10/16/24, 11:32 BISC 2202 Notes Lectures
AM 20-25
Lecture 11/15/18
➢ 3 types of cytoskeletal filaments
○ Actin - smallest, flexible. Create the cell cortex
○ Intermediate - moderate size, like a rope (twisted fibers). Provide
mechanical and tensile support
○ Microtubules - largest, rigid. Hollow cylinders. Important for
centrosomes during mitosis and for intracellular
organization/transport
➢ Intermediate filaments
○ 10 nm diameter
○ Create durable networks in the cytoplasm
○ Strengthens the nuclear envelope
○ Lots of tensile strength; resistant to stretch/deformation
○ Structure is like a braided rope
■ Monomer of structure = alpha helical domain
■ Dimer = coiled coil (2 alpha helical domains)
■ Tetramer = 2 staggered coiled coils
■ Total structure is made of 8 tetramers, so 32 total monomers
■ Monomers do not run in the same direction
○ 4 classes
■ Keratin filaments (in skin cells)
■ Vitamin filaments (in connective tissue and muscle)
■ NEurofilaments (nerves)
■ Nuclear lamins (support mesh for nucleus)
○ Abnormalities
■ Mutant keratin causes skin stretching, rupture, and blistering
■ Progeria - advanced aging - a defect in nuclear lamins. Involves
alopecia, rigid skin, bone abnormalities. Many die before age 20
due to heart attack or stroke
○ Anchored in place by plectin (accessory proteins)
➢ Microtubules
○ Highly dynamic - always growing, shrinking, moving
■ Dynamic instability* - permits quick remodeling and reshaping of the
cell
■ Driven by GTP hydrolysis. GTP-bound proteins in a microtubule
are more stable and energetically favorable
■ GTP cap - a growing end of a microtubule being made with proteins
bound to GTP
■ Can be taken apart when GTP--> GDP
○ Grow out of the cell center through a structure called a centrosome
○ Create tracks for cell transport and organelle positioning
○ Become mitotic spindles during mitosis
○ Give structure to cilia and flagella
○ Structure - hollow tube
■ Stacked into 13 parallel filaments
■ FIlaments run in the same direction
about:bl 1
, 10/16/24, 11:32 BISC 2202 Notes Lectures
AM 20-25
■ Alpha tubulin end is on one side and beta tubulin is on the other end
○ Centrioles - cylindrical array of short microtubules surrounded
by a protein matrix. Function poorly understood
○ Drugs can be used to target microtubules
■ Taxol - binds to and stabilizes microtubules
■ Colcemid - binds to tubulin dimers and prevents polymerization
○ In neurons, microtubules guide transport of vesicles and
macromolecules. All microtubules point towards the axon
○ Motor proteins use ATP to move material along microtubules
■ Kinesins** go to the + end →
■ Dyneins** go to the - end ←
■ Tail (binding sites) designate which kind of cargo they carry
○ Microtubules position organelles such as the mitochondria, ER, and golgi
○ Microtubules make up cilia in the respiratory tract, which do not
grow from the centrosome but the basal body
○ Cilia and flagella - 9 + 2 organization
■ 9 double microtubules form in a ring around a single pair of proteins
■ Dynein movement can cause flagella to move or bend.
