Biochem Lecture 9 Flashcards
(26 cards)
What are the major roles of the cytoskeleton?
Cell movement
Cell shape
Moving and positioning cell components
Mechanical strength to tissues/cells
What are the three major structural elements of the cytoskeleton?
Microfilaments (actin)
Microtubules
Intermediate filaments
What are the general properties of Microtubules?
hollow tube about 25nm in outer diameter
made up of two monomers alpha and beta tubulin
has polarity with + and - ends
is used for chromosome segregation in mitosis, intracellular transport, movement of cilia and flagella
What are the general properties of Actin?
8nm diameter two intertwined chains of F-actin made up of G-actin monomers has polarity with + and - ends used for cell shape, cell movement, muscle contraction
What are the general properties of intermediate filaments?
8-12nm diameter
made of 8 protofilaments joined end to end with staggered overlap
protofilaments are made of polypeptide dimers that have wrapped around each other and stacked end to end
no polarity
used for structural support, and provide strength to cells
What proteins are in intermediate filaments?
Keratin (epithelial cells)
Vimentin (fibroblasts)
Neurofilaments (neurons)
What causes ALS or Lou Gherig’s disease?
Neurofilaments mutate and cause an abnormal accumulation and assembly of neurofilaments which causes a progressive loss of motor neurons which leads to muscle atrophy, paralysis, and death.
What are desmosomes?
They link keratin intermediate fibers of the epithelia into a continuous protein network that provides structural stability. Desmosomes interacting with intermediate fibers allows tissues to withstand tearing and shearing forces.
What is epidermolysis bullosa simplex?
A mutation in the keratin genes prevent assembly into protofilaments so the skin blisters really easy.
How are microfilaments formed?
Microfilaments are actin based. G-actin (actin bound to ATP) is globular. It binds to the + end of the chain and assembles to make a microfilament. Eventually the ATP is hydrolyzed into ADP at the - end of the chain.
The filamentous form of actin is called F-actin.
What are three ways that actin filaments arrange into structures?
Parallel bundles: make up microvilli
Contractile bundles: make up stress fibers
Networks: cell cortex which determines cell shape
How do Myosin and actin interact and what types of Myosin are there?
Myosin I is a monomer that moves cargo along actin fibers.
Myosin II are in muscles and convert ATP into mechanical energy by muscle contraction.
Where are microfilaments found in the cell and what are they anchored to?
Located at the cell periphery at the plasma membrane.
They are anchored to adherens junctions between cells, and at focal adhesions in cell-extracellular matrix.
Where are intermediate filaments found and what are they anchored to?
Found throughout the cell.
Anchored to Desmosomes (cell-cell) and hemidesmosomes (cell-extracellular matrix).
What are the two groups that microtubules can be classified into?
- Cytoplasmic microtubules: form mitotic and meiotic spindles, spatial distribution and trafficking of vesicles and organelles
- Axonemal microtubules: form central shaft or axoneme of cilia and flagella
How do microtubules grow and disintegrate?
While GTP bound tubulin is available, the tubule will grow mostly at the plus end until GTP tubulin is no longer available. This allows the GTP at the cap of the tubule to be hydrolyzed into GDP and cause catastrophe which is depolymerization. GTP at the tip stabilizes it, but once hydrolyzed, it becomes unstable.
What are microtubule organizing centers?
These are centrosome which are made up of two centrioles. They are located near the nucleus and anchor the minus end of microtubules.
What are kinesin and dynein?
Proteins that walk along microtubules to transport vesicles and other things to and from the cell membranes. Kinesin moves towards the plus end of microtubules, dynein moves towards the minus end. Both use ATP for their duties.
How are microtubules involved with Cilia and flagella?
Axonemal microtubules form the central shaft of cilia and flagella. They bend and move through the action of dynein that makes the tubes slide past each other.
What is Kartagener syndrome?
Dynein is absent in flagella and cilia. This causes male sterility and chronic respiration infection because the flagella of the sperm can’t move, and the cilia in the lungs can’t sweep mucus up and out.
What are the two regions of the golgi and what are the two roles the golgi fulfills for the cell?
REGIONS:
- cis-Golgi network (CGN): closest to the ER and continually receives newly synthesized lipids/proteins
- trans-Golgi network (TGN); farthest from ER, proteins and lipids are packaged and bud off here
ROLES:
- Post translational modification
- Sorting of proteins to their final destination
How do proteins destined for the ER get there from the Golgi?
Proteins destined for the ER have a KDEL sequence at their tails that signal the Golgi to send them back to the ER.
What are constitutive and regulated secretion?
Constitutive: the default pathway, products are secreted as they are made, done in all cells, membrane proteins are secreted this way
Regulated: in specific cells, always mediated through calcium signaling, secretory vesicles build up and wait for a signal to release, hormones such as insulin and glucagon do this as well as neurotransmitters epinephrine and acetylcholine, also digestive enzymes
What is the pH environment inside lysosomes?
There is an H+ pump at the membrane of lysosome that creates a low pH inside the organelle.
