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BIO130 > Week 9 - Intracellular Compartments and Protein Sorting > Flashcards

Week 9 - Intracellular Compartments and Protein Sorting Flashcards

1
Q

What is the function of a Hepatocyte (i.e. liver hepatocyte)?

A

It functions in detoxification.

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2
Q

What intracellular compartment is half the cell volume, has an intermediary metabolism, and functions protein synthesis and degradation?

A

The cytosol.

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3
Q

Define organelle.

A

A subcellular compartment or large macromolecular complex, often membrane-enclosed, that has a distinct structure, composition, and function.

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4
Q

3 examples of membrane-enclosed organelles?

A
  1. Nucleus
  2. Endoplasmic Reticulum (ER)
  3. Golgi Apparatus
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5
Q

2 examples of organelles not membrane-bound?

A
  1. Nucleolus

2. Centrosomes

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6
Q

Is the ribosome an organelle?

A

No. Ribosomes are too small to be organelles.

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7
Q

What is the function of the Rough Endoplasmic Reticulum (RER)?

A
  • synthesis of transmembrane, organellar, and secreted proteins
  • has ribosomes attached
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8
Q

What is the function of the Smooth Endoplasmic Reticulum (SER)?

A
  • phospholipid synthesis

- detoxification

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9
Q

What is the function of the Golgi apparatus?

A

Modifies proteins and lipids.

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10
Q

What is the function of mitochondria?

A

ATP synthesis.

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11
Q

What is the function of free polyribosomes?

A

Protein synthesis.

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12
Q

What is the function of peroxisomes?

A

Oxidative reactions.

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13
Q

What is the function of endosomes?

A

Endocytosis.

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14
Q

What is the function of lysosomes?

A

Contain digestive enzymes for digestion and waste removal.

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15
Q

Are there more membranes around the cell or inside the cell?

A

There are more membranes inside the cell.

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16
Q

What is the function of a pancreatic exocrine cell?

A

It secretes digestive enzymes.

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17
Q

Which ER has more heptocytes than pancreatic exocrine cells?

A

The SER.

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18
Q

Which ER has more pancreatic exocrine cells than hepatocytes?

A

The RER.

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19
Q

What structures are in the endomembrane system?

A
  • endosomes
  • lysosomes
  • Golgi apparatus
  • RER
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20
Q

What do the organelles of the endomembrane system exchange?

A
  • proteins

- lipids

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21
Q

What is biosythesis in the endomembrane system (biosynthetic pathway)?

A

Proteins and lipids that were made in the ER are delivered to the membranes of other organelles.

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22
Q

What is secretion in the endomembrane system (secretory pathway)?

A

Secreted protein contents move out of the cell via exocytosis

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23
Q

What is the endocytotic pathway of the endomembrane system?

A

Contents move into the cell via endocytosis.

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24
Q

Give a brief overview of the endomembrane system.

A
  1. Proteins and lipids are made in the RER lumen
  2. Contents move into the lumen of the Golgi apparatus
  3. Contents move into the vesicle lumen
  4. Contents move outside of the cell
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25
Q

What is exocytosis?

A

A process by which the contents of a vesicle are released to the exterior through fusion of the vesicle membrane with the plasma membrane.

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26
Q

What are the steps of exocytosis?

A
  1. Vesicle membrane become part of the PM

2. Vesicle contents are delivered to the extracellular space.

27
Q

What is endocytosis?

A

The taking in of matter by a living cell by invagination of its membrane to form a vesicle.

28
Q

What are the steps of endocytosis?

A
  1. Plasma membrane (PM) forms the vesicle membrane
  2. Vesical luminal contents enter from extracellular space
  3. Vesicle membrane encloses contents.
29
Q

Do individual leaflets of endo/exocytosed membranes switch?

A

No; there is no flip-flopping in individual leaflets.

30
Q

Define vesicle.

A

Small, membrane-enclosed organelle in the cytoplasm of a eukaryotic cell.

31
Q

What do vesicles do?

A

They shuttle components back and forth in the endomembrane system (i.e. from the ER to the Golgi).

32
Q

Do transmembrane proteins stay consistent?

A

Yes; they stay consistent to which side thy are like leaflets with parts still facing their starting directions after transport.

33
Q

How are specific proteins targeted to different organelles?

A

mRNA arrives in the cytoplasm and translation starts on ribosomes in the cytosol; sorted via sorting signals.

34
Q

What is a sorting signal?

A

Specific amino acids sequences within the protein

35
Q

Where is a cytosolic protein translated?

A

Translated in the cytosol.

36
Q

Are cytosolic proteins sorted via signal?

A

No; they do not have sorting signals and their default location keeps them in the cytosol.

37
Q

Are sorting proteins to mitochondria and chloroplasts part of the endomembrane system?

A

No; but proteins are still transported there.

