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My BSI exam 2 flash cards > lectures 15-16 > Flashcards

lectures 15-16 Flashcards

1
Q

What are chemical messengers recognized by?

A

specific receptors

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2
Q

How do endocrine cells produce their effect?

A

They act throughout the body via the circulation. (endocrine involves hormones)

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3
Q

Describe paracrine

A

Chemical messengers acting locally on adjacent cells

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4
Q

Describe autocrine

A

Chemical messengers acting on the cell that secreted them

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5
Q

Describe contact-dependent

A

The chemical messenger is never released and it requires direct cell-cell contact.

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6
Q

Describe neuronal

A

The chemical messenger is released across a synapse from a neuron (neurotransmitter).

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7
Q

What is an example of contact-dependent?

A

Notch and Delta

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8
Q

Chemical messengers can affect every aspect of cell function including apoptosis. True or False?

A

True

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9
Q

What must happen in order for MOST chemical messengers to cross the membrane?

A

They must be recognized by a specific cell surface receptor.

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10
Q

After the chemical messenger is recognized by a specific cell surface receptor, what will happen if the correct messenger is bound?

A

It will cause a conformational change in the receptor (a protein), which is then transmitted intracellularly, called signal transduction

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11
Q

What are the main components in a typical signal transduction pathway?

A

Extracellular signal molecule, receptor protein, intracellular signaling molecules, effector proteins, and cell responses.

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12
Q

In many pathways, how are secondary messengers (like cAMP) generated?

A

They are generated intracellularly in response to the chemical messenger.

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13
Q

What is the function of adenylyl cyclase in regards to cAMP?

A

One molecule of the enzyme, AC, will produce many molecules of cAMP which can affect many target proteins so it acts as an amplification stage.

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14
Q

There is extensive convergence and divergence of pathways producing significant “cross-talk” between pathways which is necessary to integrate cell function. True or False?

A

True

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15
Q

Some chemical messengers are able to cross the cell membrane but they are still recognized by specific intracellular receptors. What is an important characteristic that allows them to be able to cross the cell membrane?

A

hydrophobic molecules

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16
Q

What chemical messengers are able to cross the membrane, but are still recognized by specific intracellular receptors?

A 
Steroid hormones (aldosterone, cortisol, testosterone)
thyroid hormones ( Thyroxine [T4] and Triiodothyronine [T3])
novel gaseous messengers (nitric oxide (NO) & carbon monoxide (CO))
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17
Q

What is the definition of a receptor?

A

A specific protein in either the plasma membrane or the interior of a target cell that a chemical messenger combines with, causing a response in that cell.

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18
Q

What is the definition of specificity?

A

The ability of a receptor to bind only one type or a limited number of structurally related types of chemical messengers.

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19
Q

What is the definition of saturation?

A

The degree to which receptors are occupied by messengers.

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20
Q

What is the definition of affinity?

A

The strength with which a chemical messenger binds to its receptor.

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21
Q

What is the definition of competition?

A

The ability of different molecules VERY SIMILAR IN STRUCTURE to compete with each other to combine with the SAME receptor.

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22
Q

What is the definition of an antagonist?

A

A molecule that competes for a receptor with a chemical messenger that is normally present in the body. The antagonist will bind to the receptor but will NOT trigger the cell’s response.

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23
Q

What is the definition of an agonist?

A

A chemical messenger that binds to a receptor and triggers the cell’s response. It often refers to a drug that mimics a normal messenger’s action.

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24
Q

What is the definition of down-regulation?

A

A DECREASE in the total number of target-cell receptors for a given messenger & may occur in response to chronic HIGH extracellular concentration of the messenger.

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25
Q

What is the definition of up-regulation?

A

An INCREASE in the total number of target-cell receptors for a given messenger & may occur in response to a chronic LOW extracellular concentration of the messenger.

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26
Q

What is the definition of supersensitivity?

A

The increased responsiveness of a target cell to a given messenger & may result from up-regulation of receptors.

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27
Q

Ionotropic receptors combine what two things?

A

The receptor with the effector (an ion channel)

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28
Q

In an Ionotropic receptor, if the channel conducts Na+, K+, or Cl- what will happen?

A

It will cause a change in membrane potential which is how “excitable” cells such as neurons and muscle cells work.

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29
Q

In an Ionotropic receptor, if the channel allows Ca(2+) to enter diffusing down its electrochemical gradient, what will likely happen?

A

The calcium can act as a secondary messenger like cAMP and turn on target proteins.

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30
Q

Calcium ions sometimes enter a cell and bind to, and activate specific calcium binding proteins intracellularly. What is an example of a specific calcium binding protein that calcium will bind to and activate?

A

Calmodulin

31
Q

In an Ionotropic receptor, what effect does Calcium have on the membrane potential?

A

It’s effect on membrane potential is typically negligible.

32
Q

What is the best example of an Ionotropic receptor and where is it found?

A

Nicotinic Acetylcholine Receptor (nAChR); found at neuromuscular junctions (skeletal muscle), autonomic ganglia, and in the brain

33
Q

What kind of bonds are present between protein interactions?

A

Weak, non-covalent bonds

34
Q

Do metabotropic receptors/GPRs affect membrane potential directly?

A

No, but ionotropics do!

35
Q

What does metabotropic receptors/GPRs affect?

A

They affect the function of heterotrimeric G-proteins which can then either directly interact with effectors (giving you a change in membrane potential) OR affect the production of a secondary messenger.

