Zellbiologie

Actin (6 nm)

• Subunits (g-Actin -> globular)

  • Polymer (f-Actin filamentous) intrinsic molecular polarity

• Actin Proteine = ATPase (can cleave and hydrolyze ATP)

Microtubules (24 nm)

• Subunit: alpha and beta -Tubulin dimer (both are able to bind GTP)

• only beta can hydrolize GTP

• plus end and minus end

Intermediate filaments (10 nm, lamins <6nm)

• subunit: 5 main classes (tissue specific)

• lengthy proteins

• polymer : made of tetrameric subunits

  • first dimer (same direction) -> tetramer (head to tail direction) -> 8 tetramer build one ULF (unit-lenght-filament)

  • ULFs form filament

• no nucleotide hydrolysis, no polarity

• self organizing from simple building blocks

• nucleotide cleavage

• polarity

• main element of cellular dynamics

• Nucleation (3 G-Actin form a nucleus)

• Elongation (polymerization, plus end is faster)

• steady state (G-actin concentration gets lower)

  -> plus end polymerization, minus end depolymerization

  
  

• regulate nucleation, assembly, disassembly

• profilin

  • ADP->ATP exchange factor

• ARP complex

  • actin related protein

  • ARP23 complex binds to pre existing filments -> branches

• filamin

  • promotes stabilization of actin networks

• capping protein

  • caps at plus end -> no depolimerization

• cofilin

  • promotes disassembly at minus end

• Phalloidins

  • binds and stabilzes filaments

• Cytochalasin

  • caps filaments plus end

• Latrunculin

  • binds subunits and prevents their polymerization

• Jasplaknolides

  • stabilizes actin monomers

• organized by the centrosome = main microtubule-organizing center (MTOC)

  -> always associated with the nucleus in vegetativ cells

• orientation: centrosome to periphery (- -> +)

• polymerization -> catastrophy -> rescue

• catastrophy

  • GTP hydrolysis changes subunit conformation

    -> weakens bond in the polymer

  • rapid depolimerization -> shrinking

regulate nucleation, assembly and dissasembly

• gamma TuRC

  • nucleates subunites and remains associated with minus end (Centrosome)

• satathmin

  • binds subunits prevents assembly

• kinesin 13

  • depolimerases (enhances dissasembly)

• MAPs

  • stabalize along side

• plectin

  • crosslinking to ntermediates

• Taxol

  • binds and stabilizes microtubules

• Colchicine

  • prevents their polymerisation

• Vinblastatine

  • prevents their polymerization

• Nocodazol

  • prevents their polymerization

• microtubules required for spindle formation (-> chromosome segragation)

• actin/myosin required for cleavage furrow formation during cytokinesis (contractile ring)

• characterized by centriols

• zylindrical microtubule structures

• associated with parecentreola matrix (PCM)

• PCM majorily associated with mother centriol

• mother centriol associated with appendeges (distal + subdistal)

• mother + daughter connected via fibres

• during cell cycle formation of a pro centriol

• 9 microtubule triplets

• G1 mother centriol and daughter centriol

• S formation of Cartwheel at both centriols (Plk4 polar like kinase induced), recruiting microtubules -> forming procentriols

• G2 matuaration of centreols + phosphorylation of the connection of mother and daughter (Nek2) -> form seperate spindle pols

• two identical protein chains (globular Motordomain + tail domain = alpha helical)

• Motordomains completly independent

• Steps

  1. ATP bound -> no affinity

  2. ATP hydrolyzed -> conformational change (angle motordomain/tail gets bigger)

  3. affinity to actin is high -> binding

  4. conformational change -> Phosphate is released

     -> power stroke (angel motordomain/tail decreses -> movement

  5. ADP is released

• homo dimer

• both motor domains coordinate

• Steps

  1. one domain without ATP (high affinity)

     second with ADP (low affinity)

  2. one binds ATP (power strooke)

     second moves in front of one

  3. conformational change

     one cleaves ATP -> ADP +Pi

     second releases ADP (high affinity)

  4. second releases ADP

     one releases Pi (no affinity

• motor of cilia and flagellae

• no similarity to myosin or kinesin

• pre stroke situation and post stroke

• power stroke at Pi release

• always cooperates with dynactin (Arp1 polymer = mini filament)

• dynein has two motor subunits (NudE and Lis1 are regulators)

• cargo bound to dynactin (bound to microtubules via P150)

• extension at the leading edge

• formation of new focal adhesions (integrins making contact to extracellular matrix) and pseudopods at leading edge

• translocation of the cell body (actin/myosin contractile mechanism)

• decomposition of old focal adhesions

• recycling of integrins via membrane vesicles

• actin structures are the motor of this movement

• central regulator: focal adhesion kinase (FAK)

• differentiation between leading edge and uropod

• accumulation of specific proteins

• reorganisation of the cytoskeleton

• G-protein coupled receptor (for signaling)

• phosphorylated phosphatidyl inositol (PIP3)(membrane lipids)

• signaling proteins actin, myosin

• Cdc42: filopodien formation (front)

• Rac: lammelopodien formation (front)

• Rho: stress fiber formation (middle)

• cargo molecules bind cargo receptor

• binds to adaptin -> binds clathrin

• dynamin ties off vesicles

• uncoating -> naked transport vesicle

• cargo: N- and/or C-terminal motif (C-terminal vacuolar sorting sequence = ctVSS)

• receptor: vacuolar sorting receptor 1 (VSR1)

  cytosolic tail, transmembrane, cargo/ligand binding (lumen)

• receptor + ligand are recruited into clathrin coated vesicle

• binding M6P receptor -> receptor dependent transport (clathrin coat)

