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AU13 - Biochemistry Final Exam > Furci - Membrane Receptors and Endocytosis > Flashcards

Furci - Membrane Receptors and Endocytosis Flashcards

1
Q

What is the precursor of steroid hormones?

A

cholesterol

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2
Q

What are the three groups of steroid hormones?

A
  • corticosteroids
  • androgens
  • estrogens
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3
Q

After steroid hormones are produced by gonads and adrenal cortex, they immediately diffuse out of _______ into _______.

A
  • endocrine cells

- bloodstream

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4
Q

Are steroid hormones lipid-soluble and why is this important?

A
  • lipid-soluble

- allows them to cross membranes

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5
Q

Where are steroid hormone receptors located?

A

inside the cell (cytosolic receptors)

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6
Q

Which hormones (steroid or peptide) are faster acting?

A

peptide

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7
Q

Which hormones (steroid or peptide) have a longer half-life?

A

steroid

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8
Q

Which hormones (steroid or peptide) are larger?

A

steroid

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9
Q

Do polypeptide hormones immediately enter the blood stream?

A

no

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10
Q

Where can polypeptide hormones be stored?

A

in endocrine cell vesicles

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11
Q

Are polypeptide hormones lipid-soluble or water-soluble?

A

water-soluble

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12
Q

Can polypeptide hormones pass readily through cell membranes?

A

no

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13
Q

What are polypeptide hormones sometimes called? Why did they get this nickname?

A
  • “first messengers”
  • their receptors are located externally on the cell so they are usually the first to send the message and then a “second messenger” carries this message within the cell
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14
Q

What type of molecules are usually “second messengers”? Give examples.

A
  • low molecular weight signaling molecules

- cAMP or calcium

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15
Q

Describe the location and structure of a G-protein coupled receptor.

A
  • integral membrane protein with an extracellular N-terminus
  • 7 transmembrane alpha helices
  • 3 extracellular and intracellular loops
  • intracellular C-terminal tail membrane
  • no intrinsic catalytic domain
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16
Q

Which part of the G-protein coupled receptor recruits the G-protein?

A

third intracellular loop

17
Q

Where does the ligand bind to a G-protein coupled receptor?

A

in the pocket formed by the 7 alpha helices

18
Q

What does the G-protein activate? What does that lead to?

A
  • G-protein activates adenylyl cyclase which converts ATP to cAMP
  • activates protein kinases in the cytosol (signal cascade)
19
Q

What inactivates cAMP, thus turning off the cell response of a signal cascade?

A

phophodiesterase

20
Q

Which subunit of the G-protein contains the GTP-binding site and intrinsic GTPase activity?

A

alpha subunit

21
Q

How is the signal amplified in a G-protein coupled receptor?

A

each bound hormone can stimulate many alpha subunits of G-protein

22
Q

What toxins target G-proteins?

A
  • cholera toxin

- pertussis toxin

23
Q

What does the cholera toxin do?

A
  • ADP-ribosylates the G alpha subunit making it constitutively active
  • increases in cAMP within intestinal epithelial cells leads phosphorylation of Cl- channels and efflux of water and electrolytes
24
Q

What does the pertussis toxin do?

A
  • ADP-ribosylates the G alpha subunit making it constitutively active
  • enhances cAMP levels that inhibits neutrophil functions
25
Q

What is the ratio of intracellular to extracellular calcium concentration? Why is this important?

A
  • intracellular (100 nM) to extracellular (1 mM)

- allows for rapid changes in calcium concentration via hormone ligation

26
Q

What protein binds calcium? Describe the structure of that protein.

A
  • calmodulin

- has two globular domains (binds calcium) joined by a long alpha-helix

27
Q

When calcium binds calmodulin, what happens?

A

conformational change that allows complex to bind to and modify target proteins (kinases) that initiate a signal cascade

28
Q

What is the second messenger responsible for calcium mobilization?

A

phosphatidylinositol-4,5-bisphosphate (PIP2)

29
Q

PIP2 is hydrolyzed by _______ to generate two second messengers: _______ and _______.

A
  • PIP2-specific phospholipase C (PLC)
  • inositol trisphosphate (IP3)
  • diacylglycerol (DAG)
30
Q

Which calcium second messenger is water-soluble and mobilizes calcium?

A

inositol trisphosphate (IP3)

31
Q

Where is diacylglycerol (DAG) located and why? What is its function?

A
  • anchored in plasma membrane due to hydrophobic fatty acid side chains
  • activates key protein kinase C (PKC) family
32
Q

True or false: Receptor-mediated endocytosis is selective.

A

true

33
Q

Where do the vesicles of receptor-mediated endocytosis form? What do they contain?

A
  • form at the surface of the membrane

- contain receptors and ligands

34
Q

Describe the structure of the vesicles in receptor-mediated endocytosis.

A
  • vesicles coated with three clathrin heavy chains and three light chains
  • forms a polyhedral lattice
35
Q

What is an example of receptor-mediated endocytosis?

A

iron transport via transferrin receptor

AU13 - Biochemistry Final Exam (8 decks)

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