36
Q

What are metabotropic receptors also known as?

A

G-protein receptors or GPRs

37
Q

What are metabotropic receptors/GPRs involved in?

A

They are involved in mediating the actions of many neurotransmitters muscarinic acetylcholine receptor, most amine receptors, some glutamate receptors), most peptide hormones (including all of the hypothalmic tropic factors), and Adrenaline (aka epinephrine).

38
Q

How many TMDs does a typical GPR have?

A

7

39
Q

What are each of the TMDs of a GPR typically composed of?

A

20 amino acids with hydrophobic side groups that form alpha-helices that span the cell membrane

40
Q

What do GPRs determine?

A

They determine specificity; hundreds of odorant GPRs were identified from the human genome which allows us to discriminate between many different odors

41
Q

Where is the N terminal located on the TMD?

A

Extracellularly

42
Q

Where is the C terminal located on the TMD?

A

Intracellularly

43
Q

What is located near the intracellular C-terminal and on some of the intracellular loops of the TMD?

A

Sites where specific AA residues can be phosphorylated by a kinase which will then allow it to bind to specialized proteins that turn OFF or densensitize the receptor

44
Q

What is an example of a protein that, when bound, will turn off or desensitize a receptor?

A

Arrestin

45
Q

What 3 subunits make up heterotrimeric G-proteins when they are inactive?

A

Alpha, Beta, & Gamma

46
Q

Which subunit of a heterotrimeic G-protein will bind GDP?

A

the inactive alpha subunit

47
Q

After the GPR binds the primary messenger extracellularly, the activated GPR promotes the exchange of what?

A

Promotes the exchange of GDP for GTP which will active the G-Protein, causing it to dissociate

48
Q

After the G-protein has been activated it dissociates into what?

A

alpha subunit and beta/gamma subunit (BOTH can affect effectors, such as AC or ion channels)

49
Q

Which subunit is the primary effector of heterotrimeric G-proteins? And what does it have binding sites for?

A

the alpha subunit; has binding sites for GDP and GTP

50
Q

What determines the lifetime of the alpha subunit and the beta-gamma subunit?

A

The alpha subunit

51
Q

The primary receptor (extracellularly) of the GPR is also known as what?

A

the receptors ligand or agonist

52
Q

When the alpha subunit is inactive, what is bound to it?

A

GDP plus phosphate

53
Q

After you have inactivated the alpha subunit, it now has GDP plus phosphate to it, which will go and do what?

A

It will re-associate with the beta-gamma subunits and inactivating it too.

54
Q

What can alter the rate of hydrolysis by the alpha subunit?

A

Regulators of G-protein signaling (RGS’s)

55
Q

What is cAMP synthesized from?

A

It is synthesized from ATP by adenylyl cyclases

56
Q

How is cAMP removed?

A

It is removed via phosphodiesterases. It is then AMP (not cyclic now)

57
Q

Once the phosphodiesterases remove cAMP, you are left with AMP. What happens to AMP?

A

It is recycled back to ATP

58
Q

What is the most common mechanism for G-proteins to cause their effects?

A

generation of secondary messengers

59
Q

When are secondary messengers, like cAMP, produced?

A

When AC is stimulated

60
Q

What are secondary messengers?

A

small intracellular signaling molecules

61
Q

What are some examples of secondary messengers? (Name 4)

A

diaglycerol (DAG- generated by PLC)
IP3 (also generated by PLC)
cGMP (generated by GC)
Ca (either entering thru channels in the cell membrane or released from intracellular stores)

62
Q

How can cAMP and cGMP be removed/inactivated?

A

By phosphodiesterases whose activities can themselves be regulated

63
Q

What is the actual “amount” of a secondary messenger usually determined by?

A

The relative activity of both the synthesizing/activating (AC) and degrading/inactivating(phosphodiesterases) enzymes. This produces a graded response rather than either “on” or “off”

64
Q

Mechanism 3: When the RTKs are activated (primary messenger is bound extracellularly) what then happens?

A

they are phosphorylated and either directly activate other kinases OR via adapter/docking proteins activate a different type of G-protein (LMW G-protein)

65
Q

What are LMW G-proteins sometimes called?

A

monomeric G-proteins

66
Q

How many TMDs do RTKs normally have?

A

one

67
Q

What does it take for an RTK with one TMD to be functional?

A

It is not functional until the binding of the messenger extracellularly brings 2 receptors close together (dimerization). Binding of the messenger turns on and allows tyrosine kinase activity intracellularly, so transducting the signal.

68
Q

Do adapter/docking proteins have intrinsic enzymatic activity?

A

No, they do not.

69
Q

What do GEFs promote?

A

the exchange of GDP for GTP, therefore activating the LMW G-protein

70
Q

What are some examples of a LMW G-protein?

A

Ras (growth), IGFs, Rac (cellular stress), Rab (vesicle transport and exocytosis , Rho (cytoskeleton), and Ran (nuclear trafficking)

71
Q

How is a LMW protein activated?

A

by a GEF

72
Q

What do LMW G-proteins require to turn themselves off?

A

They need accessory proteins to turn them off because they do not possess any intrinsic GTP’ase activity. (It isn’t self limiting like the alpha subunit of the heterotrimeric G protein)

73
Q

What supplies GTP’ase activity in LMW G-proteins?

A

GAPs ; without them the LMW G-protein would remain on

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