[qdeck ” bold_text=”false”]
[h] IB DP Biology HL C2.1 Chemical signaling Flashcards
[q] calcium ions can move in and out of the cell through the…
[a] calcium pump
[q] identify receptors that are present on the outer side of the target cells
[a] cell surface receptors
[q] what does the chemical N-acyl homoserin lactone trigger in Vibrio fischeri?
[a] bioluminescence
[q] what type of hormone is insulin?
[a] peptide hormone
[q] what type of amino acids are found in transmembrane receptors?
[a] found on either side of the cell membrane – hydrophilic
spanning the cell membrane – hydrophobic
[q] identify the role of a ligand in initiating signal transduction pathways by receptors
[a] it binds to the extracellular domain of the receptor
[q] identify the correct order of events in a signal transduction pathway
I. secondary messengers’ active protein kinase
II. receptor gets activated
III. ligand binds to the receptor
IV. protein kinases phosphorylates other proteins
V. gene expression is regulated
[a] III, II, I, IV, and V
[q] identify which of the following is the first step in the mechanism of action of epinephrine (adrenaline) receptors
[a] conformational change in the GPCR
[q] identify which of the following best describes positive feedback in cell signaling pathways
[a] a mechanism that amplifies the signal and increases the response
[q] identify which type of receptor is associated with positive feedback in cell signaling pathways
I. intracellular receptors
II. transmembrane receptors with tyrosine kinase activity
III. transmembrane receptors with G-protein coupling
[a] II and III only
[q] identify which of the following is an example of negative feedback in cell signaling pathways
[a] insulin signaling in response to high blood glucose levels
[q] ADH (antidiuretic hormone) is produced in the pituitary gland and targets the collecting duct of the kidney. how does it reach the target tissue?
[a] travel through the blood
[q] what effect does progesterone have on target cells in the endometrium?
[a] inhibit proliferation of endometrial cells
[q] in the context of a feedback loop, what is the function of estradiol?
[a] stimulating hormone production
[q] which of the following best describes quorum sensing in bacteria?
[a] a process by which bacteria regulate their gene expression and behavior in response to the density of their population
[q] what is the role of quorum sensing in the regulation of bioluminescence in the bacterium Vibrio fischeri?
[a] the bacteria emit light only when their population density reaches a critical threshold
[q] what initiates quorum sensing?
[a] reaching a certain population density
[q] which of the following is true about DNA replication?
[a] DNA replication happens during the S phase of the cell cycle
[q] which of the following best describes the role of transmembrane receptors with tyrosine kinase activity in insulin signaling?
[a] they bind to insulin, causing phosphorylation of tyrosine inside the cell
[q] which of the following signaling chemicals is involved in the regulation of immune responses?
[a] cytokines
[q] which of the following describes how intracellular receptors affect gene expression?
[a] hormones enable the complex to bind to specific DNA sequences, stimulating gene transcription, by binding to a site on the receptor and initiating its activation
[q] which is the second messenger in the epinephrine reaction?
[a] cAMP
[q] what is the consequence of the opening of ion channels in response to the binding of acetylcholine to its receptor?
[a] depolarization of the membrane potential
[q] neonicotinoids are compounds that used to be widely used on farms as effective insecticides.
it appeared they were easily absorbed by plants and were present in pollen and nectar, killing honeybees.
scientists discovered that neonicotinoids affect the cholinergic synapses in the nervous system of insects, causing their paralysis and death.
how do neonicotinoids affect the synapses?
[a] they block postsynaptic acetylcholine receptors so synaptic transmission is prevented
[q] what distinguishes peptide hormones from steroid hormones?
[a] peptide hormones act through second messengers
[q] identify which of the following hormones uses an intracellular receptor to affect gene expression
[a] progesterone
[q] which of the following are steroid hormones?
I. estrogen
II. cortisol
III. insulin
[a] I and II only
[q] what is the correct order of events in the initiation of signal transduction pathways by receptors?
I. binding of the signaling chemical to the receptor
II. activation of downstream signaling molecules
III. internalization of the receptor-ligand complex
IV. conformational change in the receptor protein
[a] I, II, III and IV
[q] which ion will enter the cell through the ion channel opened by the binding of acetylcholine to its receptor?
[a] sodium (Na+)
[q] when neurotransmitters bind to a receptor on the post synaptic neuron causing Na+ ion channels to open.
what function are they carrying out?
[a] the ligand or neurotransmitter is acting as a signaling molecule
[q] what is a ligand?
