Lecture 2 Flashcards
What are the three different types of protein filaments that form the cytoskeleton?
Actin filaments or microfilaments ( 7nm in diameter)
intermediate filaments ( 8- 12 nm)
microtubules (25 nm)
Functions of the cytoskeletal protein filaments?
structural support and stability organization cell division cell movement tracks for motor proteins
Functions of microtubules?
- Intracellular transport or movement of vesicles and organelles
- cell motility (movement of cilia and flagella)
- mitotic spindle (attachment of chromosomes and their movement during cell division
- rigid intracellular skeleton- shape and polarity
What is the structure of microtubules?
They are non-branching, rigid, and hollow
Made up of alpha and beta tubulin
Have positive end and a negative end
What are the structure of the centrioles?
They are made up of nine triplets of microtubules around a central axis
Each triplet is made up of one complete and two incomplete microtubules
What is the function of the centriole?
organize the centrosome
basal body formation (needed for the assembly of cilia and flagella)
mitotic spindle formation during cell division
What is the structure of the centrosome?
contains a pair of centrioles
arranged in a way that one is perpendicular to another
amorphous protein matrix (around 200)
gamma tubulin ring complexes
nucleation sites for the microtubules
What is the function of the centrosome?
organize microtubules
initiate microtubule formation
They are negative at the nucleated side and the positive end grows out to the periphery
Explain polymerization?
organized and directed by microtubule organizing centers (basal bodies and centrosome)
This mechanism is GTP dependent NOT ATP
This mechanism is highly dynamic
The positive side grows quickly while the negative end is slow growth
What is a microtubule associated protein?
Tau protein
normally found in the CNS and this protein stabilizes axonal microtubules
The hyperphosphorylation of the tau protein can result in the self-assembly of tangles found in AD
Explain the drug colchicine?
This drug is an anticancer compound that prevents the polymerization of tubulin molecules
Programmed cell death is the result
Explain vinca alkaloids?
There are two kinds vinblastine and vincristine
Both of these compounds prevent polymerization and thus lead to cell death
Explain Taxol (Paclitaxel)?
This an anticancer compound that stabilizes and prevents microtubule disassembly
arrests dividing cells during mitosis. they are unable to achieve metaphase and thus die.
The microtubule motor: dynein
This protein moves in the negative direction on the microtubule (retrograde) In other words, things are moved in the direction of the nucleus.
Binding sites for vesicles, organelles, and others
very fast movement!
What are the two families of dynein?
cytoplasmic dyneins and axonemal dyneins
axonemal (located in cilia and flagella)
Explain the kinesin family of microtubule motors?
This motor protein moves in the positive direction and thus away from the cell nucleus (anterograde)
Binding site for vesicles, organelles, and others
Cilia and flagella
very specialized motile structures
use microtubules and axonemal dynein motor proteins
The movement is produced by the bending of the axoneme
Cilia (function and structure)
microtubule based, it is a hair like structure
motile
9+2 microtubule arrangement
move fluid and particles along epithelial surfaces
the cilia are anchored to the cell via the basal body
What are the three primary cilia? what are their characteristics?
photoreceptors- sight
chemoreceptors - smell
mechanoreceptors- monitors the flow of fluid in the kidney
they have an 9+0 arrangement
connected to the cell via basal membrane
develops from one centriole following cell division
What is the structure of intermediate filaments and what functions do they have?
They are rope like filaments that are made up of a non-polar and highly variable subunits
Functions:
stabilize cell structure- maintain the position of organelles
resist shearing forces- connect with desmosomes and hemidesmosomes
essential for the integrity of cell to cell and cell to ECM junctions
What are the 6 classes of intermediate filaments?
- keratins (1 and 2)
- vimentin and vimentin like
- neurofilaments
- lamins
- beaded filaments
explain keratins?
intermediate filament
found in all epithelial cells
acid and basic cytokeratins
50 isoforms
Explain vimentin and vimentin-like?
intermediate filament
Diverse- found all over the body
vimentin is most found in mesoderm-derived cells
(muscles, blood vessels, bone etc)
vimentin-like are found in a variety of cells
desmin- muscle cells
glial fibrillary acid protein- glial cells and astrocytes
explain neurofilaments?
intermediate filament
extend from the cell body onto the ends of axons and dendrites (support)
found primarily in neurons
Explain lamins?
Found in the nucleus of all nucleated cells
found in the nuclear lamina
Lamin A and B proteins
explain beaded filaments?
eye lens specific group
intermediate filament
structure and function of actin filaments or microfilaments?
Made up of the protein actin
There is G actin (free actin molecules in the cyto) and there is F-actin (polymerized actin in filament and ATP DEPENDENT)
polarized: fast growing + end and slow - end
may be single, bundle, or networks
functions: anchorage structural core of microvilli and stereocilia cell motility extension of cell processes
Explain Phalloidin?
This is a toxin that is found in the species amanita phalloides
this molecules disrupts the normal function of actin
It promotes excessive polymerization and inhibits depolymerization…. thus cell moement is no longer possible
liver and kidney failure after 4 to 8 days
Explain cytochalasins?
another fungal product that blocks the polymerization of actin and thus inhibits cell movement, division, and leads to cell death
structure of microvilli?
cylindrical, membrane bound cytoplasmic projection
core of 25 to 30 actin microfilaments
crosslinked by villin
anchored into the terminal web (bottom)
explain stereocilia?
usually long microvilli ( 120 micrometers)
anchored to the terminal web
limited distribution:
epididymis
proximal ductus deferens
sensory hair cells in inner ear
Actin motor?
Myosin family
Myosin II generates the force for skeletal muscle contraction
formed form two heavy chains and 4 light chains
each head binds and hydrolyzes ATP
The steps to myosin structural change?
- attachment (rigor conformation)
- release (ATP binds and reduces myosin affinity for actin)
- Bending (ATP hydrolysis and conformational change)
- force generation (Weak binding of myosin to actin leads to the release of inorganic phosphate)
release triggers tight binding and power stroke
- reattachment (rigor conformation)
What are the steps to cell movement?
- protrusion
actin polymerization at the plus end protrudes lamellipodium
- attachment
focal adhesions anchor the actin cytoskeleton to extracellular matrix via integrin proteins
- contraction
Cytoplasm is drawn forward
What are the different types of protrusion structures?
- filopodia ( finger like projections)
- lamellipodia (sheet-like structures)
- pseudopodia ( 3-dimensional projections)
Explain actin polymerization?
the actin filaments mostly orientate with the + end facing forward
- end usually attached to the ARP complex
actin-related protein
the front is assembling as the rear is disassembling
Where is the ARP highly concentrated?
the front of the lamellipodia where the actin nucleation is most active
Explain the steps of neutrophil migration?
- rolling
- activation
- adhesion
- transendothelial migration (diapedesis)
explain chemotaxis and how it relates to the immune system?
movement within a tissue based on a chemotactic gradient.
towards the source of inflammation
What are the inclusions? explain them?
- lipofusin (wear and tear pigment and generally found in non-dividing cells)
- hemosiderin- (seen in the spleen,liver, and lung. formed by indigestible residues of hemoglobin)
- melanin- (produced in melanocytes, gives rise to skin and hair color, sometimes seen in certain neurons)
- glycogen- storage form of glucose
- lipid- fat droplets and energy store
