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Metabolism > 8. Membrane trafficking > Flashcards

8. Membrane trafficking Flashcards

1
Q

Exocytosis

A

Cellular secretion/ excretion

Substances contained in vesicles are discharged from cell by fusion of vesicular membrane with outer cell membrane

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2
Q

Endocytosis

A

Cellular ingestion

Plasma membrane folds inward to bring substances into cell

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3
Q

Constitutive secretion

A

secretion proteins are secreted from a cell continuously, regardless of external factors or signals.

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4
Q

Regulated secretion

A

proteins are secreted from a cell in large amounts when a specific signal is detected by the cell

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5
Q

How are proteins directed to the correct compartment?

A

Signal sequences are like address labels and direct the protein to the correct compartment

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6
Q

Types of intracellular transport

A
  1. Gated transport
  2. Transport across membranes
  3. Vesicular transport (e.g. inter-organellar transport)
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7
Q

Example of gated transport

A

Import of proteins into the nucleus

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8
Q

Nuclear envelope is perforated by nuclear pores

A

These form gates through which molecules enter or leave.
Some pore components form mesh-like structures that prevent passage of large molecules but allow small, water soluble molecules to pass freely.

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9
Q

Nuclear proteins are imported by

A

Import receptors that recognise nuclear localisation signals as the ‘address label’

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10
Q

Example of TRANSPORT ACROSS MEMBRANES

A

Translocation of newly synthesized proteins into the ER

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11
Q

2 populations of ribosomes in cells

A

Free in cytosol OR Bound to ER membrane

Both structurally and functionally identical, differ only in the type of protein they are making at any given time.

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12
Q

Free ribosomes

A

Unattached to any membrane

Make all other proteins encoded in nuclear DNA

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13
Q

Ribosomes bound to the ER membrane

A

Make all proteins that are being translocated into ER

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14
Q

Proteins destined for other organelles are 1st imported into…

A

The ER

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15
Q

Unassembled/ misfolded proteins are retained in ER then…

A

exported back into cytosol where they are degraded

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16
Q

ER: Post-translational modifications

A
  • Folding
  • Formation of disulphide bonds
  • Initial glycosylation (addition of sugars)
  • Specific proteolytic cleavages
  • Assembly of multimeric proteins
17
Q

Name a disease resulting from blocked ER exit due to misfolding

A

Cystic fibrosis

SMED-SL

18
Q

Mutations of CFTR gene affect functioning of chloride channels in the membrane

A

Leading to CF

19
Q

CF:

Most common mutation (ΔF508) results from deletion (Δ) of 3 nucleotides which causes

A

Loss of the phenylalanine (F or Phe) at the 508th position on the protein
As a result, CFTR does not fold normally and is degraded

20
Q

Discoidin Domain Receptor 2 mutations cause

A

SMED-SL

21
Q

SMED-SL characteristics

A

short limbs and abnormal calcifications

22
Q

Transport from ER to Golgi and from Golgi to other compartments occurs via

A

budding and fusion of transport vesicles

23
Q

Golgi stack has 2 distinct faces

A

Entry face= Cis face, next to ER

Exit face= Trans face, points towards plasma membrane

24
Q

Proteins are transported through Golgi from

A

Cis to trans and are sorted further at trans Golgi network

25
Q

Golgi apparatus: further protein modifications

A

Many sugar chains added in ER undergo further modifications in Golgi.
On some proteins, more complex oligosaccharide side chains are added and removed by a series of enzymes that reside in sequence as the protein passes through Golgi stack.

26
Q

The EXOCYTIC (secretory) pathway

A
  1. ER
  2. Golgi
  3. Trans-Golgi network
  4. Plasma membrane
27
Q

TGN activity:

All cells

A

Steady stream of vesicles bud from trans-Golgi network and fuse with plasma membrane

28
Q

TGN activity:

Excitable cells

A

Products are concentrated and stored in secretory vesicles until an extracellular signal stimulates their secretion

29
Q

Secretory proteins are released from the cell by

A

Regulated exocytosis
e.g. Secretory vesicles store insulin in a pancreatic β cell. Insulin is released into extracellular space in response to increased blood glucose.

30
Q

Coated vesicles

A

Vesicles that bud off from membranes have a distinctive protein coat on their cytosolic surface

31
Q

After budding, coated vesicles shed their coat…

A

Allowing the vesicle to interact with the membrane to which it will fuse

32
Q

Clathrin-coated vesicles have

A

Outer coat made up of the protein clathrin

33
Q

Clathrin-coated vesicles bud from

A

Trans-Golgi network on outward secretory pathway
and
plasma membrane on inward secretory pathway

34
Q

Steps in vesicular transport

A
  1. Cargo sorting and vesicle formation
  2. Motor Proteins move vesicles along the cytoskeleton
  3. Vesicle Tethering/Docking proteins bring vesicle and target membrane together
  4. Vesicle fusion
35
Q

3 forms of Endocytosis

A
  1. Receptor-mediated endocytosis
  2. Pinocytosis (fluid phase)
  3. Phagocytosis (fluid / particles e.g. microbes)
36
Q

Cholesterol isn’t soluble in water

A

Transported in blood in Low Density Lipoprotein (LDL) particles

37
Q

If cell needs cholesterol, it will import LDLs via

A

Receptor-mediated endocytosis

38
Q

Steps in Receptor-mediated endocytosis

A
  1. LDL particles bind to a specific LDLR
  2. LDLR gets concentrated in clathrin coated pits
  3. Vesicle forms- Outer coat of clathrin, inner core of LDL particle, bound to LDLR
  4. Uncoating of vesicle
  5. Naked vesicle fuses with endosome and delivers content
  6. LDL particle and receptor dissociate as in endosome, pH is lower
  7. LDL particles delivered via vesicles to lysosomes, degraded by hydrolytic enzymes in lysosomes, frees cholesterol
  8. LDLR packaged into recycling vesicle which brings receptor back to plasma membrane to mediate another round of endocytosis
39
Q

Disease of endocytosis: Familial Hypercholesterolaemia

A

Caused by mutations in LDLR: either not produced or not functional
Body unable to remove LDL (bad) cholesterol from blood.
-> high level of LDL in blood

Metabolism (9 decks)

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