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BIO 2B03 > Module 6 > Flashcards

Module 6 Flashcards

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1
Q

Transition Forms of Slime Mold

A

1) unicellular amoebae
2) multicellular slug
3) fruiting body

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2
Q

What’s the name of the slime mold organism? What does it consume?

A

Dictyostelium discoideum, bacteria (EX: E.coli)

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3
Q

Slime Mold [process]

A

1) VEGETATIVE GROWTH PHASE: when food is abundant, unicellular amoebae divide by mitosis
2) under starvation, unicellular amoebae aggregate into a slug in response to a cAMP signal
3) in a nutrient-rich environment, anterior cells form the stalk while posterior cells form the fruiting body containing spores
4) when food is available, spores germinate to form new unicellular amoebae

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4
Q

T or F: a single source of cAMP can cause the amoebae to aggregate together into a slug, reorganizing their intracellular actin cytoskeleton network

A

True

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5
Q

What’s the signal and receptor for the aggregation of Dictyostelium amoebae?

A

[signal] cAMP
[receptor] GPCR (transmembrane protein)

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6
Q

What physical structure allows the movement of unicellular amoebae?

A

Dynamic filopodia

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7
Q

What happens if the Dictyostelium amoeba has a mutation in the gene for the clathrin heavy gene?

A

a) vesicles necessary for transport of protein to cell membrane cannot form
b) this means the transmembrane GPCR is not transported to the cell membrane
c) even in the presence of cAMP, the amoeba will not respond to the signal due to a lack of GCPR

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8
Q

What’s the signal and receptor for the activation of neutrophils in eliminating bacteria?

A

[signal] fMLP (formylated Met-Leu-Phe, produced by bacteria)
[receptor] GPCR

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9
Q

Cell-Cell Signalling [def]

A

[def] transmission of information from one cell to another that induces a change in behaviour

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10
Q

Signal Transduction [four steps]

A

[step 1] receptor binds to a signal
[step 2] initiation of STP (signal transduction pathway)
[step 3] change in cell behaviour
[step 4] signal removal and cessation of response

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11
Q

T or F: The binding of Growth Hormone and it’s receptor is dependent on essential amino acids, a conformational change in the intracellular domain of the receptor induces the STP, leading to a cellular response

A

True

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12
Q

Specificity of the Signal Response [two levels]

A

[1] specificity of the ligand for binding to the receptor
[2] specificity of the intracellular response that’s mediated by the STP

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13
Q

T or F: A single signal always elicits the same response in different cells, meaning they activate the same intracellular transcription factors

A

False, two different cells can respond to the same signal by activating different intracellular transcription factors or even by moving or altering metabolic activity

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14
Q

T or F: cellular responses can be fast (enzyme activation) or slow (changes in gene transcription) depending on the cellular activity

A

True

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15
Q

T or F: In the graph plots the relative concentration of signal ligand against the fraction of receptors bound by the signal, the concentration of ligand to achieve half of physiological response is much higher than the concentration of ligand required to fill half of the receptors, suggesting that only a larger amount of signal can amplify the response

A

False, the concentration of ligand to achieve half of maximal physiological response is much LOWER than the concentration of ligand required to fill half the receptors, suggesting even a SMALL amount can amplify

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16
Q

Dissociation Constant [Kd]

A

[def] the concentration of ligand required to have half of maximal binding and represents receptor-signal affinity

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17
Q

Endocrine Signalling

A

a) signalling molecule = secreted hormone
b) secreted signals are released into the circulatory system
c) signalling cell and target cell are usually far away from one another

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18
Q

Paracrine Signalling

A

a) signalling molecule = growth factors and neurotransmitters
b) secreted signals are released into the extracellular space
c) signalling cell and target cell are near one another

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19
Q

What are three examples of signalling that require cell contact?

