Receptors Flashcards
(101 cards)
1
Q
Drugs bind to receptors through formation of _________, _______ and _________ bonding,
Binding of the drug results in the activation or inhibition of a _______ ______________ pathway that involves receptor/drug-dependent set of cellular signals.
A
Hydrophobic; ionic; hydrogen (non-covalent)
Signal transduction
2
Q
What is the result of non-covalent reactions being reversible?
A
Drugs dissociate from their receptors as their concentration in the plasma decreases.
3
Q
Match the following terms to their definitions:
1) Affinity
2) Law of mass action
3) KD
A) the ratio of a drug receptor dissociation k2 and association k1 rate (k2/k1)
B) tendency of a drug to combine with its receptor
C) the numbers of receptors occupied by a drug depends on the concentration of the drug
A
Affinity: tendency of a drug to combine with its receptor
Law of mass action: the numbers of receptors occupied by a drug depends on the concentration of the drug
KD: the ratio of a drug receptor dissociation k2 and association k1 rate (k2/k1)
4
Q
The lower the Kd, the ______ the affinity.
This occurs if the association rate (k1) constant is much ______ than the dissociation rate (k2).
A
higher; greater
5
Q
(T/F) When a drug binds to a receptor, it will always activate the receptor.
A
False! Binding of a drug does not mean it’s activating the receptor, it can deactivate the receptor (antagonism).
6
Q
AR* means:
A
activated drug receptor complex
7
Q
How are most receptors classified? What are two families of receptors?
A
Receptors are classified based on their PRIMARY AMINO ACID SEQUENCE.
There are 1) intracellular receptors (nuclear receptors) and there are 2) membrane receptors (tyrosine kinases, g-protein linked, and ion channels).
8
Q
Nuclear receptors are ligand activated _________ ______ that activate ______ synthesis.
A
Transcription factors; mRNA synthesis
*TF meaning it binds to the DNA
9
Q
Match the different types of regions of a nuclear receptor to their definitions:
1) Variable
2) DNA Binding Domain (DBD)
3) Hinge
4) Ligand Binding Domain (LBD)
A) important for NUCLEAR LOCALIZATION. aka D site.
B) at the C-terminus. Composes of AF-2 site. aka E/F site.
C) contains Zn2+ fingers. aka C site.
D) at the N-terminus and contains AF-1 site. aka A/B site.
A
Variable: at the N-terminus and contains AF-1 site. aka A/B site.
DNA Binding Domain: contains Zn2+ fingers. aka C site.
Hinge: important for NUCLEAR LOCALIZATION. aka D site.
Ligand Binding Domain: at the C-terminus. Composes of AF-2 site activates transcription). aka E/F site.
10
Q
Match the different types of regions of a nuclear receptor to their definitions:
1) Variable
2) DNA Binding Domain (DBD)
3) Hinge
4) Ligand Binding Domain (LBD)
A) 70 aa and HIGHLY CONSERVED
B) 200-250aa and MODERATELY CONSERVED
C) 50-500aa and VARIABLE
D) 45aa
A
Variable: 50-500aa and VARIABLE
DNA Binding Domain (DBD): 70 aa and HIGHLY CONSERVED
Hinge: 45aa
Ligand Binding Domain (LBD): 200-250aa and MODERATELY CONSERVED
11
Q
Which domain of a nuclear receptor is the most important for pharmacology?
A
Ligand binding domain
12
Q
(T/F) Receptor protein homologies reflect function and diversity of ligands. For example, steroid receptors are more homologous than non-steroids are to them.
A
True!
13
Q
How do nuclear receptors activate specific genes?
A
They recognize specific sequences of DNA called HORMONE RESPONSE ELEMENTS (HRE), which are a class of “promoter enhancers.”
There are two identical/similar parts to the HRE called “HALF SITE MOTIFS” that each bind to one nuclear receptor (bind as dimers).
When the receptors bind, the promoter is activated leading to gene expression.
*this gives them specificity
14
Q
While steroid receptors bind to DNA as ________, non-steroid receptors bind as _________ (oftern RXR).
A
Homodimers; heterodimers
15
Q
Give examples of steroid receptors and non-steroid receptors.
