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Transcript
CELLS Cells • basic structural & functional units of all living organisms Cell Theory • cell is basic structural & functional unit of all living organisms • activity of organisms depends on individual & collective activities of cells • biochemical activities dictated by subcellular structures of cells • continuity of life has cellular basis – cells are produced by divisions of preexisting cells Major Classes • Prokaryotic – no nucleus – DNA in nucleoid region – bacteria • Eukaryotic – true nucleus – contains DNA – all other cells – plant & animal Prokaryotes • surrounded by plasma membrane • outside membrane in most is cell wall • rigid • protects cells • helps maintain shape • capsule surrounds cell wall for further protection • may contain surface projections-pili – help adhere to surfaces • some have very long projections-flagella – help move Eukaryotic Cells • plant or animal • separated from external environment by phospholipid or plasma membrane • cytoplasm – stuff between nucleus & plasma membrane • consists of 2 parts • cytosol – liquid part • organelles – intracellular structures Plant & Animal Cells • same organelles • plant cells have several organelles are not found in animal cells • chloroplasts – covert light energy into chemical energy • central vacuoles – store water & chemicals Plasma Membrane • creates specific compartments- functional units-organelles • regulates exchanges with environment • controls what goes in & goes out • selectively permeability – some substances can cross easily while others have difficult time crossing or cannot cross • crucial to metabolic functioning • allows things to happen in one area without influencing another area Cell Membrane • • • • • • plasma membrane lipid bilayer thin phospholipids proteins carbohydrates Plasma Membrane • Phospholipids-composed of 2 fatty acids & PO4 group • produces molecule with globular, polar head – water loving-hydrophillic • and hydrocarbon tail • straight, non-polar – hydrophobic- water hating • head is attracted to water • tail is repealed • causes phospholipids to form a two-layer sheetphospholipid bilayer with hydrophobic tails facing each other & hydrophilic polar heads pointing outward • interior of bilayer is hydrophobic Membrane Structure & Function • structure accounts for membrane’s selective permeability • nonpolar, hydrophobic molecules are soluble in lipids & pass through membrane • polar molecules & those not soluble in lipids have more difficult time passing Proteins in Plasma Membrane • • • • • plasma membrane described as fluid mosaic – not static – phospholipids move in membrane – punctuated along its length with proteins proteins determine which hydrophilic molecules may pass through Integral proteins – form part of membrane structure – bound to it Transmembrane proteins – traverse bilayer – some form hydrophilic channels through which ions & molecules can enter or leave Peripheral proteins – loosely associated with membrane – bind to inner or outer membrane surface – cell recognition • recognize other cells as abnormal or normal • called receptors Nucleus & Nucleolus • • Nucleus – most obvious organelle in eukaryotic cells • all eukaryote cells have nucleus – typically spherical – found in center surrounded by nuclear envelope – double membrane with large number of pores • allows for passage of materials between nucleus & cytoplasm • • contains genetic information-DNA contains nucleolus – makes subunits that comprise ribosomes Ribosomes • made by nucleous • travel from nucleus to cytoplasm via nuclear pores • synthesize proteins • most attached to surface of endoplasmic reticulum (ER)-rough ER • some can be found floating free in cytoplasm Endoplasmic Reticulum • • • • • • • • • series of interconnected flattened tubular tunnels continuous with outer membrane of nucleus all eukaryotic cells contain ER responsible for communication within cell part of endomembrane system all membranous organelles belong to system Rough – attached ribosomes – making it appear spotty – takes in proteins made on ribosomes so cannot escape into cytoplasm Smooth – no attached ribosomeslooks smooth – not involved in protein synthesis – = steroid production contains enzymes required to detoxify wide variety of organic molecules storage site for calcium • • • • • • • Golgi Bodies stacks of flattened, membranous sacs associated with ER Store & modify products made by ER one side receives materials once material is received it is chemically modified once modified it is transported to sending side of Golgi from where finished secretory products are packaged into transport vesicles move to plasma membrane for export Lysosomes • bags of digestive enzymes surrounded by membranes – keeps enzymes out of cell’s cytoplasm so cell does not digest itself • breaks down macromolecules & other structures – digestive function • fuse with food vacuoles & digest food • destroy bacteria • recycle damaged organelles Vacuoles • • • • • membranous sacs larger than vesicles part of endomembrane system variety of function fresh water protests possess contractile vacuoles • plant cells have central vacuoles – contribute to plant growth by absorbing water & causing cells to expand • other plant vacuoles – store organic nutrients – contain pigments that attract insects – have poisons to protect them from plant eaters Energy Conversion Organelles • Chloroplast –plant cells • Mitochondria –animal & plant cells Mitochondria • power stations • large, usually sausage shaped • sites of cellular respiration • burn food molecules, in presence of O2, to release energy – aerobic respiration • harvest energy from sugar & convert it to ATP – chemical currency all cells • found in almost all cells of body • number depends on cell’s energy requirements Chloroplasts • site of photosynthesis in plants • light energy from sun converted into chemical energy of sugar & organic molecules • contains green pigment, chlorophyll Cilia & Flagella • Cilia – shorter & more numerous than flagella – move fluids across surfaces by producing sweeping movements • Flagella – longer – usually only one per cell – propel cells via undulating whip like movement • common in structure & movement mechanism • consist of core of microtubules wrapped in plasma membrane • Cilia and flagella • • • • • • Cytoskeleton internal framework made of protein filaments like bones & muscles of cells 3 types of fibers Microfilaments – slender protein strands of actin – helps cells change shape or contract – important in amoeboid movement Intermediate fibers – fibrous proteins giving them ropelike structure – maintain cell shape & anchor organelles Microtubules – straight, hollow tubes made of globular proteins-tubulins – reinforce cell shape – also responsible for movement of cilia & flagella Fill in the Parts of the Typical Cell Cell Surfaces • cells must communicate with each other • cell junctions • connect cells • allow communication Plant Cell Connections • cell walls are multilayered • between walls is a sticky polysaccharide – glues cells together • cell walls are thick but not completely isolated from cells next to them • channels or plasmodesmata connect adjacent cells – form communication system between cells • connects cytoplasm of one cell with its neighbor • water & small molecules are able to pass through these channels Animal Cell Connections • adjacent cells are connected with junctions • Tight junctions – binds cells closely together • Anchoring junctions • Adherens • Desmosome – attach cells with fibers forming sheets of cells • Gap junctions – form channels – allow water & small molecules to pass Cell Transport • lipid bilayers are not permeable to ions such as K+, Na+, Ca2+,Cl- & HCO3• channels are needed for passage • two basic ways materials are moved in & out • Passive transport mechanisms – require no energy • Active transport mechanisms – need energy – usually in form of ATP Transport Types • Diffusion – from higher to lower concentrations – gradient is formed – no energy required • Facilitated Diffusion – diffusion using transport protein – no energy required • Active Transport – requires energy (ATP) • Osmosis – only water – diffusion of water across semi-permeable membrane Diffusion • • • • • • • • • passive transport molecules are in constant movement due to thermal energy of heat move from areas of higher to areas of lower concentration move randomly can be made to move directionally membrane between solution with dye on one side and no dye on other dye molecules move to side where less concentrated each molecule moves randomlynet migration is to side with no dye dye will continue to diffuse until both sides have same concentration – point of dynamic equilibrium • • molecules will still move back & forth at same rate there will be no change in concentration of dye on either side of membrane • • • • • • • • Rate of Diffusion Distance – shorter distancesfaster diffusion – takes less time to eliminate concentration gradient Size of concentration gradient – larger concentration gradients proceed faster than smaller ones Molecule size – smaller molecules diffuse faster than larger ones Temperatures – higher ones tend to diffuse substances faster Electrical forces – opposite charges attract; similar ones are opposed interior of cell membrane is negative; negative charges inside cell pulls positively charged materials into cell negatively charges ones are repelled Diffusion through a Membrane Facilitated Diffusion • diffusion across cell membranes is selectively permeable • impermeable to some substances • others need a transport protein • facilitated diffusion Osmosis • diffusion of water through a selectively permeable membrane • only refers to water movement • Semi permeable membrane • total concentration of dissolved ions & molecules on either side of membrane remains same since membrane is not permeable to them • membrane is freely permeable to water • whenever there is a solute concentration gradient concentration gradient exists for water as well • water passes by diffusion from regions of lower to regions of higher solute concentration • water diffuses toward solution with higher solute concentration or down concentration gradient for water Isotonic Solutions • solutions of equal solute concentrations • do not produce osmotic flow • movement of water in = movement of water out • volume on both sides of membrane is unchanged Hypotonic Solution • solutions with lower concentrations of solute • water will enter by osmosis • cell swells • if continues cell may rupture Hypertonic Solution • concentration of solutes is greater outside cell than inside • cell shrinks Water BalanceOsmoregulation • to survive cells must have way to balance excessive water uptake or loss • plant & bacterial cells avoid bursting in hypotonic surroundings by strong cell walls • allows turgor to build • turgor pressure = osmotic pressureosmosis stops • fresh water fish-hypotonic environments use kidneys & gills to prevent water buildup • paramecium have contractile vacuoles to bail out excess water that continually enters from hypotonic pond water Active Transport • used to move molecules & ions against concentration gradients • requires energy usually-ATP • high energy bonds in ATP are broken to provide energy • concentration gradient-not required • cell can import or export regardless of intra- & extracellular concentrations • allows cells to maintain internal concentration that is different from environmental concentrations Bulk Movement • movement of larger molecules & large volumes of fluid • endocytosis • exocytosis • • • • • • • • Endocytosis cell ingestion requires energy part of plasma membrane folds inward forming a pouch pouch is pinched off from membrane so that incoming materials are enclosed in a vesicle endosome Pinocytosis – cell drinking – ingestion of fluids or small particles – occurs in almost all cells on a continuous basis – not selective Phagocytosis – cell eating – particles are engulfed & packaged into food vacuoles – occurs only in specialized cells such as neutrophils & macrophages Receptor-mediated endocytosis – cell selects what to ingest – cholesterol is taken up by this method Exocytosis • reverse of endocytosis • secretion or removal of things from a cell • membrane-bound vesicles move to cell surface • fuse with plasma membrane • release contents into extracellular fluid