[a] a signaling chemical that binds to a specific receptor
[q] which of the following is not a function of G protein receptors?
[a] maintaining cellular respiration
[q] C2.1.1—Receptors as proteins with binding sites for specific signaling chemicals
[a] Students should use the term “ligand” for the signaling chemical.
[q] C.2.1.2—Cell signaling by bacteria in quorum sensing
[a] Include the example of bioluminescence in the marine bacterium Vibrio fischeri
[q] C2.1.3—Hormones, neurotransmitters, cytokines and calcium ions as examples of functional categories of signaling chemicals in animals
[a] Students should appreciate the differences between these categories.
[q] C2.1.4—Chemical diversity of hormones and neurotransmitters
[a] Consider reasons for a wide range of chemical substances being used as signaling chemicals.
Include amines, proteins and steroids as chemical groups of hormones.
A range of substances can serve as neurotransmitters including amino acids, peptides, amines and nitrous oxide.
[q] C2.1.5—Localized and distant effects of signaling molecules
[a] Contrasts can be drawn between hormones transported by the blood system and neurotransmitters that diffuse across a synaptic gap.
[q] C2.1.6—Differences between transmembrane receptors in a plasma membrane and intracellular receptors in the cytoplasm or nucleus
[a] Include distribution of hydrophilic or hydrophobic amino acids in the receptor and whether the signaling chemical penetrates the cell or remains outside.
[q] C2.1.7—Initiation of signal transduction pathways by receptors
[a] Students should understand that the binding of a signaling chemical to a receptor sets off a sequence of responses within the cell.
[q] C2.1.8—Transmembrane receptors for neurotransmitters and changes to membrane potential
[a] Use the acetylcholine receptor as an example.
Binding to a receptor causes the opening of an ion channel in the receptor that allows positively charged ions to diffuse into the cell.
This changes the voltage across the plasma membrane, which may cause other changes.
[q] C2.1.9—Transmembrane receptors that activate G proteins
[a] Students should understand how G protein-coupled receptors convey a signal into cells.
They should appreciate that there are many such receptors in humans.
[q] C2.1.10—Mechanism of action of epinephrine (adrenaline) receptors
[a] Include the roles of a G protein and cyclic AMP (cAMP) as the second messenger.
NOS: Students should be aware that naming conventions are an example of international cooperation in science for mutual benefit.
Both “adrenaline” and “epinephrine” were coined by researchers and are based on production of the hormone by the adrenal gland;
“adrenaline” comes from Latin ad = at and ren = kidney and “epinephrine” comes from old Greek epi = above and nephros = kidney, respectively.
Unusually, these two terms persist in common use in different parts of the world.
[q] C2.1.11—Transmembrane receptors with tyrosine kinase activity
[a] Use the protein hormone insulin as an example.
Limit this to binding of insulin to a receptor in the plasma membrane, causing phosphorylation of tyrosine inside a cell.
[q] C2.1.12—Intracellular receptors that affect gene expression
[a] Use the steroid hormones estradiol, progesterone and testosterone as examples.
Students should understand that the signaling chemical binds to a site on a receptor, activating it.
The activated receptor binds to specific DNA sequences to promote gene transcription.
[q] C2.1.13—Effects of the hormone’s estradiol and progesterone on target cells
[a] For estradiol, limit to cells in the hypothalamus that secrete gonadotropin-releasing hormone.
For progesterone, limit to cells in the endometrium.
[q] C2.1.14—Regulation of cell signaling pathways by positive and negative feedback
[a] Limit to an understanding of the difference between these two forms of regulation and a brief outline of one example of each.
molecules, also known as ligands, which interact with receptors (proteins) in a target cell.
detection, and response to extracellular signaling molecules called autoinducers. These autoinducers
accumulate in the environment as the bacterial population density increases, and bacteria monitor their
concentrations through receptors to track changes in their cell numbers and collectively alter gene
expression. QS controls genes that regulate activities that are beneficial when performed by groups of
bacteria acting in synchrony, like bioluminescence and antibiotic production (Rutherford).
Vibrio fischeri is an aquatic bacterium that secretes an autoinducer which binds to the LuxR receptor in the
cytoplasm. The LuxR-autoinducer complex prompts the expression of genes coding for the enzyme
luciferase by binding to a specific DNA region. Luciferase catalyzes an oxidation reaction that releases the
majority of the energy as blue/green light. Given that V. fischeri lives in mutualism with several animals like
the bobtail squid, when the population density is high, bioluminescence occurs, which helps the squid
camouflage in moonlight to avoid predation. In return, the squid supplies the bacteria with amino acids and
sugar.