A
Steroid receptors; glucocorticoid, mineralocorticoid, progesterone, androgen, estrogen
Others: T3R (thyroid), RAR (retinoic acid), VD3R (vitamin D3) and PPAR.
16
Q
The two Zn fingers of a nuclear receptor contains four ________ in the base to coordinate a zinc ion. Thus, they are very _______!
A
Cysteines; stable
*one nuclear receptor has 2 zinc fingers; one has the P box, the other has the D box. a dimer has 4 zinc fingers!
17
Q
The two Zn fingers of one nuclear receptor contain a P box and D box, where the P box is close to the ___-terminus, and the D box is close to the ___-terminus.
P box is responsible for:
D box is responsible for:
A
C, N
Recognizing the primary nucleotide sequence and binding to it.
Spacing of the half-site motif (of the two receptors on the DNA; does not contact the DNA).
18
Q
(T/F) The P and D box are responsible for the ability of the receptors to specifically bind to certain gene enhancers to activate transcription of downstream genes.
A
True!
19
Q
On the basis of the primary nucleotide recognition sequence, nuclear receptors can be divided into two families:
A
1) glucocorticoid-R family
2) estrogen/thyroid Hormone-R family
20
Q
(T/F) The amino acid sequence of the P and the D box among nuclear receptors are highly homologous.
A
False!
The amino acid of the P box is almost identical to all receptors, while the amino acid sequence is different in all receptors for the D box.
The spacing of half-sites (caused by the D box) dictates which HREs are recognized (selectivity).
21
Q
How do the D boxes determine the length of the spacing of the half site motifs?
A
D boxes of the dimers (1 d box in one monomer) can attract or repel one another.
If they attract, there are less nucleotides (~3) between the two half site motifs. If they repel, there are more nucleotides.
22
Q
(T/F) The half sites of a dimer are palindromic sequences.
A
True!
23
Q
What is the consensus DNA sequences for enhancers (HRE) which bind and are activated by the ER/TR family?
A
They are composed of a half-site motif; A G G T C A as a repeated sequence.
ex: AGGTCAXXXAGGTCA
24
Q
While Vitamin D3’s half site motifs are separated by 3 nucleotides (direct repeat 3), the thyroid is separated by ____ nucleotides (direct repeat __), and the retinoic acid is separated by ____ nucleotides (direct repeat __)
A
4; 5
25
DNA is wound around ______ proteins in a condensed state and the DNA-histone interaction must be __________ for transcription to occur.
histone; loosened
*allows TFs to gain access to DNA
26
(T/F) The nucleosome consists of an octamer of four histones (two copies each of H2A, H2B, H3 and H4).
True!
27
What is a co-repressor and co-activator complex?
Give an example of each and describe how it works.
Co-repressor complex keeps the gene silent when there is no ligand bound.
HISTONE DEACETYLASE is an example of a co-repressor complex. It removes the negative acetyl groups, maintaining a positive charge on histones, attracting the negative DNA, causing it to be tightly wound.
Co-activator complex activates the gene when there is a ligand bound.
HISTONE ACETYLASE is an example of a co-activator complex. It adds negative acetyl groups on histones, loosening the DNA.
28
What does histone acetylation accomplish?
1) acetylation neutralizes the positive charge on histone tail to "loosen" the interaction between DNA and the histone
2) acetylation PATTERNS control the binding of non-histone proteins (RNA pol complex) to the chromatin fiber
29
(T/F) There are only synthetic ligand for nuclear receptors.
False! There are NATURAL and SYNTHETIC ligands.
30
The thyroid hormone is a critical hormone in _________; it controls _______ and _______ maturation.
It also cooperates with _______ nervous system by increasing ____________ receptors.
Most active hormone is ____ derived from _____ by _____________ in thyroid gland and in ______ and ______ tissues.
development; growth; sexual
sympathetic; adrenergic (adrenaline)
T3; T4; 5'-deiodinase; liver; muscle
31
What are the two preparations of the thyroid hormone?
Which one is given when there is a deficit in 5'-deiodinase?
1) Levothyroxine (T4)
2) Liothyronine (T3)
Liothryonine is given.
