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Bioc 406 > Protein Digestion, Lysosomes > Flashcards

Protein Digestion, Lysosomes Flashcards

1
Q

Where do amino acids come from?

A
  1. Degradation of proteins

2. Synthesis of AAs from glycolytic or TCA intermediates (only 10 AAs can be made this way, the rest come from our diet)

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2
Q

List 3 ways that proteins are degraded to attain AAs

A
  1. Ubiquitin/Proteasome System
  2. Digestive Enzymes
  3. Lysosomes
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3
Q

When proteins are degraded, what happens to the nitrogen in AAs?

A

Nitrogen in AAs can be recycled, but excess Nitrogen is excreted

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4
Q

True or False: Because we excrete excess Nitrogen, we need a consistent intake of Nitrogen from our diet.

A

True

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5
Q

Name 3 digestive enzymes (in the zymogen form)

A
  1. Pepsinogen
  2. Trypsinogen
  3. Chymotrypsinogen
    (also proelastase and procarboxypeptidase)
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6
Q

What organ(s) release digestive enzymes?

A

Pancreas and stomach

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7
Q

True or False: Digestive enzymes are stored as inactive zymogens so they do not degrade our own proteins

A

True

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8
Q

Which cells secrete pepsinogen, and where is it secreted into?

A

Chief cells release pepsinogen in the stomach

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9
Q

Discuss the structure of inactive pepsinogen and what low pH does to the zymogen

A
  • Inactive pepsinogen has an N-terminal segment blocking the active site
  • When pepsinogen is exposed to low pH, it undergoes conformational change and auto-cleavage to form Pepsin
  • at low pH, the electrostatic interactions between the N terminal segment and the rest of the protein are destabilized so now the active site is exposed
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10
Q

What organ releases serine proteases (trypsin, chymotrypsin, elastase, carboxypeptidase)?

A

The pancreas

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11
Q

What is the optimal pH of the serine proteases to be in?

A

~7

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12
Q

Name the serine protease that is anchored to the outer membrane of small intestinal epithelial cells

A

Enteropeptidase

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13
Q

What is the function of enteropeptidase?

A

It cleaves trypsinogen to activate trypsin

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14
Q

True or False: When trypsinogen is cleaved into typsin, trypsin can further activate trypsinogen to convert into trypsin

A

True

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15
Q

True or False: When trypsin is activated, it can activate chymotrypsinogen, proelastase, and procarboxypeptidase into their active forms

A

True (known as cascade of proteolytic cleavages)

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16
Q

_____ _____ _____ is stored along with zymogens inside the pancreas.

A

Pancreatic Trypsin Inhibitor (PTI)

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17
Q

What AA does PTI have that allows it to bind closely to trypsin?

A

Lysine

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18
Q

True or False: Enteropeptidase cleaves a bond between Lysine and Isoleucine

A

True

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19
Q

What organelle do lysosomes originate from?

A

The Golgi

20
Q

What do lysosomes contain?

A

Various digestive enzymes in an acidic environment

21
Q

True or False: Substrates for lysosomes come from fusion with other vesicles.

A

True

22
Q

What is the function of lysosomes?

A

Breakdown and recycle cellular components

23
Q

True or False: There is a V-type ATPase on the membrane of lysosomes which works to pump protons INSIDE the lysosome, maintaining acidity

A

True

24
Q

Name 4 lysosomal enzymes

A
  1. Lipases
  2. Amylases
  3. Proteases
  4. Nucleases
25
Q

True or False: There are no proteins on the membrane of lysosomes that are essential for allowing vesicles to fuse w/ the lysosome

A

False

26
Q

What do lysosomes degrade?

A

Lipids, proteins, nucleic acids, invading pathogens

27
Q

What is autophagy used for?

A

Degrading big cellular stuff, like mitochondria

28
Q

What factors activate autophagy? (3 things)

A
  1. Stress/Damage
  2. Starvation
  3. Invading pathogens
29
Q

What factors inhibit autophagy? (2 things)

A
  1. Nutrient abundance (insulin)

2. Microbial Virulence Factors

30
Q

Where does the isolation membrane come from in autophagy?

A

The ER

31
Q

Once the autolysosome has been formed by fusing the autophagosome w/ the lysosome, the _______ membrane is removed and the contents are degraded.

A

Inner membrane

32
Q

What is the primary method of degrading proteins?

A

Proteasome/Ubiquitin System

33
Q

What is the following protein: a 76 residue protein which is covalently attached to target proteins.

A

Ubiquitin

34
Q

True or False: Ubiquitin is found only in eukaryotes, it is highly conserved, and there is only one method of Ub modification.

A

False - the first 2 statements are true but the last is false.

35
Q

List the name of the enzymes involved in ubiquitin activation

A

E1, E2, E3

36
Q

True or False: E1 does not require ATP-dependent activation.

A

False

37
Q

True or False: MonoUb signals for DNA repair, nucleear export, autophagy, endocytosis, etc. However, PolyUb signals for proteasomal degradation.

A

True

38
Q

What is the function of DeUBiquitinases?

A

Hydrolyze isopeptide bonds between Ub and a target protein (Ub is recycled not degraded)

39
Q

What residue length are peptides that are generated by the proteasome?

A

2-15 residue long, further degraded by cellular peptidases

40
Q

What is architecture of the proteasome?

A
  • Two 19S regulatory particles (with 18 proteins in each)

- 20S core particle in the middle. 2 rings of alpha subunits, 2 rings of beta

41
Q

What is the function of beta subunits?

A

They form the proteolytic core

42
Q

What is the function of alpha subunits?

A

They can open and unfold the target protein by AAA ATPase and feed them into the B-subunit proteolytic core

43
Q

3 of the B subunits in each rings are threonine proteases with 3 diff specialties. What are the specialties?

A
  • Cleave on the carboxyl side of
  • > acidic
  • > basic
  • > or hydrophobic residues
44
Q

What is another role that proteasomes play?

A

Immune surveillance.

  • invading pathogens make proteins that are destroyed by the proteasome
  • the peptides degraded by the proteasome are displayed on MHC (in the ER) then transported to the membrane and bound to the cell surface
  • immune cells can now recognize them
45
Q

When humans are starved, have cancer, or are battling chronic diseases, muscle mass may need to be reduced and broken down my muscle proteins. This is done by the _________ system.

A

Ubiquitin/Proteasome System

46
Q

What is velcade?

A

it’s a drug for treating multiple myeloma

47
Q

What does velcade do?

A

Blocks the proteasome, thus chokes tumor cells on misfolded proteins

Bioc 406 (15 decks)

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