1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Cellular Form and Function

2.  All organisms are composed of cells  Single-cell organisms  humans  Cells are responsible for all structural and functional properties of a living organism  Workings of the human body  Mechanisms of disease  Rationale of therapy 2-2

3.  Cytology—scientific study of cells  Began when Robert Hooke coined the word cellulae to describe empty cell walls of cork  Theodor Schwann concluded, about two centuries later, that all animal tissues are made of cells  Louis Pasteur established beyond any reasonable doubt that “cells arise only from other cells”  Refutes the idea of spontaneous generation—living things arise from nonliving matter 3-3

4.  Modern cell theory  All organisms composed of cells and cell products  The cell is the simplest structural and functional unit of life  An organism’s structure and functions are due to the activities of its cells  Cells come only from preexisting cells, not from nonliving matter  Cells of all species have many fundamental similarities in their chemical composition and metabolic mechanisms. 3-4

5.  About 200 types of cells in the human body  Squamous  Polygonal  Stellate  Cuboidal  Columnar  Spheroid to ovoid  Discoid  Fusiform  Fibrous  Note: Some of these cell shapes appear as in tissue sections, but not their three-dimensional shape 3-5 Squamous Polygonal CuboidalColumnar Spheroid DiscoidFusiform (spindle-shaped) Stellate Fibrous

6. 2-6  Human cell size  Most from 10–15 micrometers (µm) in diameter  Egg cells (very large) 100 µm diameter  Barely visible to the naked eye  Nerve cell at 1 meter long  Longest human cell  Too slender to be seen with naked eye 3-6

7. 3-7 20m Growth 20m 10m m Large cell Diameter = 20  m Surface area = 20  m  20  m  6 = 2,400  m 2 Volume = 20  m  20  m  20  m = 8,000  m 3 Small cell Diameter = 10  m Surface area = 10  m  10  m  6 = 600  m 2 Volume = 10  m  10  m  10  m = 1,000  m 3 Effect of cell growth: Diameter (D) increased by a factor of 2 Surface area increased by a factor of 4 (= D 2 ) Volume increased by a factor of 8 (= D 3 )  Limitations on cell size  Cell growth increases volume more than surface area  Surface area of a cell is proportional to the square of its diameter  Volume of a cell is proportional to the cube of its diameter  Nutrient absorption and waste removal utilize surface area  If cell becomes too large, may rupture like overfilled water balloon

8.  Light microscope reveals plasma membrane, nucleus, and cytoplasm  Cytoplasm—fluid between the nucleus and surface membrane  Resolution (ability to reveal detail) of electron microscopes reveals ultrastructure  Organelles, cytoskeleton, and cytosol (ICF) 3-8 Nucleus Plasma membrane Nuclear envelope Golgi vesicle Golgi complex Mitochondria Ribosomes 2.0m

9.  Plasma (cell) membrane  Surrounds cell, defines boundaries  Made of proteins and lipids  Composition and function can vary from one region of the cell to another  Cytoplasm  Organelles  Cytoskeleton  Cytosol (intracellular fluid, ICF)  Extracellular fluid ( ECF)  Fluid outside of cell 3-9

10.  Unit membrane—forms the border of the cell and many of its organelles - Appears as a pair of dark parallel lines around cell (viewed with the electron microscope)  Plasma membrane—unit membrane at cell surface - Defines cell boundaries - Governs interactions with other cells - Controls passage of materials in and out of cell - Intracellular face—side that faces cytoplasm - Extracellular face—side that faces outward (a) Intercellular space Nuclear envelope Nucleus 100 nm Plasma membrane of upper cell Plasma membrane of lower cell

11.  Oily film of lipids with diverse proteins embedded 3-11 Extracellular face of membrane Intracellular face of membrane (b) Peripheral protein Extracellular fluid Glycolipid Glycoprotein Carbohydrate chains Transmembrane protein Peripheral protein Channel Intracellular fluid Cholesterol Proteins of cytoskeleton Phospholipid bilayer

