L4: Cytoskeleton Flashcards
Learning Objectives: - the terms microtubule, microfilament, intermediate filament - the structure and polymerisation of actin and the function of myosin - the properties of tubulin and microtubules - how tubulin polymerises and discuss factors that affect tubulin polymerisation - the role of the cytoskeleton in maintaining cell structure and shape, and in cell motility the role of motor proteins (kinesin and dynein) in organelle transport and the ATP‐dependence of their action
How is actin organised?
Bundles/meshed networks
3 features in the actin cytoskeleton
1) Stress fibres
2) Lamellipodium
3) Filopodia
What are stress fibres?
Contractile actin-myosin bundles in the cytoplasm
What is lamellipodium?
Thin, sheet-like extension containing meshwork of actin filaments
What is filopodia?
Finger-like protrusions that contain bundles of actin. filaments
What are microtubules?
Narrow, hollow tube-like structure found in cytoplasm
Function of microtubules
Support the shape of the cell
What are microfilaments?
Protein filaments in the cytoplasm that form part of the cytoskeleton
Function of microfilaments
Cell membrane motility
Structure of intermediate filaments?
Small strands in the shape of rods
Function of intermediate filaments
Mechanical strength to cells & tissues
Monomer of intermediate filaments
Monomer peptides
Monomer of microtubules
Dimers of alpha & beta - tubulin
Monomer of actin filaments
G-actin
Structure of actin filaments
2 strands in double helix
Associated motor proteins of microtubules
Kinesis & Dynein
Associated motor proteins of actin filaments
Myosin motors
What are the 2 ends on actin filaments?
Barbed & Pointed
What are the +/- ends of the actin filaments?
(-) end: Pointed
(+) end: Barbed
What is actin treadmilling?
Individual actin molecules migrate from barbed to pointed end
Function of myosin
Converts chemical energy in the form of ATP to mechanical energy
2 main groups of intermediate filaments
1) Cytoplasmic
2) Nuclear
3 sub-groups of cytoplasmic intermediate filaments
1) Keratins
2) Vimentin
3) Neurofilaments
Sub-group of nuclear intermediate filaments
Nuclear lamins
Role of tubulin
Regulates microtubule-associated proteins & kinesin motors
What does microtubules do during cell division?
Pulls daughter chromosomes into daughter cells
What are protofilaments?
Long strands of dimers attached together
How is microtubule stability regulated?
Large number of microtubule-associated proteins
Name 2 motor proteins
1) Kinesin
2) Dynein
Which direction (-) or (+) does kinesin move from?
minus (-) to plus (+) end
Which direction (-) or (+) does dynein move from?
plus (+) to minus (-) end
What is myosin?
A motor protein which interacts with actin
What are the 2 types of mysoin?
1) Myosin-I
2) Myosin-II
Role of Myosin I
Transportation of vescicles/organelles
Role of Myosin II
In muscle fibres, generated contractile force
