Print Options

Card layout:

← Back to notecard set|Easy Notecards home page

Instructions for Side by Side Printing
  1. Print the notecards
  2. Fold each page in half along the solid vertical line
  3. Cut out the notecards by cutting along each horizontal dotted line
  4. Optional: Glue, tape or staple the ends of each notecard together
  1. Verify Front of pages is selected for Viewing and print the front of the notecards
  2. Select Back of pages for Viewing and print the back of the notecards
    NOTE: Since the back of the pages are printed in reverse order (last page is printed first), keep the pages in the same order as they were after Step 1. Also, be sure to feed the pages in the same direction as you did in Step 1.
  3. Cut out the notecards by cutting along each horizontal and vertical dotted line
Print these notecards...Print as a list

38 notecards = 10 pages (4 cards per page)

Viewing:

Cell Bio

front 1

Actin filaments

back 1

  • Helical polymers G-actin
  • Flexible, linear bundles, 2D networks
  • Concentrated at cortex; beneath cell membrane
  • Strength and shape to plasma membrane
  • Structures - microvilli, extremely stable
  • Cell migration - lamellipodia and filopodia
  • Motor proteins- myosin (will move on actin fibers and transport cargo. Allow for sliding of adjacent actin fibers and is important during muscle contraction)

front 2

Microtubules

back 2

  • Long and hollow cylinder of tubulin
  • Rigid, long, and straight
  • Function - internal framework for organelles (tracks for vesicular trafficking), structural support and motion (flagella and cilia), mitotic spindle formation during cellular division
  • Motor proteins- kinesin and dynein

front 3

Intermediate filaments

back 3

  • Rope-like fibers instead of helical structure, stable
  • Heterogenous family (tissue specific)- laminin, keratin
  • Animal cell nucleus- nuclear lamina
  • Flexible and strong
  • Function - create nuclear lamina, mechanical strength for epithelial cells and layers
    • Hair and nails

front 4

Accessory proteins

back 4

  • Dynamic framework
  • Regulated by accessory proteins
    • Cell can regulate length, stability, number, and geometry
    • Can bind stabilize disrupt and create junctions of those networks
  • Cell changes cytoskeleton organization in response to signals
  • If migrating, will adjust inside of cytoskeleton that allows and facilitates movement of the cell

front 5

Actin microfilaments and actin binding proteins

back 5

  • Microfilaments are assembled into diverse structures (by means of actin binding proteins), usually associated with the plasma membrane
  • Cross-linked bundles and networks: microvilli, cell cortex, adherens belt, filopodia, lamellipodium/leading edge, stress fibers, phagocytosis, moving endocytotic vesicles, contractile ring

front 6

Actin structures

back 6

  • Highly conserved proteins across eukarya
    • Signifies that it is extremely important
  • Binds to ATP and ADP
    • ATP hydrolysis in F-form
      • Slow ATP hydrolysis
      • G-actin in f-actin able to hydrolyze ATP
  • Reversible assembly into filaments- two helices of actin subunits oriented in the same direction
  • Monomer - G-actin (globular)
  • Polymer - F-actin (filamentous)
    • Plus (barbed) and minus (pointed) polarity
    • Nucleotide binding site on minus end, where the ATP/ADP will bind
  • Able to self assemble to form a longer filament

front 7

Dynamics of actin filaments

back 7

  • Microfilaments are dynamic structures
  • Assembly and disassembly regulated process- actin binding proteins
    • Plus end - fast growing end (highly dynamic, when actin is bound to ATP it's likely to bind to the filamentous actin on the plus end. The ATP is hydrolyzed into ADP and eventually dissociates from actin filament)
    • Minus end - slow growing end
  • ATP hydrolysis promotes F-actin depolymerization
  • Actin bound to ADP less binding strength among monomers

front 8

Actin nucleation - rate limiting step structures

back 8

In vitro (test tube)

  • Nucleation- initial aggregate that allows for elongation
  • Polymerization- spontaneous (faster) in the presence of seeds (preformed filament)
  • Critical concentration (Cc) - concentration of G-actin at steady state (rate of polymerization = rate dissociation)
    • In cells, concentration of free G-actin much higher than Cc
    • Allows for dramatic and fast changes in the actin cytoskeleton
    • Has proteins that sequester G actin, liberates them when the cell needs them, allows for reshaping of cytoskeleton

front 9

Actin polymerization

back 9

  • Steady state - rate of polymerization = dissociation(depolymerization)
  • F-actin
    • T form - ATP
    • D form - ADP
  • G-actin critical concentration (Cc)
    • High in t form
    • Low in D form
    • Suggests the plus end is the growing end and the minus end is the slow growing end
  • Intermediate G-actin concentration- growth in plus end and shrinkage in negative end

