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Cell structure, Cytoskeleton - Coggle Diagram

- - - - Alpha actin
        
        Expressed in muscles
      - Beta
        
        co-exist in other cell type
      - Gamma
    - - Individual actin filaments are thin and flexible
      - Can disassemble at both ends
    - - Globular structure, barbed and pointed ends
        
        Separated by cleft where ATP is bound.
      - Structural polarity
        
        +and- end
        
        +barbed end
        
        -pointed end
    - - Multi-step process
        
        Elongation
        
        Rapid growth of actin filament at both ends
        
        Slows as free monomer concentration diminishes
        
        Steady state
        
        no net growth or shrinkage
        
        Constant exchange of monomers between filament and free monomer pool.
        
        Concentration of free actin monomers
        
        Leads to Critical concentration
        
        When G-actin is above CC, filaments form
        
        When G-actin is below CC, they stay as monomers
        
        When G-actin between two CC ranges
        
        Treadmilling
        
        2 more items...
        
        Cc differs for plus and minus ends of filament
        
        There are more monomers at plus end
        
        2 more items...
        
        Nucleation
        
        3 actin monomers initiate filament structure.
        
        Slowest stage
      - Actin filaments must provide stable structures for cell organisation
        
        Eg. Must stay constant location and length, eg. hairs in inner ear
      - Signalling pathways involved
        
        Growth factors
        
        Receptor tyrosine kinase
        
        G coupled receptors
        
        Integrins
        
        Rho family GTPases
  - - - Beta tubin at plus end
      - Alpha tubulin exposed at minus end
    - - Occurs at Microtubule Organising Centres within cells
      - Ring shaped structure.
        
        13 protofilaments
        
        gamma Tubulin Ring Complex
        
        Minus end bound TuRC, plus end towards cell
        
        Centrosome
        
        Pair of centrioles surrounded by fibrous matrix
        
        Hundreds of gama TuRCs on its surface.
        
        Microtubules extend to cell periphery
  - - - Take two forms
        
        Filopodia
        
        Thin, stiff bundle, also plus to plasma m
        
        Ruffling
        
        L and f both pull cell forward, but any that don't attach move backwards through ruffling
        
        Lamellipodia
        
        Both push cell forward to form new regions of actin cortex
        
        Anchor to surface, making focal contacts
        
        Trailing edge is retract using the traction from new anchorage points
      - Leading edge
    - - Cell movment
        
        Actin filaments rapidly assemble in a specific direction, generating force for movement
  - - - Spire
        
        Binds 4 actin monomers
        
        Generates tetramer
        
        nucleating seed for new filament
      - Formins
        
        progressive elongation machines
        
        Associate with barbed end of existing filament
        
        Generate longer filaments
    - - ARP2
      - ARP3
      - accessory proteins
    - - Rapid polymerisation of leading edge
      - Branches structure pushes the plasma membrane forward, moving cell
- - - - Exploits different properties of organelles
- - - - Nuclear lamins form strong mesh like structure under nuclear envelope
  - - - Two anti-parallel dimers = tetramer.
      - Tetramers assemble 8 side by side to form rope
  - - - Nuclear lamins
        
        Type 5
    - - Vimentin
        
        Type 3
      - Keratins
        
        Type 1 and 2
      - Neurofilaments
        
        Type 4
  - - - Connect cell to underlying cell matrix beneath.
    - - Group of transmembrane proteins
      - Associate via extracellular domains to hold cells together
      - Bind to cell via anchoring proteins
- - - - rapid shrinkage phase
        
        Catastrophe
    - - During mitosis, become more dynamic
    - - Two families
        
        Kinesins
        
        Carry binding site in tail region
        
        Similar structure to myosin
        
        Play a role in cell division
        
        Move to plus end of MTs
        
        Dyneins
        
        Axonemal dyneins sliding movements of MTs that drive ciliary and flagella
        
        Cytoplasmic dyneins
        
        Vesicle trafficking and golgi localisation
        
        Move to minus end of MTs
      - Facilitate transport along MTs
    - - Hydrolysed to GDP-tubulin
        
        Controls growth
        
        Growing or shrinking MTs generate force for moving vesicles
      - GDP-tubulin has less affinity for other tubulin dimers within microtubule
      - When GTP.... incorporated faster than hydrolysis of GTP to GDP
        