32
What does excess thyroid lead to?
Thyroid hormone controls metabolism:
1) Increases CARBOHYDRATE METABOLISM
2) Increases FAT METABOLISM (lipids are mobilized from the fat tissue)
3) DECREASES CHOLESTEROL, PHOSPHOLIPIDS and TRIGYCERIDES in the blood
4) Increases in enzymes requiring vitamins as coenzymes so INCREASED NEED FOR VITAMINS
5) BASAL METABOLIC RATE: increases metabolism in most cells of the body - TH can occasionally increase the basal metabolic rate to as much as 60-100% above normal
6) Decreases the BODY WEIGHT but increases the appetite
7) INCREASED heart rate
33
While people who have deficits in thyroid hormone are _____, people who have hyperthyroid are _____.
fat; thin
34
Thyroid deficiency can be due to:
What is it associated with? How?
Autoimmune (enzymes can attack glands and enzymes that make the TH) and iodide deficiency (leads to decrease in TH).
It is associated with GOITER.
How goiter is formed:
In the absence of TH, HYPOTHALAMUS becomes activated (T4 and T3 are negative regulators of hypothalamus).
Hypothalamus releases lots of Thyroid Releasing Hormone (TRH), which activates the PITUITARY.
Pituitary makes Thyroid Stimulating Hormone (TSH), which releases T4 and T3.
If the thyroid is functioning normally, T4 and T3 signal hypothalamus to stop making TRH. If it's not functioning properly (maybe due to iodine deficiency), hypothalamus continues to release TRH, which leads to an increased amount of T3 and T4 production, resulting in a goiter.
35
Briefly answer these questions regarding estrogen:
1) What is the active form?
2) What is its role in development?
3) What is its role in reproduction?
4) What are its preparations?
5) What are its indications?
1) β-estradiol
2) Promote formation of fallopian tubes, uterus, and female secondary sexual characteristics.
3) Essential role in menstrual cycle/ovulation in both follicular and luteal phases
4) It is derived from pregnant horses. There can be conjugated equine estrogens (suphate esters of Estrone and equilin), and Ethinyl estradiol (synthetic)
5) Hormone replacement therapy (HRT) and treatment of infertility.
36
Contraceptives are estrogens in combination with __________.
Yasim/Yaz are a type of contraceptive that contain ________ which has ___________ and __________ activities. However, they increase the risk of ______ ______ due to reduced blood volume.
Progestins (synthetic mimic of progesterone)
Drospirinone; antimineralcorticoid*; antiandrogenic; blood clots (more than normal)
*antimineralcorticoid is a diuretic, which decreases the swelling caused by the contraceptives.
37
What is the function of testosterone in development and in reproduction?
In development: promotes male secondary sexual characteristics
In reproduction: necessary for sperm production
*testosterone binds to androgen receptors
38
What are the side effects of contraceptives with estrogen? Why?
What is a safer alternative?
Side effects: 1) Increased risk (0.09%) of THROMBOSIS, 2) may promote growth of BREAST CANCERS (esp post menopause)
E2-ER ACTIVATES the transcription of the PROCOAGULANT factors; II, VII, IX, X, XII, XIII and fibrinogen and INHIBITS the transcription of natural ANTICOAGULANT protein S and antithrombin.
Safer alternative is a PROGESTIN ONLY contraceptive.
39
What does SERMs stand for? What are they used for? Give two examples.
Selective Estrogen Receptor Modulators
They are used in the treatment of ER (+) breast cancer.
Tamoxifen and Raloxifene are SERMS.
40
How do SERMs cause proliferation in some cell types (uterus) and inhibit proliferation in other types of cell (breast cancer cell)?
What is the best case scenario for a SERM drug?
SERMs elicit different effects depending on several factors in different tissues and on different gene enhancers (response elements).
Different tissues have different TFs!
Best case scenario: AGONISM in bone (prevents osteoporosis in post menopause women) and CV system and ANTAGONISM in uterus and breast.
41
Briefly answer the questions regarding Retinoids in therapeutics:
1) Why are retinoic acid (ATRA) and derivatives use in cancer therapy?
2) What kind of cancer does it treat? How?
