* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 16 Outline
Survey
Document related concepts
Cell encapsulation wikipedia , lookup
Cell membrane wikipedia , lookup
Biochemical switches in the cell cycle wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cell culture wikipedia , lookup
Cell growth wikipedia , lookup
Spindle checkpoint wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Kinetochore wikipedia , lookup
Protein moonlighting wikipedia , lookup
Extracellular matrix wikipedia , lookup
Signal transduction wikipedia , lookup
Cell nucleus wikipedia , lookup
Endomembrane system wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
List of types of proteins wikipedia , lookup
Transcript
Lecture 16 Outline The Cytoskeleton Composed of a Network of Protein Fibers Extending throughout the Cytoplasm. Three Major Roles: 1. Provides Mechanical Strength 2. Controls Cell Shape 3. Drives and Guides Movement. Three Major Components: 1. Actin 2) Microtubules 3) Intermediate Actin (Microfilaments) Two intertwined strands of actin, each a polymer of actin subunits. Linear Form: Twisted double chain of actin. Form higher ordered structure including Structural Networks or Bundles: Form as result of Accessory proteins. Major Functions in Maintenance of Cell Shape (tension bearing elements)changes in Cell Shape, Muscle Contraction, Cell Motility (Pseudopodia), Cell Division (Cleavage Furrow Formation) Actin Filaments have polarity, bind ATP, hydrolysis reduces affinity of monomers for each other- reducing polymer stability ( much like MT) Accessory proteins play key role in Actin filament formation and whether networks or bundles, etc. Drugs can influence assembly/disassembly of actin. Microtubules (MTs) Structure: Hollow Tubes (Rods) consist of 13 Protofilaments composed of Tubulin. Protofilaments are long linear strings of subunits joined end to end. Rod has 25 nm Diameter Cross Section. The Protein Subunits are composed of globular protein, Tubulin. Exist as an alpha-tubulin and beta tubulin heterodimer. Main functions include Internal Scaffolding for Support - Resist Compressive and Bending Forces Movement of Organelles- including vesicular transport from Golgi to Plasma Membrane, are the Motile Elements of Cilia and Flagella and are critical for mitosis, dissemble and reassemble into mitotic spindle. Roles in Maintaining of Internal Cell Organization and Cell Shape. Formation of Tubulin Filaments- Depends on tubulin dimer concentration High concentrations lead to growth or assemble, while Low concentrations lead to disassembly or depolymerization. Above Critical concentration (concentration of free tubulin dimers) assembly will occur, below- disassembly occurs Microtubules exhibit dynamic instability- a result of capacity to bind and hydrolyze GTP. GTP cap present on + end, that is tubulin-GTP bound form, provided addition continues always some at end. Not enough GTP tubulin available, GTP is being hydrolyzed and if assembly slows, now loses GTP cap- rapid shortening of MT. Drugs and MAPS (Microtubule Associated Proteins) can influence rate of assembly/ disassembly. Microtubules nucleate at MTOCs – centrosome is main one of animal cells. Gamma tubulin present in rings- sites for MT assembly. Serves several functions including anchoring minus end, orienting filament, regulating number of filaments, etc. Centrioles are also present in Centrosome. They are composed of MT cylinders; organize centrosome, no role in nucleation Intermediate Filaments (IMFs) : Limited to vertebrates and some other organisms lacking skeleton. Monomers of Elongated and fibrous proteins form coiled coil dimers that then assemble with another dimer in antiparallel and staggered fashion. Eight tetramers come together to form thick rope like cables with diameter of 8-12 nm (intermediate in size relative to actin and microtubules- hence the name). Unlike, MTs and MFs, IMFs lack structural polarity and do not function with motor proteins (except as cargo), do not require nucleotides for assembly. While dynamic, primarily more stable structures than MTs and MFs. IMFs include nuclear lamins that function to form nuclear lamina that strengthen and supports nuclear envelope and provide attachment sites for chromosomes and nuclear pores. Other IFs include Keratin, Vimentin and Neurofilaments. Cytoplasmic filaments like keratin function to anchor nucleus and other organelles. Function in maintenance of cell shape and prevention damage by stress. Keratin of Adjacent epithelial cells attach to large plaques called Desmosomes, critical for cells to withstand stress. Mutation of keratins can lead to blistering of skin, due to loss of ability to withstand stress. Next time more detail regarding associated proteins and regulation of various kinds of cell motility.