        GTP cap
      - When its slower
        
        GTP subunits within cap hydrolysed to GDP
        
        Rest of microtubule is GDP
        
        Thus depolymerisation continues at a catastrophic rate
    - - MTs become more dynamic, disassemble and reassemble rapidly.
  - - - Beta tubulin exposed at plus end
      - Alpha tubulin exposed at minus end of protofilament
  - - - not spontaneous - 13 protofilaments
      - Also called centrosome
      - Pair of centrioles surrounded by fibrous matrix
      - Contains hundrds of Gamma-TuRCs
      - Microtubules extend out from centrosome to cell periphery, creating tracks for transporting other cell components
    - - initiation point for microtubule growth
      - Made of gamma tubulin
      - gamma-TuRC
- - - - Free in cytosol
      - Or Exist on surface of rough ER
      - Cells need to constantly deliver proteins to appropriate organelle
  - - - Lysine
      - Aspartic
      - Glutamic acid
      - Leucine
  - - - Outer nuclear membrane continuous with ER
      - Transport molecules in both directions
        
        Proteins in
        
        RNAs and proteins out
      - Must have NLS
        
        Nuclear locator sequence
        
        For entering nucleus
        
        Guided to the pore by nuclear transport receptros
        
        Receptors interact with pore complex proteins
        
        Pulls itself and protein into nucleus
        
        Then returns to cytosol
        
        Ran-GTP hydrolysed to Ran-GDP, releasing NTR
        
        Energy dependent process
        
        Protein called Ran bound to GTP
        
        Ran-GTP binds to NTR
      - Pores made up of 30 nucleoporins
    - - Mitochondria
        
        Diffuses to contact site on inner membrane
        
        Translocase of Inner membrane (TIM)
        
        Chaperone proteins
        
        Assist in translocation and refolding of proteins inside organelle
        
        Proteins in mitochondria must be sorted and selectively delivered
        
        At contact site of the two membranes, precursor protein snakes through two sequential protein translocators
        
        Chaperone proteins bind to precursor protein to prevent backsliding
        
        Proteins for mitochondria have a signal sequence which is recognised and bound by receptor in transporter out membrane (TOM) complex
      - ER
        
        Protein entry point for Golgi, endosomes, lysosomes, cell surface and ER
        
        Once inside, proteins don't re-enter cytosol
        
        Transported by vesicles to other organelles or secreted from cell
        
        Once ER signal sequence detected by ribosomes during protein synthesis, ribosome will head to ER and allow protein to be threaded across the ER membrane
        
        Soluble proteins released into ER lumen
        
        hydrophobic stop and start transfer sequences give rise to most transmembrane proteins
        
        Two kinds of proteins moved from cytosol to ER
        
        Water soluble proteins
        
        Completely cross ER membrane
        
        All proteins directed to ER by signal sequence of small hydrophobic amino acids
        
        Sequence guided with signal recognition particle
        
        3 more items...
        
        Opens translocation channel
        
        After its been cleaved off, signal peptide is released and degraded
        
        Released into lumen
        
        Transmembrane proteins
        
        partially cross ER
        
        Become embedded in membrane
        
        Stop transfer sequence
        
        Released from translocation channel
        
        Drifts onto lipid bilayer plane, anchoring protein in the membrane
        
        Translocated protein ends up as a transmembrane prtoein inserted in membrane
    - - Continual exchange of materials between ER, Golgi, lysosomes, plasma membrane and outside cell
      - Mediate the passage of proteins
        
        Inward
        
        plasma membrane to lysosomes
        
        Outward
        
        ER to plasma membrane
        
        Vesicles pinch off membrane of one organelle and fuse it with another
      - Endocytosis
        
        Plasma membrane invaginates and pinches off cargo-filled vesicles
      - Vesicle budding through assembly of protein coat
        
        Shapes membrane into bud to capture molecules for transport
        
        Comprised of Coat protein complex (COP) proteins
        
        Used for vesicles between ER and golgi
      - Protein secretion
        
        constitutive secretion
      - Endocytosis
        
        Mediated by plasma membrane vesicles budding into cytosol
- - - - Ribosomes
        
        No nucleus or membrane bound organelles
        
        DNA floats freely within cell
        
        Cell wall of peptidoglycan
        
        polymer of amino acids and sugar
  - - - Ribosomes
        
        Nucleus, mitochondria, golgi etc
        
        DNA within nucleus
        
        1o times larger
        
        Some have cell walls
        
        None with PGN
- - - - Proteins in cytosol need NLS
        
        Nuclear Localisation Sequence
- - - - For moving around
    - - Sensory devices on cell surface
      - Eg. stereocilia in ear, tilt in response to sound
  - - - Segregates the two copies of each chromosome
- - - - Cells adopt spherical shape and stop moving
        
        Actin and myosin form contractile ring around middle of cell
        
        Once comlete, cytoskeletons reassemble into interphase structures.