Flashcards in Ch. 5 & 6 Deck (34):
Why do cells in the body need to communicate with each other? What function or purpose does it serve?
1. Maintain homeostasis
2. Cell repair - tissue maintenance and repair
3. Cell differentiation - stem cells
What type of biological molecule are receptors?
What is the first step in the action of a signaling molecule upon a cell?
Binding to receptor
Where are the receptors located?
Located on the cell surface,plasma membrane,(extracellular fluid) or inside the cell
What is the physical basis of receptor specificity?
The shape of the receptor will determine whether or not a molecule will be able to bind
Explain what it means to say that a particular type of receptor is 58% saturated.
58% saturation means 58% of all receptors are bound with ligand
For a given mid-range concentration signaling molecule, which type of receptor will have a higher percent saturation: low affinity or high affinity?
High affinity receptors are able to bind at lower concentrations for the ligand, while low affinity need higher concentrations to bind.
How would the addition of an antagonist affect saturation?
Driven by competition, the addition of an antagonist lowers percent saturation because the antagonist competes w/the signaling molecule for binding sites.
How would the addition of an antagonist affect the degree of cellular response to a messenger?
The competing ligand blocks the action of the messenger ligand. Doesn’t have the same effect on the receptor, one works and one doesn’t.
How would the addition of an agonist affect the degree of cellular response to a messenger?
The competing ligand mimics the action of the messenger ligand, both can activate the receptor.
Describe signal transduction pathways used by lipid soluble signals.
Receptors are located either in the cytosol or nucleus. Receipted activation leads to altered rates of transcription one or more genes.
Describe the signal transduction pathways used by water soluble signals.
Ligand gated ion channels - first messenger
Receptors that are enzymes - first messenger
G-protein coupled receptors - first and second messengers
Intracellular proteins are activated or deactivated by adding or removing phosphate groups.
How does the abundance of receptors affect cell sensitivity to a particular messenger?
A cell's sensitivity to a chemical message varies with the number of receptors present
How is receptor abundance regulated?
phosphorylation and dephosphorylation - adding or removing phosphate group to/from a protein. Causes a confrontational change, which activates or deactivates the protein (enzyme)
Compare and contrast a first messenger system w/a second messenger system. How are they similar? How are they different?
First - All chemical signals have a first messenger; signal binds to receptor on/in cell
Second - Some signal pathways; amplifys signal inside the cell.
A signaling molecule is lipid soluble. Where are receptors located?
Receptor is located in the cytosol or nucleus
A signaling molecule is water soluble. Where are the receptors located?
Receptors located on the extracellular side of the plasma membrane
Compare and contrast the signal transduction pathways for lipid soluble and water soluble messengers. How are they similar? How are they different?
What role do protein kinases play in certain signal transduction pathways?
Perform phosphorylation - protein is activated, adding a phosphate group to a protein.
The activity of enzymes inside the cell is strictly regulated. Describe two ways that signaling molecules can influence the activity of a particular enzyme w/in a cell.
increase/decrease protein activity (enzymes are phosphorylated/dephosphorylated.
increase/decrease protein synthesis
Explain how second messengers amplify cell to cell signal. What does that mean?
Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase + ATP = cAMP - activate protein kinases
How is cell to cell signal terminated? Describe 4 ways
reduce extracellular concentration:
1. Reuptake - secretes and takes them back in
2. Enzymatic degradation - break down signaling molecule - cant bind to receptor anymore
3. Diffusion away from synapse - molecules bounce off each other
4. receptor sequestration - w/drawn from plasma membrane
5. receptor down regulation - w/drawn and catabolized (chopped up)
6. receptor inactivation - add phosphate or change shape
Explain the concept of membrane potential.
Characteristic of a cell. On one side of the Plasma Membrane is negative charges and other side is positive charges. So membrane potential occurs when there is charge difference across the plasma membrane. Differ b/w cell types in our body. Separation of charges - form of potential energy.
What mechanisms generate and maintain a cells resting membrane potential?
- Na+/K+ pumps
- Presence of negatively charged particles trapped inside cells (non-penetrating solutes) - phosphate groups, proteins
- K+ leakage channels and Na + leakage channels
How do sodium potassium pumps contribute to membrane potential?
Sodium-potassium pumps contribute to membrane potential by creating a concentration gradient in the cell membrane. Ion channel, Leak channels, randomly fluctuating b/w open and close position. open - electrical chemical gradient, for each ATP, pump 3 Na+ out and 2 K+ in.
What are non penetrating solutes and how do they contribute to membrane potential?
non-penetrating solutes cannot "penetrate" through out the cell membrane. negatively charged groups such as phosphate and protein negatively charged and cannot exit the cell, contributing to a negative intracellular charge (can exit through exocytosis). Phosphate groups and proteins
What happens to the numerical value of a membrane potential when a neuron becomes depolarized? Does membrane potential increase or decrease in magnitude? More negative or less? Does the sign of the value change?
It becomes less negative w/the inward flow of positive ions +
Describe events that occur during cell to cell transmission at chemical synapse. Which cell releases a signaling molecule? Which cell has receptors for that molecule?
Chemical synapse occurs when synaptic vesicles are in between the presynaptic neuron and post synaptic neuron in an area called the synaptic end bulb. Voltage gated calcium ion channels, normally closed, when MP changes, they open and calcium moves into cell - calcium critical role in getting synaptic vesicle (neurotransmitters) - perform exocytosis and put neurotransmitters in the cleft and the receptors for the synaptic neuron.
What is signal transduction pathway?
Describes events that occur after the signaling molecule binds to its receptor. Events lead to or produce the cellular response. Binding of ligand > change in cell behavior
When does up-regulation happen?
Occur in response to chronic low-levels of signaling molecule. Parkinsons, huntingtons. To compensate for decreased levels of a neurotransmitter, like serotonin, the brain increases the number of receptors for that specific neurotransmitter.
When does down-regulation happen?
Occur in response to chronic presence of the signaling molecule.
What is resting membrane potential?
Resting membrane potential - an electrical potential difference across the plasma membrane.
Describe the events that occur during an action potential in a neuron. Which types of ion channels open and when? What changes in membrane potential occur? How is membrane potential restored to resting following an action potential?
Fastest action potential, shortest duration. Cell @ resting membrane potential, cell is stable here, stimulus causes ion channels to open. ions move to have membrane -70 to threshold (-55). threshold - action potential. -55, voltage gated sodium ion channels open (depolarization), membrane becomes super permeable to sodium. sodium rushes in (+) charges, inside cell - less negative, membrane potential +, sodium channel close. +30, different voltage gated ion channel open - potassium (repolarization), permeable to potassium (leaving cell), potassium leaving cell. inside cell becomes negative - hits -70, cross resting membrane potential - hyperpolarized. voltage gated potassium channels close. sodium/potassium channels restore resting balance of sodium and potassium ions - resting membrane potential.