1) They are a) ANTI-PROLIFERATIVE and b) DIFFERENTIATION INDUCING + morphogenic
2) Promyelocytic leukemia (PL). Acute PL results in the loss of ability of Hemopoietic precursors. They can not differentiate into other cells and accumulate. Retinoic acid can induce terminal differentiation into myelocytes, elevating leukemia.
42
How can retinoids reduce wrinkles and acne?
1) Inhibit METALLOPROTEINASES that break down collagen
2) Induce skin CELL PROLIFERATION under some circumstances
3) Cause EPIDERMAL DIFFERENTIATION and DRYING of the skin (isotretinoin - a derivative of RA can treat untreatable acne)
43
Retinoic acid is essential for normal development, but it can be teratogenic.
Describe teratogenesis; what it does, when it happens, how, etc.
Teratogenesis is the induction of birth defects in a developing embryo.
Retinoic acid or Vitamin A derivatives, even at very low doses, can be potent teratogen.
CRANIOFACIAL DYSMORPHISMS, CLEFT PALATE, THYMIC APLASIA, and NEURAL TUBE DEFECTS are some of the malformations caused.
The 2nd to 5th week of gestation is the critical period of exposure that causes birth defects.
Retinoic acid INHIBITS THE EXPRESSION of development genes!
44
What kind of genes are regulated by RAR/RAREs?
What happens if there is a lot of or little of retinoid?
Homeobox genes (genes necessary for formation of hands, legs, and facial structures aka pattern formation)
Too much retinoid: genes are dis regulated because they will be on too strongly relative to what they should be at normal embryo (severe abnormalities in babies)
Too little retinoid: no genes turned on!
45
Match the following scenarios to their outcomes:
1) Single RA-responsive enhancer sequentially activates entire Hox cluster
2) Multiple functionally distinct RA-responsive enhancers co-ordinate Hox gene activation
3) Cascade of gene activation by Hox proteins
A) one enhacer responsible for one Hox gene, which regulate one another
B) one enhancer governs transcription of all genes
C) one enhancer per gene, the first one activated is the strongest
Single RA-responsive enhancer sequentially activates entire Hox cluster: one enhancer governs transcription of all genes
Multiple functionally distinct RA-responsive enhancers co-ordinate Hox gene activation: one enhancer per gene, the first one activated is the strongest.
3) Cascade of gene activation by Hox proteins: one enhacer responsible for one Hox gene, which regulate one another.
46
What are the five classes of Receptor Tyrosine kinases (RTKs)?
1) Epidermal growth factor (EGF-R); EGFR1, EGFR2, EGFR3, 4
2) Insulin Receptor
3) Platelet-derived growth factor (PDGF)
4) Fibroblast growth factor (FGF)
5) Vascular endothelial growth factor (VEGF)
47
Match the following EGFs to the mouse version/alternate to human receptor :
1) EGFR1
2) EGFR2
3) EGFR3,4
A) ErbB3,4 or HER 3,4
B) ErbB1
C) ErbB2, HER2/neu
EGFR: ErbB1
EGFR2: ErbB2, HER2/neu
EGFR3,4: ErbB3,4 or HER 3,4
48
The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, ____ __________ the enzymatic activity of the ____________ catalytic domain, which causes tyrosine __________________ of cytoplasmic signalling molecules.
up-regulates; intracellular; phosphorylation
49
(T/F) Upon binding to a ligand, two receptor tyrosine kinases dimerize, where they trans autophoshorylate their tails, leading to a signal transmission.
True!
50
What is Grb2?
Epidermal growth factor ADAPTOR PROTEIN containing SH2 and SH3 domains.
51
Briefly answer the following questions about the SH2 domain:
1) What is it composed of?
2) What does it do?
3) Where is the domain found?
1) Small protein module (150aa) with some highly CONSERVED, BASIC AA
2) Primary function is to BIND PHOSPHOTYROSINES and in doing so localizing different proteins necessary to transmit proper function in signal transduction pathways.
3) It is found in a wide variety of proteins including those with "catalytic domains" structural proteins, and adaptor proteins.
51
How do SH2 domains achieve specificity?
