Term
| What are the 3 ways cells communicate? |
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Definition
Secreted messengers which interact with another cell.
Direct cell to cel contact between cell surface proteins.
Gap Junctions |
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Term
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Definition
"tunnels" connecting two adjacent cells through which ions and small molecules can flow.
important in electrical coupling
observed in cells that contact each other in tissues |
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Term
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Definition
| general term for a molecule that binds to a receptor |
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Term
| How do hydrophilic ligands interact with receptors? give an example |
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Definition
| they will bind to cell surface receptors (eg acetylcholine, insulin) |
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Term
| How do hydrophobic ligands interact with receptors? give an example |
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Definition
| will move into the cell via carrier proteins and bind to an intracellular receptor in the nucleus (e.g. steroid hormones, NO, prostoglandins) |
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Term
| What are the 3 short distance signals? |
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Definition
Contant dependent
Paracrine
Autocrine |
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Term
| What are contact dependent signals? When are these used? |
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Definition
| when two cells are so close, a membrane protein on one cell binds to the receptor on the other cell. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. |
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Term
| What are paracrine signals? When are these used? |
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Definition
signals target cells in the vicinity of the emitting cell. Neurotransmitters represent an example.
Growth factos and clotting. |
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Term
| What are autocrine signals? When are these used? |
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Definition
The signal and target cell are one cell.
An example of this are immune cells (interleukins and growth factors released from certain monocytes/leukocytes) |
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Term
| What are the two long distance cell signals? |
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Definition
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Term
| Describe synaptic signalling and give an example |
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Definition
| form of paracrine signalling that occurs across the gap (synapse) between a nerve cell and its target (eg. between a neuron and it's muscle. |
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Term
| Describe endocrine signalling and give an example |
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Definition
| Hormone is released into the ECF and thence the bloodstream to tis target organ (eg thyropoxin from the thyroid gland - affects metabolism) |
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Term
| What are the 3 major types of cell surface receptors? |
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Definition
Ion channel-linked receptors/ligand gated channels
G-protein liniked receptors
Enzyme linked receptors |
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Term
| If a ligand is hydrophobic, is it lipophobic or lipophilic? |
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Definition
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Term
| Describe the mechanism of action of lipophilic ligands |
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Definition
1. lipophobic messenger cross the plasma membrance by simple diffusion
2. once they enter the cytoplasm it binds to a cytoplasmic receptor
3. complex migrates to nucleus
4. interacts with hormones response elements and triggers transcription of mRNA and subsequent translation of a protein. |
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Term
| Describe the sodium and potassium concentrations on the inside and outside of a neuron at rest |
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Definition
Outside:
Na+ = 150mM
K+ = 4 mM
Inside
Na+ = 15mM
K+ = !40mM |
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Term
| What is ATP used for in neurons? |
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Definition
| ATP is used to generate concentration gradients of sodium/potassium ions. There is a large difference in charge. |
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Term
| What relationship does the Nernst equation describe? |
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Definition
| between ion concentration and membrane potential |
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Term
| What is the membrane resting potential? |
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Definition
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Term
| What is the membrane equilibrium potential? |
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Definition
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Term
| What is the NET electrochemical driving force? |
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Definition
| difference between membrane and equilibrium potential |
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Term
| How does resting membrane potential change? |
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Definition
| when ion channels open and ions move in (due to electrochemical driving force) the charge inside the cell changes (changing membrane potential) |
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Term
| What does the current have to reach to be able to change the membrane potential? |
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Definition
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Term
| Describe the mechanism of depolarisation |
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Definition
AP caused by influx of Na+ through voltage dependent channel
Na+ flow into cell down concentration gradient and depolarise membrane
K+ channels function similarly but remain open longer and restore resting potential |
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Term
| What is the refractory period? |
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Definition
In the absolute RP, no APs can be elicited to ensure AP propagtion is unidirectional
In the relative RP, a large stimulus can result in an AP |
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Term
| Describe the node of Ranvier |
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Definition
| gaps in the myelinated axon where there are concentrated voltage gated channels and APs only occur here. APs jump from node to node. |
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Term
| What is the strength of a signal affected by? |
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Definition
- having the appropriate receptor
- the levels of receptor on cell surface
- circulating levels of messenger
- the affinity of messenger for receptor
- the levels of components of the intracellular signal transduction pathway |
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Term
| What are 5 examples of secondary messengers? |
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Definition
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Term
| Describe the structure of a G protein coupled receptor |
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Definition
integral membrane proteins
extracellular ligand binding domain
7 transmembrane domains
intracellular region that interacts with G protein |
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Term
| Describe the structure of a G protein |
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Definition
trimeric proteins attached to the membrane
alpha unit bound to GDP
when GDP is activated it is replaced by GTP and beta-gamma subunits dissociate from alpha. |
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Term
| Describe the events that follow activation |
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Definition
GDP is replaced by GTP
beta-gamma dissociate from alpha
alpha and beta-gamma activate/inhibit other proteins |
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Term
| How do they return to an inactive state? |
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Definition
| alpha sub unit hydrolyses GTP to GDP, re-associates with beta-gamma subunits. |
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Term
| How do G-proteins modulate ion channel activity? |
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Definition
| alpha subunits bind to ion channel proteins and open them. |
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Term
| Describe the cAMP pathway |
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Definition
| Activated GPCRs cause a conformational change in the attached G protein complex, which results in the Gs alpha subunit's exchanging GDP for GTP and separation from the beta and gamma subunits. The Gs alpha subunit, in turn, activates adenylyl cyclase, which quickly converts ATP into cAMP. This leads to the activation of the cAMP-dependent pathway. |
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Term
| What does cAMP activate? what does this new activated molecule affect? |
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Definition
kinase:
-changes in gene expression
-activates enzymes
-opens ion channels |
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Term
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Definition
The Gs alpha subunit slowly catalyzes the hydrolysis of GTP to GDP, which in turn deactivates the Gs protein, shutting off the cAMP pathway.
