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Advanced Cell Biology > Lecture 12 - Intracellular compartments and Protein Sorting Part II > Flashcards

Lecture 12 - Intracellular compartments and Protein Sorting Part II Flashcards

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1
Q

Peroxisomes

A

Spherical organelles with a fine granular matrix, sometimes with crystals

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2
Q

The ER is in close contact with

A

Peroxisomes

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3
Q

Peroxisomes only have a

A

Single membrane, no DNA

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4
Q

Peroxisomes are

A

Multi-purpose
Ubiquitous, dynamic organelles with high plasticity
Essential for health

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5
Q

Peroxisomes respond to

A

Environmental stimuli

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6
Q

Function of peroxisomes (3)

A 
Lipid metabolism (produce lipids)
Protective function (detoxification of lipids)
Central regulatory role
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7
Q

Peroxisomes produce what during lipid metabolism?

A

Myelin lipids

Insulation for axons in the brains

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8
Q

Dysfunctions of peroxisomes normally cause

A

Neurological disease

myelin

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9
Q

In fungi, what is produced in the peroxisome?

A

Penicillin

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10
Q

In fireflies, what do the peroxisomes do?

A

Light producing reaction in the lantern organ

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11
Q

Peroxisomes react to environmental stimuli by (3)

A
  1. A change in number
  2. A change in enzyme composition
  3. A change in positioning in the cell
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12
Q

Peroxisomes can import

A

Completely folded, oligomeric or co-factor proteins

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13
Q

Co factor Protein

A

Non-protein chemical compound or metallic ion that is required for an enzyme’s activity
Cofactors can be considered “helper molecules” that assist in biochemical transformations

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14
Q

Oligomer

A

A macromolecular complex formed by non-covalent bonding of a few macromolecules like proteins or nucleic acids

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15
Q

Peroxisomes can be produced

A

De novo (dogma breakers)

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16
Q

Examples of how peroxisomes are odd

A

They can import large proteins that should need a gate without needing a gate (transient pore)
They can form de novo (against biochemical dogma)

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17
Q

PTS

A

Peroxisome Targeting Signal

Amino acid sequence that targets a protein to the peroxisome

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18
Q

PTS1 is found at the

A

C terminus of the protein (3 a.a)

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19
Q

PTS2 is found at the

A

N terminus of the protein (9 a.a.)

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20
Q

PTS1 and PTS2 are recognised by

A

Specific receptors

Pex 5 and Pex 7 respectively (soluble cytosolic proteins)

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21
Q

Pex 5 and Pex 7 are involved in

A

Peroxisome biogenesis

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22
Q

Catalase is a key enzyme

A

In peroxisomes

Degrades H202 produced by Oxidases

23
Q

Oxidases produce

A

H202 in peroxisomes

24
Q

Peroxisomes probably have

A

A transient pore
Allows them to import large proteins
Not been visualised by electron microscopy

25
Q

The transient pore model

A

Pex proteins (Pex5) has bacterial toxin-like properties, can insert into the membrane, interact with lipids

Pex5 forms the pore and releases the PTS1 cargo inside

No ATP required

26
Q

In the transient pore model, Pex5 is removed by

A

Pex1, 6, and 26 form a ‘lever arm’
Grab Pex5 when it is ubiquinitated
Pulls it out of the membrane

ATP required

27
Q

After it is removed from the membrane, Pex5 can either be

A

Recycled or degraded

28
Q

If Pex5 is going to be degraded, it is

A

Polyubiquitinated

29
Q

Pex5 is degraded by the

A

26S Proteosome

30
Q

Ubiquitination requires

A

ATP

31
Q

Pex1 and 6 are

A

ATPases

32
Q

Pex13, 14 and 17

A

Aid in tethering and of Pex5 and translocation of the cargo

33
Q

Example of PBDs

Peroxisome biogenesis disorders

A

Zellweger syndrome

Cerebro-hepato-renal syndrome

34
Q

Proteins go into the ER

A

Co translationally

35
Q

Co translational transport

A

While the proteins are made, they go in

‘synthesised into’

36
Q

Only certain proteins go into the ER (3)

A
  1. Extracellular proteins (sent to the Golgi to packaged into vesicles)
  2. Plasma membrane proteins
  3. Lysosomal proteins (sent to the Golgi)
    and Golgi proteins of course!
37
Q

SRP

A

Signal recognition particle

38
Q

Structure of the SRP

A

Made out of RNA and 6 proteins

Hydrophobic pocket lined with methionines recognises N terminus signal sequence

39
Q

The SRP

A

Has a translational pause domain (like a finger that stops the ribosome translating)
Brings the ribosome to the ER
SRP binds to SRP receptor in the ER membrane
Translation continues and translocaction begins

40
Q

Once the co translated protein is in the ER

A

The signal peptide is cleaved and the protein is folded

41
Q

What does the ER do to the incoming proteins?

A 
Glycosylation (important in extracellular signalling)
Disulfide bridging (stabilises proteins)
Folding
42
Q

Quality control in the ER

A

Checks if proteins are properly folded and will refold or degrade them if they are not

43
Q

When proteins leave the ER

A

They are sent to the ER for further processing

44
Q

Sec61

A

Protein translocator in the ER

Hetero trimeric complex

45
Q

Structure of Sec61

A

Bundled alpha helices with a central pore
Pore is usually closed by a small a-helix ‘plug’
Signal peptide displaces the plug allowing transport of the protein

46
Q

Two mechanisms of ER transport (4)

A
  1. Soluble proteins
  2. Single pass TM proteins I
  3. Single pass TM proteins II
  4. Multi pass TM proteins
47
Q

ER transport: Soluble proteins

A

Polypeptide binds to ER signal sequence
Polypeptide is completely transferred into ER lumen
Signal is cleaved

48
Q

ER transport: Single pass TM proteins I

A

Polypeptide binds to ER signal sequence
Polypeptide contains stop transfer signal (hydrophobic sequence)
Signal is cleaved
C terminus remains in cytosol

49
Q

ER transport: Single pass TM proteins II

A

Polypeptide binds to ER signal sequence
Then:
More positive residues before stop transfer signal = N terminus translocation inhibited
Complete transfer of C terminus part

OR

More positive residues after stop transfer signal = C terminus translocation inhibited
Complete transfer of N terminus part

50
Q

ER transport: Multi pass TM proteins

A

(multiple domains have to span the membrane)
Start transfer signals begin
Until a stop transfer signal is encountered

For more than 2 membrane passes, second start transfer signal sequences re initiate translocation

51
Q

Stop and start transfer signal sequences are

A

Internal signal sequences

Same sequences, just depends on where they are

52
Q

Transmembrane transport is used to

A

Deliver proteins to mitochondria, plastids, peroxisomes and ER
First three occur post translationally, ER is co translational

53
Q

What do signal sequences do?

A

Facilitate interactions between polypeptides and receptors/translocators

Advanced Cell Biology (31 decks)

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