Cytoskeleton Flashcards
Due to Abnormal Ciliary Dynein
- Symptoms include:
- Respiratory system abnormalities
- Situs Inversus
- Thoracic& abdominal organs on the wrong side of the body.
Kartagener’s Syndrome
Cell interior composed of:
- Cytoskeleton
- Cytosol
- Organelles
Cytosol often comprises more than ______% of a cell’s volume.
Site of ______
50%; protein synthesis
Elements of the Cytoskeleton
- Microfilaments (Actin, “thin filaments”) (6 types)
- Microtubules (Tubulin) (12 types)
- Intermediate filaments (31 types)
- Motor proteins. i.e. Myosins, Dynein, Kinesin.
The most abundant protein in most eukaryotic cells
Microfilaments
Main component of microfilaments, which are double-stranded, thin, and flexible structures
Actin
Most actin molecules work together to give support and structure to the plasma membrane and are found
near the cell membrane
Microfilaments are composed _________ , and generate force by ________, causing movement of the intervening strand.
of linear polymers of actin subunits; elongation at one end of the filament coupled with shrinkage at the other
Actin structures are controlled by the
Rho family of small GTP - binding protein:
- Rho itself for contractile acto-myosin filaments (“stress fibers”)
- Rac for lamellipodia
- Cdc42 for filopodia.
Microvilli contain
actin
Microvilli
Microtubules
- Long, hollow, cylindrical structures composed of tubulin and organized around a centrosome, an organelle usually found in the center of the cell near the cell nucleus.
- One end of each microtubule is embedded in the centrosome; the microtubule grows outward from there.
Microtubules are much more rigid than _______ molecules and have a larger diameter: _______ nanometers
They are _________ and go through a process of continuous growth and decay.
actin molecules; 25 nanometers
relatively unstable
Microtubules play key roles in:
- intracellular transport (associated with dyneins and kinesins, they transport organells like mitochondria or vesicles)
- the axoneme of cilia and flagella
- the mitotic spindle
- syntheis of the cell wall in plants
Molecules that bind to microtubules
- Colchicine (depresses MT assembly) (avidly taken up by neutrophils, which become suppressed as a treatment for gout)
- Tau (abnormal in Alzheimer’s disease)
- Motor proteins
- Dynein (moves to minus end, center)
- Kinesin (moves to plus end, outer)
Moves towards minus end (center)
Dynein
Kinesin moves towards ______ end (outer)
plus
Distribution of Cytoplasmic MT’s goes from ______ end to ______ ends
Minus ends (internal) to plus ends (outward)
Ciliated epithelium contains
microtubulues
Microtubules in cilia and flagella
Axoneme
The Axonenme structure
(9 doubletes + 2 MT’s)
Kartagener’s Syndrome
- Due to abnormal Cilary Dynein
- Symptoms
- Respiratory system abnormalities
- Situs Inversus
- Thoracic & abdominal organs are on the wrong side of the body
- Reason: Ciliary moverment aids organogenesis in the early embryo
Primary (sensory) cilia are found in many cells:
- Neurons
- Chondrocytes
- kidney epithelium, etc.)
Receptors for neurotransmitters and many other molecules localize to cilia
Disruption of the sensory functions of cilia is found in a genetic disorder,
Bardet-Biedl syndrome
CNS Neurons commonly have how many cilia?
a single cilium
_____ centrioles make a centrosome
2 centrioles make a centrosome
Triplet of microtubules
Microtubules attach to chromosomes _______
kinetochores
Rope-like and fibrous, with a diameter of approximately 10 nanometers
Intermediate filaments
These filaments extend through the cytosol and help to resist stress and increase cellular stability.
Intermediate filaments that form a network surrounding the nucleus
nuclear lamina
Intermediate filaments maintain cell-shape by
bearing tension (microtubules, by contrast, resist compression)
micro and intermediate filaments- cables
microtubules - cellular support beams.
Intermediate filaments organize the internal tridimensional structure of the cell by:
- anchoring organelles
- serving as structural components of the nuclear lamina and sarcomeres
Participate in some cell-cell and cell-matrix junctions
Different intermediate filaments are:
- Keratins: in epithelial cells
- Desmin: in muscle cells
- Vimentin: in connective tissue cells
- Neurofilaments: in nerve cells
- GFAP: Glial Fibrillary Acidic Protein of Astrocytes
- Lamins: in all cell types: govern shape of nucleus and interconnects nuclear pores
Myosin
- A family of ATP-dependent motor proteins involved in muscle contraction and in a wide range of motility processes.
- Responsible for actin-based motility.
A large number of genes have been discovered.
Myosin was originally thought to be restricted to muscle cells (hence, “myo”), but there is no single “myosin” but rather a huge superfamily of genes whose protein products share the basic properties of:
- Actin binding
- ATP hydrolysis (ATPase enzyme activity)
- Force transduction
Virtually all eukaryotic cells contain myosin isoforms. Some isoforms have _________, while other isoforms are ______.
specialized functions in certain cell types (such as muscle); ubiquitous
Myosin structure
- Head domain
- Neck domain
- Tail domain
Domain that binds actin, and uses ATP hydrolysis to generate force and to “walk” along the filament towards the barbed (+) end
- (with the exception of myosin VI, which moves towards the pointed (-) end).
Head domain
Domain that acts as a linker and as a lever arm for transducing force generated by the catalytic motor domain. Also serve as a binding site for myosin light chain which are distinct proteins that form part of a macromolecular complex and have regulatory functions.
Neck domain
Myosin I
Myosin II
Myosin, Actin, & Cell Movement
