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Human Physiology (BIOL 2410/2420) > Cell Communication > Flashcards

Cell Communication Flashcards

1
Q

What are the two types of signals in cell signalling?

A

Electrical signals: changes in membrane potential

Chemical signals: ligands secreted by cells into the extracellular fluid

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2
Q

What are the 3 basic methods of local communication?

A
  1. Gap junctions
  2. Contact-dependent signals
  3. Paracrine and autocrine
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3
Q

What is a gap junction, what is it made of, and where can you find them?

A

Closeable protein channel that creates a cytoplasmic bridges between adjacent cells for small moelcules and ions to diffuse. It is made of two connexons made of 6 connexins each. It is common in the heart, smooth muscle, and some neurons.

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4
Q

How does contact-dependent signalling work and where is it used in?

A

Glycoprotein acts as ligand to receptor in the membrane of another cell. Typically used in the immune system and during development.

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5
Q

What do paracrine and autocrine signalling have in common and how do they differ?

A

Both involve the diffusion of a signalling molecule into the interstitial fluid

Paracrine: signals to cells in the immediate vicinity

Autocrine: signals to self

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6
Q

What are the two types of long-distance communication?

A

Chemical: endocrine system

Electrical: nervous system

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7
Q

What is the endocrine system? How does it differ from the exocrine system?

A

Endocrine: secretes chemical signals into the blood (e.g. insulin)

Exocrine: secretes chemical signals into a duct (e.g. pancreatic enzymes)

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8
Q

What are three neurocrine molecules?

A

Neurotransmitters: Diffuses from neuron across synapse to a target cell and causes a rapid effect. (e.g. neurotransmitters)

Neurohormones: Diffuses into the blood ofr body-wide distribution.

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9
Q

What features do all signal pathways share?

A
  1. Signal molecule (first receptor) is a ligand that binds to a protein receptor
  2. Ligand binding activates receptor
  3. Receptor activates an intracellular signal molecule
  4. Last signal molecule in the pathway creates a response by modifying existing proteins or initiating synthesis of new proteins
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10
Q

What is the difference between a lipophilic signal molecule and a lipophobic signal molecule?

A

Lipophilic: enters cells by simple diffusion and bind to receptors in cytoplasm OR nucleus. Usually alters gene expression and is relatively slow.

Lipophobic: does not enter cells, but binds to receptor proteins on the cell membrane to initiate a cascade. Response time is very rapid.

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11
Q

What are 4 types of cell membrane receptors involved in signal transduction?

A
  1. Receptor channel
  2. Receptor-Enzyme
  3. G protein-couples receptor
  4. Integrin receptor
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12
Q

What is a signal transduction? What is a transducer?

A

Transduction: Process where extracellular signal molecule (first messenger) activates a membrane receptor that alters intracellular molecules (second messenger) to create a response.

Transducer: device that converts a signal from one form into a different form

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13
Q

What are the roles of membrane receptors and second messengers?

A

Membrane receptors: activate protein kinases and aplifyer enzymes that create intracellular second messengers

Second messengers: Alter ion gated channels, increase intracellular calcium to alter protein shape and function, and chaneg enyme activity of protein kinases or protein phosphatases.

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14
Q

What is signal amplification?

A

turning one signal molecule into multiple second messenger molecules via amplifier enzyme turned on by the ligand-receptor complex.

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15
Q

How does a receptor channel work?

A

ligand (typically neutransmitter) binds to the ion channel, opening it to allow ions to enter/leave cells (e.g. synaptic transmission) as well as Ca++ ions.

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16
Q

How do integrin receptors work?

A

Ligand binds to ECM protein (integrin/laminin) which stimulates changes in the cytoskeleton. Used in cell movement, growth, and wound healing.

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17
Q

What is a G protein coupled receptor?

A

Membrane spanning proteins with seven MSR. The cytoplasmic tail of the protein is linked to a G protein.

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18
Q

What is a G protein and what is it named after?

A

Three part membrane transducer called a G protein, named after their ability to bind guanine molecules. Their activ ation leads to the generation/release of second messengers.

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19
Q

What is the general pathway of a GPCR?

A
  1. Ligand binds to receptor
  2. Activated receptor activates G protein for signal transduction
  3. G protein activates amplifier enzyme
  4. Amplifier generates/releases second messengers
  5. Second messengers activate kinases and/or increase intracellular Ca2+
  6. Kinases phoshorylate proteins and calcium activates calcium binding proteins which stimulates a cell response.
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20
Q

What are 3 examples of GPCR?

A

Adenylyl cyclase, Phospholipase C, Arachidonic acid

21
Q

What are the steps of the Adenylyl Cyclase pathway?

A
  1. Ligand bonds to GPCR and activates several G proteins.
  2. Each G protein diffuses along the inside of the membrane to activate amplifier enzyme Adenylyl Cyclase.
  3. Adenyl cyclase converts several hundred ATP into cAMP (second messenger)
  4. cAMP activates protein kinase A
  5. PKA diffuses throughout cell and phosphorylates many other proteins.
22
Q

What is the difference between a Gs protein and a Gi protein in the Adenylyl cyclase pathway?

A

Gs is a G-protein that stimulates adenylyl cyclase

Gi is a G-protein that inhibits adenylyl cyclase.

23
Q

What is the pathway for phospholipase C?

A
  1. Ligands binds to GPCR and activates G-protein (Gq)
  2. G-protein activates phospholipase-C amplifier enzyme
  3. Phospholipase C degrades membrane phospholipids into diacyglycerol (associates with membrane lipids) and Inositol triphosphate (diffuses through cytoplasm)
  4. DAG activates protein kinase C which phosphorylates other proteins.
  5. IP3 binds to IP3 receptor on endoplasmic reticulum which activates IP3 receptor and releases stored Ca++
24
Q

What are classic second messengers?