A

[integral membrane proteins] the signal and receptor are transmembrane proteins of two cells, requires cell adhesion
[animal/plant junctions] junction between two cells that connects the cytoplasm of neighbouring cells, allowing cytosolic signals to travel across cells, plasmodesmata in plants, gap junctions in animals

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20
Q

Autocrine Signalling [def]

A

[def] the process in which a cell communicates with itself

a) cell produces a secreted signal and also carries receptors for that signal
b) EX: growth factors that induce or stop cell division

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21
Q

3 Main Receptors & Pathways

A

1) Cytokine Receptors
2) Receptor-Tyrosine Kinases (RTK)
3) G-protein Coupled Receptors (GPCR)

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22
Q

T or F: Red blood cells (erythrocytes) develop in the bone marrow and circulate for four months in the body before being recycled by macrophages

A

True

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23
Q

When are red blood cells replaced?

A

when mitotically-proliferating pluripotent stem cells stop dividing and start to differentiate into a specific cell type

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24
Q

What’s the signal for maturation of erythrocytes?

A

Erythropoietin (Epo)

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25
What regulates the expression of erythropoietin?
an oxygen-binding transcription factor in our kidney cells
26
What kind of cells carry the erythropoietin receptor?
Erythrocyte progenitor cells
27
Describe How Erythropoietin Works
[def] a cytokine signal that promotes maturation of erythrocytes, regulated by an oxygen-binding transcription factor found in kidney cells a) only erythrocyte progenitor cells carry the receptor for Epo b) linked to the JAK-STAT STP c) without Epo, cells undergo apoptosis
28
Components of JAK-STAT Pathway
[signal] erythropoietin (Epo) [receptor] epo receptor (EpoR) [intracellular transduction] JAK kinases, STAT transcription factors [cellular response] transcription of STAT target genes, inhibition of apoptosis
29
Erythropoietin Receptor
[three domains] cytosolic, transmembrane alpha-helix, extracellular a) each EpoR has a JAK kinase attached to cytosolic domain b) Epo binds, causing dimerization of two EpoR, bringing two JAK kinases close together c) autophosphorylation, since they are close together, JAK kinases can phosphorylate a neighbouring JAK kinase d) Active JAK kinases phosphorylate tyrosine residues of the EpoR
30
What happens once EpoR is activated?
a) Phosphorylated docking sites become available for binding b) STAT transcription factors bind to these docking sites via SH2 (protein-protein interaction domain) c) JAK Kinase phosphorylates STAT monomers, allowing STAT dimerization d) Causes a change in conformation that reveals a nuclear localization sequence e) STAT dimer is transported into the nucleus to activate transcription of target genes
31
SH2 Domain [STAT]
a) essential to the function of the JAK-STAT signalling pathway b) target peptide sequence: Pro-Asn-pTyr-Glu-Glu-Ile-Pro (Pro Aspas Tired QQ Iso Pro) c) When tyrosine is phosphorylated, SH2 domains will bind with high affinity and specificity
32
Which protein-protein interaction domains are reversible or not reversible?
[reversible] SH2, PTB, 14-3-3 (bind to pTyr) [not reversible] PDZ (hydrophobic residues at C-terminus), SH3 and WW (bind to proline rich domains)
33
T or F: Protein-protein interaction domains that bind to a phosphorylated protein can be reversed because the protein can be unphosphorylated
True
34
What does STAT5 do?
a) when the erythropoietin receptor is activated, STAT5 increases the expression of genes necessary for differentiation of erythroid progenitor cells into mature red blood cells b) EX: Bcl-xL gene codes for the Bcl-xL protein that inhibits apoptosis, which allows cells to eventually differentiate
35
T or F: bone marrow is the only source of erythrogenesis
False, red blood cells are also formed in the liver, during development, all red blood cells are formed in the fetal liver
36
T or F: Mutations in the genes coding for the erythropoietin signal itself, the JAK kinase, STAT protein, and even Bcl-xL protein can prevent the production of red blood cells
