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From Molecules to Cells > Lecture 3: Mitochondria and ER nuclear export > Flashcards

Lecture 3: Mitochondria and ER nuclear export Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is the matrix?

A

Contains enzymes needed for oxidation and citric acid cycle

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2
Q

What is the inner membrane of mitochondria?

A

Folded up into cristae
Contains proteins that do oxidative phosphorylation
Contains transport proteins that transport in and out of the matrix Impermeable

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3
Q

What is the outer membrane of the mitochondria?

A

Contains porins
Permeable to molecules of 5000 daltons or less

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4
Q

What is the intermembrane space?

A

Contains enzymes that use ATP from matrix to phosphorylate other nucleotides
Contains proteins that are released during apoptosis

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5
Q

Where are mitochondria located in the cell?

A

They move around the cell and can divide and fuse
Near sites that use a lot of ATP

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6
Q

What are mitochondrial targeting signal sequences?

A

Have high content of Arg and SER
At the N terminus
20-80 amino acids long
Cleaved after import into matrix

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7
Q

What is the structure of mitochondrial targeting sequences?

A

They form an amphiphilic alpha helix with two different faces
One side is positive residues One side is non polar

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8
Q

What structure must the protein be in before mitochondrial import?

A

Unfolded or loosely folded

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9
Q

How are mitochondrial proteins imported?

A
  1. MTS is recognised by receptor in outer membrane
  2. Translocator channel moves protein into inter-membrane space
  3. Signal binds to second translocator in inner membrane
  4. Chaperone proteins (hsp70) pull protein into the matrix and refold it. Driven by ATP hydrolysis
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10
Q

What is the structure of the ER?

A

Extensive membrane system
Network of sacs and tubules

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11
Q

What are the two types of ER?

A

Smooth - does lipid synthesis Rough - does protein synthesis

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12
Q

Which cells have a large amount of rough ER?

A

Pancreatic cells

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13
Q

Which type of cells have a large amount of smooth ER?

A

Hepatocytes

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14
Q

Why do different cells have different amounts of smooth and rough ER?

A

Depends on how much they need protein and lipid synthesis

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15
Q

What are the two types of proteins that enter the ER?

A

Soluble proteins
Integral membrane proteins

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16
Q

What are soluble proteins?

A

Water soluble
Secretory
In the lumen of organelles of the endomembrane system

17
Q

What are integral membrane proteins?

A

Hydrophobic sequences
Form membrane spanning domains
Embedded in the lipid bilayer of membranes of endomembrane system and plasma membrane

18
Q

If proteins are destined for different organelles what do they have to enter first?

A

The ER

19
Q

ER signal sequence features

A

8+ hydrophobic amino acid residues usually near N-terminus

20
Q

What happens to ribosomes synthesising proteins without a signal sequence?

A

They remain free in the cytosol

21
Q

What happens to the ribosome synthesising proteins with an ER signal sequence?

A

They are directed to the ER while the protein is still being translated

22
Q

What is co-translational translocation?

A

When translation happens at the same time as translocation

23
Q

What is the difference between the translocation of the ER proteins and the mitochondrial and nuclear proteins?

A

ER does co-translational translocation
Mitochondrial and nuclear proteins do post-translational translocation

24
Q

What is the role of SRP (signal recognition particle) in targeting to the ER?

A
  1. SRP in cytosol binds to ERSS when it leaves ribosome and translation is paused
  2. SRP binds to SRP receptor in ER membrane
  3. SRP is displaced and the Ribosome passes to the translocator and translation is resumed
25
Q

What is the Sec61 channel?

A

A multi-subunit complex of proteins forming a channel in the ER membrane

25
Q

What is the function of the Sec61 channel?

A

It allows the protein chain to be translocated across the ER membrane through a central pore
The pore is closed when there is no translating polypeptide

26
Q

What is the process of the ERSS binding to the Sec61 channel?

A
  1. ERSS binds to Sec61 translocator and the channel opens
  2. The polypeptide containing the ERSS enters the channel as a loop, as ERSS is held in Sec61, while translation happens
  3. ERSS cleaved by signal peptidase and lets only the protein through the membrane

From Molecules to Cells (23 decks)

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