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Transcript
Cell Structure and Function What color are cells in the body? • clear Functions of the Cell • • • • • • Basic unit of life Protection and support Movement Communication Cell metabolism and energy release Inheritance Cell Characteristics • Plasma (cell) Membrane – Outer cell boundary • Cytoplasm – Composed of cytoplasmic organelles • ER, ribosomes, centrioles, mitochondria, Golgi complex, lysosomes and vacuoles • Organelles – Specialized structures that perform specific functions Plasma Membrane • Intracellular versus extracellular • Selectively permeable • Fluid-mosaic model: regulate the passage of nutrients and waste • Composed of proteins and lipids Nucleus • DNA dispersed throughout; controls and integrates the function of the entire cell • Consists of : – Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out – Chromatin: Condenses to form chromosomes during cell division – Nucleolus: Assembly site of large and small ribosomal units where rRNA is manufactured Cytoplasm • Cellular material outside nucleus but inside plasma membrane • Cytosol: Fluid portion • Cytoskeleton: Supports the cell – Microtubules – Microfilaments – Intermediate filaments • Cytoplasmic inclusions Organelles • Small specialized structures for particular functions • Most have membranes that separates the interior of organelles from cytoplasm • Related to specific structure and function of the cell Ribosomes • Sites of protein synthesis • Composed of a large and small subunit • Types – Free – Attached to endoplasmic reticulum • Found in both eukaryotes and prokaryotes Endoplasmic Reticulum • Extension of outer nuclear membrane • Types – Rough • Attached ribosomes • Proteins produced and modified for secretion and for internal use – Smooth • No attached ribosomes • Manufacture lipids • Cisternae: Interior spaces isolated from rest of cytoplasm • Transports nutrients to the nucleus and provides some cell structure Golgi Apparatus • Modification, packaging, distribution of proteins and lipids for secretion or internal use produced by ER • Flattened membrane sacs stacked on each other Function of Golgi Apparatus Mitochondria • Provide energy for cell • Major site of ATP synthesis • Membranes – Crista: Infoldings of inner membrane – Matrix: Substance located in space formed by inner membrane Centrioles • In specialized zone near nucleus: Centrosome • Each unit consists of microtubules • Before cell division, centrioles divide, move to ends of cell and become spindle fibers in eukaryotic cells Cilia • Appendages projecting from cell surfaces • Capable of movement • Moves materials over the cell surface Flagella • Similar to cilia but longer • Usually only one exists per cell • Move the cell itself in wavelike fashion • Example: Sperm cell Microvilli • Extension of plasma membrane • Increase the cell surface • Normally many on each cell • One tenth to one twentieth size of cilia • Do not move Prokaryotes • Simple cells which lack a membrane bound nucleus • Initial or primitive cell type found on earth • Less complex than eukaryotes – Have no organelles (microtubules or centrioles) – Examples include bacteria • Division is by binary fission Eukaryotes • Evolved from prokaryotes; they have a true nucleus • Structurally and biochemically more complex – Examples include protozoa, fungi, algae, plant and animal cells • Golgi apparatus is the structure in eukaryotic cells which secretes substances Viruses • Acellular: neither prokaryotic or eukaryotic • Contain nucleic acid and either RNA or DNA but not both • Depend on the energy of the host cell • Has protective coat which makes them hard to control; antibiotics have no effect • Bacteriophage: virus which invades bacteria • Examples of viral diseases: measles, chickenpox, mumps, mono, hepatitis, AIDs Overview of Cell Metabolism Movement through the Plasma Membrane • Four different modes – Directly through the plasma membrane • Small, uncharged, hydrophobic molecules • Osmosis – Membrane channels • Rapid movement of water, charged small molecules – Carrier molecules • Large polar molecules that are not lipid soluble • Glucose – Vesicles • Large non-lipid soluble molecules, small pieces of matter, whole cells • Small sac surrounded by membrane Movement through the Plasma Membrane • • • • Diffusion Osmosis Filtration Mediated transport mechanisms – Facilitated diffusion – Active transport – Secondary active transport Diffusion • Movement of solutes from an area of higher concentration to lower concentration in solution • Only applies to small, hydrophobic, uncharged molecules • Factors that influence rate of diffusion – – – – Temperature of solution Distance Size of diffusing molecules Concentration or density gradient • Difference between two points – Viscosity • How easily a liquid flows Osmosis • Diffusion of water (solvent) across a selectively permeable membrane (water most abundant compound in cell) • Important because large volume changes caused by water movement disrupt normal cell function • Cell shrinkage or swelling – Isotonic: equal concentration on both sides • cell neither shrinks nor swells – Hypertonic: Less water/more solute than other side • cell shrinks (crenation) – Hypotonic: More water/less solute than other side • cell swells (lysis) Osmosis • Osmotic pressure – force required to prevent the movement of water a solution by osmosis across a selectively permeable membrane • The greater the concentration of the solution (the more hypertonic the solution) the greater the osmotic pressure • The greater the osmotic pressure the greater the tendency for water to move into the solution Osmosis Filtration • Works like a sieve • Depends on pressure difference on either side of partition • Moves from side of greater pressure to lower – Example: In kidneys in urine formation Osmosis