3- Cytoskeleton and ECM Flashcards
What are three tubule/filaments that help organize the cell?
- Actin: form microvilli, also act below microvilli to help form cell to cell junctions
- Intermediate filaments: anchored to desmosomes (cell to cell adhesions) and hemidesmosomes (between cell and extracellular matrix).
- Microtubules run vertically from top to bottom of cell. Can grow and shrink depending of GTP. Grow on positive end.
How does cytoskeleton change cell shape?
This is regulated by a signal.
Filaments are made of smaller subunits, upon signal activation polymers will disassembe and rearrange elswhere in the cell.
Structure of microtubule
Made of long protofilaments (aligned parallel) which are made of small subunits containing TUBULIN HETERODIMER (a and B tubulin subunit)
Subunits point in the same direction. Have GTP bound to them.
Can grow and shrink. Grow on PLUS side ( by the B subunit)
Formed from their minus end.
Structure of Actin Filament
Made of Actin monomers. Has nucleotide bound in pocket in monomer. (ATP, ADP when part of filament)
Also grows from PLUS end.
Mature form is two protofilaments wound around each other.
Growing and shrinking.
If the microtubule is growing it will have a GTP cap.
Most important thing is exchange GTP and GDP
Catastrophe and rescue
GTP is hydrolyzed from growing microtubule and now it starts to rapidly shrink.
Rescue- if enough GTP is added to make a cap and continue to grow.
Intermediate filaments Structure
Two identical monomers (proteins) dimerize
Two dimers form line up antiparrellel to from antiparallel tetramer (soluble subunit of intermediates), offset
Since it is offset it can align with another tetramer
Final 10nm ropelike, 16 dimers make up helical packed rope.
Does not grow in dynamic fashion like other two.
What are the four types of intermediate filaments we should know?Nuclear lamins
Nuclear lamina: found in nuclear periphery. Structure proteins
Vimentinlike proteins: Often in developmental stages. In Muscle, glial cells and neurons
Keratin: Important for epithelial cells and derivatives (skin, nails…)
Neuronal: in neurons
How is progeria related to cytoskeleton?
Mutation in gene codes for lamina protein.
Nuclei not shaped properly= disregulation in gene expression and chromosomal integrity.
Progeria= rapid aging.
Skin with mutant in keratin gene
Filaments can disconnect from keratin filament network and the cell will slough off between the nucleus and the hemidesosomes.
What are some of the ways drugs that target actin and microtubules work?
Actin- stabilizes or severs filament, caps plus end, or binds subunits and stops monomerization
Microtubules- bind to prevent polymerization or binds and stabilizes microtubules.
Should we know the drugs specifically?
Nucleation of microtubules
Always formed at minus end with plus end growing outward. Grow out from MTOC (microtubule organizing center).
Y tubular complex (with accessory proteins)- serve as template for subunits to grow. forms microtubule with 13 protofilaments
Form from centromeres that have ring like structures around them.
Nucleation of ACTIN
catalyzed by the ARP complex and forming at the plasma membrane.
ARP 2 and 3 are held by accessory proteins, blocks activation
Activation factor binds complex and conforms it to be like PLUS end. Actin filaments now assemble on struction.
Formin can also act (separate from ARP) as nucleation factor, form dimeric complex that can act as initiation factor.
Specific proteins that assist with microtubule growing and shrinking.
- MAP (microtubule associated proteins)- stabilize end (cap it) so you have longer microtubules that are less dynamic
- XMAP215 the specific protein she wants us to remember - Catastrophin: increase shrinking mechanism for microtubule
- kinesin-13
a actinin
forms contractile bundle
Allows for weak packing and allows for myosin II to enter bundle.
Remember structure = function
accessory protein (help package filaments)
fimbrin
Forms PARALLEL BUNDLE
tight packing, prevents myosin II from entering.
Noncontractile
accessory protein (help package filaments)
ERM family proteins
Anchor actin to plasma membrane
signal regulated
When phosphorylated or bound by PIP2, becomes active with 2 domains (membrane and actin binding domains)
Bind transmembrane protein and actin filament
What are the 3 motor proteins?
Myosin II- interact with actin in muscle contractions
Kinesins- motor proteins to walk along microtubules
Dynein-motor proteins to walk along microtubules
Kinesins and dynein- transport vesicles.. move along axons?
Myosin II
made of 2 heavy chains and 4 light chains
Two types of light chains, one present on each head.
Coil coil confirmation formed by two a helices winding around each other.
Kinesin
Walks along microtubules. 4 superfamily members
Kinesin I- motor domain at N terminus
Kinesin-5-
Kinesin-13- binds to microtubule ends to promote depolarization
Kinesin-14-
Motor domain use legs to walk around microtubule, other end binds to cargo.
Kinesin walking steps
Lagging head is tightly bound to microtubule and ATP
Leading head is loosely bound to microtubule and ADP
ATP hydrolysis allows for neck linker to shift from rear to front. shift pulls domain forward once detached from microtubule and bound ADP
Walks towards Plus end of microtubules.
Dynein
Also walks along microtubules but to MINUS end (retrograde movement).
In ATP bound state, coiled stalk detached from microtubule.
Hydrolysis causes stalk-microtubule attachment.
Release of ADP and Pi create rotation of head and stalk related to the tail.
Myosin II
Walks along actin filament.
- Nucleotide binds, head dissociates from actin
- hydrolysis, head pivots and binds new subunit
- Pi releas- head pivots and moves filament
- ADP release, then start over.
Sarcomere
Small functional units in myofibril of muscle.
Thick filament= myosin
Thin filament= actin
Contraction movement brought on by upstream signaling, typically Ca2+
