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BMS241 final exam > Topic 7 - Intracellular compartments & transport > Flashcards

Topic 7 - Intracellular compartments & transport Flashcards

1
Q

Main functions of cytosol…

A

contains many metabolic pathways; protein synthesis

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2
Q

Main functions of nucleus…

A

contains main genome; DNA & RNA synthesis

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3
Q

Main functions of ER… (this chapter)

A

synthesis of most lipids; synthesis of proteins for distribution to many organelles and to the plasma membrane

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4
Q

Main functions of golgi apparatus… (this chapter)

A

modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle

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5
Q

Main functions of lysosomes… (this chapter)

A

intracellular degredation

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6
Q

Main function of endosomes… (this chapter)

A

sorting of endocytosed material

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7
Q

Main functions of mitochondria…

A

ATP synthesis by oxidative phosphorylation

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8
Q

Main function of chloroplasts…

A

ATP synthesis and carbon fixation by photosynthesis

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9
Q

Main function of peroxisomes…

A

oxidation of toxic molecules

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10
Q

3 largest intracellular compartments in the cell…?

A

cytosol > ER > nucleus…

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11
Q

Smallest intracellular compartment in the cell…?

A

peroxisome

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12
Q

Membranes of the ER, Golgi apparatus, endosomes & lysosomes are believed to have originated by invagination of?

A

plasma membrane

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13
Q

Which organelle is considered most ‘prominent’?

A

nucleus

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14
Q

What are the 3 mechanisms of protein import? proteins folded/unfolded?

A
  1. transport via nuclear pores (nucleus) - folded
  2. transport across membranes (chloroplasts, mitochondrion, peroxisome) via protein translocators - unfolded
  3. transport vesicles (golgi app.) - folded
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15
Q

Nuclear pores function as …?

A

selective gates - actively transporting macromolecules & free diffusion from smaller molecules

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16
Q

T or F - energy is required for all of these transport processes

A

true

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17
Q

What is a ‘signal sequence’? what else does it contain?

A

a continuous stretch of AAs (15-60) that directs the protein to the organelle in which it is required (often removed from finished protein)
N-terminal

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18
Q

What happens to a protein destined for the ER that has its N-terminal signal sequence removed?

A

it remains in the cytosol

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19
Q

What happens to a protein destined for the cytosol that has an N-terminal signal sequence added?

A

it gets redirected to the ER

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20
Q

How can signal sequences be removed or added to a protein?

A

via recombinant DNA techniques

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21
Q

Re. signal sequences, ‘red’ AAs are …?

A

+vely charged

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22
Q

Re. signal sequences, ‘blue’ AAs are …?

A

-vely charged

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23
Q

Re. signal sequences, extended blocks of ‘green’ AAs are …?

A

hydrophobic

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24
Q

The membrane that is continuous with the ER is ?