Different SH2 domains have different affinities for phosphotyrosines (surrounding sequences can confer specificity).
- change SH2 domain slightly or change the amino acids surrounding/of the phosphotyrosines
51
What determines if a protein will bind to an RTK and be phosphorylated?
The sequences C-terminal to the consensus phosphotyrosine binding domain determine if a protein will bind to an RTK and be phosphorylated.
52
Briefly answer the following questions about the SH3 domain:
1) What is it composed of?
2) What does it do?
1) β-barallel of 5-6 anti parallel β strands
2) It mediates protein-protein interactions by binding to PROLINE-RICH regions (polyproline helix) in other proteins.
53
What is SOS?
It is a GUANINE NUCLEOTIDE EXCHANGE PROTEIN that facilitates the activation of the Ras protein (reversible reaction).
Ras.GDP (inactive) -----(SOS)-----> Ras. GTP (active)
53
After the phosphorylated RTK binds to Grb2, Grb2 interacts with ______ through the ____ domain.
SOS, SH3
*SOS must have a polyproline helix
54
What kind of kinase is raf?
serine/threonine kinase
55
Briefly answer the following questions regarding the insulin RTK:
1) What is it composed of?
2) How is it different from other RTKs?
3) What happens to it when an insulin binds?
1) It is composed of 2 alpha and 2 beta units, making it a HETEROTETRAMER
2) Insulin binding (at the alpha site) leads to change in the structure!
3) When insulins bind to the alpha subunit, the beta subunits get activated, which phosphorylate tyrosine residues on the cytoplasmic domains and on the Insulin Receptor Substrate (IRS). Oncer IRS is activated, it can bind a lot of proteins, primarily through the SH2 domains, triggering a number of signalling pathways.
56
Which pathways are triggered by insulin binding to insulin RTK?
What is the primary function?
1) Growth/proliferation
2) Survival (antiapoptosis)
3) Cell motility
4) Glucose metabolism - stimulates movement of glucose transporter proteins from the ER to the cell membrane.
#4 is the primary function.
57
In ________ muscle and ________ tissue, insulin stimulates both _____ _________ and ________ _______.
skeletal; adipose
gene expression; glucose uptake
58
Briefly describe how binding of insulin to the insulin TKR leads to glucose uptake.
1) Insulin binds to the alpha subunit of receptor, causing beta subunit to phosphorylate itself and IRS.
2) IRS binds to PI3 Kinase through its SH2 domain.
3) PI3 Kinase activates Protein Kinase C (PKC) and Protein Kinase B (PKB).
4) PKC and PKB are reponsible for a series of phosphorylation that results in release of GLUT4 from the storage vesicles in the ER to the cell membrane (TRANSLOCATION).
5) Glucose is able to come inside the cell now!
59
What is the difference between type I and type II diabetes?
Type 1: Juvenile - destruction of beta cells of pancreas that make insulin (can't make insulin)
Type 2: Adult onset - often associated with OBESITY and INSULIN RESISTANCE and can involved autoimmunity to the insulin or receptor defects (can make insulin but don't respond to it)
60
Match the organs/tissues to what insulin actions:
1) Liver
2) Skeletal muscle
3) Adipose
A) insulin stimulates the conversion of GLUCOSE TO FATTY ACIDS and STORAGE as TRIGLYCERIDES (sugar causes obesity this way)
B) provides glucose during fasting and therefore insulin stimulates the liver to STORE GLUCOSE IN THE FORM OF GLYCOGEN
C) provides glucose during fasting and therefore insulin stimulates the liver to STORE GLUCOSE IN THE FORM OF GLYCOGEN
Liver: provides glucose during fasting and therefore insulin stimulates the liver to STORE GLUCOSE IN THE FORM OF GLYCOGEN
Skeletal muscle: depends on insulin for GLUCOSE UPTAKE to provide energy
Adipose: insulin stimulates the conversion of GLUCOSE TO FATTY ACIDS and STORAGE as TRIGLYCERIDES (sugar causes obesity this way)
61
What are some acute and chronic pathologies caused by diabetes?
