Lecture 4 Flashcards
Physiological signals include:
- electrical signals: changes in the membrane potential of a cell
- chemical signals: molecules secreted by cells into ECF, bind to specific receptor on (usually) or in target cells
Communication methods between cells (local)
- Gap junction
- Contact-dependent
- Autocrine
- Paracrine
Communication methods between cells (long distance)
- Neuronal
- Endocrine
Gap junctions
Enable communication between cytoplasms of adjacent cells
Contact-dependent signals
Contact-dependent signals require interactions between membrane molecules on two cells
Autocrine signals
Act on the same cell that secreted them
Paracrine cell
Are secreted by one cell and diffuse to adjacent cells
Example of long distance communication (endocrine)
Hormones are secreted by endocrine glands or cells into the blood. Only target cells with receptors for the hormone will responds to the signal.
For example insulin is secreted from the pancreatic b cells and binds to the insulin receptor on the target cell enabling glucose to enter these cell
Example of long distance communication (neurotransmitters)
Neurotransmitters are secreted by neurons that diffuse across a small gap to the target cell
Example acetylcholine is a neurotransmitter that can be used to elicit skeletal muscle contraction
What is a hormone that is released by neural tissue not endocrine tissue called
Neurohormone (oxytocin)
Long distance communication (neurohormones)
Neurohormones are chemicals that are released by neurons into the blood for action at distant targets
Example: oxytocin Is released by neurons into the blood target uterine smooth muscle (if there is a receptor) and stimulates contractions during labour.
Steroid hormones are ….
Hydrophobic
Intracellular signal receptors
In cytosol (steroid hormone —->hydrophobic)
Cell membrane receptor
Extracellular signal molecule binds to a cell membrane receptor
In the plasma membrane (insulin—-> hydrophilic)
Receptor-enzyme
Ligand binding to a enzyme receptor activates intracellular enzymes
Example: insulin receptor acts as an enzyme, it phosphorylates stuff and the result inside the cell is glucose party
Integrin receptor
Ligand binding to a integrin receptor alters the cytoskeleton
What do we call signal transduction when it is sensitive
Signal amplification (volume control)
When a signal transduction is tightly regulated this means
Cascade —> when one turns on the next
G protein stands for
Guanosine nucleotide-binding protein
GPCRs stand for
G protein coupled receptors
GPCR:
Ligand binds with a receptor that is physically coupled with a guanosine nucleotide- binding (G) protein
1/3 of all pharmaceutical drugs target GPCRs
Largest family of cell surface receptors
Bind to and activate G proteins
When G proteins are activated they may:
- directly alter ion channels
- alter activity of another enzyme
2 main enzymes modified by GPCR activation are
- Adenylate Cyclase (AC)
- Phospholipase C
GPCR and AC
Once ligand binds to receptor and activates G protein…
1. GS (a flavour of G protein) stimulates Adenylate cyclase
2. AC trigger production on CAMP
3. cAMP binds to and activates protein kinase A (PKA)
4. Phosphorylates protein and we receive cell response
GI —> another flavour of G protein, inhibits AC
GPCR and PLC
- Ligand binds to receptor and activates GQ ( a flavour of G proteins)
- GQ activates phospholipase C (PLC) an amplifier enzyme
- PLC converts membrane phospholipids into DAG which stays in the membrane and IP3 that diffuses in the cytoplasm
- DAG activates PKC which phosphorylates proteins —> giving cellular response
- IP3 causes release of Ca2+ from the endoplasmic reticum to increase intracellular concentration of Ca2+
- The increased Ca2+ and altered protein function leads to cellular response