12.  98% of molecules in plasma membrane are lipids  Phospholipids  75% of membrane lipids are phospholipids  Amphiphilic molecules arranged in a bilayer  Hydrophilic phosphate heads face water on each side of membrane  Hydrophobic tails—directed toward the center, avoiding water  Drift laterally from place to place  Movement keeps membrane fluid 3-12

13.  Cholesterol  20% of the membrane lipids  Holds phospholipids still and can stiffen membrane  Glycolipids  5% of the membrane lipids  Phospholipids with short carbohydrate chains on extracellular face  Contributes to glycocalyx—carbohydrate coating on the cell surface 3-13

14.  Membrane proteins  2% of the molecules in plasma membrane  50% of its weight  Transmembrane (integral) proteins  Can drift about freely in phospholipid film  Some anchored to cytoskeleton  Peripheral proteins  Adhere to one face of the membrane  Usually tethered to the cytoskeleton 3-14 Carbohydrate Phospholipid bilayer Cytoskeletal protein

15.  Functions of membrane proteins include the following:  Receptors, second-messenger systems, enzymes, ion channels, carriers, cell-identity markers, cell-adhesion molecules 3-15 Chemical messenger Breakdown products Ions CAM of another cell (a) Receptor A receptor that binds to chemical messengers such as hormones sent by other cells (b) Enzyme An enzyme that breaks down a chemical messenger and terminates its effect (c) Ion Channel A channel protein that is constantly open and allows ions to pass into and out of the cell (d) Gated ion channel A gated channel that opens and closes to allow ions through only at certain times (e) Cell-identity marker A glycoprotein acting as a cell- identity marker distinguishing the body’s own cells from foreign cells (f) Cell-adhesion molecule (CAM) A cell-adhesion molecule (CAM) that binds one cell to another

16.  Cell communication via chemical signals  Receptors—surface proteins on plasma membrane of target cell  Bind these chemicals (hormones, neurotransmitters)  Receptor usually specific for one substrate  Messenger (chemical) binds to a surface receptor  Triggers changes within the cell that produce a second messenger in the cytoplasm  Involves transmembrane proteins and enzymes 3-16

17.  Transmembrane proteins with pores that allow water and dissolved ions to pass through membrane  Some are constantly open  Some are gated channels that open and close in response to stimuli  Ligand (chemically)-regulated gates  Voltage-regulated gates  Mechanically regulated gates (stretch and pressure) 3-17

18.  Transmembrane proteins bind to glucose, electrolytes, and other solutes  Transfer them across membrane  Pumps consume ATP in the process 3-18

19.  Glycoproteins contribute to the glycocalyx  Carbohydrate surface coating  Acts like a cell’s “identification tag”  Enables our bodies to identify which cells belong to it and which are foreign invaders 3-19

20.  Adhere cells to each other and to extracellular material  Cells do not grow or survive normally unless they are mechanically linked to the extracellular material  Special events: sperm–egg binding; binding of immune cell to a cancer cell requires CAMs 3-20

21.  Unique fuzzy coat external to the plasma membrane  Carbohydrate moieties of membrane glycoproteins and glycolipids  Unique in everyone but identical twins  Functions  Protection– Cell adhesion  Immunity to infection– Fertilization  Defense against cancer – Embryonic development  Transplant compatibility 3-21

22.  Extensions of membrane (1–2  m)  Serves to increase cell’s surface area  Best developed in cells specialized in absorption  Gives 15 to 40 times more absorptive surface area  On some cells they are very dense and appear as a fringe—“brush border”  Milking action of actin  Actin filaments shorten microvilli  Pushing absorbed contents down into cell 3-22

23. 2-23 Actin microfilaments are centered in each microvilli (a) 1.0m (b) 0.1m Glycocalyx Actin microfilaments Microvillus

24.  Hairlike processes 7–10  m long  Single, nonmotile primary cilium found on nearly every cell  “Antenna” for monitoring nearby conditions  Sensory in inner ear, retina, nasal cavity, and kidney  Motile cilia—respiratory tract, uterine tubes, ventricles of the brain, efferent ductules of testes  Beat in waves  Sweep substances across surface in same direction  Power strokes followed by recovery strokes 3-24 (a) Mucus Saline layer Epithelial cells 1234567 Power strokeRecovery stroke (b) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

25. 3-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cilia (a) 10 µm a: Custom Medical Stock Photo, Inc.

