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From Molecules to Cells BIOL10232 > L7- Exocytosis, endocytosis and the plasma membrane > Flashcards

L7- Exocytosis, endocytosis and the plasma membrane Flashcards

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Organic Chemistry 101 flashcards
1
Q

There are 2 types of exocytosis

  1. What is constitutive secretion?
  2. What is regulated secretion?
A
  1. A constant stream of transport vesicles moving from the trans- face (exit face) of the golgi network to the plasma membrane. =default pathway
  2. Present only in specialised cells like pancreas. Secretory cells make cargoes like hormones. Sorted into secretory vesicles. Accumulate near membrane. Don’t exit until signals tell them to.
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2
Q
  1. Constitutive exocytiosis supplies the PM with new proteins and lipids made in the ER. What does this allow?
A
  • Plasma membrane growth before cell division
  • Protein secretion
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3
Q

Regulated secretion only release content after stimulation by extracellular signals. What’s the advantage of this?

A

A rapid response. The vesicles have already been made and ar ready to go, just need signals.

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4
Q

If transport vesicles are constantly fusing with the plasma membrane, why doesnt it get bigger?

A

It maintains homeostasis- membrane components are also removed by endocytosis. This balances it out so the PM stays roughly the same size.

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5
Q

Where does the endocytic pathway deliver lipids and proteins to? (so they can be re-used)

A

The endosomes

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6
Q

What’s the main sorting point in endocytosis?

A

The endosomes

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7
Q

How is an endocytic vesicle formed?

A

A portion of the PM buds inwards and pinches off to form an endocytic vesicle

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8
Q

What happens to the material taken up by endocytosis?

A

The material taken up is eventually delivered to the lysosome and degraded.

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9
Q

What is pinocytosis?

A

The non-selective uptake of fluid and small particles by endocytic vesicles.

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10
Q

What is receptor-mediated endocytosis?

A

Uses cell-surface receptors for uptake of specific components. (up to 1000x more selective)

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11
Q

What is an important example of receptor-mediated endo.?

A

Uptake of cholesterol by animal cells

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12
Q

How is cholesterol transported in the blood?

A

Cholesterol is extremely insoluble so transported in blood as low density lipoproteins. (LDLs) secreted by the liver.

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13
Q

How does cholesterol enter cells and where does it go in the cell?

A

The LDL binds to recpetors. Then the LDL/receptor complexes are endocytosed and delivered to endosomes.

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14
Q

What can cause atherosclerosis and how is it treated?

A

Defective LDL receptors, cholesterol accumulates. Have to take statins.

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15
Q

Why does the LDL dissociate from its receptor in the endosome?

A

The pH becomes more acidic in the endosome. So detaches from receptor.

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16
Q

After LDLs detach from their receptors, where do they go?

A

After release, LDLs are delivered to the lysosome, where they are degraded and the cholesterol is released to the cytosol for membrane synthesis.

17
Q

What happens to the LDL receptors after dissociation?

A

The LDL receptors are recycled to the cell surface.

18
Q

What is it about endosomes which makes most receptors release their cargo?

A

Their acidic environment

19
Q

After cargo release where do most receptors go?

A

Recycled to the plasma membrane

20
Q

Where do the other recpetors go- the ones that don’t go to the plasma membrane?

A

Some are sorted to the lysosomed and degraded

21
Q

What is transcytosis?

A

Other receptors are directed to a different domain of the PM and move their cargo from one extracellular space to another.

22
Q

What is in lysosomes?

A

About 40 hydrolytic enzymes which can degrade proteins, DNA etc.

23
Q

What pH are the lysosomes at? WHat does this mean for the enzymes?

A

pH 5. So if they leak out into the cytosol they are inactive. (cytosol pH 7)

24
Q

How do the lysosomes maintain their pH?

A

They use ATP to pump protons into the lysosomes

25
Q

How do the lysosomal enzymes end up in the lysosome?

A

Lysosomal enzymes are made at the ER. They follow the normal exocytic route until they reach the trans-golgi network.

26
Q

How do lysosomal enzymes know not to be secreted?

A

They’re specifically directed to lysosomes via the receptor mediated sorting of mannose-6-phosphate tags. added to the N-linked glycans.

27
Q

WHat is phagocytosis?

A

Uptake of large particles or microorganisms by specialised cells like macrophages

28
Q

What is autophagy?

A

Removal of obsolete parts of the cell and damaged organelles such as mitochondria

29
Q

What happens in autophagy?

A

Obsolete bits of cell are surrounded by membrane from a donor organelle to form- autophagosomes

30
Q

What do autophagosomes fuse with? What’s this catalysed by?

A

They then fuse with the lysosome to degrade cellular components (mitochondria).

Catalysed by SNARE proteins

31
Q

WHat is characteristic of autophagosomes because of the way theyre made?

A

The double membrane

32
Q

where are the different lipids in the plasma membrane made?

A

The ER

33
Q

WHere are the lipids for the PM modified?

A

The Golgi- e.g. glyosylation

34
Q

How are they distributed in the plasma membrane?

A

Distributed asymmetricallu- almost all glycolipids will face outside of cell.

35
Q

Which enzymes in the Golgi selectively redistribute lipids to make them asymmetrical?

A

Flippases

36
Q

What are integral membrane proteins?

A

Protein made of ~20 hydrophobic amino acids that fold into an alpha-helix. They cross the bilayer once or more.

37
Q

How else can proteins be attached to the membrane? (other than integral membrane proteins)

A

Amphiphatic helix, liipid anchor or soluble protein that’s bound to an integral TMP. =peripheral protein.

38
Q

How do you remove:

  1. Peripheral proteins from the membrane?
  2. How would you remove integral proteins?
A
  1. Disrupting protein-protein interaction using pHor salt
  2. Only by solubilising the whole membrane using a detergent

From Molecules to Cells BIOL10232 (17 decks)

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