Phosphodiesterase also breaks down cAMP into AMP |
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Term
| What effect does reduced cAMP levels have? |
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Definition
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Term
| What effect does increased cAMP levels have? |
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Definition
altered gene expression.
Cell will express different levels of some proteins |
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Term
| What are the cytoplasmic targets of protein kinase A? and what are their effects? |
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Definition
glycogen phosphorylase and pyruvate dehydroxygenase (both enhance glucose production)
chloride channels (stimulates Cl- secretion) |
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Term
| Describe the cholera toxin pathway |
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Definition
1. cholera toxin binds to membrane ganglioside
2. toxin subunit enters the cell causing sustained activated of Gs
3. Gs activated adenylyl cyclase
4. cAMP is produced and activates protein kinase A
5. PKA phosphorylates chloride chanel and enhances Cl- secretion
6. Loss of -ve Cl- causes +ve Na+ ions to follow them
7. Water is lost by osmosis. |
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Term
| What does the cleavage of PIP2 produce? and what are their effects? |
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Definition
DAG -> activated protein kinase C
IP3 -> releases Ca2+ from the endoplasmic reticulum |
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Term
| What role does phospholipase C play? |
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Definition
| Phospholipase C is activated by G protein (Gq) and cleaves PIP2 into DAG and IP3 |
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Term
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Definition
DAG activates protein kinase C
ATP + protein kinase C -> ADP and protein kinase C -P --> cell response |
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Term
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Definition
IP3 bind to receptors on the endoplasmic reticulum and Ca2+ are released
Ca2+ + calmodulin -> protein kinase -> cell response
OR
Ca2+ -> cell response |
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Term
| What enzymes are involved in the synthesis and breakdown of cGMP |
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Definition
S: membrane bound guanylate cyclase and soluble guanylate cyclase (from GTP)
B: phosphodiesterase breaks it into CMP |
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Term
| Describe synthesis of cGMP |
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Definition
NO binds to soluble guanylate cyclase and produces cGMP
ANP binds to membrane bound guanylate cyclase and produces cGMP |
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Term
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Definition
| inhibits phosphodiesterase thus increasing cGMP |
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Term
| What are the effects of cGMP? |
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Definition
activates protein kinase G which has cellular effects:
phototransduction, vasodilation |
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Term
| What is the role of NO in smooth muscle relation in blood vessel walls? |
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Definition
1. acetylcholine released from nerve terminals in blood vessel wall activates NO synthesis in endothelial cells lining the blood vessel
2. NO diffuses out and into smooth muscle cells where it binds to and activates guanylyl cyclase to produce cGMP
3. cGMP triggers a response that causes the SMC's to relax, enhancing blood flow through the vessel |
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Term
| Describe the phototransduction pathway |
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Definition
1. light stimulates rhodopsin which activates a G protein
2. activates g protein actives cGMP.PDE
3. PDE hydrolyses cGMP, reducing its concentration
4. This leads to close Na+ channels and hyperpolarised neuron |
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Term
| Give the primary effector, secondary messenger and secondary effector for cAMP pathway: |
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Definition
adenylyl cyclase
cAMP
protein kinase A |
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Term
| Give the primary effector, secondary messenger and secondary effector for phosphoinsterol pathway: |
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Definition
Phospholipase C
IP3 and DAG
Ca2+ release and protein kinase C |
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Term
| Give the primary effector, secondary messenger and secondary effector for cGMP pathway: |
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Definition
membrane bound/soluble guanylate cyclase
cGMP
protein kinase G |
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