Acute:
- hyperglycemia resulting glycosuria (sugar urine), osmotic diuresis (as sugar goes out, many things go out w it), and dehydration
- electrolyte depletion
- increased lipolysis stimulated by glucagon leading to ketone production in the liver --> KETOACIDOSIS (abnormal respiration)
- coma, death
Chronic:
- many vascular issues due to high blood pressure levels that result in glycosylated proteins (like hemoglobin)
- coronary artery disease
62
What is the difference between fast-acting and long-acting analogues of insulin?
Fast-acting has rapid effects (onsets in minutes), and is used to treat POST-PRANDIAL HYPERGLYCEMIA
Long-acting has long-acting effects (onsets in 1/2 hours) and is for maintenance; slow release due to AGGREGATION OF MOLECULES therefore DISSOCIATION is required.
63
(T/F) Since RTKs can function as growth factor receptors, they are potential oncogenes. Thus, many cancer cells have an increased number of RTKs (Activation) or they have a mutation that makes them constantly active (Constitutive activity).
True!
64
While in epithelial cancers, ______ are overexpressed/mutated, _____ are amplified/mutated in breast cancers.
EGFR1; EGFR-2/Her2/neu
*About 15-20% of breast cancers overexpress HER2!
65
What are the two therapeutic strategies to target the RTK family?
1) EGFR-tyrosine kinase inhibitors (monoclonal antibodies - ~145,000Da)
2) Anti-EGFR antibody inhibitors (small molecules - ~447Da)
66
Match the following inhibitors to their RTK targets:
For monoclonal antibodies:
1) Trastuzumab
2) Bevicizumab
A) VEGFR
B) ERBB2
For small molecules:
1) Imatinib
2) Erlotinib
3) Gefitinib
4) Sorenfenib
A) EGFR
B) Raf kinase, VEGFR and PDGFR
C) EGFR
D) PDGFR & others
For monoclonal antibodies:
1) Trastuzumab: ERBB2
2) Bevicizumab: VEGFR
*mab; monclonal antibodies
For small molecules:
1) Imatinib: PDGFR & others
2) Erlotinib: EGFR
3) Gefitinib: EGFR
4) Sorenfenib: Raf kinase, VEGFR and PDGFR (very potent)
67
(T/F) VEGF can cause "Wet Macular Degeneration" and loss of central vision.
WMD: chronic eye disease that causes vision loss in the center caused by abnormal blood vessels that leak fluid/blood into the region.
True!
68
What is receptor downregulation?
Receptor downregulation is a mechanism to protect cells from overstimulation.
Bound ligand results in ENDOCYTOSIS of tyrosine kinase receptors and eventually DEGRADATION.
When the degradation exceeds synthesis (desensitization), there is a net receptor down regulation, which leads to attenuation of cellular responses.
69
What was the first receptor to be characterized?
β-adrenergic receptor (G-protein coupled receptor)
70
Which statement of G-protein coupled receptor is false?
1) G-protein stands for GTP binding protein
2) Many hormones work through GPCRs
3) There are as many as 4000 different GPCRs
4) 1/20 proteins are GPCRs in Caenorhabditis (worm)
5) 1/4 of prescription drugs work through GPCRs
3! There are as many as 2000 different GPCRs
71
Briefly describe the basic structure of GPCRs; which part is strongly conserved vs less conversed?
GPCRs are usually 400-500 amino acids in length with SEVEN TRANSMEMBRANE (α) HELICAL segments aka serpentine receptors.
The helices are very strongly conserved. Extracellular amino terminus and the intracellular carboxy termini vary in length and sequence and are less well conserved.
72
(T/F) GPCRs are defined by their ability to bind to G-protein; the seven helices form a circle to bind to the ligand.
True!
73
Point mutation of the ____ ________ loop destroys signalling, which is the region which couples to the G protein.
Swapping this loop between different receptors alters their:
Third cytoplasmic
G-protein selectivity
74
Where is the ligand binding (of GPCRs) domain buried? What has its structure allowed to do?
Ligand binding domain is buried within the membrane on 1 or more helical domains.
Structure of the ligand binding domain has allowed pharmacologists to design synthetic agonists.
75
(T/F) GPCRs all work in the same way through heterotrimeric G-proteins (α, β, γ) and turn on effector molecule (found in the cell membrane) which makes the second messenger.
