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
2
Q
Why do eukaryotes develop adaptations?
A
cope with this increased volume
3
Q
Give examples of eukaryotic adaptations
A
- internal membrane profusion
- organelles
4
Q
Describe the adaptivity of internal membrane profusion
A
- increase SA:Vol
- increase rate of metabolic reaction
- facilitating membrane specialisation.
5
Q
Describe organelles
A
- key feature of the eukaryotic cells
- supply greater membrane functions
- half of the cell volume
6
Q
the organelles of a eukaryotic cell can be bisected into the
A
nucleus and the cytoplasm
7
Q
Within the cytoplasm there exists
A
- the cytosol
- the suspended cytoplasmic organelles
8
Q
What is the cytosol?
A
The aqueous element of the cytoplasm
9
Q
Mitochondria
A
involved in metabolism of lipids, cofactors and energy
10
Q
Endoplasmic reticulum and membrane-bound polyribosomes
A
protein modification and lipid synthesis
11
Q
Peroxisomes
A
oxidative metabolism
12
Q
Endosomes
A
a series of organelles endocytosed particles pass through
13
Q
Lysosomes
A
digestive enzymes degrade defunct organelles, endocytosed particles and macromolecules
14
Q
Organelles exhibit
A
topological relationships
15
Q
Give examples of topological relationships between organelles
A
- difference
- equivalence
16
Q
Describe topological equivalence
A
allow molecules to laterally transfer between compartments without crossing a membrane
17
Q
What explains the inter-organelle topological relationships?
A
evolutionary origins
18
Q
Give the two organelles that maintain topological difference
A
- mitochondria
- chloroplasts
19
Q
Describe the topological difference of the mitochondria and the chloroplasts
A
- double-membraned
- isolated from inter-organelle traffic
- endosymbiotic generation
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
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
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
23
Q
Describe MICOS and optic atrophy-1
A
two conserved multiprotein complices
24
Q
How is returning proton leakage across the crista membrane prevented?
A
the respirasome exists along the side of the crista.
25
Describe the respirasome
diverse ETC supercomplices
26
Describe the insulation of cristae
dual origin, from both:
- limited diffusion provided by the narrow cristae terminal junctions
- high density of ETC supercomplices
27
Describe evolution of the chloroplast stroma
evolved from the cytosol of its bacterial progenitor
28
Describe maximisation of energetic metabolism of chloroplast
extensive invagination of the internal membrane system, optimising SA:Vol for rate of metabolic reaction.
29
What is the chloroplast?
a differentiated plastid from its proplastid progenitor and latterly from the etioplast
- specialised to better fulfil its function.
30
List some differentiated plastids
- gerontoplasts
- dessicoplasts
- chromatoplasts
- leucoplasts
- elaioplasts
- amyloplasts
31
Describe gerontoplasts
senescing chloroplasts
32
Describe dessicoplasts
found in extremophilic, dessiccation-tolerant plants
33
Describe chromatoplasts
carotenoid synthesis and storage plastids for fruits, flowers and roots
34
Describe leucoplasts
synthesis and storage plastids
35
Describe elaioplasts
lipid storage plastids
36
Describe proteinoplasts
protein storage plastids
37
Describe amyloplasts
starch (in the form of both amylose and amylopectin) storage plastids for the roots and tubers
38
What necessitates inter-organelle transport between the topologically different and equivalent organelles?
- greatly reduced genome of both topologically different organelles
- still require >1000 varying proteins to fulfill their diverse functions
39
Describe the human mitochondrial genome
- 13 genes for ETC subunits
- 22 for tRNAs
- 2 for rRNAs
- totalling 37 genes
40
Describe the chloroplast genome
- 79 protein-coding genes
- 7 for rRNA
- 28 for tRNA
- totalling 114
41
Describe formation of mature mitochondrial proteins
- 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
TOM
translocase of the outer membrane
43
TIM23
translocase of the inner membrane-23
44
For thylakoid import, there exists ... pathways
4
45
Describe the sec pathway
protein translocation is achieved by Sec-homologues
46
Sec-homologues
bacterial proteins that facilitate protein translocation across the bacterial plasmemembrane
47
Describe the SRP-like pathway
uses a chloroplast-homologue of the signal-recognition particle
48
Describe the TAT pathway
signal peptide has two critical arginine residues
49
TAT
the twin arginine translocation
50
Describe the spontaneous insertion pathway
does not require any protein translocator
51
Describe the chaperone-protein unwound thylakoid precursor protein
containing a thylakoid signal sequence
52
TOC
Translocator of the Outer Chloroplast Membrane
53
TIC
Translocase of the Inner Chloroplast Membrane
54
Describe the initial steps of any of the 4 mature chloroplast protein generation processes
- 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
Why are chloroplasts and mitochondria capable of fusion and fission?
In order to dynamically control their relative abundance inside a given cell at a given time.
56
How can chloroplasts and mitochondria capable of fusion and fission be visualised?
experimentally by differential red-green fluorescent tagging of a photo activated, protein-labelled mitochondria
57
Describe mitochondrial fission
- 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
Describe dynamin-1 dimers
form larger oligometric structures in pairing with GTP hydrolysis
59
interaction of dynamin assemblies with the outer membrane proteins
through speiciric adaptor proteins
60
hydrolysis-driven constriction
a GTP-hydrolysis event in the dynamin subunits produces conformational changes
61
Describe mitochondrial fusion
must occur in two stages: both the outer and inner membrane.
62
Describe mitochondrial outer membrane fusion
formation of a complex of outer-membrane GTPase including subunits anchored in the two fusing membranes, where GTP is low
63
inner membrane fusion is achieved by
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
Describe the peroxisome basics
- highly diverse
- evolutionarily mystifying
- enzyme composition varies with both conditions and cell type
65
Describe the peroxisome specifics
- 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
Describe the oxidative enzymes of peroxisomes
use diatomic oxygen to remove hydrogen atoms from substrate molecules, generating hydrogen peroxide in the equation RH2 + O2 R + H2O2
67
Describe peroxisome flexibility in methylotrophic yeasts
- under sugar nutrition, peroxisome number and size is small
- under methanol and fatty acid nutrition respectively peroxisome number and size is large
68
Explain peroxisome flexibility in methylotrophic yeasts
- methylotrophic oxidation
- β-oxidation forming acetyl CoA
69
In yeast and plants, peroxisomes are the
- sole site of β-oxidation
- essential for respiration
70
Describe the similarities of peroxisomes and mitochondria and chloroplasts
- 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
Describe the differences of peroxisomes and mitochondria and chloroplasts
- 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
Describe an evolutionary theory for the innovation of peroxisomes
- 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
