WEEK 5 (Cytoskeleton & Cell Motility) Flashcards
What is the most diverse class of filaments?
Keratin filaments
What is Epidermolysis bullosa simplex disease associated with?
Mutations in keratin genes
What is the Cytoskeleton?
A network of protein filaments that extends throughout the cytoplasm which gives a cell its shape, offers support and facilitates movement
Microtubules are formed of which protein?
Tubulin
Microfilaments are composed of the protein __________
actin
Cytoskeletal filaments are polymers of __________
Proteins
Microtubules of a dividing cell form the mitotic spindle (TRUE/FALSE)
TRUE
EXPLANATION: Microtubules of a dividing cell form the mitotic spindle required for chromosome segregation
The Cytoskeleton framework plays a role in positioning of the cell organelles (TRUE/FALSE)
TRUE
Explanation: The internal framework of a cell (the cytoskeleton) is responsible for positioning the various organelles.
Which protein filaments make up the cytoskeleton?
- Intermediate filaments
- Microtubules
- Actin filaments
Describe Intermediate Filaments
Ropelike fibers that are made of fibrous intermediate filament proteins
What are the properties of Intermediate Filaments?
- Forms NUCLEAR LAMINA meshwork beneath the inner nuclear membrane
- Provides MECHANICAL STRENGTH and distributes MECHANICAL STRESS in epithelial tissue by spanning cytoplasm
- VERY FLEXIBLE
- GREAT TENSILE STRENGTH
- DEFORM under stress but DO NOT RUPTURE
Describe Microtubules
Hollow cylinders made of the protein tubulin. They are long and straight and have one end attached to a single microtubule-organising centre called a CENTROSOME.
What are the properties of Microtubules?
- More RIGID than actin filaments or intermediate filaments
- Rupture when stretched
- Long and straight
- Hollow cylinders made of TUBULIN
Describe Actin Filaments/Microfilaments
Helical polymers of the protein ACTIN that are organised into a variety of linear bundles, two-dimensional networks and three-dimensional gels.
What are the properties of Actin Filaments?
- Flexible structures
- Dispersed throughout cell but highly concentrated in CORTEX (layer of cytoplasm just beneath the plasma membrane)
What are the different properties of Microtubules?
SUBUNITS INCORPORATED INTO POLYMERS: GTP-aB-tubulin heterodimer
PREFERENTIAL SITE OF INCORPORATION: + End (B-tubulin)
POLARITY: Yes
ENZYMATIC ACTIVITY: GTPase
MOTOR PROTEINS: Kinesins, Dyneins
MAJOR GROUP OF ASSOCIATED PROTEINS: MAPs
STRUCTURE: Stiff, hollow, inextensible tube
DIMENSIONS: 25nm outer diameter
DISTRIBUTION: All eukaryotes
PRIMARY FUNCTIONS: Support, intracellular transport, cell organisation
SUBCELLULAR DISTRIBUTION: Cytoplasm
What are the different properties of Intermediate Filaments?
SUBUNITS INCORPORATED INTO POLYMERS: -70 different proteins, likely incorporated as tetramers
PREFERENTIAL SITE OF INCORPORATION: Internal
POLARITY: No
ENZYMATIC ACTIVITY: None
MOTOR PROTEINS: None
MAJOR GROUP OF ASSOCIATED PROTEINS: Plakins
STRUCTURE: Tough, flexible, extensible filament
DIMENSIONS: 10-12nm diameter
DISTRIBUTION: Animals
PRIMARY FUNCTIONS: Structural support, mechanical strength
SUBCELLULAR DISTRIBUTION: Cytoplasm + nucleus
What are the different properties of Actin Filaments?
SUBUNITS INCORPORATED INTO POLYMERS: ATP-Actin monomers
PREFERENTIAL SITE OF INCORPORATION: + End (barbed)
POLARITY: Yes
ENZYMATIC ACTIVITY: ATPase
MOTOR PROTEINS: Myosins
MAJOR GROUP OF ASSOCIATED PROTEINS: Actin-binding proteins
STRUCTURE: Flexible, inextensible helical filament
DIMENSIONS: 8nm diameter
DISTRIBUTION: All eukaryotes
PRIMARY FUNCTIONS: Motility, contractility, intracellular transport
SUBCELLULAR DISTRIBUTION: Cytoplasm
What is the difference between the function of microtubules in epithelial and neurons and the dividing cell?
Microtubules of the epithelial and neurons = Support and organelle transport
Microtubules of the dividing cell = Form the mitotic spindle
What are the functions of the Intermediate Filaments?
Provide structural support for both the EPITHELIAL CELL and NEURON
What are the functions of Microfilaments?
- Support microvilli of epithelial cell
- Integral part of motile machinery involved in NEURONAL ELONGATION and CELL DIVISION
Describe how microtubules have a critical organising role in all eukaryotic cells
Microtubules are LONG and RELATIVELY STIFF hollow tubes of protein that can rapidly disassemble in one location and reassemble in another
Describe the Microtubules’s role in mitosis
When a cell enters mitosis, the cytoplasmic microtubules disassemble and then reassemble into an intricate structure called the MITOTIC SPINDLE
Why are Peroxisomes closely associated with Microtubules?
Microtubules are the tracks over which the peroxisomes are transported in mammalian cells
What is Tubulin?
A dimer composed of two very similar globular proteins called a-tubulin and B-tubulin
Where are Microtubules found?
- Cytoskeleton
- Mitotic spindle
- Centrioles
- Core of cilia and flagella
Where do microtubules function?
In diverse activities such as SUPPORT of the cell and movement of materials between the cell body and axon terminals of a neuron
Where does Tubulin polymerise from?
Nucleation sites on a centrosome
Describe the Centrosome
- Centrosome consists of a pair of centrioles surrounded by a matrix of proteins
- Centrosome matrix includes hundreds of RING-SHAPED STRUCTURES called Y-tubulin
- Each Y-tubulin ring complex serves as the NUCLEATION SITE for the growth of one microtubule
What is the difference between the minus and plus end of a microtubules?
- MINUS END = embedded in the centrosome having grown from a y-tubulin ring complex
- PLUS END = extends into the cytoplasm
- MINUS END = protected by organising centres from which the microtubules grow
- PLUS END = initially free but can be stabilised by binding to specific proteins
Describe how growing microtubules display dynamic instability
Each microtubules grows and shrinks independently of its neighbours -> Array of microtubules anchored in a centrosome is CONTINUALLY CHANGING as new microtubules grow and old microtubules shrink -> It might shrink partially then suddenly start growing again or might disappear completely
What happens when a growing microtubule disappears completely?
It gets replaced by a new microtubule that grows from the same y-tubulin ring complex
The selective stabilisation of microtubules can _________________ a cell
polarise
A newly formed microtubules will persist only if both its ends are protected from ____________________
depolymerisation