1. Basic cytoskeleton, vesicle transport Flashcards
The cytoskeleton is a highly dynamic network of reorganizing filaments that extends throughout the cytoplasm. What are the functions of the cytoskeleton in plant, animal and fungal cells?
- movement of the cells (more relevant in animals)
- intracellular movement of organelles, vesicles, chromosomes
- cell shape changes
- cell wall microfibril orientation (plant cell)
- support for the structure of the cells (more important in wall-less organisims e.g. animal cells)
The filament systems of the cytoskeleton
Microtubules (in plants) intermediary filaments (laminale filamente in animal cells) microfilaments = actin filaments (in plants)
Microtubules
see in electron microscope
Durchmesser: 25nm
Subunits: alpha and beta filaments
attached to MTOC (micotubuli orginasation center)
in animals called centrosom (not in plants, less centered)
- are long, hollow cylinders made of the protein tubulin
- much more rigid (starr) than actin
-speciality of plant cells: cortical microtubules
How can microtubles built up themselves?
They are associated with a GTP-bound tubulin heterodimer ar the plus-end of the microtubles (bind GTP)
13 protofilaments (in average - can be 12 or 17, variable from organisim to organisim) make 1 microtubule (alpha, beta, alpha, beta…)
beta: + end
alpha: - end
Microfilaments = actin filaments
helical filaments of the protein actin
diameter: 8nm
organized in viarity (linear bundels, 2D networks and 3D gels
most concentrated in cortex, just beneath plasma membrane
strongly associated with the nucleus (i.e. perinuclear as they lagely contribute nuclear migration in plants
- thinner and more flexible than microtubulins
subunits: G-action (globulin actin) arranged in F-actin (filamtens) (douple helix)
+ and - end (ATP bound and ADP bound end)
Microtubuls need GTP
Facts about microtubuls
- anchored with their minus end to microtubule organization centeres (MTOCs)
- an animals cells, the centrosoms constitutes a major central MTOC while
- in plant cells, microtubuls originate from many different less well defined MOTCs
- the basal body of the cilia and flagella represent major MOTXs als in some algea and geamtes of e.g. mosses, ferns and Ginko
- the kinetochores of chromosomes, where microtubules originate during mitosis, also constitute MTOCs)
MTOCs of animal centrosomes containing ….
gamma-tubulin (pink rings on the surface), microtubuls are growing from gamma- tubulin ring complexes of the centrosome
How can animal microtubule dynamics can be visiulized?
By
-tubulin fused with GFP (green fluorescent protein) one can see growing and shrinking all the time
-GFP-EB1 is a microtubule-binding protein that binds to the GTP-loaded + end –> traces the growing
EB1: Endbinding protein 1 binds only on GTP bound end (stabilizes GTP end, is a marker)
Microtubules: dynamic instability - what is that? How can you explain it?
microtubules depolymerize 100x faster from an end containing GDP-tubulin than from one containing GTP tubulin
A GTP cap favors growth , but if it s lost, than depolymerisation ensues (folgt)
GTP bound: growing
GDP bound: shrinking
Individual microtubules can therefore alternate between a period of slow growth and rapid disassembly, a phenomene called dynamic instability
MTOC in plants
Centrosones are absent in higher plant cells, they contain many dispersed MTOCs (not 1 central centrosom)
Microtubule motor proteins - what can you say about them?
they confer differential movement along icrotubules towards the plus and minus ends
motor proteins move vesicles, chomosomes… along microtubilin
Kinesin; plus end directed motor (some kinesins)
Dynein: munis end directed motor
These motors fuelled with ATP
Special in plants:
Dynein consists of a light and a heavy chain BUT genes coding heavy chains and most of the light chains are no linger present in the genom of most flowering plants –> Dynein got lost and actin and myosin got their exercises (and Kinesin? TALK ABOUT THAT!)
Plants kinesin (and microtubules) are required for…
- organelle movement (in some cases)
- chromosome movement
- Phragmoplast formation
- cellulose microfibril alignment (????)
- cell morphogenesis inducing polarity (???)
