Intercellularity and unicellular motility o What moves in a cell Subcellular components vesicles chromosomes Cells bacteria gametes Body part limbs head tongue heart Whole organism walk run swim fly o Motility depends on applied force Force is applied against a stationary object Long fibers inside cell cytoskeleton Hard structure endo or exoskeleton External media soil water air o Subcellular motion Located in cytoplasm Need two components for motility in the eukaryotic cell 1 Structural protein o Three filaments Microfilaments 2 strands actin help with cell shape muscle contraction cell motility work with myosin motility protein cell division cleavage furrow Works with myosin motor protein Grows at end by adding more subunits Microtubules tubulin makes hallow tube maintenance of cell shape cell motility cytokinesis pulls chromosomes apart into two daughter cells Many proteins neurotransmitters are made in cell body and send down axons via microtubules like a highway Grows at end and removes subunits from end Regulated by Ca2 and GTP GDP ratios Intermediate filaments keratin 2 Motor proteins move along cytoskeleton structural proteins o Head stalk and tail regions o Both need ATP to change motor protein hinge head region o Kinesin phosphorylated intermediate vesicles of material around the cell uses ATP walks down microtubule and moves organelles and ADP helps kinesin bind to microtubule ADP is release and ATP binds which causes the neck linker to cock forward ATP then hydrolyzes to ADP enabling the back foot to come unbound front foot then binds ATP and cocks its neck linker forward pulling the rear foot forward to it is located ready for the next stroke kinesin moves to plus end of microtubule o Dynein works with microtubule moves organelles the other o Myosin moves along microfilaments to contract muscles way towards end uses ATP Present in most of animal kingdom and some plants Types of movement from actin myosin Animal movement Amoebas and slime mold Plant cytoplasmic streaming Cell division Types of interactions o Motor is stationary and structure moves o Structure is stationary and motor moves o Unicellular motility Prokaryotes use flagella and cilia to generate motion Push against force of surrounding fluids Built with microtubules Types of movement apply force to medium outside of cell membrane Swimming prokaryotic flagella Corkscrewing endoflagella in spirochetes Gliding non swimming movement across solid surface Prokaryotic flagella swimming movement Long whip like appendages attached to one end of cell Made of many different proteins Attached to rotary motor driven by protons in membrane spins flagella Irreducibly complex complex ancestral trait or could have arisen independently as derived trait Can help cells move in certain directions towards or away from stimulus chemotaxis aerotaxis phototaxis magnetotaxis o Taxis directed movement in response to chemical and physical gradients signals Chemtaxis Phototaxis chemicals light Algae have light sensitive channels rhodopsin that when stimulated by light opens ion channels depolarizes flagellum moves cell moves Optogenetics put light sensitive neurons in organisms DNA stimulate neuron with light causes neuron to depolarize can open close channels and control neurons to control behaviors oxygen concentration Aerotaxis Magnetotaxis magnetic field Material Properties o Bodies are made of complex materials exoskeletons endoskeletons hhydrostatic skeletons o Types of mechanical forces Aligned forces act along single axis Compression Tension pushes molecules closer together pulls molecules further apart load failure Nonaligned forces act along different axes parallel forces but displaced twisting tangential forces that pull molecules apart load Shear Torsion failure o Materials respond to applied force Stress force area Force is applied across the entire cross sectional area Can change length Response to force is measured as strain causes material to shrink change length Tensile force causes materials to stretch Compressive force causes materials to shrink Strain L L o Strain depends on applied stress If area is constant more force more stress more strain o Some materials act like elastic springs Stress is linearly proportional to strain Stress is on y axis and strain is on x axis applying stress and thinking about resulting strain Rubber band or elastin shallow slope small E Wood block or collagen steep slope large E Slope stiffness Intrinsic property stress material of an object will determine how it responds to If apply same stress to two objects of same material both sizes have same strain E stiffness slope of stress strain curve Stress E x strain o Strain is larger on smaller objects o If E is small strain is larger stretchy objects o If E is large strain is smaller stiffer objects If apply same force to two objects of same material smaller object is going to have larger strain and stress Stress force area o Objects do not always act elastic Can be elastic for small forces but then become plastic Elastic strength and elastic extensibility change Tensile strength stress at which material fails max elastic strength levels off Extensibility maximum strain at which material fails eventually will break o Biological materials Designed to withstand certain kinds of forces Composites Ex skin multiple complex components fibers woven together Collagen provides tensile strength o 3 strands of protein woven together o Ideal for resisting pulling not pushing o Bent originally uncoiled in elastic region fibers start to break plastic in plastic region Ex chitin in invertebrates Long strands of N acetylglucosamine o Derivative of glucose similar to cellulose o Wound healing Ex cellulose in plants Ex endoskeletons Cartilage o Cells inside produce surrounding extracellular matrix Collagen fibers Elastin fibers Proteoglycans Bone o Present in mammalian embryos remains in nose and ribs o Strength and flexibility replaces cartilage o Hard extracellular matrix not flexible o Extracellular matrix consists of collagen fibers and mineral deposits Calcium phosphate Calcium carbonate Hydroxyapatite o Osteoblasts deposit matrix osteoclasts reabsorb it o Properties change with age Young high density Old low density fails at lower stresses Ex spider silk Has high tensile strength and extensibility Levers and Terrestrial Motion o Movement is sign of convergent evolution o Muscles pull on bones at joint make one part move relative to another o Lever
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