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Bio 209 > Lecture 8 - Intracellular Compartments + Protein Sorting > Flashcards

Lecture 8 - Intracellular Compartments + Protein Sorting Flashcards

1
Q

Major compartments/organelles of endomembrane system of eukaryotic cells

A
  • Lysosome
  • Golgi apparatus
  • Mitochondrion
  • Endoplasmic Reticulum
  • Nucleus
  • Plasma membrane
  • Peroxisome
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2
Q

Lysosome function

A

Protein destruction

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3
Q

Golgi Apparatus function

A

Protein modification and export

trans golgi faces plasma membrane

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4
Q

Mitochondrion function

A

Energy production

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5
Q

Endoplasmic Reticulum function

A

Smooth: lipid production, detoxification

Rough: protein production, particularly for export out of cell

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6
Q

Nucleus function

A

DNA storage

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7
Q

Peroxisome function

A

Lipid destruction

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8
Q

Endosymbiosis theory and what organelles are present based on this.

A

Anaerobic eukaryote took in aerobic prokaryote, evolution caused aerobic bacterium to multiply w/in => anaerobic eukaryote and aerobic prokaryote form symbiotic relationship => membrane of mitochondria/chloroplast derived from eukaryotic cell host

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9
Q

3 major modes of protein transport

A
  1. Gated transport
  2. Transmembrane transport
  3. Vesicular transport
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10
Q

What is gated transport?

A

The movement of proteins b/t cytosol and nucleus (nuclear pore complexes: display specificity), also import of transcription factors, nuclear factors, DNA pol, etc.

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11
Q

What is transmembrane transport?

A
  • Proteins transported from cytosol to mitochondria, ER, plastids, or peroxisomes
  • Facilitated by TM protein translocators
  • Cargo unfolds to pass through translocator
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12
Q

What is vesicular transport?

A
  • Proteins transported from ER to Golgi, Golgi to late endosome/lysosome/early endosome/cell exterior, cell exterior, secretory vesicles/cell exterior
  • Membrane-enclosed transport intermediates ferry proteins from one compartment to another via membrane fusion.
  • Proteins transported this way never cross membranes
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13
Q

Properties of lipid vesicles and vesicular transport

A

Vesicles bud and fuse during vesicular transport b/c membranes share structural and physical properties

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14
Q

Signal sequences: function. Don’t memorize actual AA sequences of these, though! Where located?

A

Serve as indicator of where proteins should be targeted

On N terminus

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15
Q

Nuclear import from cytosol: features of the nucleus and nuclear envelope

A

Features of nucleus/nuclear envelope:
- double membrane
- contiguous w/ ER
- has nuclear pore complexes -> gateways through which things get into/out of nucleus (gated diffusion barrier via size, active transport for larger molecules)
- Nuclear lamina network of intermediate filament provide structural integrity to nucleus

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16
Q

What are nuclear localization signals?

A

Signals that act as ID for molecules to enter nucleus

17
Q

What do nuclear import receptors bind?

A

NPC proteins and nuclear localization signals on cargo proteins

18
Q

Nuclear import from cytosol: role of Ran proteins, GTP hydrolysis, regulation

A

GTP-binding proteins that facilitate nuclear transport

GTP hydrolysis by Ran proteins provide directionality to nuclear transport

Regulated by type of bound guanine nucleotide => cycle b/t GDP/GTP bound forms via exchange reactions

19
Q

Nuclear import from cytosol: control of nuclear envelope formation/breakdown (slide 19).

A
  • Dynamic assembly/disassembly of nuclear lamina is important for things like cell division
20
Q

Transport of proteins into mitochondrion: features, requirements, steps.

A

Two mitochondrial protein translocators:
- TOM complex: receives protein
- TIM23 complex: spans both membranes, brings protein into matrix

Requires:
- ATP hydrolysis
- Membrane potential

Steps:
- Protein has a signal sequence that binds to import receptors
- TOM Complex has receptor, triggers insertion into membrane
- TIM23 Complex translocates protein into matrix
- Signal is cleaved by signal peptidase

21
Q

Transport of proteins from the cytosol into ER: features, components, steps.

A

2 ways: Co-translational (destined for ER) or Post-translational translocation (destined elsewhere)

Co-translational:
- Ribosome translates mRNA, produced protein has signal
- SRP binds to signal peptide => pause translation
- SRP-bound ribosome attaches to SRP receptor in ER membrane
- Translation continues and translocation begins
- SRP and SRP receptor displaced/recycled

22
Q

Differences b/w SER & RER, how they can be isolated.

A

Differences: SER microsomes have low density and stop sedimenting/float at low sucrose concentration; RER microsomes have high density and stop sedimenting/float at high sucrose concentration

Separation: High speed centrifugation w/ density gradient

23
Q

The signal hypothesis of protein translocation, the SRP

A

The signal hypothesis of protein translocation: translocation is signal sequence specific, and the signal determines target compartment

Signal-recognition particle (SRP): directs ER signal sequences to a specific receptor in the RER membrane

24
Q

Translocation of soluble proteins from cyt to ER

A
  • Protein w/ signal attaches to inactive protein translocator => active translocator
  • Signal peptidase cleaves signal
  • Mature soluble protein in ER lumen
25
Q

Translocation of single TM proteins w/ terminal ER sequence from cyt to ER

A
  • Signal acts as start transfer sequence, stop-transfer sequence is internal
  • Translocator translocates protein until it hits stop-transfer sequence => signal peptidase cleaves signal
  • ER communicates w/ other organelles => bud off protein in membrane as vesicle to transport for destined location
26
Q

Translocation of single TM proteins w/ internal ER sequence from cyt to ER

A
  • The sequence acts as both the start and stop sequence, w/ the protein orientation dependent on the location of flanking positively charged amino acids w/ respect to internal ER sequence
27
Q

Translocation of 2 TM domain proteins from cyt to ER

A
  • Signal sequence is internal and acts as start-transfer, stop-transfer also internal
28
Q

Translocation of multiple TM domain proteins from cyt to ER

A
  • Multiple internal start and stop sequences in protein
29
Q

Glycosylation of proteins: what is it? Functional importance?

A
  • Protein modification during folding => attachment of sugars to specific AA residues

Glycoslyation can be either N-linked (asparagine) or O-linked (hydroxylate AA like serine, threonine)

Function: important for ensuring eventual folding of protein in ER lumen, if not properly folded => ubiquitination (degradation of protein)

30
Q

Degradation of misfolded proteins.

A
  • Misfolded protein is brought to protein translocator
  • In cytosol, ubiquitin attaches to lysine residues and protein is brought to proteasome where proteins die
31
Q

GPI-linked proteins

A

Some proteins are linked to glycosylphosphatidl-insoitol (GPI), anchoring them to membrane

Bio 209 (10 decks)

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