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Unformatted text preview: KIN 216 Applied Human Anatomy
Chapter 2 Introduction to Cells Cells: basic unit of structure (smallest living unit) Cyto: comes from Greek kytos = hollow vessel Cytology: the study of cells; relatively new due to discovery of microscope Cytolysis: splitting of cells Cytotoxin: Greek toxicos = of or for a bow (basically refers to poison arrow) Myocyte: muscle cell 10100 m diameter (many different shapes, sizes, and functions) Largest cell = ovum 140 m can be seen w/naked eye Body has 50100 TRILLION cells 1665: Robert Hooke Historical Timeline 16321723: Antoni van Leeuwenhoek British, studied cork looked like it contained "little rooms" coined the term cell First person to view individual living cells with microscope Came up with cell theory: all living things are composed of cells and cell is basic unit Extended cell theory, stating that cells can only arise from other cells (but cell division wasn't understood for quite some time after that) Won Nobel prize in 1974 Determined in 1940s that mitochondria produce ATP for energy Also showed ribosomes are site of protein synthesis Used electron microscope to make discoveries about cells 183839: Theodore Schwann and Mathias Schleiden 1855: Rudolf Virchow 1953: George Palade Cellular Chemistry Atoms or elements: major ones in body (make up 96% of body's weight) Other major elements found in body are K, Na, Mg, Ca ***Most abundant COMPOUND in human body is water (H2O) ~60% of body weight Oxygen (O): most abundant by weight (only because it weighs a lot 16x bigger than H) 65% body weight found in gas, water, etc. (mol. Wt. = 16) Carbon (C): 18% of body weight (mol. Wt. = 12) Hydrogen (H): 10% of body weight (mol. Wt. = 1) Nitrogen (N): 3% of body weight (mol. Wt. = 14) Classes of compounds Compounds Examples of inorganic compounds (common to human body) Organic: contain carbon atoms, connected in chains to other carbon atoms (or H atoms) AND present in living organisms Inorganic: have either no carbons or single carbons Water (hydro = water) Atmospheric gases ~60% of body weight Most abundant component of muscle (~70%) Fat tissue contains almost no water N2 (78%), O2 (21%), CO2 (~1%), CO (<1%) Electrolytes: compounds that break down into ions when dissolved in water Acids: all acids are NOT inorganic (some organic), ionize to release H ions Bases: ionizes to release hydroxyl ions (OH) that combine with H ions Salts: substance formed by reaction between acid and base Carbohydrates (CHO) Organic Compounds Functions of CHO in body Relatively small Water loving (hydrophilic) (to be hydrophobic = afraid of water) Carbo = carbon, hydrate = water Ratio = 1C:2H:1O Simple sugars (ose = sugar) are called monosaccharides Double sugars: sucrose = glucose + fructose Complex CHO = chain of sugars (ex. Glycogen, which is chains of glucose) Glycogen is storage form of sugar (1/3 stored in liver, 2/3 stored in muscle) Major source of energy Contributes to cellular structure Part of DNA, RNA, ATP (nucleotides) Can be used to synthesize both lipids and proteins Amount of CHO in body is relatively small (~1% of total body weight), about 500 g (12 lbs) Organic Compounds (2) Lipids Mostly made of C, H, some O is basically composed of LONG hydrocarbon chains (often 1220 C in a row) Ratio is 1C:2H, 1520H:1O Different forms Functions of lipids in the body All lipids are fairly large (bigger than CHO) and hydrophobic Fatty acid (give up H): acid part = COOH (called a carboxylate group), ex. Palmitate C16H32O2 Triglycerides: 3 fatty acids + glycerol (which is a 3C CHO), is storage form of fat (is neutral no charge) Cholesterol: involved in cell membrane structure, has large hydrocarbon ring structure C27H46O Amount stored in body depends on fitness level (less fit have more), gender (females have more), age (older have more) Primary energy source for metabolism THE primary source of stored energy Forms cell membrane structure (cholesterol and phospholipids) Insulation / protection (organs, etc.) Structural basis for steroid hormones Organic Compounds (3) Proteins Functions of protein in body Contain C, H, O and N (KEY element) Very large and complex (more than CHO, lipids) Synthesized in ribosomes Basic unit = amino acids, of which there are 20 in human body (ex. Are lysine, glycine, glutamate, etc.) Side chain determines type of AA Structural components