front 10

Actin treadmilling

back 10

  • At steady state, rate of growth in plus end is equal to shrinkage in minus end (Net addition of actin subunits at the plus end while simultaneously losing subunits at minus end)
  • Size of F-filament remains constant
  • Allows filament to move

front 11

Inhibitors of actin

back 11

All are toxic to cells- suggesting dynamic equilibrium G-actin - F-actin are essential

front 12

Latrunculin

back 12

Depolymerizes, binds actin subunits

front 13

Cytochalasin B

back 13

Depolymerizes, caps filament plus ends

front 14

Phalloidin

back 14

Stabilizes, binds along filaments

front 15

Actin binding proteins

back 15

Important in the regulation of this dynamic equilibrium between G-actin and F-actin

Actin monomers, monomer-sequestering protein, bundling protein, myosin motor protein, side-binding protein (tropomyosin), capping (plus end blocking) protein, cross-linking protein, severing protein, nucleating protein

front 16

Actin treadmilling- regulation

back 16

Actin turnover and filament length regulated by actin-binding proteins

front 17

Monomer availability: Thymosin

back 17

Binds G-actin to provide reserve G-actin when it is needed

Sequesters free G-actin (releases it when the cell needs to reshape actin cytoskeleton)

front 18

Monomer availability: Profilin

back 18

Enhances the exchange of ADP for ATP on G-actin

Promotes polymerization and F-actin formation on plus end

front 19

Actin-nucleating proteins

back 19

Key proteins from which an actin filament can grow- straight of branched filaments

front 20

Formins family

back 20

  • Straight filaments (promote polymerization of plus end and make it faster)
  • Location- plus end of F-actin
  • Long actin filaments (stress fivers, contractile ring)

front 21

Arp2/3 complex

back 21

  • Branched filaments
  • Location- minus end of F-actin
  • Act most efficiently on existing filaments (act as nucleation factor, promote growth and association of new G-actin)
  • Branched F-actin networks (ex: leading edge of motile cells)

front 22

Filament: Gelsolin

back 22

  • Actin severing protein- fragments of F-actin
  • Fate of fragments depends on other actin binding proteins

front 23

Filament: Cofilin

back 23

  • Enhances the rate of loss of ADP-actin from the minus end
  • Promotes depolymerization on the minus end

front 24

Filament: Capping proteins

back 24

  • Stabilize F-actin (prevent polymerization and depolymerization)
  • If attached to plus end, can't grow any longer

front 25

Higher structural levels- accessory proteins

back 25

  • Higher structural levels of actin filaments can be achieved with accessory proteins
  • Crosslink different actin filaments
  • Attach to other proteins, associations with each other or other types of proteins

front 26

Myosin

back 26

  • Motor proteins that move along actin filaments
  • Crosslink and slide filaments relative to one another or transport cargo
  • Powered to ATP hydrolysis -> conformational change
  • Move towards plus end of actin

front 27

Myosin structure

back 27

  • Two heavy chains + 4 light chains
  • Head: motor region (actin binding and ATP hydrolysis)
  • Neck: lever-arm/hinge region
  • Tail: tail-tail interaction and cargo binding

front 28

Myosin class 2

back 28

Assembles into bipolar fragments- muscle contraction

front 29

Myosin class 1

back 29

Facilitates binding actin filaments to the membrane -> important during endocytosis

front 30

Myosin class 4

back 30

Transport vesicle on the F-actin

front 31

Myosin mechanical work

back 31

  • Myosin converts ATP hydrolysis to mechanical work by amplifying a small conformational change in the head when bound to F-actin
  • ATP hydrolysis- change in conformation- reduced affinity for actin
  • Propels forward (power stroke)

front 32

Sarcomere

back 32

  • Skeletal muscle: contractile myofibirils are composed of thousands of repeating units called sarcomeres
  • Myosin thick filaments and actin thin filaments

front 33

Accessory actin binding proteins

back 33

Stabilize actin filaments

front 34

CapZ

back 34

plus end cap

front 35

Tropomodulin

back 35

minus end cap

front 36

Nebulin

back 36

Regulates length of thin filament, surrounds F-actin

front 37

Titin

back 37

Molecular spring

Enables during muscle relaxation back to achieve the normal size of the a-band

front 38

Skeletal muscle contraction

back 38

ATP-dependent sliding of myosin thick filaments along actin thin filaments to shorten the sarcomere and hence the myofibril