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Transcript
Cell - Basic unit of all living things Plasma membrane – Outer boundary of the cell Nucleus – Located centrally Directs cell activities Cytoplasm – Located between plasma membrane & nucleus Contains cytosol and organelles • Outermost component of cell • Boundary that separates substances Intracellular (inside the cell) vs. extracellular (outside the cell) materials • Selective permeable • Allows some substances to cross it more easily than others • Consists of lipids and proteins • Consists of 45-50% lipids • 45-50% of protein • 4-8% of carbohydrates • • • • Predominate lipids are: Phospholipids and cholesterol Phospholipids: lipid bilayer Polar heads facing water in the interior and exterior of the cell (hydrophilic); nonpolar tails facing each other on the interior of the membrane (hydrophobic) • Cholesterol: Interspersed among phospholipids • Determines fluid nature of the membrane • Provides stability • Fluid-mosaic model: • Plasma membrane is neither rigid nor static • Highly flexible • Fluid nature of membrane provides – Distribution of molecules within the membrane – Phospholipids automatically reassembled if membrane is damaged Proteins are dispersed into the phospholipid bilayer of plasma membrane Integral or Intrinsic Proteins – Embedded in the membrane Peripheral or extrinsic Proteins – Attached to either the inner or outer surfaces of the lipid bilayer Membrane proteins function as: Markers, attachment sites, channels, receptors, enzymes, or carriers • Marker Molecules • Allow cells to identify one another or other molecules • Are mostly glycoproteins and glycolipids • eg. Ability of immune system to distinguish between self and foreign cells • Organ transplant • Attachment Proteins • Integral proteins function as attachment protein • Allow cell to attach to other cells • Or to extracellular molecule & intracellular molecules • Also function as cell communication Transport Proteins Are integral proteins, allow ions or molecules to move from one side of plasma membrane to other Transport proteins are: Channel proteins Carrier Proteins ATP-powered pumps Channel Proteins Hydrophilic region of integral protein faces inward Ions or small molecules of right size, charge and shape can pass through the channel Charge in hydrophilic part of channel proteins determine molecules can pass eg. Flow of H+ to inner mitochondrial membrane for ATP production Carrier Proteins (transporters) Are Integral proteins move ions from one side of membrane to the other – Have specific binding sites – Protein changes shape to transport ions or molecules – Resumes original shape after transport – eg. Transports sodium and potassium ions across a nerve cell membrane • ATP-Powered Pumps • Are transport proteins that move specific ions and molecules from one side of plasma membrane to the other • Requires ATP • Receptor Proteins • Are Proteins or glycoproteins in membranes with an exposed receptor site • Can attach to specific chemical signal molecules • Chemical signal can attach only to cells with that specific receptor • Binding acts as a signal that triggers a response Receptors Linked to Channel Proteins Attachment of specific chemical signals (e.g., acetylcholine) to receptors causes change in shape of channel protein Causes channel opens or closes Changes permeability of plasma membrane and some ions can pass through ion channels • Enzymes: • Some membrane proteins functions as enzymes • Catalyze reactions at outer/inner surface of plasma membrane • Eg. Surface cells of small intestine produce enzymes that breaks dipeptide into amino acids • • • • • Diffusion/Osmosis • water diffuses through the membrane • Lipid soluble substances go across Filtration • Moves particles with pressure difference Passive Transport (= facilitated diffusion) • No energy required • selectively allow certain types of molecules in and out through channel proteins Active Transport • Required energy = ATP Endocytosis and Exocytosis • Large mol. enters to cell by endocytosis • Large mol. leaves cell via exocytosis • Diffusion: – net movement of molecules down a concentration gradient towards areas of lower concentration – Allows oxygen, carbon dioxide, and lipids to cross • Concentration Gradient – Conc. Of ions/molecules on one side not same as other • Diffusion affected by different conditions – Temperature: • High temp increases rate of diffusion – Size: • Small molecules go down conc. gradient faster – Electronic gradient: • charges of molecules/ions affect diffusion rate • Dropping a dye in a cup of water – drop diffuses to the areas of the cup w/out the dye – goes down the concentration