A

cAMP, cGMP. IP3, DAG, Ca++

25
Q

How is calcium a second messenger?

A
  1. Binds to calmodulin which activates other proteins
  2. Binds to motor proteins which allows action of the cytoskeleton and motor proteins
  3. Binds to synaptic proteins to trigger exocytosis
  4. Binds to ion channels to modulate their gating
  5. Initiates development in fertilized eggs
26
Q

What is a receptor enzyme?

A

A receptor with a receptor region on the extraceullular side of the cell and an enzyme region on the cytoplasmic side. (e.g. Tyrosine kinase)

27
Q

What is the typrosine kinase pathway?

A
  1. Signal molecule binds to surface receptor on extracellular side
  2. Activates the Tyrosine kinase on the cytoplasmic side
  3. Tyrosines on proteins are phosphorylated on the TK binding site
28
Q

How does an insulin receptor work?

A
  1. Alpha units (extracellular) of insulin receptor bind insulin
  2. Binding of insulin dimerizes receptors and autophosphorylate, activating a kinase domain in the cytoplasm.
  3. Beta units (intracellular) transmit signal from bound insulin to the cytoplasm
  4. Kinase domains on the receptor phosphorylate proteins, including substrates for insulin receptors.
29
Q

What gases are used as second messengers?

A

Nitric oxide (NO), carbon monoxide. and hydrogen sulfide

30
Q

What is nitric oxide and its function as a second messenger?

A

Synthesized by N-Synthase in endothelial cells of arteries or neurons of parasympathetic NS and diffuse into adjacent arterial smooth muscle.

It activates guanylyl cytclase, production of cGMP, activation of protein kinase G, and leads to the relaxation of smooth muscle.

31
Q

How does the aracidonic acid pathway work?

A
  1. ligand binds to G-protein which activates phospholipase A2 (amplifier enzyme)
  2. Phospholipase A2 degrades phospholipids into arachidonic acid
  3. Arachodonic acid and its eicosanoid metabolites act as second messengers and diffuse out of the cell to act as a paracrine and autocrine ligand.
32
Q

What are leukotrienes and prostanoids?

A

Arachidonic acid-derived paracrine molecules.

Leukotrienes: secreted by white blood cells, aid in asthma and anaphylaxis

Prostanoids: prostaglandins and thromboxanes involved in sleep, inflammation, pain and fever.

33
Q

What is a promiscuous receptor?

A

A receptor that can be activated by more than one ligand

34
Q

How are receptor numbers down-regulated and why?

A

Endocytosis and desensitization (via phosphorylation) downregulates receptor numbers due to stages in development, homeostatic challenges, and states of disease.

35
Q

what is the difference between the feedback pathway of a negative and positive loop?

A

Negative: Stimulus, response, decreased stimulus, response loop shuts off.

Positive: stimulus, response, increased stimulus, outside factor shuts off feedback cycle.

36
Q

What’s the difference between negative feedback and positive feedback?

A

Negative: keeps a system near a setpoint by negating the stimulus. It restores homeostasis but cannot prevent the stimulus.

Positive: brings a system further from a setpoint by reinforcing the stimulus until an outside factor shuts it off.

37
Q

What is feedforward control? What are some examples?

A

Anticipates change and anticipates a response due to sensory input. (e.g. mouth watering, response to exercise, fight or flight response.)

38
Q

What is the difference between neural and endocrine control systems in terms of speed and specificity?

A

neural: specific target, fast acting, short lived, frequency = intensity

endocrine: target based on receptors, slow acting, long lasting, amount of hormone = intensity

39
Q

What is the electrochemical gradient?

A

Combination of an electrical gradient and chemical gradient that ions are subjected to.

40
Q

What is the membrane potential of a cell?

A

Electrical gradient across a cell membrane established by ATPase transporters and measured in mV. It may change due to movement of ions.

41
Q

What is the resting membrane potential?

A

Special case of membrane potential where there is a steady state balance between active transport and leakage of ions. It is usually between -20mV and -90mV

42
Q

How is membrane potential measured?

A

Recording electrode is placed into the cell and goes through a voltmeter and into a recorder. Potential is measured “inside with respect to the outside”

43
Q

What is the difference between depolarization, repolarization, and hyperpolarization?

A

Depolarization: resting membrane potential becomes less polar (less negative)

Repolarization: From depolarized state, membrane potential returns to resting mV (more negative)

Hyperpolarization: resting membrane potential becomes more polar (more negative)

44
Q

What is equilibrium potential?

A

Amount of voltage necessary to keep an ion inside or outside the cell based on the electrochemical gradient. Independent of concentration of other ions.

45
Q

What is the Nernst Equation?

A

Equilibrium potential of a single ion = 61/z * log([ion in]/[ion out])

z = valency of ion

46
Q

What is the Goldman equation?

A

Resting Membrane potential = 61 * log{(Pk[K+]out + PNa[Na+]out + PCl[Cl-]in) / (Pk[K+]in + PNa [Na+]in + PCl[Cl-]out)}

47
Q

What is the relative concentration inside the cell, the equilibrium potential, and direction of movement from ion channels in K+, Na+, Ca++, Cl-?

A

K+: high, -90mV, out
Na+: low, +60mV, in
Ca++: low, +122mV, in
Cl-: low, -81mV, in

48
Q

How does a cell attempt to make membrane potential = equilibrium potential?

A

When ion channels open, the ion will ALWAYS move to make the resting membrane potential of the cell equal to the equilibrium potential.

If RMP is more negative: +ve ions go in, and -ve ions go out.

If RMP is more positive: -ve ions go in, or +ve ions go out

Human Physiology (BIOL 2410/2420) (8 decks)

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