True!
76
(T/F) G proteins can not diffuse around the membrane and can't interact with several different GPCRs (so restricted to one type of GPCR).
False! G proteins can diffuse around the membrane and can interact with several different GPCRs (not restricted to only one type of GPCR).
77
Match the steps of GPCR:
1) Step 1
2) Step 2
3) Step 3
4) Step 4
5) Step 5
6) Step 6
7) Step 7
8) Step 8
Step 1: When receptor combines with ligand, receptor changes shape and binds the
78
Match the steps of GPCR:
1) Step 1
2) Step 2
3) Step 3
4) Step 4
5) Step 5
6) Step 6
7) Step 7
8) Step 8
A) Relay - the α subunit dissociates from β,γ and associates with effector, producing second message. (β,γ stay together & second message is made for duration of binding).
B) α subunit hydrolyzes GTP into GDP, deactivating itself.
C) G-protein-coupled-receptor kinase (GRK) phosphorylates receptor at the C-terminal loop.
D) When receptor combines with ligand, receptor changes shape and binds the α subunit of the G protein.
E) α subunit binds other two subunits - now INACTIVE.
F) Activation of the g protein - α then exchanges a GDP for a GTP, entering activated state (the receptor/ligand can activate several G proteins, as long as ligand is bound).
G) Arrestin protein binds to phosphorylated receptor to prevent G-proteins from binding - DESENSITIZATION.
H) Activated effector produces second messenger.
Step 1: When receptor combines with ligand, receptor changes shape and binds the α subunit of the G protein.
Step 2: Activation of the g protein - α then exchanges a GDP for a GTP, entering activated state (the receptor/ligand can activate several G proteins, as long as ligand is bound).
Step 3: Relay - the α subunit dissociates from β,γ and associates with effector, producing second message. (β,γ stay together & second message is made for duration of binding).
Step 4: Activated effector produces second messenger.
Step 5: α subunit hydrolyzes GTP into GDP, deactivating itself.
Step 6. α subunit binds other two subunits - now INACTIVE.
Step 7: G-protein-coupled-receptor kinase (GRK) phosphorylates receptor at the C-terminal loop.
Step 8: Arrestin protein binds to phosphorylated receptor to prevent G-proteins from binding - DESENSITIZATION. This is done to prevent overstimulation.
79
The GTPase activity of g-proteins is sometimes induced by __________ ___________ _______.
Regulator of G-protein Signaling (RGS)
80
How can a specific G-protein coupled receptor only control one kind of effector?
Not completely understood but not all G proteins are identical; they have several different α subunits.
81
What are the 5 main types of Gα proteins?
Gs, Gi, Gq, Gt, G12
82
(T/F) In some cases inhibitory and stimulatory GPCRs have the same target effector. Gs and Gi stimulate and inhibit adenylate cyclase respectively. This allows different receptors to exert opposite effects on a target effector enzyme in the presence of agonist.
True!
83
Match the following G proteins to their effectors:
1) Gαs
2) Gαq
3) Gαi
A) activates phospholipase C
B) inactivates adenylate cyclase but activates cyclic GMP phosphdiesterase
C) stimulates adenylate cyclase
Gαs: stimulates adenylate cyclase
Gαq: activates phospholipase C
Gαi: inactivates adenylate cyclase but activates cyclic GMP phosphdiesterase (c-GMP is impt in function of rhodopsin).
84
Adenylate cyclase/cAMP system induces ______ ______ ___ which then phosphorylates many different substrates.
Protein Kinase A (PKA)
85
What happens when Phospholipase C (PLC) is activated by Gαq?
Phospholipase C (PLC) releases diacylgycerol (DAG) and inositol phosphate (IP3) from PIP2.
DAG induces Protein Kinase C (PKC), which phosphorylates several proteins which then regulate downstream signalling.
IP3 releases intracellular Ca2+ from the ER to regulate the activity of Ca2+ dependent enzymes.
86
What are ionotropic receptors? Give examples.
Ionotropic receptors are channel linked receptors. These channels are activated directly by bound ligand. They are responsible for fast post-synaptic responses.
