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)
