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Biochemistry > Membrane Receptors and Endocytosis > Flashcards

Membrane Receptors and Endocytosis Flashcards

1
Q

Cellular signal transduction cassettes detect, amplify, and integrate external signals comprised of:

A

Specific cell surface membrane receptors
Effector signaling elements
Regulatory proteins

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2
Q

Six steps of cellular signal transduction

A
  1. Synthesis of the signaling molecule (ligand)
  2. Release of the signaling molecule (ligand)
  3. Transport of the signaling molecule to target cell
  4. Binding of the ligand by a specific receptor protien and CHANGE IN CONFIRMATION
  5. Change in cellular metabolism, function, and development = cellular response
  6. Removal of ligand, terminating cellular response
  7. Degradation of ligand
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3
Q

Chemical messengers made by endocrine cells and secreted into the bloodstream affect…

A

gene expression and protein synthesis

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4
Q

Autocrine

A

act on same cell that secreted them

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5
Q

Paracrine

A

act on other cells (neighboring cells)

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6
Q

Hormones are…

A

chemical messengers made by endocrine cells and secreted into the bloodstream

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7
Q

Types of Hormones

A

Steroids
Amine (amino acid-derived)
Peptide (usually lumped together w/ polypeptides)
Polypeptide

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8
Q

A steroid hormone..

  1. solubility?
  2. receptors?
A
  • a cholesterol
    1. lipid soluble (can cross the membrane)
    2. have intracellular (cytoplasmic receptors) located inside target cells
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9
Q

Cholesterol precursors:

A

corticosteroids
androgens
estrogens

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10
Q

Steroid hormones diffuse out of endocrine cells when?

A

immediately diffuse out into the bloodstream

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11
Q

Steroids have a ____ acting/ _____ half life than peptide hormones

A

slower acting, and longer half- life than peptide hormones

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12
Q

Amine hormones are…derived by what? when/stored/how enter bloodstream? Type of receptor?

A
  • Tyrosine and tryptophan derived
  • Stored in endocrine cell until secreted
  • Receptor located on the cell surface or intracellular
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13
Q

Polypeptide hormones are

  1. when/how they enter into the bloodstream
  2. water or fat soluble?
  3. Types of receptors?
A
  1. do not immediately enter the bloodstream
  2. water soluble
  3. No, they do not readily pass through the cell membrane so they have external receptors
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14
Q

These types of hormones are termed “first messengers”

A

Polypeptide hormones via binding to external receptors.

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15
Q

The secondary messengers for intracellular effects are…

A

low molecular-weight signaling molecules: cyclic adenosine monophasphate (cAMP) or calcium

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16
Q

Intergral membrane proteins with (extracellular N-terminus)

A

g-protein coupled receptors

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17
Q

This g-protein coupled receptor has ___transmembrane-spanning alpha helices (ligand binds to pockets). With ___extracellular and intracellular loops.

A

seven transmembrane

three extra/intracellular (third intracellular loop recruits G-protein)

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18
Q

g-protein coupled receptors have/don’t have intrinsic catalytic domains

A

don’t have intrinsic domains

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19
Q

G protein (guanine nucleotide binding) activates____, converting ____ to _____.

A

adenylyl cyclase; converting ATP to cAMP

Note: this molecule is activated by the alpha subunit of the G protein called Gs

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20
Q

When adenylyl cylclase is activated…what happens?

A
  1. activates protein kinases in the cytosol (signal cascade)
  2. phosphodiesterase inactivates cAMP (turns off cell response)
  3. Specificity conferred by the alpha subunit which contains the GTP binding site and intrinsic GTPase activity
21
Q

The amplification of the orginal hormone signal can be done by…

A

the binding of more molecules of hormones which stimulate many Gs alpha subunits

22
Q

Bacterial toxins that target G-proteins

A
  1. Cholera toxin- increase in cAMP levels withing intestinal cells which leads to the phosphorylation of Chlorine channels thus leading to the efflux of electrolytes and water causing severe diarrhea
  2. Pertussis toxin (whooping cough) - enhances cAMP levels that inhibits neutrophil functions
23
Q

This type of receptor has no intrinsic enzymatic activity..