True
37
T or F: An overproduction of red blood cells leads to elevated hematocrit, which is an elevate red blood cell count, this would increase the viscosity of blood, potentially blocking narrow capillaries
True
38
When would increasing hematocrit be advantageous?
Some athletes practice "epo doping", which increases red blood cell count to increase the capacity to carry oxygen, increasing endurance
39
How is the cytokine/JAK-STAT pathway typically turned off? [two methods]
[short-term regulation] SHP1 phosphatase has two SH2 domains, allowing it to bind to the same docking sites that STAT would, this leads to dephosphorylation of JAK kinase, turning off the signalling pathway [long-term regulation] SOCS binds to phosphorylated docking sites via an SH2 domain, it's also an E3 ubiquitin ligase which targets JAK kinase for ubiquitinylation and degradation, removing JAK kinase
40
When is SOCS expressed?
In response to high oxygen levels in the body
41
Erythropoietin Gene Mutations
a) Results in erythropoietin receptors with shorter docking sites b) Decreased sensitivity to negative regulators of JAK-STAT pathway, like SHP-1 and SOCS c) Results in a higher red blood cell count (hematocrit)
42
What hormone signals utilize RTK pathways?
1) Nerve Growth Factor (NGF) 2) Platelet Derived Growth Factor (PDGF) 3) Epidermal Growth Factor (EGF) 4) Insulin
43
Components of RTK Pathway
[signal] growth hormone [receptor] RTK [intracellular transduction] GRB2, Ras Protein (GTPase), GEF & GAP, MAP kinase, transcription factors [cellular response] transcription
44
How is RTK activated?
a) growth hormone signal binds to extracellular RTK, leading to dimerization of transmembrane receptors b) this brings two intrinsic kinase domains very close together, leading to autophosphorylation of the neighbouring activation lip of the tyrosine kinase c) Kinases phosphorylate tyrosine residues on the RTK receptor
45
What proteins can bind to the RTK phosphorylated docking sites?
[adaptor protein] monomeric, two or more protein interaction domains, indirectly links other proteins to RTK [scaffold proteins] multiple protein-protein interaction domains, can assemble proteins in an ordered series
46
GRB2 [domains]
a) one SH2 domain & two SH3 domains b) SH2 recognizes phosphorylated tyrosine residues on the RTK docking site c) terminal SH3 domains bind to the next proteins in the pathway via proline-rich domains on partner proteins
46
Once RTK is activated, what happens?
a) activation of GTPase switch protein (GTP-binding), Ras b) GTP = active, GDP = inactive c) GTP-binding protein switches (glycine, threonine) interact with the negative charge of terminal phosphate of GTP d) GTPase activity is required for turning protein "OFF" e) GTPase hydrolyzes the terminal phosphate, releasing the terminal phosphate and eventually GDP f) In the "OFF" state, switches fold out instead
47
What proteins assist in the regulation of G-protein inactivation and activation?
[GEF] guanine nucleotide exchange factor, promotes dissociation of GDP and allows GTP to enter the binding pocket, a G-protein activity activator [GAP] GTPase activating protein, promotes inactivation of G-protein by enhancing GTPase activity, can accelerate intrinsic GTPase activity by 100 fold [GDI] guanine nucleotide dissociation inhibitor, increases affinity of binding pocket for GDP, keeping G-protein "OFF"
48
Describe the Ras-GDP/GTP cycle
a) Inactive G-protein can be maintained when GDI promotes GDP binding, but GEF can promote dissociation of GDP b) GTP replaces GDP, leading to active G-protein that can bind with target protein, GEF dissociates c) After signal pathway is over, GAP promotes GTPase activity, hydrolyzing GTP to GDP, G-protein is "OFF"
49
T or F: The idea of a cellular clock is that G-protein remains ON for a fixed amount of time, determining how much target protein is activated and for how long, if GAP was removed, there'd be prolonged signalling
True
50
What GEF does Ras interact with?
a) Ras G-protein interacts with SOS, a type of GEF b) SOS binds indirectly to RTK via SH3 domains from GRB2 c) This brings SOS close to the membrane-anchored Ras G-protein, allowing the activation of Ras
51
What GAP does Ras interact with?
