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Download Lecture 03 - Eukaryotic Cells
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Eukaryotic Cells Animals & Plants The Cell Building block of the all organisms, from single-celled to human. 200 Types of cells in the human body, categorized by cell shape. Cell size limited by the volume and surface area ratio. If the cell is too big, it cannot support itself or absorb nutrients/excrete wastes effeciently. Classes of Cell Shapes Squamous: Thin & flat cells covering surfaces or lining “tubes” Cuboidal: Square or cube shaped; approximately as wide as they are tall. Example: Lining of the intestines Spheroid: Egg cells and fat cells; round or oval. Fusiform: Thick in the middle and tapered towards the ends. Example: Liver cells Columnar: Much taller than they are wide. Example: Skin, lining of the esophagus Example: Smooth muscle cells Stellate: Star-shaped cells. Example: Some nerve cells Cell Theory Based on Robert Hook, Theordore Schwann, & Louis Pasteur Modern Cell Theories’ Generalizations: All organisms are composed of cells and cell products. The cell is the simplest structural and functional unit of life. All functions and structures are ultimately due to the activities of cells. Cells come only from pre-existing cells. The cells of all species have many fundamental similarities. General Cell Structure Eukaryotic cells all have the following general structures: Cell Membrane Cytoplasm Nucleus Intracellular Organelles Cell Membrane All cells are surrounded by a plasma membrane made up of proteins and lipids Bilayer of lipids with diverse proteins embedded in it 98% of membrane molecules are lipids 75% of these are phospholipids Cell Membrane Phospholipid Bilayer: Two phospholipid layers thick Hydrophilic heads facing the water on each side of the cell membrane. Hydrophobic tails directed toward the center of the membrane (avoiding the water) Membrane is dynamic and “fluid” Cell Membrane Cell Membrane is the target site of many pharmaceutical agents Proteins only make up 2% of the molecules in a plasma membrane, but are larger then lipids and make up around 50% of the membrane weight. Cell Membranes Integral or Transmembrane Proteins: Pass across the plasma membrane and are responsible for many functions. Integral proteins function as… Receptors: Specific for one messenger Second-messenger Systems: Triggered by messengers that bind with surface receptors Enzymes: Produce second messengers and help with digestion in the small intestine Channel Proteins: These molecules have “pores” & allow passage of water & other solutes through the membrane Carriers: Also called “PUMPS” they actively transport molecules into the cell utilizing ATP in the process Glycocalyx The “fuzzy” coat external to the plasma membrane on all animal cells, including humans Acts as an “identification” tag that enables the body to distinguish its own healthy cells from transplanted tissue, invading organism, and diseased cells. Surface Extensions Surface extensions aid in absorption, movement, and sensory processes. Microvilli: Extensions of the plasma membrane; serve primarily to increase a cell’s surface area; best developed in cells that specialized in absorption (e.g. the cells lining the small intestine) Surface Extensions Cilia: Multiple hairlike processes that project from the surface of the cell Nonmotile Primary Cilium: Nearly every human cell has a single nonmotile primary cilium. Motile Cilia: Less widespread but occur widely in respiratory tract and fallopian tubes; “wave” to help move materials through internal tubes Surface Extensions Flagella: A single whip-like structure much longer than cilia. The only functional flagellum in humans is the tail of the sperm cell. Cytoplasm Cytoplasm: The fluid that is contained inside the plasma membrane. Crowded with fibers, tubules, passageways, and compartments. Contains cytoskeleton (supportive framework) and intracellular organelles embedded in the cytosol or Intracellular fluid (ICF). Extracellular Fluid Extracellular fluid (ECF) is the fluid outside the cell. Nucleus Nucleus: The structure at the center of the cell containing the genetic information for the organism. Nucleus Nucleic Acid: DNA or RNA. DNA is the principle type of nucleic acid contained in the cell nucleus. DNA contains the genetic code for organisms and is involved in protein synthesis, cell division (mitosis), and reproduction of the organism. Plasma