Accessory proteins form links to slide, bend ,etc
■ Cilia move in one direction to move material/fluid across the surface
➢ Actin filaments
○ Flexible, 7 nm diameter, thinnest type
○ Create cell shape
○ Needs accessory proteins to remain stale
○ Form microvilli, pseudopods
○ Structure - two stranded helix
■ Strands run in the same direction
■ Uses ATP to bind monomers together
■ Monomers are attached faster than they fall off, so it is able to grow
■ Treadmilling* - exclusive to actin filaments - when rates of
degradation and attachment are equal, monomers slowly
cycle through the actin filament
○ Drugs exist to both stabilize and degrade actin
○ Actin binding proteins control actin behavior
■ Thymosin/profilin bind and sequester actin
■ Formin/ARPs promote actin growth
○ Actin cortex can assist in movement of the cell by pushing an edge
of a cell in a direction, causing the rest of the cell to drag forward
○ Lamellipodias - made by ARPs which promote branching
○ Fillopodias - made by formins which promote growing without branching
○ Important for cell signaling and motility
○ RHO GTPases affect actin filament organization
○ Muscle cells: made of actin and myosin
■ Both use ATP to work
about:bl 2
AM 20-25
Lecture 11/15/18
➢ 3 types of cytoskeletal filaments
○ Actin - smallest, flexible. Create the cell cortex
○ Intermediate - moderate size, like a rope (twisted fibers). Provide
mechanical and tensile support
○ Microtubules - largest, rigid. Hollow cylinders. Important for
centrosomes during mitosis and for intracellular
organization/transport
➢ Intermediate filaments
○ 10 nm diameter
○ Create durable networks in the cytoplasm
○ Strengthens the nuclear envelope
○ Lots of tensile strength; resistant to stretch/deformation
○ Structure is like a braided rope
■ Monomer of structure = alpha helical domain
■ Dimer = coiled coil (2 alpha helical domains)
■ Tetramer = 2 staggered coiled coils
■ Total structure is made of 8 tetramers, so 32 total monomers
■ Monomers do not run in the same direction
○ 4 classes
■ Keratin filaments (in skin cells)
■ Vitamin filaments (in connective tissue and muscle)
■ NEurofilaments (nerves)
■ Nuclear lamins (support mesh for nucleus)
○ Abnormalities
■ Mutant keratin causes skin stretching, rupture, and blistering
■ Progeria - advanced aging - a defect in nuclear lamins. Involves
alopecia, rigid skin, bone abnormalities. Many die before age 20
due to heart attack or stroke
○ Anchored in place by plectin (accessory proteins)
➢ Microtubules
○ Highly dynamic - always growing, shrinking, moving
■ Dynamic instability* - permits quick remodeling and reshaping of the
cell
■ Driven by GTP hydrolysis. GTP-bound proteins in a microtubule
are more stable and energetically favorable
■ GTP cap - a growing end of a microtubule being made with proteins
bound to GTP
■ Can be taken apart when GTP--> GDP
○ Grow out of the cell center through a structure called a centrosome
○ Create tracks for cell transport and organelle positioning
○ Become mitotic spindles during mitosis
○ Give structure to cilia and flagella
○ Structure - hollow tube
■ Stacked into 13 parallel filaments
■ FIlaments run in the same direction
about:bl 1
, 10/16/24, 11:32 BISC 2202 Notes Lectures
AM 20-25
■ Alpha tubulin end is on one side and beta tubulin is on the other end
○ Centrioles - cylindrical array of short microtubules surrounded
by a protein matrix. Function poorly understood
○ Drugs can be used to target microtubules
■ Taxol - binds to and stabilizes microtubules
■ Colcemid - binds to tubulin dimers and prevents polymerization
○ In neurons, microtubules guide transport of vesicles and
macromolecules. All microtubules point towards the axon
○ Motor proteins use ATP to move material along microtubules
■ Kinesins** go to the + end →
■ Dyneins** go to the - end ←
■ Tail (binding sites) designate which kind of cargo they carry
○ Microtubules position organelles such as the mitochondria, ER, and golgi
○ Microtubules make up cilia in the respiratory tract, which do not
grow from the centrosome but the basal body
○ Cilia and flagella - 9 + 2 organization
■ 9 double microtubules form in a ring around a single pair of proteins
■ Dynein movement can cause flagella to move or bend.
Accessory proteins form links to slide, bend ,etc
■ Cilia move in one direction to move material/fluid across the surface
➢ Actin filaments
○ Flexible, 7 nm diameter, thinnest type
○ Create cell shape
○ Needs accessory proteins to remain stale
○ Form microvilli, pseudopods
○ Structure - two stranded helix
■ Strands run in the same direction
■ Uses ATP to bind monomers together
■ Monomers are attached faster than they fall off, so it is able to grow
■ Treadmilling* - exclusive to actin filaments - when rates of
degradation and attachment are equal, monomers slowly
cycle through the actin filament
○ Drugs exist to both stabilize and degrade actin
○ Actin binding proteins control actin behavior
■ Thymosin/profilin bind and sequester actin
■ Formin/ARPs promote actin growth
○ Actin cortex can assist in movement of the cell by pushing an edge
of a cell in a direction, causing the rest of the cell to drag forward
○ Lamellipodias - made by ARPs which promote branching
○ Fillopodias - made by formins which promote growing without branching
○ Important for cell signaling and motility
○ RHO GTPases affect actin filament organization
○ Muscle cells: made of actin and myosin
■ Both use ATP to work
about:bl 2
