Lecture 7 Flashcards
Cytokines.
Synthesized and secrete by all nucleated cells, they are chemical messengers; act more locally than a hormone would, and are not produced by specialized cells (cytokines act on a broader spectrum). They control cell development, differentiation, and immune responses. Made on demand; not stored.
Protein receptors are important in medicine.
Basis for actions of many drugs.
Location of a protein receptor depends on…
Whether the ligand is hydrophobic or hydrophilic.
Which class of molecules can freely diffuse across the phospholipid bilayer?
Hydrophobic molecules (this also means lipophilic).
Endocrine system compared to the nervous system.
The endocrine system is slow to kick in, bu this prolonged effects compared to the nervous system.
To enter the cell, lipophobic molecules must…
Bind to extracellular receptors and cause a cascade of events to occur; this is rapid within the endocrine system. This impacts transcription factors and gene expression of the cell.
Steroid hormones and their receptors.
They can bind to membrane receptors and intracellular receptors: they diffuse into the cell and bind to a receptor in the cytosol or nucleus.
Primary signals converts chemical signals into cellular responses; second messengers come into play.
Second messengers alter the negating of ion channels, increase intracellular calcium, and changes activity of enzymes like protein kinases (phosphorylate) and protein phosphatases (remove a phosphate group).
Tyrosine kinase: an example of a receptor-kinase signalling pathway.
Tyrosine kinase transfers a phosphate group from ATP to a tyrosine (amino acid) of a protein; an insulin receptor protein, for example.
Most signal transduction uses which type of protein?
G-protein: GPCR are the largest and biggest family of membrane-spanning proteins; they cross the phospholipid bilayer 7 times. There is a cytoplasmic tail linked to GPCR: this is a 3-part transducer molecule.
GPCR pathway: adenylyl cyclase-cAMP system .
First messenger binds to GPCR and activates it This converts AMP to cAMP. cAMP then phosphorylated protein kinase A, which phosphorylates other proteins.
GPCR pathway: the phospholipase C system.
Ligand binds to G-protein and activates it. G-protein activates phospholipase C (an amplifier enzyme). Phospholipase C is converted into DAG and IP3 (DAG activates protein kinase C , which phosphorylates; IP3 creates a calcium signal by causing calcium release from the ER); they trigger a response in the cell.
Function of DAG in phospholipase C system of GPCR.
Activates protein kinase C, which phosphorylates.
Function of IP3 in phospholipase c system of GPCR.
Triggers calcium release from the ER, which triggers a cellular response.
Channels can be linked to G proteins.
Causes a change in permeability, causing an electrical signal that creates a voltage difference, which triggers a cellular response.
What happens when calcium binds to calmodulin in smooth muscle?
It alters protein activity.
Process of calcium as an intracellular messenger.
Electrical change causes an influx of calcium, which causes exocytosis of a neural signal. This electrical signal (neural signal) allows for calcium to be released from its stores.