Microfilaments: the actin cytoskeleton
Plant microfilaments mediate many intracellular movement
- movement of Golgi stacks
- movement from the Golgi to the vacuole
- movement of endosomal compartments
- movement of peroxisomes
- movement of the nucleus
- morphogenesis e.g. cell shape and polarity
- movement from trans-Golgi network to plasmamembrane
Myosin is ….what?
a plus end-directed motor for actin filaments (wieso FOR???) -2 heavy chains (C terminus) -neck or hinge (Schanier) region -light chain connected with the -N Terminus run on ATP (as all motors does)
Specials about the plant genome in plants (Myosin 11-type)
The genome of plants in addition to other myosins habour (aufweisen) a specific Myosin XI-subclass. Currently known functions of diverse plant XI-type myosins -Chloroplast movement -Golgi movement -Movement of endoplasmatic reticulum -Cytoplasmic streaming -nuclear movements !!! -Actin structure
The Eucariotic Cell Division Cycle
Interphase (G1 Phase, S Phase, G2 Phase), M Phase (MITOSIS??? Talk about!), G1 Phase
Gphase = Gap-Phase (currently nothing happens)?
G1: enough nutrients? right size? Check!
S- Synthesis (of DNA + replication)
G2: Check for errors and miss match repaire
Chromosomenreplikation –> Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase = Chromosomenseperation und Kondensation) –> Cytokinesis (Zellplasma teilt sich in 2 Tochterzellen)
Steps of a Plant Cell Division
- Chromosomenkondensation
- mit Spindeln in Center
- Seperation der Schwesterchromosomen
- Membranforming Vesikelfusion
- Dekondensation
Devision takes place inside out and not outside in as in animals
DAPI can label DNA. We’re in the Mitosis right now.
What do you know about the Prophase, the first step?
Chromosomes condense
cortical microtubules coalesce (verschmelzen) into the preprophase band, prophase spindle forms around the nuclear envelope (die Kernhülle)
In the Cortex (äußerer Rand der Zelle): Tubulin disassemble everywhere but assemble as a preprophase band
Preprophase band is around the whole cell and just in plants
Band marks, where division will appeare, even it disappears later
Prometaphase (seccond step during mitosis)
Preprophase band disappears
nuclear envelope breaks down
kinetochores mature
mitotic spindle captures (erfassen) chromosomes
Chromosomes congress (versammeln sich) to the spindle equator
Spindel not fully formed
Metaphase (third step during mitosis)
mitotic spindle fully formed
chromosomes aligned at the spindle equator
this is different to animals, because the spindle are not pointed, no centrosomes, no centriole
Anaphase (fourth step during mitosis)
Chromosomes move toward the poles and the poles separate
Telophase (5th step durng mitosis)
nucleare envelope forms
Chromosomes start to decondensate
mitotic spindle break down
Phragmoplast is formed (vesicles are fusing to plate which becomes the cell wall later on, before: accumulation of vesicles)
Cytokinesis (after Mitosis)
Cortical microtubules return
phragmoplast reaches parent cell wall to build a new wall between the daughter cells
(microtubles are assembled in the cortex (not needed anymore) and vesicles for the phragmoplast are still needed
plant: cortical microtubules
Cell division: Difference between animals and plants?
Plants: Preprophase band, phragmoplast and cell plate, cortical microtubule array
Animals: Centrosomes/Centrioles: astral microtubules (nur während der Mitose entstehen)
Contractile ring, cleavage furrow (Furche), Midbody
Nicht so punktierters Chromosomen auseinander ziehen
How can you label actin?
phalloidin binds to actin and it can be fluorescently labled
#fact: was Desmosomen für Tiere sind, sind Plasmodesmata für Pflanzen Model of cell plate formation right now?