Amount of protein stored in body varies due to age, gender, fitness Young, fit male ~18% of body weight ; Young, fit female ~15% of body weight Enzymes (ase) catalyze reactions (energy metabolism) Hormones (nonsteriod) Motion = muscle contraction, cell motion (e.g., flagella on sperm) Immune protection Receptors sensory, hormone MINOR energy source (starving, extreme stress) Transport and storage of other compounds (e.g., Hb) Membranes Framework and support Fibers (actin, myosin) Organic Compounds (4) Nucleotides Nitrogenous base Functions of nucleotides in body Sugar (ribose) Phosphate group (can be mono, bi or tri) Adenine (A), guanine (G), cytosine (C), thymine (T) ATP (adenosine triphosphate) Nucleic acids (RNA, DNA) Chains of nucleotides, basis of genetics Nucleotides create "recipe" for making of proteins Adenine + ribose + 3 phosphates (basic energy currency in cells) Guanosine triphosphate (GTP) serves as link between hormones and receptors on outside of cell interacts with mechanisms inside cell CoA, NADH based on adenine used in energy metabolism Cell signaling systems Coenzymes Amount of nucleotide in body is <<1% of body weight Summary of Body's Compounds Inorganic Organic Water 60% body wt Other inorganics (mineral, electrolyte) 34% Lipids 1530% Proteins 1020% CHO 1% Nucleotides <<1% Characteristics of Cells Obtains nutrients and other essential substances Disposes of waste, maintains shape and integrity Replicate Organelles carry out the cell's functions Three main parts to cell: plasma membrane, cytoplasm, nucleus Structure (fluid mosaic model) Plasma Membrane Phospholipid bilayer with proteins embedded (proteins can move around within bilayer) Polar "head" is charged (and attracted to water hydrophilic), nonpolar tail has fatty acid chains that avoid water (hydrophobic); tailtotail organization Plasma Membrane Components Cholesterol (affects fluidity and stability, esp. in cold) Glycolipids small amount, function not known too well, believed to be cell recognition; ~10% of outer lipids Proteins control cell membrane function Plasma Membrane Membrane protein functions integral, peripheral Transport Communication (ion channels, hormone receptors) Sugar chains attach to integral proteins and form external cell surface Plasma Membrane (2) Functions Protective barrier Receptors (proteins can allow some substances to bind) Controls passage of molecules into and out of cell divides intracellular and extracellular fluid Read p. 28 (selectively permeable, osmosis, diffusion) Largest molecules (macromolecules) travel via vesicular (bulk) transport Exocytosis (exo = out of) Bulk Transport Most secretion processes (e.g., mucus) Substance is housed in vesicle (membrane sac) Proteins vesicle membrane and plasma membrane to bind Endocytosis (endo = into) Bulk Transport Substance is taken into folding part of plasma membrane, vesicle formed and pinched off Phagocytosis ("cell eating") Pseudopods engulf material, forming phagosome often fuses with lysosomes (more on these later) Endocytosis Bulk Transport Pinocytosis (aka fluid phase endocytosis or "cell drinking") Infolding plasma membrane surrounds extracellular fluid Receptormediated endocytosis Substances bind to receptors on cell membrane, vesicle forms, moves into cytoplasm binds with lysosome; receptors recycled Cytoplasm Cytosol Cytoplasmic organelles Internal to plasma membrane, external to nucleus Fluid, 8090% water, rest is dissolved or suspended See p. 35, Table 2.1 Small functional units within cell, most have their own membrane (similar to plasma membrane) Location where metabolism takes place Temporary structures may or may not be present in given cell type (e.g., pigments, food stores) Inclusions *FOR each organelle know function, relative size, structure, and type of cell in which it predominates Mitochondrion (mitochondria) old term was sarcosome Organelles Large size (5001000nm, or .51 micrometers), but need electron microscope to see inside it FUNCTION TYPE OF CELL IN WHICH IT'S FOUND "Powerhouse" of the cell, responsible for aerobic energy production Performs oxidation (takes nutrients and changes them into ATP) uses O2, produces CO2 Muscle, liver, kidney HIGHEST density of mitochondria = heart (35% of cardiac muscle cell volume is mitochondria) FEW in adipocytes, leukocytes and NONE in RBCs (anaerobic metabolism) STRUCTURE
