The Endoplasmic Reticulum And The Secretory Pathway Flashcards

1
Q

Explain the structure of the ER

A
  • single membrane compartment (a continuous network of tubular and flat vesicular structures in the cytoplasm)
  • space inside is connected with the space between the two membrane surfaces of the nuclear membrane (filled with a fluid- not cytoplasm)
  • two parts with different functions
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2
Q

RER facts?

A
  • has ribosomes
  • found near the nucleus
  • originated from nuclear membranes
  • mainly composed of cisternae
  • involved with the synthesis, folding and transport of proteins
  • well developed in protein forming and secretory cells
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3
Q

SER facts?

A
  • found closer to the cell membrane
  • originates from rough ER by giving off ribosomes
  • mainly composed of tubules
  • synthesis and transport of lipids
  • mainly present in lipid forming cells
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4
Q

Functions of the RER

A
  • protein synthesis
  • glycosylation
  • Folding and assembly of multi protein complexes
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5
Q

Functions of SER

A
  • lipid synthesis (cholesterol, phospholipids)
  • Ca2+ sequestration
  • detoxification by cytochromes P450 enzymes
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6
Q

What is Ca2+ sequestration?

A

The binding or confining of calcium ions so they are separated from other components of a biological system

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7
Q

Where are newly synthesised proteins targeted to?

A

ER, nucleus, mitochondria or peroxisomes

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8
Q

What are signal sequences?

A

Amino acids at the N-terminal end of the protein that are recognised by enzyme systems within the cell that transport the protein to the correct destination

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9
Q

What do the free ribosomes in the cytosol do?

A

Send proteins to the nucleus, peroxisomes, mitochondria or chloroplasts

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10
Q

What do the membrane bound proteins on the RER do?

A

Send proteins to plasma membrane, endoscopes, secretory vesicles or lysosomes

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11
Q

What are the four steps of signal sequences directing proteins to the ER signal recognition particle? (SRP)

A
  • recognition of the signal peptide by the ribosomes
  • SRP protein bonds to the ribosome - nascent chain complex (ribosome and aa chain that is growing)
  • the complex binds to SRP receptor which is attached to the ER membrane. GTP must be present.
  • signal peptide is transferred from the SRP complex to the translocation channel
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12
Q

What are the steps for protein modification in the RER?

A
  • Proteolysis (signal peptide)
  • disulphides bond formation
  • glycosylation
  • deglycosylation
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13
Q

What does glycosylation/ deglycosylation mean?

A

Sugars being added/ taken from proteins as they enter the ER

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14
Q

What is important about the sugar groups that come from glycosylation?

A

They’re important for the recognition of proteins- especially if they’re going to be secreted

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15
Q

What happens if a protein fails a quality check?

A

They are not exported from the ER and are degraded by ubiquitination and protease ERAD (endoplasmic reticulum associated protein degradation)

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16
Q

Golgi apparatus structure

A
  • Single membrane compartment consisting of 4 to 8 stacked layers of thin, flat, enclosed residues (cisternae) lying near one side of the nucleus.
  • three networks: cis, medial and trans
17
Q

Golgi apparatus functions

A

Protein modification, lipid synthesis and protein and lipid sorting

18
Q

How do things deposit their cargo into the golgi complex?

A

Budding- movement- fusion

19
Q

What groups does the golgi sort the proteins and lipids into?

A
  • secretory granules
  • plasma membrane
  • basolateral vs apical membrane
  • endosomes
  • lysosomes
20
Q

How do proteins get from one cisternae to another?

A

Using vesicles

21
Q

How is the destination of a protein determined?

A

In the ER when the protein binds to a specific receptor. Various characteristics of the cargo protein are recognised

22
Q

Where do vesicles transport proteins from/to?

A
  • Golgi apparatus to lysosomes, plasma membrane or exterior
  • plasma membrane to lysosomes
  • endosomes to the plasma membrane
23
Q

What is bud formation facilitated by?

A

The binding of different coat proteins (COPs)

24
Q

What happens once the transport vesicle is formed and released?

A

The coat proteins are removed and the V-SNARE is revealed