A

tyrosine kinase-linked receptor

24
Q

Ligand binding forms dimer that activates tyrosine kinases that phosphorylate downstream targets (signal cascade)..what type of receptor?

A

tyrosine kinase-linked receptor

25
Q

A receptor in which a ligand triggers protein kinases and forms dimers upon ligand binding (similar to tryosine-linked receptors) and the ligand/receptor complex directly acts as a____ which ____.

A

Receptor = intrinsic enzymatic activity receptors which directly ACTS as a tyrosine kinase when the ligand/receptor complex forms and WHICH phosphorylates other kinases.

26
Q

What does phosphorylation do to other protein kinases?

A

phosphorylates them ( thus the tyrosine kinase-linked receptor and intrinisc enzymatic activity receptor does

27
Q

In an ion-channel receptor…ligand binding______.

A

changes the confirmation of receptor and allows specific ions (sodium and potassium) to flow through the channel

28
Q

A bacterial toxin that affects ion channels (not directly)?

A

botulinum toxin–prevents the release of Acetylcholine and cleaves proteins involved in docking of the neurotransmitter vesicles

29
Q

Calcium binds to _______protein inducing a_______.

A

binds to calmodulin …inducing a confirmational change. This binding is two globular domains joined by a long alpha helix

30
Q

What does a calcium/calmodulin complex bind to and modify?

A

Bind to target proteins (kinases) that initiate signal cascade

31
Q

Secondary messenger responsible for calcium mobilization.

A

Phosphatidylinositol 4,5-bisphosphate (PIP2)

32
Q

What two second messengers are generated when PIP2 is hydrolyzed by its specific phospholipase?

A
  • Inositol trisphosphate (IP3) (water soluble and mobilizes calcium)
  • Diacylglycerol (DAG) (anchored in the plasma membrane due to its hydrophobic fatty acid side chains; this activates key protein kinase C families (PKC)
33
Q

What is produced when Phosphatidylcholine is hydrolyzed by other phospholipases?

A
  • different species of DAG
  • Phosphatidic acid
  • Arachidonic acid
34
Q

Arachidonic acid and prostaglandins are key for….

A

inflammatory and pain mediator

35
Q

Precursors of eicosanoids

A

Prostaglandins and leukotrienes (they act like hormones and signal via G-protein coupled receptors)

36
Q

What modulates smooth muscle contraction, platelet aggregation, gastric acid secretion, and salt & water balance

A

Arachidonic acid and prostaglandins

37
Q

Arachidonic acid conversion to prostaglandins involves…

A

cyclooxygenase isoforms

- COX-1 (constiutive) and COX-2 (response to inflammatory mediators)

38
Q

Stimulates inflammation, regulates blood flow to organs such as kidney, control ion transport across membranes, modulate synaptic transmission, and induces sleep

A

prostaglandins

39
Q

cyclooxygenase inhibitors

A

-nonsteroidal anti-inflammatory drugs (NSAIDs)= aspirin & ibuprofen
These block cylooxygenase conversion to prostaglandins.
Note: aspirin irreversibly inactivates both forms

40
Q

Arachidonic acid is converted to leukotrienes by

A

lipoxygenases

41
Q

Nitric oxide stimulates ______, which generates____ which ____ the blood vessels

A

stimulates guanylate cyclase…generates cGMP…relaxing the blood vessels

42
Q

______is a low molecular weight moleucle that crosses the plasma membrane and directly modulates the activity of the catalytic domains of transmembrane receptors

A

Nitric oxide (NO)

43
Q

Packaging of extracellular materials in vesicles at the cell surface

A

endocytosis

44
Q

Does endocytosis require ATP?

A

yes

45
Q

Three types of endocytosis:

A

pinocytosis
phagocytosis
receptor-mediated endocytosis

46
Q

______=cell drinking endocytosis; nonspecific absorption

A

pinocytosis

47
Q

______= cell eating endocytosis which is activated by attachment to_________.

A

phagocytosis activated by attachement of pathogen-associated molecular patterns (PAMPS)

48
Q

Movement of receptors to a different membrane from one in which it was endocytosed

A

transcytosis

Biochemistry (9 decks)

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