Block 3 - Lecture 3 Notes Flashcards
Signal transduction
Cellular signaling
Cellular signaling is mainly initiated by…
secretion of chemical messengers such as hormones, growth factors, and neurotransmitters
Cellular signaling is additionally initiated by…
External signals such as odorants or tastants and metabolites
Types of cellular receptors
- Ligand-gated ion channels
- GPCRs
- Catalytic receptors
- Nuclear receptors
Ligand gated ion channels
Integral membrane proteins interact with ion channels and modify flux across channel.
Ion acts as the initial second messenger.
Nicotinic ACh receptors
Ligand-gated ion channels
Critical for muscle response to signals from the nervous system to contract.
ATP-sensitive K+ channels
Ligand-gated ion channels
Critical for insulin secretion from beta cells of the endocrine pancreas
G Protein-Coupled Receptors
- Large class of integral membrane proteins.
- Activate a heterotrimeric complex G Protein.
- Subsequent modulation of an enzyme or ion channel.
- Product of enzymatic activity (ion) is initial second messenger.
Examples of GPCRs
B-adrenergic receptors
Alpha 1 and alpha 2 adrenergic receptors
Glucagon receptor
Catalytic Receptors
- Activation of enzymatic activity of the receptor itself OR
- Initiation of series of events that (through protein-protein interactions) activate an enzymatic complex.
Insulin receptor is which type of cellular receptor
Catalytic
Nuclear Receptors
- Located either in the cytoplasm or the nucleus
- Acts as transcription factors to modulate the transcription of specific genes.
- No second messengers are utilized.
Initiation of Signaling Event by Plasma Membrane Receptors
- Recognition
- Transduction
- Transmission
- Modulation of effector
- Response
- Termination
Recognition
Ligand binds to exofacial aspect of receptor
Transduction
Ligand binding induces conformational change in receptor, producing a second messenger
Transmission
Second messenger interacts with various intracellular effectors
Modulation of the effector
Interaction activates a protein kinase or phosphatase; changes in phosphorylation state of a downstream target alter functionality.
Response
Signaling events modify cellular function in highly specific ways
Termination
Feedback mechanisms stop signaling events and return cellular function to a basal state
Amplification
Increased production of second messengers at each step of multi-signaling cascade –> enhanced activation of a cellular process by several orders of magnitude
