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MCB 2050 > Mitochondria and Chloroplasts - Chloroplasts > Flashcards

Mitochondria and Chloroplasts - Chloroplasts Flashcards

1
Q

what are chloroplasts

A

semi-autonomous plant cell organelle

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2
Q

what are chloroplasts involved in

A

photosynthesis
fatty acid and amino acid biosynthesis
nitrogen and sulfur assimilation

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3
Q

how are chloroplasts often highly mobile

A

they move along cytoskeleton elements via molecular motors

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4
Q

what kind of organelle is a chloroplast

A

double membrane bound

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5
Q

what does the chloroplast envelope consist of

A

outer and inner membranes

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6
Q

what does the outermembrane contain

A

porins that are not as permeable to ions/small molecules as mitochondria

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7
Q

qualities of inner membrane

A

highly impermeable, contains various transports

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8
Q

what are thylakoids

A

3rd membrane system

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9
Q

thylakoid morphology

A

flattened membranous discs arranges in stacks or between stacks

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10
Q

grana thylakoid

A

thylakoid in stack

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11
Q

stromal thylakoid

A

thylakoid between stacks

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12
Q

what are thylakoid membranes

A

site of ATP synthase
maintain H+ gradient in thylakoid lumen

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13
Q

thylakoid lumen

A

aqueous interior of thylakoid with high [H+]

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14
Q

what is the stroma

A

aqueous interior - space inside envelope and outside of thylakoids

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15
Q

what does the storm contain

A

enzymes involved in carb synthesis and plastid genome

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16
Q

what is the plastid genome in stroma

A

circular
encodes ribosomal proteins, some Ps proteins
ribosomes

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17
Q

how are chloroplasts often connected

A

via stromules

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18
Q

what are stromules

A

long, stroma-filled membrane tubules
branched and dynamic

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19
Q

what do stromules allow for

A

efficient metabolite transfer and communication

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20
Q

what do stromules do rapidly

A

extend and contract

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21
Q

how do chloroplasts multiply

A

fission

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22
Q

what is chloroplast fission

A

divide in synch in response to environmental stimuli and/or developmental signals

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23
Q

example of developmental signals that get a response by fission

A

at the end of G1 - organelle duplication prior to S phase

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24
Q

what are the 2 sets of protein machineries involved in chloroplast division

A

FtsZ and PD

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25
Q

what do FtsZ and PD both form

A

ring-like structures either on inside or outside of chloroplast envelope

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26
Q

what do the rings formed by FtsZ and PD do

A

tighten and pinch organelle into 2 daughter chloroplasts

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27
Q

what kind of machinery does FtsZ have

A

internal machinery on stroll side of inner membrane

28
Q

what does FtsZ include

A

FtsZ1 and FtsZ2

29
Q

what are FtsZ1 and FtsZ2

A

soluble stromal proteins
homologs of bacterial division protein FtsZ

30
Q

what do FtsZ1/2 spontaneously assemble into

A

long, filamentous polymers at midway point (equator) on inner membrane surface

31
Q

what do FtsZ1/2 form

A

FtsZ-ring at future chloroplast division site

32
Q

what is the initial positioning of the FtsZ proteins at equator mediated by

A

soluble stromal proteins:
ARC3
MinD
MinE

33
Q

what is mediated by ARC6

A

linkage of Z-ring to inner membrane at chloroplast division site

34
Q

what is the integral inner membrane-spanning protein localized to in dividing chloroplast

A

the equator

35
Q

what does the stromal-facing domain of ARC6 do

A

links to and stabilizes FtsZ-ring

36
Q

what can disrupt the fission process

A

mutation in ARC6 gene - results in formation of 1-2 giant chloroplasts

37
Q

what does ARC6 control

A

tightening of FtsZ-ring

38
Q

what does ARC6’s interaction with Z-ring signal the start of

A

chloroplast constriction process

39
Q

what does the IMS-facing domain of ARC6 bind to

A

Plastic Dividing (PD) machinery in chloroplast outer membrane

40
Q

what does PD machinery include

A

PDV1 and PDV2

41
Q

what are PDV1 and PDV2

A

hetero-dimeric, integral outer transmembrane proteins recruited to midway point in dividing chloroplast via ARC6

42
Q

what do PDV1 and PDV2 also bing to

A

ARC5

43
Q

what is ARC5

A

cytoplasmic, soluble dynamin-related GTPase protein

44
Q

what does ARC5 assemble into

A

spiral-like structures to from PD-ring

45
Q

what does the PD-ring do

A

wraps around outside of chloroplast - tightening via GTP-hydrolysis causes constriction of outer envelope

46
Q

what work together for division

A

FtsZ and PD machineries

47
Q

how do the 2 daughter chloroplasts get formed

A

through concerted action of both internal Z-ring and external PD ring

48
Q

what do all chloroplast proteins possess

A

unique targeting sequences

49
Q

what do the specific sequences of amino acids serve as

A

zipcodes

50
Q

what do the amino acid zip codes mediate

A

protein targeting from cytoplasm to chloroplast surface
protein targeting from cytoplasm to specific sub chloroplast compartment

51
Q

what do most stromal-destined proteins possess

A

stromal import sequence

52
Q

where is the stromal import sequence located

A

proteins N-terminus

53
Q

what is the stromal import sequence enriched in

A

hydroxylated residues and small hydrophobic resides

54
Q

does a amphipathic alpha-helix get formed by stromal import sequence

A

no

55
Q

when does the stromal import sequence get cleaved

A

following protein import into stroma

56
Q

what is the stromal import sequence responsible for

A

targeting nascent stromal protein to cytoplasmic surface of chloroplast
subsequent translocation across out and inner membranes

57
Q

what is the Toc complex

A

multi protein complex that includes receptor subunits, transmembrane channel and various accessory proteins

58
Q

why is GTP involved in binding stromal import sequence to Toc receptor

A

there is energy requirement for import

59
Q

when are Toc and Tic complexes adjacent to each other

A

contact sites

60
Q

how does precursor protein translocation occur across both membranes

A

sequentially - unlike mitochondria NOT mediated by [H+] electrochemical potential

61
Q

how does Hsp93 act as a molecule motor

A

undergoes ATP dependent conformational changes that pulls protein into storm and prevent backsliding

62
Q

what does Hsp93 assist with

A

protein folding

63
Q

what doe molecular chaperone proteins in stroma ensure (Hsp93)

A

cleaved, mature protein properly folded

64
Q

what are TOC and TIC complexes also involved in

A

import or insertion of other chloroplast proteins

65
Q

how do all nuclear-encoded chloroplast proteins access chloroplast

A

through Toc and/or Tic complexes

66
Q

what does folded protein import in pH dependent pathway reply on

A

energy from proton (change in pH) gradient between stroma and lumen

67
Q

which [H+] is larger in pH-dependent pathway

A

[H+] thylakoid lumen is larger than [H+] stroma

MCB 2050 (11 decks)

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