Exam3 Flashcards
What can an external signal be?
Anything. Chemical, light, protein, etc.
How do we know there are signaling molecules?
Otto Loewi’s experiment. He took a frog heart with nerves and put it in a ringer solution and used electrodes to measure heart rate. He then took the ringer solution from that container and placed it in container B, with a frog heart whose nerves had been removed. The frog’s heart rate responded to the solution with a change. That indicates molecules in solution caused a response in heart rate, even if nerves were not there.
What are four signaling types in animal cells?
Endocrine, paracrine, neuronal/synaptic, contact dependent signaling
What is endocrine signaling?
Hormone driven. Systemic. Long range. Examples of hormones are insulin, glucagon, steroids.
What does systemic mean?
Throughout the entire organism.
What is paracrine signaling?
Diffusible. “Local mediators”. Short range, several cell layers. Examples are cytokines in inflammatory response.
What is synaptic/neuronal signaling?
Short or long range, depending on axon length. Performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses, which are often located far away from the neuronal cell body.
What is contact dependent signaling?
Signal bound to plasma membrane of signaling cell. Proteins or polysaccharides. Huge for development. Requires in direct membrane contact. Webbed mouse foot example.
Do cells only receive one signal at a time?
No. They receive many signals at once. Integrated effects.
Does a signal always have the same effect?
No. One signal can have different effects on different cell types. In heart pacemaker cells, acetylcholine decreases rate of firing. In salivary gland cells, acetylcholine increases secretion. In skeletal muscle cells, it causes contraction.
How are signal recognized by target cell?
Each signal always has a receptor in/on target cell. Always a protein that suffers a conformation change upon biding ligand.
What does signal binding always lead to?
A response. Responses occur through signal transduction cascades.
What is transduction?
When initial signal is turned into a different form.
What are effector molecules?
Secondary messengers.
What are the three targets of secondary messengers?
Metabolic enzyme, cytoskeletal rearrangements, gene regulation
How long is metabolic enzyme reaction?
Seconds to minutes
How long is cytoskeletal rearrangement action?
Seconds to minutes
How long is gene regulation action?
Minutes to hours.
What are examples of mechanisms for activating signaling proteins?
De/phosphorylation. GTP binding. Ras-MAP kinase signaling. Removal of inhibitors or derepression. Polyubiquitination. Proteolysis.
What is used to phosphorylate? Dephosphorylate?
Protein kinase with ATP to ADP to phosphorylate. Protein phosphatase to dephosphorylate.
Describe GTP binding process?
Start with molecule turned off with GDP attached. Change GDP to GTP with GEF and turn signal on. Remove GTP and replace with GDP, using GAPs for GTP hydrolysis, and turn signal off.
What kind of receptor does Ras-MAP kinase signaling have? What does it accomplish?
Tyrosine. Both gene expression and metabolic activation.
What substances make up secondary messengers?
Small organic molecules or ions. cAMP is small molecule. Ca2+ is ion.
What makes cAMP?
Adenylyl cyclase
What do both cAMP and Ca2+ do?
Bind signaling protein and turn it on or off
How many calcium ion binding sites does calmodulin have?
4
How do we observe cytosolic Ca2+?
Take jellyfish ER. Ca2+ leaves lumen and goes into cytosol, where it binds with aquorin and gives off blue hv, which contacts GFP, which gives off green fluorescent light. The amount of blue light or green light helps us determine how much Ca2+ there is in cytosol.
Why does cascade signaling have so many steps?
To fine tune. The more steps, the more chances to regulate process.
Two approaches to identify receptors?
Biochemical approaches vs. genetic approaches
Biochemical approach to identify a receptor:
Radiolabel a ligand, which binds to receptor. Lyse cell and run SDS page to find the protein with the label attached to it. Find a way to keep label on receptor instead of signal that goes through it.
Genetic approach to identify a receptor:
Mutagenesis. Look for mutants that don’t respond to signals.
What is prosystemin?
A plant protein that remains inactive until the plant is wounded or suffers an herbivore attack.
What does prosystemin turn into when activated? How big is it?
18 aa peptide systemin
What label is used to label systemin?
Photoactive azido
What are the two types of receptors?
Intracellular and cell surface receptor.
Which receptor is least common?
Intracellular
What molecules use intracellular receptors?
For small hydrophobic signals like NO, steroids, etc.
How do intracellular receptors work?
Can be cascade or simply bind to transcription factor and generate direct response.
What are cell surface receptors made of?
Transmembrane proteins
What uses cell surface receptors?
Large, polar molecules
What are the three types of cell surface receptors?
Ion-channel coupled, G-protein coupled, Enzyme-linked
Ion-channel coupled receptor? Initial transduction?
Is ligand gated. Initial transduction: membrane depolarization or Ca2+ enters cell and binds proteins to turn them on/off. Calmodulin is an example.
G-protein coupled receptor initial transduction?
Protein-protein interaction.
Enzyme-linked receptors are usually? Initial transduction?
Are usually kinase. Initial transduction: phosphorylation and protein-protein interaction.
How many genes code for GPCRs?
About 1000
What do about about ½ of medications use to achieve their effect?
GPCRs.
What is the hallmark of the GPCR?
7-pass transmembrane domain
What kind of protein is a G protein? How is it linked to plasma membrane.
Heterotrimetric and covalently attached by lipid tails to plasma membrane.
Describe GPCR pathway
Signal binds with 7-pass transmembrane domain, switches GDP to GTP. Receptor undergoes conformation change and binds other proteins like ion channels, kinases/phosphatases or other enzymes, like adenylyl cyclase.
Adrenal GPCR example pathway
Fright stimulates adrenal gland to produce adrenaline. Adrenaline binds with GPCR. G alpha protein dissociates from G Beta and Gamma, loses GDP, gains GTP, and activates adenylyl cyclase, which uses ATP to make cAMP. cAMP is the secondary messenger. cAMP binds protein kinase A (PKA) and turns it on.
What does PKA do when it is turned on by cAMP?
It turns on metabolic enzymes (glycolysis), cytoskeletal regulatory proteins, and DNA-binding proteins, all of which lead to an increase in energy.
How to turn off GPCR pathway?
Phosphorylation of receptor by recruiting arrestins, endocytosis, during which receptor is sent to lysozome, and cAMP phosphodiesterase, which turns cAMP to AMP.
What inhibits cAMP phosphodiesterase?
Caffeine
Example of a plant growth regulator?
Ethylene
What is the ethylene-mediated triple response? When does it happen?
If shoot encounters obstacle, seedling will thicken its stem to exert more force on obstacle. The seedling will shield the tip of the shoot by increasing the curvature of a specialized hook structure. Third, it reduces the shoot’s tendency to grow away from the direction of gravity, so as to avoid the obstacle.