Membrane Plasma Membrane: Acts as a barrier and gateway between the cytoplasm and the extracellular fluid. Selectively SemiPermeable: The plasma membrane lets some things through and blocks other things; this is tremendously important in clinical practice! Plasma Membrane Methods of Transporting Substances: Passive and Active transport. Passive Transport includes… Filtration Diffusion Osmosis Active Transport requires ATP and includes… Active transport Vesicular transport Filtration Filtration: The process by which particles are driven through a filter, or selectively permeable membrane, via hydrostatic pressure exerted on a membrane by water. Example: Coffee Filter Weight of water forces water through the grounds and coffee filter. Filter holds back the larger particles (coffee grounds) Most important filtration in the human body occurs in the capillary wall – transfer of water, salts, nutrients, etc. from blood stream to tissue and extracellular fluid & wastes to kidneys Simple Diffusion Simple Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration. The result of constant, spontaneous movement of molecules known as Brownian Movement. Concentration Gradient: When the concentration of a substance differs from one point to another. Movement occurring down or with the concentration gradient is movement from the higher concentration area to the lower. Simple Diffusion IF the membrane is semi-permeable and permeable to that substance, than diffusion will occur. IF the membrane is not permeable to the substance, it will not diffuse across the membrane. Diffusion Rates Diffusion Rates: Important to cell survival because they determine how quickly a cell can acquire nutrients or rid itself of wastes. Factors affecting diffusion rate: Temperature: The higher the temp, the faster the diffusion rate. Molecular Weight: Heavy molecules diffuse more slowly. Membrane Surface Area: The more surface area the faster the diffusion rate. “Steepness” Of Concentration Gradient: The greater the concentration difference, the faster the diffusion. Membrane Permeability: The permeability of the membrane. Diffusion Distance: Distance diffusion occurs across. Facilitated Diffusion: Whether a solute binds to a specific transporter (changes the shape and releases the solute on the other side of the membrane). Osmosis Osmosis: The diffusion of water through a selectively permeable membrane from the area of higher concentration to the area of lower concentration. The higher solvent (water) concentration area has a low solute concentration. The higher solute concentration has a low solvent concentration. Tonicity Tonicity: The ability of a solution to affect the fluid volume and the pressure in a cell. If a solute cannot pass through a plasma membrane, but remains more concentrated on one side of the membrane than on the other, it triggers osmosis. Tonicity Hypotonic Solution: Area surrounding a cell has a lower concentration of nonpermeating solutes than the intracellular fluid. Hypertonic Solution: Area surrounding cell has a higher concentration of nonpermeating solutes than the intracellular fluid. Cells absorb water, swell, and lyse (burst). Cells will lose water and crenate (shrivel). Isotonic Solution: The area surrounding the cell has the same total concentration of nonpermeating solutes as the intracellular fluid. Cells will neither loose nor gain water molecules & do not change size or shape. Active Transport Active Transport: The carrier-mediated transport of a solute through a plasma membrane but against a concentration gradient. Utilizes ATP and energy to move against the normal concentration gradient from an area of low concentration to high concentration. Example: The sodium-potassium pump. Sodium-Potassium Pump Used to regulate the balance of sodium and potassium within the cell. 1 ATP molecule exchanges 3 sodium atoms (Na+) for 2 potassium (K+) atoms. Keeps the potassium higher and sodium lower within the cell. Plasma membrane continuously leaks Na+ and K+, so the pump keeps the balance corrected. Na+ and K+ play a critical part in nerve impulses and cardiac function. Vesicular Transport Vesicular transport moves large particles and droplets of fluid or numerous molecules through the plasma membrane all at once. Endocytosis: Vesicular processes that bring matter into the cell. Two types: Phagocytosis: “Cell eating” where foreign particles are engulfed (e.g. monocytes) Pinocytosis: “Cell drinking” where