• dissociation at acidic pH -> lysosomal hydrolase precursor

• -> MP6 receptor in budding vesicle (retromer coat) -> receptor recycling

• multivesicular body/prevacuolar compartment

• endosome -> fusion to MVB/PVC

= endosomal sorting complex required for transport

• generates intraluminal vesicles

• cargo (ubiquitinated) and PIP3 bind to ESCRT0

• -> ESCRT1 -> ESCRT2

• ESCRT3 formation of intralumenal vesicle (negative curvature of endosome membrane)

• induction of stress

• Phagophore formation (may occure at ER)

• Autophagosome (double membrane) -> outer membrane fusion with vacuole -> degradation

• establishment of a counterpressure to the water potential of the protoplast (exoskelett)

• determines mechanical stability

• conductive elements

• holds cell together in a tissue context

• determines and limits elongation growth of plant cell

• contributes to water balance (tugor pressure - cell volume)

• diffusion barrier

• barrier for pathogens

• Carbohydrates: Pectin, Hemicellulose, Cellulose

• Proteins: structural proteins, modifying proteins

• hydrophobic polymers: lignins, cutins, suberines

• middle lamella, primary wall

• protopectin (mixture of Galacturonans + Rhamnogalacturonans)

  • monomer Galacturonic acid methyl ester =pecitin

  • polymer with Ca2+ or Mg2+ bridges

• Pectin Methyl esterase (PME)

  • catalyzes transformation to Non-esterified pectines

• Rhamnogalacturonan = Galacturonic acid + Rhamnose (alterned)

• main component of the primary wall

• Pentose, Hexoses

  • example Xyloglucan (Glucose + Xylose)

    • Glucose (beta1 -> 4) + branched Xylose (alpha -> 6)

  • can be cut and crosslinked

    • donor xyloglucan picked up by Xyloglucan endotransglucosylase (XET)

    • XET catalyzes breakage of existing xyloglucan chain

    • XET adds new xyloglucan chain

• primary and secondary wall

• linear glucan

• very long chain and straightened out

• HRGP (hydroxyproline rich glucoprotein) -> Cambium

• PRP (proline rich protein) -> Xylem

• GRP (glycin rich prtein) -> primary Xylem and Phloem

• AGP (arabinogalactan protein) -> varied cell specific expression

• hemicellulose and pectins synthezised in the golgi

• cellulose synthezised at plasmamembrane (Cellulose synthase complex)

• scattered or random texture

• parallel alignment of microfibrils (bundles of Microfibrils)

• parallel arrangement of microtubules and Microfibrils

• vectorial Cellulose synthesis is determined by cortical microtubules

• rosett complex = cellulose synthase complex

  • hexameric

  • synthase subunit (CESA)

• orientation of newly deposited cellulose Microfibrils (randomly or transverse)

• initiation of cell wall precursor delivery during cell plate formation

  • phragmoplast appear after seperation

  • cell plate forms as vesicles fuse

  • cell plate grows radially outward -> near edge of cell

  • cellulose synthation after fusion

• cell plate forms -> ER reaches through plate -> Plasmodesma

• determine the direction of growth

  
  

• cell undertugor -> connection cellulose microfibrils prevent seperation/elongation

• secretion of expansin breaks the connection -> elongation

• fully elongated cell with large vacuole

• bunching of microtubules

• ribs of secondary wall

• cell dies, walls perforate , tube is lignifid

• Lignin formed by crosslinking of phenolic subunits

  
  

• forms a diffusion barrier in the cell walls of root endodermal cells

• contains Lignin

• building:

  • CASP scaffold protein

  • NADH oxidase and peroxidase

  • mono-lignois and oxidised mono-lignols

  • polymerized lignin

• AUX/LAX regulate Auxin uptake

• ABCB and PIN transporter control Auxin efflux

• APB1 = ER auxin binding protein deconjugates IAA

• PINs control auxin transport across the ER membrane

absence of Auxin

• AUX/IAA repressor inhibits ARF (auxin response factor)

• ubiquitin undergoes ATP dependent activation by E1

• transferred to E2 -> formes complex with E3 ligase (F-box)

• target protein is ubiquitinated by E2-E3 complex

• degradation in Proteasom

presence of Auxin

• IAA binds to repressor -> binding of F-box (E3 ligase)

• AUX/IAA repressor is ubiquitinated -> degradation

• ARF is actiated

• absence of hormone -> repressor is active

• presence F-box binds repressor -> ubiquitination -> degradation

• Jasmonate (JAZ repressor, MYC2 transkription factor)

• Gibberlilin (DELLA repressor, PIF3/4 transkription factor)

• Auxin (AUX/IAA repressor, ARF transkription factor)

• steroid hormone

• presence of brassinolide repressor kinase gets inactivated

• absence of brassinolides repressor switched off via repressor kinase (BIN2 = brassinoid insensitive 2)

  • phosphorylates to BES1 and BZR1 -> exit nucleus

• binding of brassinosteroids to BR1 -> conformational change with BAK1

• BR1 autophosphorylates

• phosphorylation BSK -> activates BSU1

• dephosphorylates BIN2 repressor kinase

• abscence of ABA

  • ABA receptor binds phosphatase 2C (PP2C)

  • dephosphorylates Kinase -> inactive

• presence of ABA

  • ABA binds receptor (PYR) -> PP2C active

  • phosphorylates SnRK2 -> active

  • phosphorylates bZIP ion channels

• two component system

• hybrid sensor histidine kinase (cytokinin receptor)

• input domain, transmitter domain, reciver domain

  
  

• dark -> COP1 repressor enters nucleus

  • represses HY5

• light/day -> COP1 leaves nucleus -> active HY5

• upon germination gibberellins are being syntheziesed

• diffuse into aleuron layer

• induce transcription of amylase

• hydrolysis of starch -> release sugar -> support growth