Grainy threads (mitos = thread) Outer membrane is smooth Inner membrane is arranged in folds called cristae, which fold into matrix (and create surface for chemical reactions) Some are free floating, some are attached to ER Ribosomes FUNCTION Free make proteins for cytosol, attached make proteins for export or cell membrane (rough ER) Protein synthesis Small ~30nm in diameter SIZE STRUCTURE Ribosomes TYPE OF CELL WHERE YOU'D FIND THEM Membranous sac contains RNA, AAs, proteins, but no membrane surrounds it Each ribosome has two sub units that fit together The mRNA (from nucleus) tells ribosome which AAs to link in which order to produce a specific protein translation Muscle, glands (secretions contain proteins), liver Endo = inner, plasm = mold/form, reticulum = network; (large in size) STRUCTURE Endoplasmic Reticulum FUNCTION Network of interconnected membranes that have spaces in between (spaces are called cisternae) Transport and storage of substances within a cell TYPES OF CELL WHERE YOU'D FIND IT Two types Same as ribosomes, for rough ER Smooth is present in most cells common in cells with lipid metabolism, detoxification (liver) Rough (has ribosomes on it) Smooth **NOTE: there is a specialized type of ER in muscle cells called the sarcoplasmic reticulum handles protein storage and transport, as well as calcium storage FUNCTION Golgi Apparatus SIZE Synthesizes CHO and is involved in secretions Combines the CHO with proteins to form glycoproteins that accumulate in channels of Golgi When channels get full, vesicles break off, are carried to cell membrane, and are released from cell (what is this process called?) OR go to lysosomes (or cell membrane) Does sorting, processing, and packaging Relatively large (about the size of mitochondrion) Flattened disks of membrane (310 discs of cisternae) bound by membrane attached to rough ER Cells that secrete a lot, like pancreas, salivary glands STRUCTURE WHERE FOUND? Lysosomes and Peroxisomes STRUCTURE FUNCTION Resemble each other structurally, look like membranous sacs Breakdown, cleanup ~100nm SIZE LYSOSOMES PEROXISOMES Contain powerful digestive enzymes (acid hydrolases) Part of phagocytosis = "eat cells" Degrade worn out cell parts, and entire cell in which they reside if necessary ***LOTS found in WBCs Contain enzymes called oxidases and catalases Degrade toxic substances Some of the enzymes help break down fat and produce hydrogen peroxide ***LOTS found in liver, kidneys Cytoskeleton Network of rods in cytosol that supports structures and cell movements 3 types Microtubules Microfilaments Largest diameter, all come from centrosome, made of protein Stiff but bendable give cell shape and organize organelles Thinnest elements Strands of actin (protein) interact with myosin for cell contraction (more in muscle section) Tough, insoluble protein fibers most stable Intermediate filaments Centrosome and Centrioles Centrosome Centrioles Spherical structure in cytoplasm near nucleus No membranes, contains matrix (helps with growth of microtubules) and centrioles Lie perpendicular to each other, barrelshaped Help form cilia, flagella, and mitotic spindle Nucleus Not all nuclei are located in center of cell; Some cells, like muscle are multinucleated; One cell, the red blood cell (RBC) is anucleated FUNCTION Directs protein synthesis hence, regulates cell activity (contains DNA) Nucleus SIZE/STRUCTURE Largest single organelle in cell (up to cell diameter ~5 micrometers) Nuclear envelope Double layer of membrane, similar to cytolemma Nucleoplasm Area inside, jelly like fluid similar to cytoplasm Holds chromatin and nucleoli Nucleus SIZE/STRUCTURE Nucleoli: composed of RNA MAKE ribosomes (later are ejected from nucleus) Chromatin: coiled, threadlike mass IS the genetic material of the cell, composed of DNA (is double helix composed of nucleotides) When cell divides, chromatin shortens into chromosomes Chromosomes contain genes, which code for specific proteins transcription (DNA coded into mRNA) Overview of Protein Synthesis Basic mechanism Organelles involved DNA is a doublestranded helix that gets split and coded to mRNA (called transcription) mRNA goes into cytosol and over to a ribosome Inside ribosome, RNA gets changed to proteins (called translation) Proteins go out into ER and are stored, transported If transported, proteins go to Golgi for modification, packaging Nucleus, ribosome, ER, Golgi ...
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- Spring '08