L15 Flashcards

1
Q

what was believed about porteins before the 1940s

A

that we kept all of out proteins for our entire life’s but because of radioactive isotopes during the wars we learned that this was not the case

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2
Q

how do lysosomes break down proteins

A

they break down the peptide bonds between amino acids

they can also break down nucleic acids and sugars

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3
Q

describe the range in 1/2 life of proteins around the body

A

Protein stability (1/2 life) varies from a few minutes (e.g. cyclins which regulate mitosis) to a lifetime (proteins in the lens of the eye)

when proteins in the lense of our eye die you get cataracts .

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4
Q

what does protein 1/2 life refer to

A

Protein half-life refers to an experimental measurement: The time that half of the original population of protein remains. Or the time that half of the original population of protein has been degraded.

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5
Q

why are proteins degraded

theres 5

A

to regulate the function/activity of a protein and therefore the cell. E.g., ion
channels and transporters in epithelia to change ion transport pathways.

to allow replacement with new proteins.

to inactivate them e.g., ligands, cell cycle proteins.

to recycle amino acids of nonfunctional proteins e.g., misfolded or misassembled proteins in the ER.

as they are extracellular proteins from pathogens

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6
Q

why do different proteins have different 1/2 lifes

A

Lifetime of a protein depends on the function of a protein and the cellular
pathway it is involved in.

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7
Q

what degrades proteins

A

Degraded in the lysosome or the proteasome

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8
Q

what do lysosomes break down

A

extracellular or transmembrane proteins brought into the cell by endocytosis and

aged or defective organelles (also called autophagy)

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9
Q

what is autophagy

A

it is when a lysosome breaks down aged or defective organelles

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10
Q

what does the lysosome contain

A
Contain enzymes (acid hydrolases) that work best at acidic pH (not in cytosol). The
enzymes break down
proteins, sugars and nucleic acids.
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11
Q

what is the main enzyme that lysosomes contain

A

acid hydrolases

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12
Q

how does the lysosome maintain its low pH

A

Two transport proteins pump H+ and Cl- into the lysosome

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13
Q

what does autophagy mean

A

self eating

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14
Q

describe the process of autophagy

A

Uptake of random area of cytoplasm or defective organelles (phagophore)

Phagophore forms a complete ‘vesicle’ (autophagosome)

Autophagosome begins to fuse with lysosome

Autolysosome formed, degradation begins

Organelles and any uptake substances degraded and recycled

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15
Q

what is the difference between a phagophore, autophagosome and a autolysosome

A

phagophore = the beginning of engorgement and is the start of the formation of an autophagosome

an autophagosome is when the phagophore has completely engulfed the organelle in a continuous membrane

an autolysosome is when the autophagosome and lysosome come together and the contents of both mixes

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16
Q

what is the difference between ubiquitin-proteasome system for protein degradation and autophagy

A

the ubiquitin system is highly controlled and not random like autophagy

17
Q

what are 4 things ubiquitin-proteasome system does

A

Highly controlled process for degrading unwanted proteins, terminating or activating signaling pathways, regulating the cell cycle and providing an important source of amino acids for de novo protein synthesis.

Proteins are covalently tagged with a small 8kDa protein called ubiquitin which then leads to them being degraded

18
Q

other than degradation, what else can ubiquitination lead to

A

endocytosis (monoubiquitin) or to change the location of a protein.

19
Q

in the ubiquitin-proteasome pathway, what is E1, E2, and E3

A

E1 (activating enzyme),

E2 (conjugating enzyme)

E3 (ligase)

20
Q

what is the role of E1, E2 and E3 in the ubiquitin-proteasome pathway

A

E1 catalyses the breakdown of ATP –> Amp which transfers ubiquitin onto the enzyme

E1 then transfers ubiquitin onto the E2 enzyme and then to the E3 enzyme

E3 then puts ubiquitin onto the protein

21
Q

what is needed to remove ubiquitin from a protein

A

Deubiquitinating enzymes or DUBs remove ubiquitin from

proteins.

22
Q

where are ubiquitinated proteins bound for

A

the protostome

23
Q

what is the process of how ubiquitin and the protostome degrade a protein

A

Ubiquitin binds proteasome and orients the protein at the regulatory particle so that the protein comes dont into the protostome (which is shaped like a cylinder)

the protein is then degraded in proteasome by
peptidase

Peptides and amino acids are recycled

24
Q

what is the protostome made up of

A

regulatory particle and a core particle

25
how does ubiquitin tagging promote endocytosis of ion channels what are 2 examples of proteins regulated by this
1. ENaC and ROMK1 are monoubiquitinated, promoting endocytosis to the apical sorting endosome Ubiquitinated proteins trafficked onto common endosome where fate of the channel is determined Deubiquitination leads to recycling. Ubiquitinated proteins move on to lysosome for degradation through the late endosome
26
what causes liddle's syndrome to occur
In Liddle’s syndrome (hypertension) ENaC cannot be tagged with ubiquitin due to loss of the binding site for an E3 ubiquitin ligase. Therefore less ENaC endocytosis, more ENaC at the plasma membrane and more Na+ reabsorption leading to high ECF volume and pressure
27
what is monoubiquitination
a single addition of a ubiquitin to a protein
28
what is multi-ubiquitination
a single ubiquitin at multiply sights on a protein
29
what is polyubiquitination
a chain of ubiquitin attached to a single amino acid of a protein
30
what part of the protein does ubiquitin bind to
Ubiquitin is covalently linked to lysines or to the N-terminal amino acid of the target/substrate protein.
31
what are monoubiquitination and multi-ubiquitination signals for
These are signals | for endocytosis or movement through the endosome system.
32
what is polyubiquitination a signal for
Chains of ubiquitin signal degradation of the target protein in the proteasome.
33
what enzymes do Lysosome, Proteasome, and Autophagy contain
Lysosome = Acid hydrolases Proteasome = Peptidases Autophagy = Acid hydrolases
34
what do Lysosome, Proteasome, and Autophagy degrade
Lysosome = proteins, sugars, DNA/RNA Proteasome = Proteins (ubiquitin recycled) Autophagy = Damaged organelles, microbes, cytosolic components
35
describe the regulation of Lysosomes, Proteasomes, and Autophagy
Lysosome = Somewhat random, ubiquitin tagging Proteasome = Highly regulated Autophagy = Random, but some regulated
36
what are the different cofactors between Lysosomes, Proteasomes, and Autophagy
Lysosome = no cofactors Proteasome = Requires a series of three enzymes: E1, E2 and E3 Autophagy = no cofactors
37
what are the general targets of Lysosomes, Proteasomes, and Autophagy
Lysosome = Cell surface and extracellular proteins Proteasome = Cytoslic, nuclear, ER proteins (ERAD) Autophagy = Cytosolic components
38
what is the structure of Autophagy
Autophagy = Double membraned | autophagosome
39
Lysosomes only degrade proteins BECAUSE monoubiquitin is used as a tag for degradation in the endocytosis pathway
the first statment is false and the second is true the first statment is false because of the work only