Since some target cells can be found in many places around the body, hormones often have widespread effects.
Neurotransmitters are secreted by the presynaptic neuron and travel through the synaptic cleft to be received by the postsynaptic neuron in order to either stimulate or inhibit the nerve impulse.
Cytokines are small proteins that act on the single cell that produced them, or nearby ones.
Calcium ions are involved in chemical signalling within muscle fibers and neurons.
Include amines, proteins and steroids as chemical groups of hormones.
Intracellular receptors are found in the cytoplasm of the target cell and bind to hydrophobic signalling chemicals, such as steroid hormones.
Extracellular receptors are transmembrane proteins found within the target cell’s plasma membrane and bind to hydrophilic ligands (which cannot pass through the hydrophobic core of the plasma membrane) from outside the cell.
Intercellular receptors alter gene expression to achieve a specific cellular activity.
Extracellular (transmembrane) receptors change their conformation upon ligand binding, and through a series of mechanisms involving effectors and secondary messengers, specific cellular responses are carried out.
• G-protein-coupled receptors
• Enzyme-coupled receptors
• Ion-channel-coupled receptors
1. In the G-protein’s inactive form, the Gα subunit is attached to GDP on its binding site
2. When the ligand (first messenger) binds to GPCR, the transmembrane undergoes a conformational change
3. This triggers the Gα subunit to exchange GDP for GTP
4. GTP activates Gα causing it to dissociate from the Gβ and Gγ subunits (the βγ remain linked as dimers)
5. In turn, activation of the Gα subunit activates an effector molecule (i.e. adenylyl cyclase), which stimulates second messenger synthesis
6. The second messenger then activates an intercellular process, often involving target proteins, in response to the stimulus (i.e. alters metabolism, gene expression, cell growth / death, etc.)
7. The activated Gα subunit rapidly converts GTP back to GDP, which reattaches the βγ subunits to Gα and returns the G-protein back to its inactivate state
1. The hydrophilic ligand (epinephrine) binds to its transmembrane receptor, which is associated with an intracellular component – the G protein
2. Binding of the ligand to its receptor activates the G-protein, which in turn activates the effector adenylyl cyclase (an enzyme)
3. Adenylyl cyclase catalyzes the conversion of ATP to cAMP, a secondary messenger
4. cAMP activates another enzyme in the cytosol called protein kinase
5. The activated protein kinase initiates a phosphorylation cascade in which numerous cellular proteins are phosphorylated by these kinases
6. In liver cells the enzyme glycogen phosphorylase is eventually activated by kinases and catalyzes the catabolism of glycogen into glucose phosphate, which is quickly released into the bloodstream
ATP to a protein, so a tyrosine kinase transfers the phosphate groups to tyrosine (a protein).
1. A ligand binds to the extracellular domain of two nearby tyrosine kinase receptors, causing them to dimerize (bond together)
2. Phosphate groups are then added to the tyrosine residues (auto-phosphorylation) on the intracellular domain of the receptors, triggering the assembly of an intercellular signalling complex
3. The phosphorylated tyrosine residues act as binding sites for signalling proteins, which pass the signals onto target proteins to achieve a specific cellular response
For example, when insulin binds to tyrosine kinase receptors, vesicles containing glucose transporters move towards the plasma membrane and fuse with it, embedding the transports into the membrane in order to allow glucose to diffuse into the cell for respiration)
For example, when acetylcholine is secreted from the presynaptic neuron and binds to its receptor on the postsynaptic neuron, a conformational change occurs and causes the opening of ligand-gated sodium ion channels.
2. The complex moves towards the chromatin in the nucleus and binds to a specific DNA segment, triggering transcription of a target gene to mRNA
3. The mRNA is translated into the target protein in the cytosol, which alters cell activity
For example, testosterone binds to the androgen receptor, upregulating the expression of the FADS1 gene in order to increase the production of fats in prostate cells.
For progesterone, limit to cells in the endometrium.
Progesterone diffuses into uterine cells and enhances the transcription of several genes involved in the maintenance of the endometrial lining during the proliferative phase of the menstrual cycle.
In negative feedback signalling pathways, a rise in the end product of a pathway inhibits the starting point of the same pathway.
[x] Exit text
[/qdeck]