a) Ras-G protein interacts with NF1, a type of GAP b) presence of NF1 will shorten the length of time that Ras is active, accelerating GTPase c) Without NF1, Ras will remain active for longer than it should d)
52
T or F: Experiments tested four models, if RTK activates Ras, if Ras activates RTK, if they independently operate or if both are need, and results indicated that RTK functions downstream of Ras, meaning Ras activates RTK
False, Ras functions downstream of RTK, which means RTK activates Ras
53
What types of mutations are associated with constitutively active Ras proteins?
a) elimination of a single glycine residue in Ras, preventing GAP from binding b) mutation in Her2 (receptor tyrosine kinase) leads to uncontrolled cell division (breast cancer) c) if NF1 is absent, result is uncontrolled cell division
54
Once Ras is activated, then what happens?
a) phosphorylated residues on Raf are normally bound by 14-3-3 adaptor proteins, inhibited b) binding of Raf to Ras leads to release of Raf from binding 14-3-3, activating Raf
55
What happens due to Raf activation?
[def] serine/threonine kinase protein a) phosphorylates serine and threonine b) Raf, MAP kinase kinase kinase phosphorylates target protein MEK (MAP kinase kinase) c) Then, MEK phosphorylates MAP kinase at tyrosine and threonine, activating it d) Map Kinase dimerizes upon activation and is translocated to the nucleus where target transcription factors are phosphorylated and activated e) Change in conformation of activation lip reveals ATP and substrate binding pockets
56
MAP Kinase [function]
a) phosphorylates P90 RSK kinase in the cytoplasm b) translocates both itself (MAP kinase) and P90 RSK kinase into the nucleus c) inside the nucleus, they both phosphorylate a target transcription factor d) MAP kinase: ternary complex factor (TCF) e) P90 RSK: serum response factor (SRF) f) Trimer of TCF + 2 SRF bind to a DNA sequence called the serum response element (SRE) g) This promotes assembly of RNA polymerase and transcription of target genes, including c-fos h) c-fos is a gene that codes for another transcription factor that enhances transcription of genes required for regulating and turning on the cell cycle
57
What is the change in cell behaviour due to the Ras-RTK pathway?
a) transcriptional activation b) induction of cell division c) differentiation
58
T or F: Each kinase enzyme can target multiple proteins, allowing amplification of the signal at each step, one EGF signal could lead to millions of activated MAP kinase proteins and in turn, millions of copies of target proteins required for cell division, meaning cells can be very sensitive to even low concentrations of hormones
True
59
G-protein Couple Receptors [composition]
a) seven transmembrane alpha helix domains that form the receptor b) creates four extracellular segments, E1 to E4, which fold in the extracellular space to form the signal-binding domain c) creates four cytosolic segments, C1 to C4, which fold to form the internal domain that binds w/ trimeric G-protein
60
Examples of GPCRs
1) receptors that initiate stress responses 2) light-activated rhodopsins in the eye 3) odourant receptors in the mammalian nose 4) hormone/neurotransmitter receptors 5) plant growth hormone receptors 6) glucose-sensing GPCR in yeast
61
Components of GPCR-Stress Pathway
[signals] catecholamines (water-soluble signals in the bloodstream): epinephrine, norepinephrine, dopamine [receptor] GPCR [intracellular transduction] trimeric G-protein, adenylyl cyclase (effector enzyme), cAMP [cellular response] release of stored energy (fast response via enzymes or slow response via transcription)
62
Types of Adrenergic Receptors
1) alpha-2 adrenergic receptors (inhibitory) 2) beta adrenergic receptors (stimulatory)
63
Beta Adrenergic Receptors [locations]
a) liver/adipose cells: glycolysis and lipolysis (important for fuel mobilization) b) heart muscle: increases contraction (increase blood supply to tissues) c) intestinal smooth muscles: increase in smooth muscle relaxation, saves energy for major locomotory muscles note: all important for fight/flight response
64
Alpha-2 Adrenergic Receptors
a) blood vessels of skin, kidney, and intestinal smooth muscle b) cause arteries to constrict, reducing supply of blood to periphery note: more important for rest and digest response