38
Q

How are nuclear-encoded proteins of mitochondria and chloroplasts sorted?

A
  1. Protein is translated in the cytosol
  2. Translated protein is targeted by a signal sequence
  3. Protein is imported into the organelle

Note: sorting is POST-translational

39
Q

What keeps proteins unfolded in the cytosol?

A

Association with hsp70 chaperones.

40
Q

What is the first step in the endomembrane system for a secreted protein?

A
  1. mRNA arrives in the cytoplasm and translation starts on ribosomes in the cytosol; signal sequence comes first and signals to be taken to the ER.
41
Q

While translation of a secreted protein is still occurring, what else happens?

A

While the rest of the protein is being made, it is being translocated into the ER lumen (while translating, also moving; a.k.a co-translational translocation).

42
Q

What is co-translational translocation?

A

The process of a protein being simultaneously moved to the ER and translated.

43
Q

What does a signal recognition particle/protein (SRP) do?

A

It recognizes signal sequences.

44
Q

What happens after the SRP recognizes the signal sequence?

A

Translations STOPS in order to take the protein to the SRP receptor on the ER membrane.

45
Q

What does a signal peptidase do?

A

It cuts off the signal sequence after it has been used to get to the ER.

46
Q

What does the SRP receptor transfer the translated protein to?

A

It transfers it to the translocon in the ER membrane to be transferred into the ER lumen.

47
Q

If all signal sequences start with methionine (AUG), how come not all secreted proteins start this way?

A

The signal sequence gets cut off by signal peptidase after transfer to the ER lumen, changing the starting order of the protein.

48
Q

What is a pulse chase experiment?

A

An experiment that uses pancreatic cells to follow the path of newly synthesized proteins; provide cells with a short pulse of radioactive AA’s, and follow the path of the AA’s as they get incorporated.

49
Q

In a pulse chase for pancreatic cells, proteins go through the RER, Golgi Apparatus, and Secretory vesicles in what order?

A

RER -> Golgi -> Secretory vesicles

50
Q

What are the 2 pathways of the secretory pathway?

A
  1. Constitutive pathway

2. Regulated pathway

51
Q

What is the function is the constitutive pathway and where does it function?

A

A pathway of the secretory pathway; continual production of secreted proteins in ALL eukaryotic cells.

52
Q

What is the function os the regulated pathway and where does it function?

A

A pathway of the secretory pathway; proteins are stored in secretory granules ready for export in response to a stimulus in SPECIALIZED cells.

53
Q

You are investigating ribosomes and developed a technique to only label the RER-associated ones at the beginning. Where do you expect to find those ribosomes 30 mins later?
A.) Cytosol only
B.) RER and cytosol
C.) Golgi apparatus

A

B.) RER and cytosol

*NOT C.) as the golgi has proteins, not ribosomes.

54
Q

What are the 3 kinds of protein sorting mechanisms?

A
  1. Gated
  2. Transmembrane
  3. Vesicular
55
Q

Where and what does a gated protein sorting mechanism sort?

A

Proteins move between the cytosol and the nucleus through Nuclear Pore Complexes (NPCs); can go both ways.

56
Q

Where and what does a Transmembrane protein sorting mechanism sort?

A

Translocon proteins are needed to transport specific proteins across a membrane. (i.e. Cytosol to Mitochondria/ER/Plastids/Peroxisomes).

57
Q

Where and what does a Vesicular protein sorting mechanism sort?

A

Membrane enclosed transport vesicles ferry proteins from one compartment to another;

most go both ways, except: Golgi to cell exterior, late endosome to lysosome, early endosome to late endosome, and secretory vesicles to cell exterior.

58
Q

What are signal sequences recognized by?

A

Signal recognition particle/protein (SRP’s).

59
Q

Are signal sequences part of the protein?

A

Yes; they are a stretch of the amino acid sequence of the protein; they are HYDROPHOBIC

60
Q

What are the 2 locations of signal sequences on a protein?

A
  1. N-terminus (a.k.a. N-terminal start transfer sequences); sometimes removed
  2. Internal signal sequences (a.k.a. internal start transfer sequence); NEVER removed.
61
Q

Are internal start transfer sequences removed?

A

NO; they remain part of the protein and are NEVER removed by peptidases.

62
Q

What is a signal peptidase’s function?

A

To remove some N-terminal signal sequences of secreted proteins.

63
Q

Brief overview of secreted protein sorting?

A
  1. Translation on cytosolic ribosomes
  2. Signal sequences directs to ER
  3. Protein co-translationally translocated to the ER membrane via translocon protein.
  4. Signal sequence cleaved, protein folds in ER lumen.
  5. Secreted protein moves via transport vesicles of secretory pathway.
  6. Released by Exocytosis into cytosol towards Golgi. .

BIO130 (12 decks)

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