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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
Q

T or F - traffic occurs only in one direction thru the nuclear pores

A

false - thru both directions
proteins -> in from cytosol
RNA & ribosomal subunits -> out

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26
Q

The outer nuclear membrane is bound by?

A

ribosomes

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27
Q

structures that guide proteins to the nuclear pore…

A

fibrils

28
Q

Passage of larger molecules (RNA & proteins) thru nuclear pores requires …?

A

a sorting signal

29
Q

The signal sequence that directs a protein from the cytosol into the nucleus is called a ? What recognises it?

A

Nuclear localisation signal (NLS), which is recognised by nuclear transport receptor (NTR) - lives in cytoplasm

30
Q

nuclear localization signal (NLS), typically consists of one or two short sequences containing several

A

+vely charged lysine or arginines (basic AAs)

31
Q

importing proteins into the nucleus requires energy in the form of ?

A

GTP hydrolysis

32
Q

Details of how proteins are imported into mitochondria…

A

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
Q

T or F - ER proteins are synthesised by the same ribosomes that make cytosolic proteins

A

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
Q

What is the role of the signal recognition particle (SRP)?

A

slows protein synthesis down & chaperones ER-destined mRNA -> SRP receptor in ER membrane (remember diagram slide 30 & vid 15.4)

35
Q

What is cotranslational translocation ?

A

proteins that are passed thru the translocation channel

36
Q

What are the start & stop signals for single & double pass transmembrane proteins?

A

start - hydrophobic region of the signal sequence (start-transfer sequence)
stop - hydrophobic stop-transfer sequence

37
Q

What do all resident ER proteins contain ?

A

KDEL sequence

38
Q

What are the roles of the protein coat?

A

shapes membrane vesicle

helps to capture molecules for onward transport

39
Q

How is the protein coat direct vesicle formation?

A

cargo molecule -> receptor on membrane -> adaptin -> clathrin coat -> dynamin pinches off vesicle ->

40
Q

What are the protein coats made up of?

A

Clathrin molecules with TRISKELION structure

41
Q

TYPE OF COATED VESICLE Clathrin-coated with COAT PROTEINS clathrin + adaptin 1 originate where? end up where?

A

originate: golgi
destination: lysosomes

42
Q

TYPE OF COATED VESICLE Clathrin-coated with COAT PROTEINS clathrin + adaptin 2 originate where? end up where?

A

originate: plasma membrane
destination: endosomes

43
Q

TYPE OF COATED VESICLE COP-coated with COAT PROTEINS COP proteins originate where? end up where?

A

pathways:
ER -> GA
Golgi cisterna -> golgi cisterna
GA -> ER

44
Q

Explain vesicle docking tethers & SNAREs…

A 
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
Q

Why can’t Clathrin vesicles bind to ER?

A

because of tSNARE & vSNARE specificity (only recognise COP-coated vesicles)

46
Q

Explain how proteins are glycosylated in the ER… (ie. from protein -> glycoprotein) players involved…

A

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
Q

Asparagines that are glycosylated are always present in the tripeptide sequences…?

A

asparagine-X-serine (N-X-S)

asparagine-X-threonine (N-X-T)

48
Q

Exit from the ER Is Controlled to Ensure Protein Quality. How?

A

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
Q

Name a condition that is caused by the over-efficiency of ER-exit-control mechanism

A

cystic fibrosis

50
Q

What does the unfolded protein response (UPR) do?

A

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
Q

What happens when expanded ER cannot expand anymore? What pathology could this cause?

A

UPR program directs apoptosis just like in adult-onset diabetes

52
Q

Pathway thru golgi app…?

A

cis Golgi network -> cis cisterna -> medial cisterna -> trans cisterna -> trans Golgi network

53
Q

What signalling occurs at the Golgi?

A

post-translational mods; glycosylation…

54
Q

What is constitutive secretion?

A

exocytosis is always on which provides plasma membrane with new lipids & proteins

55
Q

What is regulated secretion?

A

exocytosis is regulated by extracellular signals (eg. hormone or neurotransmitter)

56
Q

Eg. of regulated secretion?

A

+++ blood sugar -> signal for insulin secretion by secretory vesicles in pancreatic beta cells

57
Q

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…

A
  • 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
Q

How do phagocytotic cells engulf their ‘prey’?
Egs of phagocytosis…
How does TB prevent this process?

A

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
Q

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

A

own volume = 25% per hour

Plasma membrane = 3% per minute or 100% per half hour

60
Q

What are the roles of pinocytosis?

A

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
Q

What is receptor-mediated endocytosis? Eg?

A

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
Q

Conditions in the endosome compartment…?

A

low pH (5 - 6) cos of ATPase H+ pump

63
Q

The routes taken by receptors once they have entered an endosome differ according to the type of receptor: what are the 3 fates?

A
  1. recycling - same plasma membrane (eg. LDLs)
  2. degradation - lysosome
  3. transcytosis - different domain of the plasma membrane
64
Q

Recycling & degradation depends on what…?

A

Recycling - monoubiquitination

Degradation - polyubiquitination

65
Q

Principle sites of intracellular digestion? Details…

A

lysosomes
pH - 5 via ATPase H+ pump
membranous sacs of hydrolytic enzymes that break various bonds with water

66
Q

Name some of the acid hydrolases in lysosomes…

A 
proteases
nucleases
lipases
glycosidases
phospatases
phospholipases
sulfatases
67
Q

What is autophagy?

A

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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