PART I Why Do Cells Need a Cytoskeleton PART I Why Do Cells Need a Cytoskeleton? How do cells move vesicles and themselves? CH 15 and a bit of 16 (Last for CH Test #3 Friday) Oct 27, Oct 30 and Nov 1 Cytoskeletal Components: microtubules, microfilaments and intermediate fibers Cytoskeleton is required by all eukaryotic cells! Microtubule functions/characteristics Microfilament functions/characteristics Intermediate filament functions/characteristics Calcium, Actin and Myosin=> contraction Skeletal and Cardiac Muscle VS. Smooth Muscle Intermediate assembly and hair

Practice Quiz: Signal Transduction 1) With respect to activation of adenylyl cyclase, which G-protein subunit can be present in stimulatory or inhibitory forms? Alpha Beta Gamma Delta Omega How does a hormone receptor change the function of this subunit? 2) Which 2nd messenger is produced by phospholipase-C for the purpose of opening specific ligand-gated Ca++ channels? Diacylglycerol Calmodulin Inositol triphosphate Cyclic AMP Cyclic GMP Ca++ How is PL-C activated in this regard? 3) Which of the following is a voltage gated channel that you would expect to find at a pre-synaptic (nerve ending) where vesicles release acetylcholine (neurotransmitter). K+ Na+ Ca++ Cl- How do vesicles get from the nucleus to the end of the axon? 4) What second messenger activates protein kinase A? What enzyme creates this second messenger and what G-protein subunit is important in this regard? 5) Why do some hormones need amplification? What hormones don’t need amplification? Why don’t some hormones need second messengers? 6) How does a tyrosine kinase work? Name three examples of tyrosine kinases and their functions.

Work Requires Structure for “Leverage”: Cells must respond to stresses and changes in shape, they must also perform intracellular mechanical work. Work Requires Structure for “Leverage”: Exocytosis/Endocytosis/Vesicle Transport Shape changes and morphogenesis Nuclear and cellular division The Cytoplasm has 3 types of filament: 1-Microtubules: 25nm diameter-Largest subunit type Movement in the cell Tubulin: alpha/beta subunits 2-Microfilaments: 8 nm diameter- Smallest subunit type Movement of the cell G-actin subunits 3-Intermediate Filaments: 8-12 nm dia-Intermediate size Structural support in/around cell Tissue specific proteins These 3 filaments function to create an intracellular matrix for organization, attachment and intracellular motion.

Sites of Special Importance: 1-Formation of Mitotic Spindle Microtubules consist of tubulin protein dimers (α and B) that guide intracellular transport vesicles and proteins to the proper location within a cell. Sites of Special Importance: 1-Formation of Mitotic Spindle One Kinetochore for each chromosome Chromosomes microtubule elongation separates the chromosomes at anaphase 2- Guiding Vesicles: exocytosis/endocytosis Clathrin is important especially in endocytosis 3-Critical for axoplasmic flow in axons/dendrites Carry vesicles with NT to axon or recycle NT to nucleus 4- Important to structure of flagella and cilia -9+2 pattern of microtubules 5- Inhibiting tubule synthesis kills cell (antimitotic)! Cancer Drugs: Vinblastine: no MT formed Taxol: MT not disassembled for division

How are microtubules made at specific nucleation cites How are microtubules made at specific nucleation cites? Alpha/Beta monomers DimersTubes(25nm dia) Tubulin-GTP is added at the positive end of the tube and removed from the negative end of tube. XXX XXX

What events inside a cell are dependent upon proper the formation/destruction of microtubules (MTs) at locations called microtubule organizing centers (MTOCs)?

Dynein and Kinesin proteins crawl along microtubules and carry vesicles with them using ATP as the energy source. Dynein: moves toward Negative Direction. Kinesin: moves toward Positive Direction Similar proteins form the radial spokes of flagella and cilia.

Dynein and kinesin proteins can be active at the same time and move vesicles in opposite directions (- or +) on the same microtubules!

Flagella and Cilia: Dynein arms move across adjacent MTs causing sliding/axoneme bending motion

Visualization of Dynein/ATP-dependent sliding action across adjacent axonemes in a flagella. In terms of the ATP that drive this process, why do sperm carry mitochondria? Where do your mitochondria come from? How could a genetic defect in dynein result in linkage of male sterility and respiratory disease?