Testosterone
Transcription factors:
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
Steroid hormones:
Bind to specific receptors in the cytosol or the nucleus.
The hormone-receptor complex binds to HRE’s on DNA and affects transcription rate.
HRE’s
Hormone Response Elements
Hydrophilic signalling molecules:
Bind to transmembrane receptors and do not enter the cytosol.
Transmembrane receptors:
Change conformation when the ligand binds and signal is transduced across the membrane.
Act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
Transduced hydrophilic signals
Involve G-proteins or cascades of phosphorylation by kinase enzymes.
G-proteins:
Relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Phosphorylation cascades:
Allow more than one intracellular signalling pathway to be activated.
Involve a series of events with one kinase
activating the next in the sequence and so on.
Can result in the phosphorylation of many proteins as a result of the original signalling event.
Binding of peptide hormone to insulin:
Causes a conformational change that triggers phosphorylation of the receptor.
This starts a phosphorylation cascade inside the cell, leading to GLUT4- containing vesicles being transported to the cell membrane.
Diabetes mellitus
Type 1: Caused by failure to produce insulin.
Type 2: Loss of receptor function. Associated
with obesity. Exercise helps as it
improves uptake of glucose to fat and
muscles cells by triggering GLUT4
recruitment.