droplets of extracellular fluid containing molecules used by cells are taken in. Exocytosis: Vesicular processes that release matter from the cell. Organelles Organelles: The internal structures within a cell that carry out specific functions. Some are surrounded by one or two layers of a unit membrane and are therefore referred to as “membranous organelles.” Membranous Organelles: Nucleus, mitochondria, lysosomes, endoplasmic reticulum, golgi complex. Non-Membranous Organelles: Ribosomes, centrosome, centrioles, basal bodies. Membranous Organelles: Nucleus Nucleus: The largest organelle, spheroid in shape. Most cells have a single nucleus Nucleus surrounded by nuclear envelope or membrane Nucleoplasm: The material contained within the nucleus. Includes… Chromatin (DNA and protein) Nucleoli (produces ribosomes) Membranous Organelles: Endoplasmic Reticulum (ER) Endoplasmic Reticulum: “Little network within the cytoplasm” A system of interconnected channels that extend through the cytoplasm and reach the nuclear membrane. Channels called Cisternae Membranous Organelles: Endoplasmic Reticulum (ER) Two Types: Rough Endoplasmic Reticulum: Channels are covered with ribosomes (synthesize proteins). Smooth Endoplasmic Reticulum: Extends from the Rough ER to form membranous tubules network. Smooth ER synthesizes steroids & lipids Rough ER is responsible for detoxifying alcohol and other drugs Rough ER most abundant in cells that produce large amounts of proteins – such as those in the digestive glands Membranous Organelles: Golgi Complex Golgi Complex: The small system of cisternae which synthesize carbohydrates and put the finishing touches on protein and glycoprotein synthesis. Membranous Organelles: Golgi Complex Primary function is to package protein into membrane-bound golgi vesicles Some become secretory vesicles and store cell products such as breast milk & digestive enzymes Some of these can become lysosomes Membranous Organelles: Lysosomes Lysosomes: A package of enzymes which are bounded by a single unit membrane – usually produced by the Golgi complex Primary function is to hydrolyze or digest proteins, nucleic acids, complex carbohydrates, and phospholipids Autophagy: The digestion of surplus cells by their own lysosomal enzymes (as in the liver). Membranous Organelles: Peroxisomes Peroxisomes: Resemble lysosomes but are smaller and contain different enzymes (oxidase) and are not produced by the Golgi Complex\ Membranous Organelles: Mitochondria Mitochondria: Organelles specialized for synthesizing ATP Power-house of cells Bean shaped Outer and inner membranes Generate most of the cell’s ATP Cristae contain enzymes for aerobic respiration Matrix enclosed in the inner membrane; site of oxidation of organic molecules; contains DNA and ribosomes. Non-Membranous Organelles: Ribosomes Ribosomes: Small granules of protein and ribosomal RNA found in several places in the cytoplasm: On Rough ER In the Nuclear Envelope Floating freely in cytoplasm Primary function is protein synthesis. Non-Membranous Organelles: Ribosomes Responsible for assembling amino acids based on messenger RNA codes. Non-Membranous Organelles: Centrioles Centrioles: A short cylindrical assembly of microtubules. 2 centrioles lie at right angles to each other within a small clear area of cytoplasm called the centrosome Play a role in cell division – Mitosis Cytoskeleton Cytoskeleton: A collection of protein filaments and cylinders that determine the shape of a cell. Lend structural support Organize cellular contents Help move stuff through the cell Contribute to movements of the cell Connected to integral proteins of the plasma membrane Made up of microfilaments and microtubules Inclusions Inclusions: 2 Kinds Stored cellular products such as glycogen granules or fat droplets OR foreign bodies such as dust particles NO unit membrane Not essential to cell survival Not organelles Temporary structures; not permanent Mitosis Mitosis: The process by which cells divide to grow or to repair damage. 4 Stages: Prophase Metaphase Anaphase Telophase Mitosis Prophase: Condensing of chromatin fibers into chromatid pairs Mitosis Metaphase: The chromatid pairs line up along the metaphase plate Mitosis Anaphase: The centromeres joining the chromatids split, identical sets move to opposite sides of the cell Mitosis Telophase: Nucleoli reappear around two new sets of chromosomes and cell begins to split for cytokinesis – the division of the cell material.