65
Epinephrine
a) product of the adrenal gland, a small endocrine gland on top of the kidneys b) norepinephrine is different, as it's secreted by nerve cells, acts as a neurotransmitter c) epinephrine can bind to alpha-2 or beta receptors d) increases supply of ATP via breakdown of energy stores like glycogen in liver (glycolysis) and triacylglycerol in adipose tissue (lipolysis)
66
In the GPCR-stress pathway, what happens once GPCR is activated?
a) GPCR is activated by the binding of an extracellular signal b) Allows GPCR to bind to a trimeric G-protein, which dissociates GDP and allows binding of GTP to G-protein c) Trimeric G-protein dissociates, releasing the G-alpha subunit, which interacts with the effector enzyme d) The activated effector will only remain active for a short period, dependent on GTPase activity e) Once GTP is hydrolyzed to GDP, the G-protein becomes inactive, releasing the G-alpha subunit, inactivating the effector enzyme f) G-alpha subunit re-associates with G-beta and G-gamma
67
Describe the GPCR-Stress Pathway more specifically [beta adrenergic receptors]
a) associated with stimulatory G-protein: Gs b) GTP associated Gs alpha-subunit dissociates from the trimeric complex and binds to and activates adenylyl cyclase c) adenylyl cyclase increases the intracellular concentration of the secondary messenger, cAMP d) GTPase hydrolyzes GTP to GDP, resulting in re-association of the trimeric complex and decreased concentration of cAMP
68
Describe the GPCR-Stress Pathway more specifically [alpha-2 adrenergic receptors]
a) same as the beta adrenergic receptor but inhibits production of energy b) has a Gi-alpha subunit instead of the normal Gs alpha subunit, same G beta and gamma subunits c) Gi alpha subunit interacts with a different region of adenylyl cyclase and inhibits function, meaning no increase in cAMP
69
GPCRs Hormone Signals
1) Epinephrine 2) Glucagon 3) ACTH
70
GPCRi Hormone Signals
1) PGE1 2) Adenosine
71
How does adenylyl cyclase make caMP?
It converts ATP into cAMP, releasing diphosphate
72
T or F: If adenylyl cyclase is inhibited, there will be a drop in cAMP concentration due to phosphodiesterase activity, which catalyzes the breakdown of cAMP into 5' AMP, counteracting the actions of adenylyl cyclase
True
73
cAMP
a) secondary messenger that responds to GPCR signalling pathways b) modulates activity of proteins like PKA (Protein Kinase A, serine/threonine kinase)
74
Activation of PKA
a) Inactive PKA is a tetramer of two regulatory subunits and two catalytic subunits b) In low concentration of cAMP, the pseudo-substrate domain of the regulatory subunit binds with the substrate binding domain of the catalytic subunit c) In higher concentration of cAMP, binding sites of regulatory subunits are filled, releasing the catalytic subunits, activating PKA
75
What are the targets of PKA?
a) glycogen, a major storage form of glucose, which can be used to produce ATP b) glycogen is synthesized by glycogen synthase, which is then degraded by glycogen phosphorylase c) to release glucose from glycogen, we must inhibit glycogen synthase and promote glycogen phosphorylase
76
What happens to glycogen in the muscle?
Glycogen is metabolized into Glucose-6-Phosphate (G-6-P), which can be used to produce ATP to power muscles in the fight or flight response
77
What happens to glycogen in the liver?
a) glycogen is metabolized into Glucose-6-Phosphate, occurs when PKA phosphorylates and activates glycogen phosphorylase (which breaks down glycogen) b) liver cells also inhibit the production of more glycogen, since PKA also phosphorylates and inactivates glycogen synthase c) this is a fast short-term response to epinephrine that requires only the modification of enzymes present in the cell
78
What is the slow-long term response to the PKA pathway for producing more glucose?
a) catalytic subunit of PKA is translocated into the nucleus where it phosphorylates transcription factors like CREB b) CREB binds to cAMP response element, an enhancer sequence c) When CRE is bound by CREB, it enables assembly of transcription machinery to initiate transcription, including genes required for production of glucose

BIO 2B03 (10 decks)

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