Biochem Lectures 7&8 Flashcards
(37 cards)
What is signal transduction?
Process by which an outside signal produces a reaction inside the cell.
What are the four basic categories of signaling?
Autocrine: short distance, to same cells
Paracrine: short distance, to different cells
Endocrine: Long distances
Neuronal: Long and short distances
What is contact dependent signaling?
Direct contact is made between the cells. This can be classified as autocrine or paracrine also.
It is used as cell recognition and aids in restricting cell growth.
What are some common endocrine hormones?
Estrogen Progesterone Testosterone Insulin Glucagon Cortisol Epinephrine
What two phases of signal transferring is required in neuronal signaling?
- Through the neuron via electrical potential.
2. Across the synapse through action of a neurotransmitter.
What are the two mechanism for ligand-induced signaling?
- Intracellular receptors: the ligand is hydrophobic and diffuses across the membrane to a receptor inside the cell.
- Cell surface receptors: hydrophilic signal molecules bind to receptors on the cell surface and the transmembrane proteins transfer the signal into the cell.
How are steroids transferred through the body and into cells?
Steroids are derived from cholesterol and are therefore non-polar. They need carrier proteins to be transported through the blood stream, but they diffuse on their own across the plasma membrane.
What are the five main steroids that we should know?
Testosterone Estradiol Progesterone Cortisol Aldosterone
What is the general mechanism of steroid action inside the cell?
The steroid crosses the membrane and binds to its receptor protein in the cytosol. The receptor complex relocates to the nucleus and binds to the DNA at a regulatory site for a gene. It induces transcription of the gene and the corresponding protein is produced.
Explain nitric oxide signaling.
NO is produced by nitric oxide synthase (NOS) which converts arginine to NO and citrulline.
NO is soluble in aqueous and lipid media. Once made, it only affects local cells because it has a short half life.
Acetylcholine is released from a nerve terminal and is received by an endothelial cell of the blood vessel. This causes eNOS to produce NO which diffuses out of the cell and into a nearby smooth muscle cell. NO reacts with iron in the active site of guanylyl cyclase which produces cyclic GMP. cGMP initiates a pathway that signals rapid relaxation of the smooth muscle cell. This cause vessel dilation.
How is nitroglycerin related to nitric oxide?
Nitroglycerin is converted to NO in the body and causes dilation of blood vessels. This is used to treat angina where too little oxygen is getting to the heart. This process does not require NO synthase.
What proteins phosphorylate other proteins?
Kinase proteins. They phosphorylate serine, threonin, and tyrosine because they have hydroxyl groups.
What proteins dephosphorylate?
phosphoratases
Extracellular ligands can bind to two types of transmembrane receptors that cause phosphorylation cascades, what are they?
G-Protein coupled receptor (GPCR): a single protein coiled through the membrane 7 times
Receptor tyrosine kinase (RTK): these are two separate proteins that work together
What do phosphorylation cascades do to the signal? How is the signal changed?
The signal is transmitted very quickly, and it is amplified along the way.
What are the targets of kinase proteins?
- Other kinases: to amplify the signal
- Phosphates: to increase dephosphorylation of certain substrates
- Metabolic enzymes: to simultaneously activate or inactivate several enzymes in a given pathway
- Transcription factors: to have an effect on gene expression
What is the speed of the response from phosphorylation and gene expression signals?
Phosphorylation takes seconds to have an effect. Gene expression and protein synthesis can take hours or days.
What kind of binding site do most growth factors bind to?
Most bind to receptor tyrosine kinases.
What is the largest class o cell surface receptor cells?
G-protein coupled receptors.
What kind of receptor do epinephrine and glucagon bind to?
Both bind to GPCR’s.
What is the protein inside the cell that transmits the signal from GPCR’s into the cell?
It is a protein that has three parts: alpha, beta, gamma and is a GTP-binding protein.
What do the three types of alpha proteins do that are part of the GTP binding protein complex?
Galpha-s: activates the enzyme adenylate cyclase
Galpha-i: inhibits the enzyme adenylate cyclase
Galpha–q: activates the enzyme phospholipase C
How do GTPases work?
GTPase is inactive when bound to GDP. When it binds a GTP molecule, it becomes active until it hydrolizes the GTP into GDP + P and becomes inactive again. The time this process takes is a kind of molecular timer.
What is the step by step process of GPCRs getting activated?
- The trimeric protein is bound on the inside of the membrane to the inactive GPCR. The alpha subunit is bound to a GDP molecule.
- Activation of the receptor by a ligand stimulates the alpha subunit to release GDP and bind GTP. This activates it.
- Activated alpha leaves beta gamma and moves along the membrane to activate other proteins.
- The beta and gamma units stay together and also move around to activate other proteins.
- After a given time, the GTP gets hydrolized by alpha, and it becomes inactive.
- Alpha, beta, gamma reunite to a GPCR and wait for another signal.
