Module 3: Lesson 2 Flashcards
(17 cards)
What are the protein filaments that make up the cytoskeleton?
Intermediate filaments, microtubules, and actin filaments.
What are microtubules?
Hollow cylinders made of the protein tubulin. They are long, straight, and have a centrosome.
What is the function of microtubules?
Intracellular movements, cell shape, cell division, and cell motility. They create a system of tracks within a cell for transport, and position membrane-enclosed organelles within the cell.
How does actin polymerization occur?
Through ATP hydrolysis. Once ATP is hydrolyzed, they have less binding affinity and depolymerize.
What is the architecture of a microtubule?
Heterodimer proteins called alpha- and beta-dimerize are the subunits that polymerize a microtubule. Head-to-tail polymerization makes a protofilament, and side-to-side make a hollow tube. Microtubules are made from 13 protofilaments.
Are individual microtubules dependent or independent from the centrosome?
Microtubules grow independently from the centrosome.
What are the steps for a growing microtubule?
GTP-tubulin dimers add to growing end of microtubule (typically on the + end). Addition proceeds faster than GTP hydrolysis by dimers.
What are the steps for a shrinking microtubule?
GTP hydrolysis is faster than addition of new GTP-tubulin dimers. Protofilaments containing GDP-tubulin peel away from microtubule wall. GDP-tubulin is released to the cytosol.
What is the Microtubule Organizing Center (MTOC)?
y-TuRC (a regulating protein) tends to localize to specific regions/structures in the cell. They have the common ability to nucleate, anchor, and/or organize microtubules.
What are Microtubule Associated Proteins (MAPs)?
Proteins that bind along the length of the microtubule, and promote microtubule stability and organization (like bundling).
Example: Tau in neurons, which when aggregated, can lead to Alzheimer’s disease.
What are microtubule motors?
Kinesins and dyneins are ATPases that serve as MT motors. Kinesins move toward the + end, while dyneins move toward the - end.
How do microtubule motors function?
ATP hydrolysis loosens attachment to head 1 of microtubule. ADP release and ATP binding change conformation of head 2, which pulls head 1 forward. They are recruited to cargoes using adaptor proteins, like Rab.
What are the characteristics of intermediate filaments?
Impart strength providing mechanical supports to cells and tissues, various IF proteins, no known motor proteins, do not bind nucleotides (ATP or GTP), structurally non-polar filaments, tough and durable.
What types of intermediate filaments are there? Are they cytosolic or nuclear?
Cytosolic: keratin filaments, vimentin and vimentin-related filaments, neurofilaments.
Nuclear: Nuclear lamins.
What are characteristics of keratins?
Forms 3-D meshwork throughout epithelial cell cytoplasms. Forms structural network that links cytoplasmic components and provides intracellular connections.
What is plectin?
An IF accessory protein that further stabilizes the network by linking them to microtubules, actin filaments, and adhesive structures in desmosomes. Mutations cause epidermolysis bullosa simplex (EBS), muscular dystrophy, and neurodegeneration.
What are the characteristics of lamins?
IFs that line the inside of the nuclear envelope and provide mechanical support.