26.  Axoneme—core of cilia that is the structural basis for ciliary movement  Has 9 + 2 structure of microtubules  Nine pairs form basal body inside the cell membrane  Anchors cilium  Dynein arms “crawl” up adjacent microtubule, bending the cilia  Uses energy from ATP  Saline layer  Chloride pumps pump Cl - into ECF  Na + and H 2 O follows  Cilia beat freely in saline layer 3-26

27.  Saline layer at cell surface due to chloride pumps move Cl - out of cell. Na + ions and H 2 O follow  Cystic fibrosis—hereditary disease in which cells make chloride pumps, but fail to install them in the plasma membrane  Chloride pumps fail to create adequate saline layer on cell surface  Thick mucus plugs pancreatic ducts and respiratory tract  Inadequate digestion of nutrients and absorption of oxygen  Chronic respiratory infections  Life expectancy of 30 3-27 Mucus Saline layer Epithelial cells

28.  Tail of a sperm—only functional flagellum  Whiplike structure with axoneme identical to cilium  Much longer than cilium  Stiffened by coarse fibers that support the tail  Movement is more undulating, snakelike  No power stroke or recovery stroke as in cilia 3-28

29.  Structures in the cytoplasm  Organelles, cytoskeleton, and inclusions  All embedded in a clear gelatinous cytosol 3-29

30.  Cytoskeleton—collection of filaments and cylinders  Determines shape of cell, lends structural support, organizes its contents, directs movement of substances through the cell, and contributes to the movements of the cell as a whole  Composed of:  Microfilaments: 6 nm thick, actin, forms terminal web  Intermediate fibers: 8–10 nm, support, strength, and structure  Microtubules: 25 nm, tubulin, movement 3-30

31. 3-31 Microvilli Microfilaments Secretory vesicle in transport Desmosome Intermediate filaments Centrosome Microtubule undergoing disassembly Mitochondrion Terminal web Lysosome Microtubule Nucleus Microtubule in the process of assembly Intermediate filaments (a) Basement membrane Hemidesmosome Kinesin

32.  A microtubule is a cylinder of 13 parallel strands called protofilaments  Each protofilament is a long chain of globular proteins called tubulin  Microtubules radiate from centrosome and hold organelles in place, form bundles that maintain cell shape and rigidity, and act somewhat like railroad tracks  Motor proteins “walk” along these tracks carrying organelles and other macromolecules to specific locations in the cell  Not permanent structures, they come and go moment by moment 3-32 Dynein arms Protofilaments (c) (b) (a) Microtubule Tubulin

33.  Internal structures, carry out specialized metabolic tasks  Membranous organelles  Nucleus, mitochondria, lysosomes, peroxisomes, endoplasmic reticulum, and Golgi complex  Nonmembranous organelles  Ribosomes, centrosomes, centrioles, basal bodies 3-33

34. 3-34  Nucleus—largest organelle (5  m)  Most cells have one nucleus  A few cells are anuclear or multinucleate  Nuclear envelope—two unit membranes surround nucleus  Perforated by nuclear pores formed by rings of protein  Regulate molecular traffic through envelope  Hold two unit membranes together  Nucleoplasm—material in nucleus  Chromatin (threadlike matter) composed of DNA and protein  Nucleoli—one or more dark masses where ribosomes are produced