- Assembly matrix with microtubules=Phragmoplast
- Tubular vesicular network
- Tubular network
- Fenestrated sheet
at the end of the cell plate: vesicles are needed
Vesicle transport Import
Endocytosis (Endosomen entstehen, bei Tieren auch Lysosomen)
endosomes/prevacular compartment, trans-Golgi network, Vacuole, plants
Vesicle transport Export
Exocytosis via the secretory pathway, endoplasmatic reticulum and golgi
The Endoplasmatic reticulum (ER) (just facts, no functions)
- provides the entry platform to secretory pathway
- network like, mobile labyrinth of branching tubules, cicternea, and falttened sacks extending through the sytosol
- 2 membranes enclosing an internal space: the ER lumen
- rough ER and smooth ER, the rough ER has many ribosomes i.e. polysomes attached
- site for co-translational process
- pankreas: much proteins secreted (rauer ER)
- connected to the nucleulus
ER Functions
- place of biosynthesis as well as place for intracellular transport and in many cases the enty to the secretory pathway
- ER membrane is the site of synthesis of many lipids and proteins that enter the secretory pathway
- first step of protein glycosylation take place in the ER
Composition of the Golgi stacks: Dictyosom
cis: takes up proteins and leave ER in form of vesicles to Golgi dictyosom in animals near the nucleus trans: leaving vesicles Cis-Golgi network cis csiterna medial cisterna trans cisterna trans-Golgi network (vesicles float around)
Golgi apperatus in plants
- place of the synthesis of oligo- and polysaccaride sell wall components (except cellulose) such as pectins and hemicellulose (e.g. glucans and xyloglucans from glucose=
- place of continued protein and lipid glycosylation
e. g. of cell wall protein inducing hydroxypropyline-rich glycoproteins (HRGPs) such as extensins ans arabinogalactan proteins (AGPs) - cell wall polysaccarides enter the secretory pathway here in order to be exocytosed
Golgi: difference between animals and plants
(most) Animal Cells: Golgi concentrated in a perinuclear region; animal cells: transport Golgi-derived transport vesicles via microtubules
Plant cells: dictyosomes (individual Golgi stacks and assiciated trans-Golgi network)spread throughout the cytoplasm
Plant cells: transpost of dictyosomes/golgi stacks via actin filaments
Btw: Dictyosome=single Golgi stacks and associated trans-Golgi network
How does the forward (anterograde) transport from ER to Golgi works?
vesicles go from cisternae to cisternae
this transport requires coat protein II (COPII)-coated vesicles (needed for anterograd transport)
Now the retrograd transport from the Golgi to the ER occures via …
Coatamer protein I (COPI) coated vesicles
transport back for things, that escaped the ER but shouldn’t, like chaperones - chaperones fold proteins in the ER and should stay there) –> proteins can be recycled
Anterograd (forward) versus reterograd (backward or retrieval (wiedergewinnung) pathways
In ER: secretory proteins and resident (einwohner) proteins, außerdem KDEL (HEDL often in plants, bindet an C-Terminus der Proteine wenn Golgi erreicht wurde- wie Rücksendungsschein zu ER)
Sobald gebunden wurde: Rücksendung zumER wird eingeleitet
Exocytosis and vascular vesicle transport
in Vauole zB digestion proteins
2 Routen (zur VAkuole + Exozytosis zu Zellmembrane)+1 retrograd route)
Exocytose für zB: pectines or cell wall modifing proteins
Für Weg zur Vakuole: Prävakuoläres Kompartiment (PVC) auch “multivaskulärer Körper” (MVB)
What require exocytosis and other membrane fusion events fro docking and fusion?
v(esicle)-SNAREs and t(argent)-SNAREs
every v SNARE has their t SNARE <3
SNAREs also exist in Golgi - there are ~115 SNAREs in Plants)
Docking of transport vesicle and membrane fusion
Zu transportierende Proteine= cargo Proteine
Specific pairing of cpmlementary v SNARE and t SNARE allows fusion of transport vesicles
with the correct target membrane
Clathrin coated vesicles, uncoating… what do you know?
dynein: pinch vesicles off (GTPases in animals and in plants “dynein related proteins”)
Clathrin heavy and light chains
uncoated by heat shock protein
Vesicle formation (cargo protein, cargo receptor, adaptin and clathrin) –> clathrin coat –> coated vesicle –> uncoating –> naked transport vesicle
