DEBBIE 3 Flashcards
How do cells sense signals and how do they decide which signals to receive?
Cells have receptors on their surface that are used to receive signals (ligands)
Cells only receive signals for which they have receptors
Why is it important that each signal is short lived?
Want cells to give the appropriate response and then be done
And then cells get ready to respond to next signal
Ex: insulin (want it to stop because u dont want to die from too much sugar)
How do cells sense NO (nitric oxide) ?
NO goes through cell membrane
Binds to intracellular receptor
Cause production of cGMP
Relaxes muscles and blood vessels = increase blood flow
How do steroid hormone receptors work?
Steroid passes through cell membrane
Activate genes by binding to steroid hormone receptor, then binds to DNA
Inhibitor breaks off
Gene turns on and gets cell response
Why are most receptors in the plasma membrane?
Most signals are polar and cannot penetrate membrane
What are the three types of plasma membrane receptors?
Gated ion channels
enzyme-linked receptors
G-protein linked receptors
How do gated ion-channels work?
Channel is either open or closed
It is then open or closed by the presence of a signal called a neurotransmitter which binds to the receptor
Channel is specific to the ion (Ca2+ channel only lets Ca2+ through)
How do enzyme-linked receptors work?
Signal binds receptor
An enzyme is activated
Response occurs
What is special about phosphorylated tyrosine?
Phosphate can be added to tyrosine (an amino acid that is part of the protein) because it has an OH- in the R group once phosphate is attached, then the protein is activated
What does it mean to phosphorylate? activates molecules (protein)
Phosphorylated protein is _____
Dephosphorylated is ______
to add a phosphate to a molecule
activates molecules (protein)
Phosphorylated protein is active
Dephosphorylated is inactive
Kinase:
Phosphatase:
enzyme that adds a phosphate to a protein (activates protein)
enzyme that removes a phosphate (deactivates protein)
What is a common way to control proteins in signaling pathways?
phosphorylation/dephosphorylation of proteins
Why are phosphorylation cascades frequently encountered in biological signal transduction?
Each protein kinase can phosphorylate MANY enzymes, thereby activating them
Then each of those enzymes can catalyze a lot of reactions
Therefore one receptor bound to its signal can result in thousand of molecules of products
Why are phosphatases important components of many signaling pathways?
Phosphatases remove phosphates which stop the reaction
Why do defects in the Ras protein cause cancer?
Cell division is no longer regulated
What is a G-protein linked receptor and what do they all have in common?
G-protein linked receptor is a receptor linked to a G-protein
Ligand binds to receptor to activate it
Signal is first messenger but it cannot pass through the membrane
How does a G-protein linked receptor work?
- Ligand (signal) has to bind the receptor
- Receptor will change shape which will cause the G protein to twist causing it to bind to GTP
- Now that the G protein is bound to GTP, the G protein is activated - Activated g protein diffuses away from receptor and binds to an effector somewhere else in the membrane; this will start a chain of reactions that brings about the cells response
- G proteins activate effectors which generate 2nd messengers; 2nd messengers activate intracellular receptors and a response occurs
- Two 2nd messengers: cAMP & IP3 (inositol triphosphate)
Why are G-protein-linked receptors used to detect so many different kinds of signals?
they can reset?
What is a G-protein?
G protein is a GTP binding protein
Rest of answer is #13 & #14
Guanine triphosphate
What is a “effector enzyme” and what is an “second messenger?”
Effectors are___which make the second messenger____:
Effector enzyme: enzyme in the plasma membrane that are activated by activated G proteins (activated G proteins is attached to a GTP)
Effector enzymes will then make second messengers which relay the message and trigger a cell response
Adenylyl cyclase which will make cAMP
Phospholipase C which will make IP3
Second messenger: small molecule produced by effector enzymes
Second messengers trigger responses by the cell by binding to intracellular receptors
How do cells “reset” a G-protein, and how do cells “reset” a G-protein linked receptor?
Reset G-protein by remove P from GTP; GTP becomes GDP and the G protein is now inactive
G protein goes back to the G-protein linked receptor and now we wait for the next signal
What are the differences between the cAMP and IP3 pathways and what do they have in common?
DIFFERENCES: which effector and therefor which second messenger produced
SAME: signal binds G-protein linked receptor; G activated with GTP; activated G protein; activated G protein moves to effector and causes effector to make second messenger
- If effector is adenylyl cyclase; then cAMP will be produced as second messenger
- If effector is phospholipase C; then IP3 is the second messenger; binds Ca2+ channels to cause response
in both pathways…signal is amplified
What is calmodulin and what does it do?
Calmodulin is a protein that binds Ca2+
This complex then initiates the next step in the reaction / cascade
Important in IP3 pathway
Why do cells need to amplify the signal generated when a receptor binds its ligand and how do they do it?
There is only so much room in the cell membrane for receptors
So, there are not a lot of receptors in the cell membrane
The small signal generated by the first messenger is magnified inside the cell by a cascade of reactions where, at each step, more and more product is produced
How can a single adrenaline molecule trigger the release of 10,000,000,000 glucose molecules?
1 adrenaline binds to receptor
1 receptor activates 100 G proteins {100x}
Each G protein activates 1 adenylyl cyclase
Each adenylyl cyclase makes 1000 cAMP {1000x}
Each cAMP activates 1 protein kinase A
Each protein kinase A activates 100 glycogen phosphorylase {100x}
Each glycogen phosphorylase produces 100 glucose molecules
1 signal results in 10 billion glucose molecules
