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Chapter 3 *Lecture PowerPoint Cellular Form and Function
*See separate FlexArt PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Introduction 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
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Cell Shapes and Sizes About 200 types of cells in the human body
Squamous—thin and flat with nucleus creating bulge Polygonal—irregularly angular shapes with four or more sides Stellate—starlike shape Cuboidal—squarish and about as tall as is wide Columnar—taller than wide Spheroid to ovoid—round to oval Discoid—disc-shaped Fusiform—thick in middle, tapered toward the ends Fibrous—threadlike shape Note: Some of these cell shapes appear as in tissue sections, but not their three-dimensional shape
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Cell Shapes and Sizes Figure 3.1 Squamous Cuboidal Columnar Polygonal
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Squamous Cuboidal Columnar Polygonal Stellate Spheroid Discoid Fusiform (spindle-shaped) Fibrous Figure 3.1
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Cell Shapes and Sizes 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
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Basic Components of a Cell
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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Apical cell surface Microvillus Microfilaments Terminal web Desmosome Secretory vesicle undergoing Fat droplet exocytosis Secretory vesicle Intercellular space Golgi vesicles Centrosome Centrioles Golgi complex Free ribosomes Lateral cell surface Intermediate filament Nucleus Lysosome Nucleolus Microtubule Nuclear envelope Rough endoplasmic reticulum Smooth endoplasmic reticulum Mitochondrion Plasma membranes Hemidesmosome Basal cell surface Basement membrane Figure 3.5
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© Don Fawcett/Photo Researchers, Inc.
The Plasma Membrane 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma membrane of upper cell Intercellular space Plasma membrane of lower cell Nuclear envelope Nucleus (a) 100 nm © Don Fawcett/Photo Researchers, Inc. Figure 3.6a
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The Plasma Membrane Oily film of lipids with diverse proteins embedded
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extracellular fluid Peripheral protein Glycolipid Glycoprotein Carbohydrate chains Extracellular face of membrane Phospholipid bilayer Channel Peripheral protein Intracellular face of membrane Cholesterol Transmembrane protein Figure 3.6b Proteins of cytoskeleton Intracellular fluid (b) Oily film of lipids with diverse proteins embedded
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Membrane Lipids 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
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Membrane Lipids Cholesterol Glycolipids 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
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Membrane Proteins Membrane proteins Transmembrane proteins
2% of the molecules in plasma membrane 50% of its weight Transmembrane proteins Pass through membrane Have hydrophilic regions in contact with cytoplasm and extracellular fluid Have hydrophobic regions that pass back and forth through the lipid of the membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carbohydrate Transmembrane protein: Hydrophilic region Hydrophobic region Phospholipid bilayer Figure 3.7 Cytoskeletal protein Anchoring peripheral protein
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Membrane Proteins Cont. Peripheral proteins Most are glycoproteins
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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carbohydrate Transmembrane protein: Hydrophilic region Hydrophobic region Phospholipid bilayer Figure 3.7 Cytoskeletal protein Anchoring peripheral protein
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Membrane Proteins Functions of membrane proteins include the following: Receptors, second-messenger systems, enzymes, ion channels, carriers, cell-identity markers, cell-adhesion molecules Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical messenger Breakdown products CAM of another cell Ions (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 that binds one cell to another Figure 3.8
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Receptors 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
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Second-Messenger Systems
Messenger (chemical) binds to a surface receptor Triggers changes within the cell that produce a second messenger in the cytoplasm Involves transmembrane proteins and peripheral proteins
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Enzymes Enzymes in plasma membrane carry out final stages of starch and protein digestion in small intestine Help produce second messengers (cAMP) Break down chemical messengers and hormones whose job is done Stops excessive stimulation
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Channel Proteins 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) Play an important role in the timing of nerve signals and muscle contraction Channelopathies—family of diseases that result from defects in channel proteins
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Carriers or Pumps Transmembrane proteins bind to glucose, electrolytes, and other solutes Transfer them across membrane Pumps consume ATP in the process
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Cell-Identity Markers
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
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Second Messengers Chemical first messenger (epinephrine) binds to a surface receptor Triggers changes within the cell that produces a second messenger in the cytoplasm Receptor activates G protein An intracellular peripheral protein Guanosine triphosphate (GTP), an ATP-like compound G protein relays signal to adenylate cyclase which converts ATP to cAMP (second messenger)
