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Molecular Mechanisms

Molecular Mechanisims

What do cell surface receptors interact with? Hormones/neurotransmitters
If there is a metabolic response what is the conc of the hormones/neurotransmitters? 10^-3 to 10^-4 M
When there is a second messenger what is the conc of the hormones/neurotransmitters? 10^-8 to 10^-6 M
Name examples of second messengers Calcium, cAMP and cGMP
What is the G-proteins often coupled with? Receptors
What activates adenylate cyclase? Gs
Describe G-protein coupling Net result is GDP is released, GTP is able to bind & then you enter the active state of the G-protein which is the signaling process. You end up with an GTP bound alpha and a beta-gamma complex
cAMP generation and removal Made by adenylate cyclase using ATP. Removed by cAMP-selective phosphodiesterases. Regulation at both the generation and removal of cAMP. Signaling depends on subcellular region
Receptors with hormone bound and inhibitors Hormone will bind to receptor and change conformation and there are also receptors that will inhibit adenylate cyclase
Describe adenylate cyclase inhibition Directly by alpha subunit. beta-gamma subunits are able to increase the local conc of beta-gamma subunits and speed up reversal process that inhibits adenylate cyclase.
DAG and IP3 Produced by a receptor regulated enzyme called Phospholipase C (activated by Gq)
Describe DAG (Diacyl glycerol) Has glycerol, 2 fatty acid & usually middle fatty acid is polyunsaturated. DAG activates a protein kinase
Describe IP3 (inostiol triphosphate) 6 carbon sugar, inostiol and has 3 phosphate groups. IP3 is going to regulate intracellular calcium
How does PI (phosphotidyl inositol) start? With a glycerol backbone, 2 fatty acids & then attached to the phosphate group is the inositol sugar which just has OH groups on it, no phosphates. Phospholipid is 90% in form of PI & 5% in PIP and PIP2 form.
Calcium level on outside of cell 1muM The total calcium is higher that that but it often binds to proteins so the actual available Ca is 1muM
Intracellular resting level calcium conc. .1muM. For every one molecule of Ca in the intracellular environment, there are 10,000 molecules of Ca in the extracellular environment
Name the 2 types of Ca channels Voltage: As cell membrane moves towards depolarization, channels open up & let Ca in. Receptor: An organelle involved is Sarcoplasmic Reticulum in muscle cells (Calsisome is in non-muscle cells)
Describe the process of IP3 binding to receptor When IP3 binds to receptor, Ca is released. Depletion of SR Ca play a major role in communicating the influx of Ca from extracellular
Ca regulated K channels Most cells are at -50mV & not -90mV which is equilibrium potential for K. Open K channels=more negative, hyperpolarizes. When you lose Ca--depolarization & voltage channels open
Removal of Calcium Uptake of Ca back into SR. Pump involved is SERCA which maintains a low Ca intracellular environment conc.
Mitochondria role in Calcium Acts as a sensor for cellular calcium, instead of using membrane potential to make ATP, uses it to pump Ca into the mitochondria. It can bring huge amounts by bringing in phosphate and making Ca-phosphate
cGMP generation and removal Made by enzyme guanylate cyclase. Removed by cGMP selective phosphodiesterases.
Difference b/w cAMP and cGMP cGMP has a membrane bound form (doesn't have a g-protein regulation on it) and soluble form of guanylate cyclae. Receptor is directly bound to GC & makes cGMP from GTP
What regulates soluble guanylate cyclase? NO (nitric oxide). NO binds to heme group & NO binds to iron of GC & promotes the conversion of GTP to cGMP. Chemical reaction of NO with superoxide removes NO easily from signaling of GC
NADPH NADPH generates superoxide, which is readily converted in the intracellular environment to hydrogen peroxide. H2O2 is metabolized=key to signaling
How do second messengers signal? Protein Kinases is a major way. Some are regulated by sequence of events where 1 PK will phosphorylate another PK and turn it off
Role of Protein phosphatases Removes the phosphate group=unphosphorylated state--down regulation of the signaling or it will turn it off
PKA Has 2 regulatory subunits and 2 catalytic subunits. IT is inactive w/o cAMP bound.
How many sites does cAMP have on PKA? 4 sites, 2 on each regulatory subunit. After cAMP binds the catalytic subunits are released and active (phosphorylates other proteins)
What is the difference b/w cGMP and cAMP when it comes to catalytic subunits? There is no dissociation of the catalytic subunits. It becomes active without dissociation.
Ca binding proteins Set up to bind to calcium over the .1 to 1muM range involved in signaling.
How does H2O2 regulate? H2O2 (range of 1-10 nanomolar) is being metabolized by enzymes like glutathione peroxidase or peroxiredoxins
Peroxiredoxins Oxidizes thioredoxin which has 2 thiol groups that are made into a disulfide and used by other enzymes to modify thiols



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