gradient – dye goes towards a uniform mixture in water – In osmosis, water molecules diffuse across a selectively permeable membrane • From an area of low solute concentration • To an area of high solute concentration • Until the solution is equally concentrated on both sides of the membrane • Osmotic concentration – concentration of all molecules dissolved in a solution • Hypertonic solution – solution with higher concentration of solutes • Hypotonic solution – Solution with lower conc. of solutes • Isotonic solutions – solutions with equal conc. of solute The survival of a cell depends on its ability to balance water uptake and loss – Isotonic: cell neither shrinks nor swells – Hypertonic: cell shrinks (crenation) – Hypotonic: cell swells (lysis) • Works like a sieve • Depends on pressure difference on either side of a partition • Moves from side of greater pressure to lower • Eg: urine formation in the kidneys Blood pressure moves water and small molecules from the blood through the filtration membrane while large molecules remain in the blood • Like diffusion, but uses carrier or channel protein • Selective Permeability – Cell controls what comes in and goes out • Certain channel or carrier proteins – allow only certain molecule types entry • Molecules/ions go with concentration gradient • No energy required – Active transport requires energy to move solutes against a concentration gradient • ATP supplies the energy • Transport proteins move solute molecules across the membrane • Eg. Glucose, amino acids • Macromolecules transported into or out of the cell through plasma membrane by vesicle formation – Endocytosis – Cells engulf substances and plasma membrane extends outward and surround food particle and pinches off and forms the vesicle • Phagocytosis – Vesicle contains large solid particles • Pinocytosis – Vesicle contains liquid or small particle • Receptor-Mediated – Plasma membrane contain specific receptor that allows certain substances to be transported by phagocytosis or pinocytosis • A vesicle may fuse with the membrane and expel its contents outside the cell • Examples – Secretion of digestive enzymes by pancreas – Secretion of mucous by salivary glands – Secretion of milk by mammary glands • Cytoplasm: Cellular material outside nucleus but inside plasma membrane • Composed of Cytosol, Cytoskeleton, Cytoplasmic Inclusions, Organelles • Cytosol: fluid portion • Dissolved molecules (ions in water) and colloid (proteins in water) • Is a network of fibers extending throughout the cytoplasm • Gives mechanical support to the cell • Maintain cell shape • Assists in cell movement • Consists of three types of protein fibers: • Microtubules • Actin or Microfilaments • Intermediate filaments Microtubules Found in cytoplasm Hollow rods – 25 nm in diameter, 0.25 m – 25 m in length made up of protein – tubulin Shape and support the cell Guide movement of organelles Responsible for separation of chromosomes during cell division Essential components of centrioles, spindle fibers, cilia and flagella Actin filaments or Microfilaments Solid rods – 7 nm in diameter Twisted double chain of actin – globular protein Mechanical support for microvilli in intestinal cells Enable cells to change shape and move Eg. Muscle cells, actin filaments are responsible for muscle`s contraction Intermediate filaments fibrous proteins supercoiled into thicker cable 10 nm in diameter larger than microfilaments but smaller than microtubules Support cell shape Provide mechanical strength to cells eg. Support the extensions of nerve cells • Are aggregates of chemicals either produced or taken in by cells • For eg. Lipid droplets store energy-rich molecules • hemoglobin in red blood cells transport oxygen • melanin – skin color pigment • Minerals, dye etc.- cytoplasm • Small specialized structures with particular functions • Most have membranes that separate interior of organelles from cytoplasm • Each organelle is responsible for performing specific function • Nucleus is the largest organelle of the cell • The nucleus is the cell's genetic control center • Contains the cell's DNA • Forms long fibers of chromatin that make up chromosomes • Human body cell has 46 chromosomes • Nucleus is large, membrane-bound structure • Consists of nucleoplasm and surrounded by double membrane nuclear envelope • Pores in the envelope control flow of materials in and out • Nucleus contains ball-like structure – nucleolus • Ribosomes are synthesized in the nucleolus • Chromosome Structure: • Consist of chromatin, a complex of DNA and histone proteins • Before cell division, chromosome duplication takes place • Each chromosome consists of two chromatids • Chromatids are joined together at the centromere •Chromosome Structure: • When the cell divides, the sister chromatids separate from each other • Cell divides into two daughter cells • Each with a complete and identical set of chromosomes – DNA Controls cellular activities by directing protein synthesis – Protein regulate most chemical reactions – DNA transfers its coded information to RNA • RNA carries the information from nucleus to cytoplasm to make proteins – Sites for protein synthesis – Assembled in nucleolus of nucleus – Then move through nuclear pores into the cytoplasm – Composed of a large and a small subunit – Consists of ribosomal RNA (rRNA) & protein – Some ribosomes are suspended in cytosol, other are attached to ER – The endoplasmic reticulum (ER) • Main manufacturing facilities within the cell • A continuous network of flattened sacs and tubes in the cytoplasm • Internal spaces of sacs and tubes - Cisternae • ER is composed of • Rough ER • Smooth ER – Rough endoplasmic reticulum (rough ER) is studded with ribosomes • Are place where proteins are produced and modified – Transported to other organelles – Smooth endoplasmic reticulum (smooth ER) lacks attached ribosomes – Has variety of functions • Synthesizes lipids, including fatty acids, phospholipids and steroids • Detoxify toxins and drugs in liver cells • Stores calcium ions that function in muscle contraction • The Golgi apparatus consists of stacks of flattened membranous sacs • Packaging and distribution center • Receives, modifies, packages and distributes proteins & lipids manufactured by ER • Ships modified products to other organelles or the cell surface via secretory vesicles – A lysosome is a membraneenclosed sac form from Golgi apparatus • It contains digestive enzymes • The enzymes break down macromolecules • Lysosomes have several types of digestive functions • They fuse with food vacuoles to digest the food • Destroy bacteria that have been ingested into white blood cells • Recycle damaged organelles • Abnormal lysosomes can cause fatal diseases – Lysosomal storage diseases • Result from an inherited lack of one or more digestive enzymes found in lysozymes • Seriously interfere with various cellular functions • eg. Pompe`s disease – lack of glycogen-digesting enzyme • Cause weakening of heart muscle • Tay-Sachs disease – lack of lipid –digesting enzyme • Accumulation of excess lipid damage brain • Peroxisomes – Smaller than lysosomes – Contains two sets of enzymes – One enzyme break down fatty acids and amino acids – Hydrogen peroxide is a byproduct of breakdown (toxic) – Another enzyme Catalase convert hydrogen peroxide into water and oxygen – More peroxisomes – kidney and liver for detoxification • Proteasomes – – – – – Tunnel-like structure not surrounded by membrane Consist of large protein complexes Found in nucleus and cytoplasm Include several enzymes that break down and recycle unneeded or damaged proteins in cell • Major site of ATP synthesis • Consists of two membranes • Outer membrane – smooth • Inner membrane – Cristae: Infoldings of inner membrane – Matrix: Enzymes located in space formed by inner membrane • Mitochondria increase in number when cell energy requirements increase. • Mitochondria contain DNA that codes for some of the proteins needed for mitochondria production. • Located in Centrosome: specialized zone near nucleus • Center of microtubule formation • Contains pair of centriole • Each with nine triplets of microtubule – ring • Before cell division – Centriole replicate • During cell division, centrioles divide, move to ends of cell and organize spindle fibers • Facilitate the movement of chromosomes during cell division • Appendages projecting from cell surfaces • Capable of movement • Cilia move in a coordinated back-and-forth motion • Occur in large no. on cell surface • Cylindrical in shape • 0.25 m in diameter, 10 m in length • Moves materials over the cell surface • eg. Respiratory tract – removes mucus • Similar to cilia but longer (45 m) • Usually only one per cell • Move the cell itself in wave-like fashion • Eg: sperm cell Direction of swimming 1 µm Motion of flagella – The structure and mechanism of cilia and flagella are similar • Ring of 9 microtubule doublets surrounds a central pair of microtubule – 9 + 2 arrangement – Extend into basal bodies – Using energy from ATP, movement of dynein arms ( motor proteins) produces microtubule bending • • • • • • • Extension of plasma membrane Normally many microvilli on each cell One tenth to one twentieth size of cilia Do not move, supported by actin filaments Increase the cell surface area Found in kidney, intestine Main function is absorption