Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Cell Cytoskeleton Chapter 17 Watch this animation http://multimedia.mcb.harvard.edu/ anim_innerlife.html The Inner Life of Cells Questions in this chapter you should be able to answer: Chapter 17: 1 - 11, 13 - 23 The Cell Cytoskeleton 1 All of these movements are made possible by the cell “Cytoskeleton” What is the Cell Cytoskeleton? -- long protein filaments -- extend through the cytoplasm A variety of purposes Three families • Microtubules • Actin filaments • Intermediate filaments Tick and Sick - 8 2 The Cell Cytoskeleton What are the 3 primary types of cytoskeletal proteins? Intermediate filaments -- resist mechanical stress Microtubules -- cytoplasmic transport -- axoneme movement -- chromosome movement Actin filaments -- membrane contraction -- muscle cells -- cytokinesis -- cell movements The Cell Cytoskeleton 3 What is the structure of intermediate filaments Cable-like arrangement Extended molecular interactions Anchoring to desmosomes Intermediate Filaments The Cell Cytoskeleton 4 Intermediate filaments -- help hold cells & tissues together Human lung carcinoma Tick and Sick - 8 5 Intermediate filaments also occur in the nucleus Cytoplasmic -- keratins – skin integrity -- in neurons -- in muscle, connective tidssue Nuclear -- lamins Tick and Sick - 8 6 Microtubules & Actin filaments make possible different types of movements Cell migration Neutrophil Flagella and cilia Cytoplasmic movements Muscle contraction Mitosis and Cell division Cytoplasmic transport Membrane movements Membrane ruffling Tick and Sick - 8 7 Cytosolic Microtubules Helps to distribute materials through the cell This highway is ‘dynamic’ Tick and Sick - 8 8 The ‘spindle apparatus’ controls chromosome movements -- Attached to “kinetochores” on duplicated chromosome Cell Division Kinetochore function Spindle Apparatus Tick and Sick - 8 9 What is the fundamental structure of microtubules? Alpha and beta tubulin subunits 13 member ring Why do MTs have polarity? ‘MT Organizing Center’ Why are MTs said to display ‘Dynamic Instability’? Dynamic Instability The Cell Cytoskeleton 10 Motor proteins carry “cargo” along microtubules Two motor proteins Opposite directions Kinesin walking How does Kinesin ‘walk”? Kinesin walking Organelle movement Organelle movement Tick and Sick - 8 11 What is the mechanism of MT growth and retraction? Binding, hydrolysis and release of GTP ‘Capping’ at cell membrane MT with EB1 cap Question 17-3, p 583 How would a change in [tubulin] affect MT dynamics? ..if only GDP were present? … or a nonhydrolizable GTP analog? The Cell Cytoskeleton 12 What is the structure and movement of an axoneme? Cilia & flagella “9 + 2 Structure” Living Cell video The Cell Cytoskeleton 13 Where are human cilia and flagella found? Various places Respiratory cilia Some genetic conditions cause cilia not to function Symptoms of IMS Respiratory infection; Fertility problems Etc… and ‘situs inversus‘’ (50%) Tick and Sick-1 14 An interesting congenital genetic disorder -- “Immotile Cilia Syndrome” Symptoms: • • • • Respiratory tract infections Infertility Digestive problems Situs Inversus -- Affects ~50% of people with IMS - IDA - ODA - IDA Tick and Sick-1 15 What is the link between cilia and Left/Right orientation? Cilia occur in the “embryonic node” -- very early stage of development Generate oriented flow of signal molecule Why 50% affected? Embryonic node cilia Tick and Sick-1 16 What is the distribution and structure of actin filaments? treadmilling The Cell Cytoskeleton 17 How are actin filaments organized in the cytoplasm? The cell cortex Actin binding proteins The Cell Cytoskeleton 18 How does actin mediate cell movements? Cell crawling What are Lamellipodia and Filopodia? Membrane ruffling Listeria movement The Cell Cytoskeleton 19 Actin Filaments are involved in muscle contraction What happens when muscles contract? Nerve impulses activate contraction at neuromuscular junction Tick and Sick - 8 20 What is structure of muscle cells? Some basic anatomy. . . “Muscles” are bundles of muscle cells Sarcomeres -- are the smallest contractile unit of muscles Tick and Sick - 8 21 Some details of Sarcomeres, Actin and Myosin… Nerve impulse triggers Ca++ release Inside of cell -- Myosin pulls on actin -- Pulls sarcomere shorter Ca++ quickly removed -- leads to relaxation Muscle contraction Tick and Sick - 8 22 Sarcomeres create visual ‘striations ‘of “Striated muscles” (skeletal muscles) Tick and Sick - 8 23 Muscle spasms and cramps (“Charley Horse”) Imbalance in excitatory and inhibitory signals -- self-reinforcing cycle occurs Tick and Sick - 8 24 How does the sliding filament model explain sarcomere contraction? Myosin is attached ATP binds -- Myosin head detaches ATP is hydrolyzed -- Myosin Head cocks -- loosely binds to actin Pi is released -- which triggers …. Powerstroke -- during which… ADP is released Myosin remains attached myosin The Cell Cytoskeleton 25 How is muscle contraction triggered? Motor neuron & action potential Sarcoplasmic reticulum T-tubules Ca++ release The Cell Cytoskeleton 26 How does Ca++ trigger the muscle contraction? The tropomyosin / troponin complex Sarcomere The Cell Cytoskeleton 27 Question In order to keep cytosolic Ca++ levels low, muscle cells possess an ATP driven Ca++ pump in the sarcoplasmic reticulum and a Ca++/Na+ ATPase in the cell membrane. The cells also possess the Na+/K+ ATPase in the cell membrane. The Na+/K+ ATPase is partially inhibited by drugs such as ouabain and digitalis, whereas the Ca++/Na+ ATPase is inhibited by binding to a protein called phospholamban. A. Draw a diagram showing the expected arrangement and orientation in the membranes of these membrane proteins. B. Would treating a patient with either of these drugs weaken or strengthen muscle contraction (they are usually given to cardiac patients)? Explain. C. The regulatory protein “protein kinase C” (PKC) regulates activity of the Ca++ ATPase. PKC can phosphorylate (covalently add a PO4) to the Ca++ ATPase, which increases its affinity for Ca++. What would be the expected effect of Ca++ ATPase phosphorylation on the strength of muscle contraction? The Cell Cytoskeleton 28