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Hilary Term 1 > Introduction to the Organelles of the Eukaryotic Cell > Flashcards

Introduction to the Organelles of the Eukaryotic Cell Flashcards

1
Q

How much larger are eukaryotic cells than the average Escherichia coli?

A

1,000-10,000 fold

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2
Q

Why do eukaryotes develop adaptations?

A

cope with this increased volume

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3
Q

Give examples of eukaryotic adaptations

A
  • internal membrane profusion
  • organelles
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4
Q

Describe the adaptivity of internal membrane profusion

A
  • increase SA:Vol
  • increase rate of metabolic reaction
  • facilitating membrane specialisation.
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5
Q

Describe organelles

A
  • key feature of the eukaryotic cells
  • supply greater membrane functions
  • half of the cell volume
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6
Q

the organelles of a eukaryotic cell can be bisected into the

A

nucleus and the cytoplasm

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7
Q

Within the cytoplasm there exists

A
  • the cytosol
  • the suspended cytoplasmic organelles
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8
Q

What is the cytosol?

A

The aqueous element of the cytoplasm

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9
Q

Mitochondria

A

involved in metabolism of lipids, cofactors and energy

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10
Q

Endoplasmic reticulum and membrane-bound polyribosomes

A

protein modification and lipid synthesis

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11
Q

Peroxisomes

A

oxidative metabolism

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12
Q

Endosomes

A

a series of organelles endocytosed particles pass through

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13
Q

Lysosomes

A

digestive enzymes degrade defunct organelles, endocytosed particles and macromolecules

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14
Q

Organelles exhibit

A

topological relationships

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15
Q

Give examples of topological relationships between organelles

A
  • difference
  • equivalence
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16
Q

Describe topological equivalence

A

allow molecules to laterally transfer between compartments without crossing a membrane

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17
Q

What explains the inter-organelle topological relationships?

A

evolutionary origins

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18
Q

Give the two organelles that maintain topological difference

A
  • mitochondria
  • chloroplasts
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19
Q

Describe the topological difference of the mitochondria and the chloroplasts

A
  • double-membraned
  • isolated from inter-organelle traffic
  • endosymbiotic generation
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20
Q

Describe the evolution of the mitochondrial matrix

A

evolved from the cytosol of its free living alphaproteobacterial ancestor post-engulfment by the host archeon

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21
Q

Describe the energetic metabolism of mitochondria

A
  • maximised through extensive invagination of the internal membrane system
  • optimising SA:Vol for rate of metabolic reaction
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22
Q

Describe the cristae

A
  • very specific functional organisation. - between the crista and the intermembrane space there exists a junction formed by MICOS and optic atrophy-1
  • membrane curvature is created by the angle formed by two ATP synthase dimers, which exist at the cristae terminals
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23
Q

Describe MICOS and optic atrophy-1

A

two conserved multiprotein complices

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24
Q

How is returning proton leakage across the crista membrane prevented?

A

the respirasome exists along the side of the crista.

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25
Q

Describe the respirasome

A

diverse ETC supercomplices

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26
Q

Describe the insulation of cristae

A

dual origin, from both:
- limited diffusion provided by the narrow cristae terminal junctions
- high density of ETC supercomplices

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27
Q

Describe evolution of the chloroplast stroma

A

evolved from the cytosol of its bacterial progenitor

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28
Q

Describe maximisation of energetic metabolism of chloroplast

A

extensive invagination of the internal membrane system, optimising SA:Vol for rate of metabolic reaction.

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29
Q

What is the chloroplast?

A

a differentiated plastid from its proplastid progenitor and latterly from the etioplast
- specialised to better fulfil its function.

30
Q

List some differentiated plastids

A
  • gerontoplasts
  • dessicoplasts
  • chromatoplasts
  • leucoplasts
  • elaioplasts
  • amyloplasts
31
Q

Describe gerontoplasts

A

senescing chloroplasts

32
Q

Describe dessicoplasts

A

found in extremophilic, dessiccation-tolerant plants

33
Q

Describe chromatoplasts

A

carotenoid synthesis and storage plastids for fruits, flowers and roots

34
Q

Describe leucoplasts

A

synthesis and storage plastids

35
Q

Describe elaioplasts

A

lipid storage plastids

36
Q

Describe proteinoplasts

A

protein storage plastids

37
Q

Describe amyloplasts

A

starch (in the form of both amylose and amylopectin) storage plastids for the roots and tubers

38
Q

What necessitates inter-organelle transport between the topologically different and equivalent organelles?