Examples - neurotransmitters: GABAA receptor, Nicotinic Acetylcholine receptor, 5-HT3 receptor.
87
Briefly describe the structure of ionotropic receptors.
It has 2 α, one β, one γ and one δ.
Each subunit spans membrane 4 times (M1, M2, M3, and M4), resulting in 20 membrane spans.
M2 form the lining of the channel.
88
Most ionotropic receptors are are at the ______-_______ membranes of neurons but _________ receptors are found in muscle at the __________ junction.
post-synaptic; acetylcholine; neuromuscular
89
(T/F) The ionotropic receptors get the membrane depolarization started at the synapse, then the voltage-gated Na+ channels propagate the current.
True!
90
Activation results in transient _______ in permeability to particular ions.
Average duration for which a single channel stays open is only about ___-___ _______ aka channel lifetime.
Increase
Ex. Na+ and K+ increase permeability induced by Ach (muscle) and by glutamate (CNS), which results in depolarization and the formation of an "action potential."
1-2 millisec
Ex. nACH-R allows the flow of 10^7 ions/sec
91
Describe how the ACh channel behaves when it is in the unliganded state vs when ACh binds to it.
In the unliganded state, the α-helices in the M2 subunits are kinked inwards halfway through membrane resulting in constriction of the channel.
When ACh binds, it straightens or swings open the α-helices, leading to the pore opening up.
92
What causes an ionotropic receptor's specificity to switch from cation to anion selectivity?
Point mutation of a critical aa in the M2 helix
93
A nicotinic receptor has ____ subunits, while a glutamate receptor has ____ subunits per receptor.
5; 4
94
NMDA receptors are located at _____-____ density region of ________ synapses.
They are permeable to ____ and _____ ions.
NR1 and NR2 _______ subunits are associated in a _______ stoichiometry in the membrane.
Post-synaptic; excitatory
K+ and Ca2+
Glutamate; Tetrameric (NMDA receptors are composed of subunits that can make up the glutamate subunits)
95
For most receptors, channel _________ is the same for different agonists. However, agonists differ in channel _________ they induce.
Conductance; lifetime
96
Match the following to their definitions:
1) Opening constant of a ligand
2) Closing constant of a ligand
3) High efficacy
4) Low efficacy
5) Antagonist
A) β > α
B) β = 0
C) α > β
D) β
E) α
Opening constant of a ligand: β
Closing constant of a ligand: α
High efficacy: β > α - a large proportion of receptors are active at any given time
Low efficacy: α > β - fewer receptors are active at a time
Antagonist: β = 0
97
Match the ionotropic receptors to their definitions:
1) AMPA/glutamate receptor
2) GABA receptor
3) Nicotinic Ach receptor
A) EXCITATORY increase in Na+ and K+ conductance. Present in postsynaptic neuron and at NEUROMUSCULAR JUNCTION.
B) Heteromeric combinations of Glu R1-4 subunits. Mediate fast EXCITATORY synaptic transmission. Increased Na+/K+ CATION permeability (but not for Ca2+). Localization and clustering through interaction with "PDZ-domain"-containing protein.
C) Ligand-gated chloride channels (ANION). At post-synaptic membrane of GABA-ergic synapses. INHIBITORY neurotransmitter; other ligands include barbiturates and benzodiazapines.
AMPA/glutamate receptor: Heteromeric combinations of Glu R1-4 subunits. Mediate fast EXCITATORY synaptic transmission. Increased Na+/K+ CATION permeability (but not for Ca2+). Localization and clustering through interaction with "PDZ-domain"-containing protein.
GABA receptor: Ligand-gated chloride channels (ANION). At post-synaptic membrane of GABA-ergic synapses. INHIBITORY neurotransmitter; other ligands include barbiturates and benzodiazapines.
Nicotinic Ach receptor: EXCITATORY increase in Na+ and K+ conductance. Present in postsynaptic neuron and at NEUROMUSCULAR JUNCTION.
98
What are PSD proteins, rapsyn and utrophin?
They are responsible for stabilizing and locating receptor proteins in the proper place in the membrane.
NR2 C-terminus mediates interaction with a large multiprotein complex in which the main protein is PSD-95.