35.  Endoplasmic reticulum—system of interconnected channels called cisternae enclosed by unit membrane  Rough endoplasmic reticulum— composed of parallel, flattened sacs covered with ribosomes  Continuous with outer membrane of nuclear envelope  Adjacent cisternae are often connected by perpendicular bridges  Produces the phospholipids and proteins of the plasma membrane  Synthesizes proteins that are packaged in other organelles or secreted from cell 3-35

36.  Smooth endoplasmic reticulum  Lack ribosomes  Cisternae more tubular and branching  Cisternae are thought to be continuous with those of rough ER  Synthesizes steroids and other lipids  Detoxifies alcohol and other drugs  Manufactures all membranes of the cell  Rough and smooth ER are functionally different parts of the same network 3-36

37. 3-37 (c) Rough endoplasmic reticulum Cisternae Ribosomes Smooth endoplasmic reticulum

38. 3-38  Golgi complex—a small system of cisternae that synthesize carbohydrates and put the finishing touches on protein and glycoprotein synthesis  Receives newly synthesized proteins from rough ER  Sorts them, cuts and splices some of them, adds carbohydrate moieties to some, and packages the protein into membrane-bound Golgi vesicles  Some become lysosomes  Some migrate to plasma membrane and fuse to it  Some become secretory vesicles for later release

39.  Lysosomes—package of enzymes bound by a single unit membrane  Extremely variable in shape  Functions  Intracellular hydrolytic digestion of proteins, nucleic acids, complex carbohydrates, phospholipids, and other substances  Autophagy—digest and dispose of worn out mitochondria and other organelles  Autolysis—“cell suicide”: some cells are meant to do a certain job and then destroy themselves 3-39 1  m (a) Lysosomes Mitochondria Lysosomes Golgi complex

40. 0.3  m (b) Peroxisomes Smooth ER Peroxisomes  Peroxisomes—resemble lysosomes but contain different enzymes and are not produced by the Golgi complex  General function is to use molecular oxygen to oxidize organic molecules  These reactions produce hydrogen peroxide (H 2 O 2 )  Catalase breaks down excess peroxide to H 2 O and O 2  Neutralize free radicals, detoxify alcohol, other drugs, and a variety of blood-borne toxins  Break down fatty acids into acetyl groups for mitochondrial use in ATP synthesis  In all cells, but abundant in liver and kidney 3-40

41.  Mitochondria—organelles specialized for synthesizing ATP  Variety of shapes: spheroid, rod-shaped, kidney-shaped, or threadlike  Surrounded by a double unit membrane  Inner membrane has folds called cristae  Spaces between cristae called matrix  Matrix contains ribosomes, enzymes used for ATP synthesis, small circular DNA molecule – Mitochondrial DNA (mtDNA)  “Powerhouses” of the cell  Energy is extracted from organic molecules and transferred to ATP 3-41 Matrix Crista Outer membrane Inner membrane Intermembrane space Mitochondrial ribosome 1 m

42.  Ribosomes—small granules of protein and RNA  Found in nucleoli, in cytosol, and on outer surfaces of rough ER, and nuclear envelope  They “read” coded genetic messages (messenger RNA) and assemble amino acids into proteins specified by the code 3-42

43.  Centriole—a short cylindrical assembly of microtubules arranged in nine groups of three microtubules each  Two centrioles lie perpendicular to each other within a small, clear area of cytoplasm called the centrosome  Play role in cell division  Cilia and flagella formation  Each basal body of a cilium or flagellum is a single centriole oriented perpendicular to plasma membrane  Basal bodies originate in centriolar organizing center  Migrate to plasma membrane  Two microtubules of each triplet elongate to form the nine pairs of peripheral microtubules of the axoneme  Cilium reaches full length in less than an hour 3-43

44.  Two kinds of inclusions  Stored cellular products  Glycogen granules, pigments, and fat droplets  Foreign bodies  Viruses, intracellular bacteria, dust particles, and other debris phagocytized by a cell  Never enclosed in a unit membrane  Not essential for cell survival 3-44

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