A
  • greatly reduced genome of both topologically different organelles
  • still require >1000 varying proteins to fulfill their diverse functions
39
Q

Describe the human mitochondrial genome

A
  • 13 genes for ETC subunits
  • 22 for tRNAs
  • 2 for rRNAs
  • totalling 37 genes
40
Q

Describe the chloroplast genome

A
  • 79 protein-coding genes
  • 7 for rRNA
  • 28 for tRNA
  • totalling 114
41
Q

Describe formation of mature mitochondrial proteins

A
  • cytosolic protein unfolded by chaperone proteins, in order to pass through the translocase pore
  • signal sequence of the new protein precursor binds to the import receptors which is then transported to the receptor protein in the TOM, which facilitates membrane insertion
  • protein is then translocated into the matrix from the TOM complex to the TIM23 complex
  • undergoes cleavage by a signal peptide to form a mature mitochondrial protein in the matrix space
42
Q

TOM

A

translocase of the outer membrane

43
Q

TIM23

A

translocase of the inner membrane-23

44
Q

For thylakoid import, there exists … pathways

45
Q

Describe the sec pathway

A

protein translocation is achieved by Sec-homologues

46
Q

Sec-homologues

A

bacterial proteins that facilitate protein translocation across the bacterial plasmemembrane

47
Q

Describe the SRP-like pathway

A

uses a chloroplast-homologue of the signal-recognition particle

48
Q

Describe the TAT pathway

A

signal peptide has two critical arginine residues

49
Q

TAT

A

the twin arginine translocation

50
Q

Describe the spontaneous insertion pathway

A

does not require any protein translocator

51
Q

Describe the chaperone-protein unwound thylakoid precursor protein

A

containing a thylakoid signal sequence

52
Q

TOC

A

Translocator of the Outer Chloroplast Membrane

53
Q

TIC

A

Translocase of the Inner Chloroplast Membrane

54
Q

Describe the initial steps of any of the 4 mature chloroplast protein generation processes

A
  • chaperone-protein unwound thylakoid precursor protein binding to a receptor complex in the TOC complex
  • passed to the TIC complex
  • undergoes GTP- or ATP- dependent translocation into the stroma
  • cleavage of the chloroplast signal sequence creates an exposed thylakoid signal sequence.
55
Q

Why are chloroplasts and mitochondria capable of fusion and fission?

A

In order to dynamically control their relative abundance inside a given cell at a given time.

56
Q

How can chloroplasts and mitochondria capable of fusion and fission be visualised?

A

experimentally by differential red-green fluorescent tagging of a photo activated, protein-labelled mitochondria

57
Q

Describe mitochondrial fission

A
  • assembly-driven constriction
  • controlled by dynamin-1 dimers
  • constriction achieved through the targeted interaction of dynamin assemblies with the outer membrane proteins, forming a GTP-dynamin spiral
  • hydrolysis-driven constriction
  • results in fission
58
Q

Describe dynamin-1 dimers

A

form larger oligometric structures in pairing with GTP hydrolysis

59
Q

interaction of dynamin assemblies with the outer membrane proteins

A

through speiciric adaptor proteins

60
Q

hydrolysis-driven constriction

A

a GTP-hydrolysis event in the dynamin subunits produces conformational changes

61
Q

Describe mitochondrial fusion

A

must occur in two stages: both the outer and inner membrane.

62
Q

Describe mitochondrial outer membrane fusion

A

formation of a complex of outer-membrane GTPase including subunits anchored in the two fusing membranes, where GTP is low

63
Q

inner membrane fusion is achieved by

A

formation of an oligometric tethering complex by a dynamin-related protein, including subunits anchored in the two inner membranes fusing, where GTP is high

64
Q

Describe the peroxisome basics

A
  • highly diverse
  • evolutionarily mystifying
  • enzyme composition varies with both conditions and cell type
65
Q

Describe the peroxisome specifics

A
  • contain oxidative enzymes to such a degree that their crystalloid protein core is visible in electron micrographs
  • function is essential to both respiration and photosynthesis
66
Q

Describe the oxidative enzymes of peroxisomes

A

use diatomic oxygen to remove hydrogen atoms from substrate molecules, generating hydrogen peroxide in the equation RH2 + O2 R + H2O2

67
Q

Describe peroxisome flexibility in methylotrophic yeasts

A
  • under sugar nutrition, peroxisome number and size is small
  • under methanol and fatty acid nutrition respectively peroxisome number and size is large
68
Q

Explain peroxisome flexibility in methylotrophic yeasts

A
  • methylotrophic oxidation
  • β-oxidation forming acetyl CoA
69
Q

In yeast and plants, peroxisomes are the

A
  • sole site of β-oxidation
  • essential for respiration
70
Q

Describe the similarities of peroxisomes and mitochondria and chloroplasts

A
  • peroxisomes must also utilise a traslocase pore for cytosolic protein import, due to their isolation from cellular vehicular traffic
    -peroxisome abundance in the cell is controlled by dynamically-mediated fission
71
Q

Describe the differences of peroxisomes and mitochondria and chloroplasts

A
  • some cytosolic vehicular import is facilitated in peroxisomes by ER vesicle fusion, forming precursor vesicles
  • peroxisomes do not have a local genome
  • peroxisomes are only single-membrane bound, suggesting a lack of symbiogenetic origin
72
Q

Describe an evolutionary theory for the innovation of peroxisomes

A
  • vestige of an ancient endomembrane-derived organelle that evolved to use up O2 to keep levels low in the rest of the cell, thus avoiding oxygen toxicity
  • since the oxygen-consuming function of the peroxisome was duplicated by mitochondrial acquisition, this may explain the sharing of oxidative metabolism between peroxisomes and mitochondria in modern eukaryotic cells

Hilary Term 1 (61 decks)

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