A

the outer nuclear membrane

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25
T or F - traffic occurs only in one direction thru the nuclear pores
false - thru both directions proteins -> in from cytosol RNA & ribosomal subunits -> out
26
The outer nuclear membrane is bound by?
ribosomes
27
structures that guide proteins to the nuclear pore...
fibrils
28
Passage of larger molecules (RNA & proteins) thru nuclear pores requires ...?
a sorting signal
29
The signal sequence that directs a protein from the cytosol into the nucleus is called a ? What recognises it?
Nuclear localisation signal (NLS), which is recognised by nuclear transport receptor (NTR) - lives in cytoplasm
30
nuclear localization signal (NLS), typically consists of one or two short sequences containing several
+vely charged lysine or arginines (basic AAs)
31
importing proteins into the nucleus requires energy in the form of ?
GTP hydrolysis
32
Details of how proteins are imported into mitochondria...
see slide 25 (movie 15.2) precursor protein + signal sequence -> receptor protein near protein translocator -> lateral diffusion to 'CONTACT SITE' -> transported as unfolded protein thru translocator -> signal sequence cleaved off by signal peptidase (chaperone proteins assist with translocation & refolding of protein)
33
T or F - ER proteins are synthesised by the same ribosomes that make cytosolic proteins
slide 28...true - start translation in the cytosol -> it stalls translation until the ribosome docks on the SRP receptor on the ER membrane & enters a membrane translocation channel -> rest of the protein is synthesised into the translocator
34
What is the role of the signal recognition particle (SRP)?
slows protein synthesis down & chaperones ER-destined mRNA -> SRP receptor in ER membrane (remember diagram slide 30 & vid 15.4)
35
What is cotranslational translocation ?
proteins that are passed thru the translocation channel
36
What are the start & stop signals for single & double pass transmembrane proteins?
start - hydrophobic region of the signal sequence (start-transfer sequence) stop - hydrophobic stop-transfer sequence
37
What do all resident ER proteins contain ?
KDEL sequence
38
What are the roles of the protein coat?
shapes membrane vesicle | helps to capture molecules for onward transport
39
How is the protein coat direct vesicle formation?
cargo molecule -> receptor on membrane -> adaptin -> clathrin coat -> dynamin pinches off vesicle ->
40
What are the protein coats made up of?
Clathrin molecules with TRISKELION structure
41
TYPE OF COATED VESICLE Clathrin-coated with COAT PROTEINS clathrin + adaptin 1 originate where? end up where?
originate: golgi destination: lysosomes
42
TYPE OF COATED VESICLE Clathrin-coated with COAT PROTEINS clathrin + adaptin 2 originate where? end up where?
originate: plasma membrane destination: endosomes
43
TYPE OF COATED VESICLE COP-coated with COAT PROTEINS COP proteins originate where? end up where?
pathways: ER -> GA Golgi cisterna -> golgi cisterna GA -> ER
44
Explain vesicle docking tethers & SNAREs...
``` slide 46-48... Rab proteins on vesicle surface->tethering proteins->dock then vSNARE (vesicle) bunds to tSNARE (target membrane) pulls lipid bilayers very close squeezing out any trapped water mol's -> lipids to coalesce & fuse together ```
45
Why can't Clathrin vesicles bind to ER?
because of tSNARE & vSNARE specificity (only recognise COP-coated vesicles)
46
Explain how proteins are glycosylated in the ER... (ie. from protein -> glycoprotein) players involved...
newly formed protein in ER gets glycosylated by addition of oligosaccharide side chain (bound to dolichol) via catalysis of enzyme (oligosaccharide protein transferase) to amino group of ASPARAGINE SIDE CHAIN
47
Asparagines that are glycosylated are always present in the tripeptide sequences...?
asparagine-X-serine (N-X-S) | asparagine-X-threonine (N-X-T)
48
Exit from the ER Is Controlled to Ensure Protein Quality. How?
Misfolded or incorrectly assembled proteins are retained in the ER by chaperone proteins until proper folding occurs-> transport vesicles. If proper folding does not occur -> cytosol for degradation
49
Name a condition that is caused by the over-efficiency of ER-exit-control mechanism
cystic fibrosis
50
What does the unfolded protein response (UPR) do?
when +++ misfolded proteins in ER -> bind to receptors -> transcription regulator -> nucleus -> activates chaperone gene -> chaperone mRNA -> ribosome on ER membrane -> +++chaperone proteins in ER thus normal protein folding- AND more ER
51
What happens when expanded ER cannot expand anymore? What pathology could this cause?
UPR program directs apoptosis just like in adult-onset diabetes
52
Pathway thru golgi app...?
cis Golgi network -> cis cisterna -> medial cisterna -> trans cisterna -> trans Golgi network
53
What signalling occurs at the Golgi?
post-translational mods; glycosylation...
54
What is constitutive secretion?
exocytosis is always on which provides plasma membrane with new lipids & proteins
55
What is regulated secretion?
exocytosis is regulated by extracellular signals (eg. hormone or neurotransmitter)
56
Eg. of regulated secretion?
+++ blood sugar -> signal for insulin secretion by secretory vesicles in pancreatic beta cells
57
Biochemical, genetic, and molecular biological and microscopic techniques also provide a means for studying how proteins shuttle from one cel- lular compartment to another. List 3 ways how they can be tested...explain one...
- test tube - mutant yeast cells - GFP test tube method: add radioactively labeled protein + or - signal sequence and isolated organelle -> incubate -> centrifuge -> free protein stays on top while labaled protein co-sediments with organelle (slide 64)
58
How do phagocytotic cells engulf their 'prey'? Egs of phagocytosis... How does TB prevent this process?
Via pseudopods that form phagosomes -> lysosomes for digestion - neutrophil engulfing bacteria - macrophage engulfing erythrocytes (RBCs) TB prevents fusion that unites the phagosome with a lysosome -> instead of being destroyed, engulfed organism survives & multiplies within macrophage
59
A macrophage, for example, swallows ...% of its own volume of fluid each hour. Thus removes ...% of its plasma membrane each minute, or ...% in about half an hour
own volume = 25% per hour | Plasma membrane = 3% per minute or 100% per half hour
60
What are the roles of pinocytosis?
to maintain balance in fluid & membrane fluxes caused by exocytosis (mainly constitutive) mainly via clathrin coated pits & endocytosis. also lipids & proteins from the plasma membrane
61
What is receptor-mediated endocytosis? Eg?
pinocytosis via clathrin-coated vesicles provide efficient way of taking up macromolecules Eg. cholesterol transport in LDLs -> LDL receptor -> endocytosed in clathrin-coated vesicles -> endosome (acidic) dissociates from LDL receptor -> LDL -> lysosome -> free cholesterol & AAs
62
Conditions in the endosome compartment...?
low pH (5 - 6) cos of ATPase H+ pump
63
The routes taken by receptors once they have entered an endosome differ according to the type of receptor: what are the 3 fates?
1. recycling - same plasma membrane (eg. LDLs) 2. degradation - lysosome 3. transcytosis - different domain of the plasma membrane
64
Recycling & degradation depends on what...?
Recycling - monoubiquitination | Degradation - polyubiquitination
65
Principle sites of intracellular digestion? Details...
lysosomes pH - 5 via ATPase H+ pump membranous sacs of hydrolytic enzymes that break various bonds with water
66
Name some of the acid hydrolases in lysosomes...
``` proteases nucleases lipases glycosidases phospatases phospholipases sulfatases ```
67
What is autophagy?
pathway used for degrading obsolete parts of the cell itself via autophagosome -> lysosome -> destruction Eg. lysosomes digesting mitochondria, as well as other organelles

BMS241 final exam (5 decks)

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