The Cell Cytoskeleton1 Chapter 17 Questions in this chapter you should be able to answer: Chapter 17: , Watch this animation anim_innerlife.html The Inner Life of Cells

Tick and Sick - 82 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

The Cell Cytoskeleton3 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 Cytoskeleton4 What is the structure of intermediate filaments Cable-like arrangement Extended molecular interactions Anchoring to desmosomes Intermediate Filaments Intermediate Filaments

Tick and Sick - 85 Intermediate filaments -- help hold cells & tissues together Human lung carcinoma

Tick and Sick - 86 Intermediate filaments also occur in the nucleus Cytoplasmic -- keratins – skin integrity  -- in neurons -- in muscle, connective tidssue Nuclear -- lamins

Tick and Sick - 87 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 - 88 Helps to distribute materials through the cell This highway is ‘dynamic’ Cytosolic Microtubules

Tick and Sick - 89 The ‘spindle apparatus’ controls chromosome movements -- Attached to “kinetochores” on duplicated chromosome Spindle Apparatus Kinetochore function Cell Division

The Cell Cytoskeleton10 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

Tick and Sick Kinesin walking Motor proteins carry “cargo” along microtubules Two motor proteins Opposite directions How does Kinesin ‘walk”? Organelle movement Kinesin walking Organelle movement

The Cell Cytoskeleton12 What is the mechanism of MT growth and retraction? Binding, hydrolysis and release of GTP ‘Capping’ at cell membrane Question 17-3, p 583 How would a change in [tubulin] affect MT dynamics?..if only GDP were present? … or a nonhydrolizable GTP analog? MT with EB1 cap

The Cell Cytoskeleton13 What is the structure and movement of an axoneme? Cilia & flagella “9 + 2 Structure” Living Cell video

Tick and Sick-114 Where are human cilia and flagella found? Various places Some genetic conditions cause cilia not to function Symptoms of IMS Respiratory infection; Fertility problems Etc… and ‘situs inversus‘’ (50%) Respiratory cilia

Tick and Sick-115 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-116 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

The Cell Cytoskeleton17 What is the distribution and structure of actin filaments? treadmilling

The Cell Cytoskeleton18 How are actin filaments organized in the cytoplasm? The cell cortex Actin binding proteins

The Cell Cytoskeleton19 How does actin mediate cell movements? Cell crawling What are Lamellipodia and Filopodia? Membrane ruffling Listeria movement Listeria movement

Tick and Sick Actin Filaments are involved in muscle contraction What happens when muscles contract? Nerve impulses activate contraction at neuromuscular junction

Tick and Sick 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 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 Sarcomeres create visual ‘striations ‘of “Striated muscles” (skeletal muscles)

Tick and Sick Muscle spasms and cramps (“Charley Horse”) Imbalance in excitatory and inhibitory signals -- self-reinforcing cycle occurs

The Cell Cytoskeleton25 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 How does the sliding filament model explain sarcomere contraction? myosin

The Cell Cytoskeleton26 How is muscle contraction triggered? Motor neuron & action potential Sarcoplasmic reticulum T-tubules Ca ++ release

The Cell Cytoskeleton27 How does Ca++ trigger the muscle contraction? The tropomyosin / troponin complex Sarcomere

The Cell Cytoskeleton28 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 PO 4 ) 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?