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Second Messengers cAMP activates a kinase in the cytosol
Kinases add phosphate groups to other cellular enzymes Activates some enzymes, and inactivates others triggering a wide variety of physiological changes in cells Up to 60% of modern drugs work by altering activity of G proteins
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Second Messenger System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 A messenger such as epinephrine (red triangle) binds to a receptor in the plasma membrane. First messenger Receptor Adenylate cyclase G G Pi 2 The receptor releases a G protein, which then travels freely in the cytoplasm and can go on to step 3 or have various other effects on the cell. ATP Pi 3 The G protein binds to an enzyme, adenylate cyclase, in the plasma membrane. Adenylate cyclase converts ATP to cyclic AMP (cAMP), the second messenger. cAMP (second messenger) 4 cAMP activates a cytoplasmic enzyme called a kinase. Inactive kinase Activated kinase P 5 Kinases add phosphate groups (Pi) to other cytoplasmic enzymes. This activates some enzymes and deactivates others, leading to varied metabolic effects in the cell. Inactive enzymes i Activated enzymes Figure 3.9 Various metabolic effects
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Membrane Transport Plasma membrane—a barrier and a gateway between the cytoplasm and ECF Selectively permeable—allows some things through, and prevents other things from entering and leaving the cell Passive transport mechanisms require no ATP Random molecular motion of particles provides the necessary energy Filtration, diffusion, osmosis Active transport mechanisms consumes ATP Active transport and vesicular transport Carrier-mediated mechanisms use a membrane protein to transport substances from one side of the membrane to the other
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Filtration Filtration—process in which particles are driven through a selectively permeable membrane by hydrostatic pressure (force exerted on a membrane by water) Examples Filtration of nutrients through gaps in blood capillary walls into tissue fluids Filtration of wastes from the blood in the kidneys while holding back blood cells and proteins Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood pressure in capillary forces water and small solutes such as salts through narrow clefts between capillary cells. Solute Water Capillary wall Red blood cell Clefts hold back larger particles such as red blood cells. Figure 3.13
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Simple Diffusion Simple diffusion—the net movement of particles from area of high concentration to area of low concentration Due to their constant, spontaneous motion Also known as movement down the concentration gradient—concentration of a substance differs from one point to another Down gradient Up gradient Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 3.14
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Simple Diffusion Diffusion through lipid bilayer
Nonpolar, hydrophobic, lipid-soluble substances diffuse through lipid layer Diffusion through channel proteins Water and charged, hydrophilic solutes diffuse through channel proteins in membrane Cells control permeability by regulating number of channel proteins or by opening and closing gates
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Osmosis Osmosis—flow of water from one side of a selectively permeable membrane to the other From side with higher water concentration to side with lower water concentration Reversible attraction of water to solute particles forms hydration spheres Makes those water molecules less available to diffuse back to the side from which they came Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Side A Side B Solute Water (a) Start
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Osmosis Aquaporins—channel proteins in plasma membrane specialized for passage of water Cells can increase the rate of osmosis by installing more aquaporins Decrease rate by removing them Significant amounts of water diffuse even through the hydrophobic, phospholipid regions of the plasma membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Side A Side B Solute Water (a) Start Figure 3.15a
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Osmosis Osmotic pressure—amount of hydrostatic pressure required to stop osmosis Reverse osmosis—pressure applied to one side, overrides pressure, drives against concentration gradient Heart drives water out of capillaries by reverse osmosis—capillary filtration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Osmotic pressure Hydrostatic pressure (b) 30 minutes later Figure 3.15b
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Osmolarity and Tonicity
Hypotonic solution Has a lower concentration of nonpermeating solutes than intracellular fluid (ICF) High water concentration Cells absorb water, swell, and may burst (lyse) Hypertonic solution Has a higher concentration of nonpermeating solutes Low water concentration Cells lose water + shrivel (crenate) Isotonic solution Concentrations in cell and ICF are the same Cause no changes in cell volume or cell shape Normal saline
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Effects of Tonicity on RBCs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Hypotonic (b) Isotonic (c) Hypertonic © Dr. David M. Phillips/Visuals Unlimited Figure 3.16a Figure 3.16b Figure 3.16c Hypotonic, isotonic, and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells.
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Carrier-Mediated Transport
Transport proteins in the plasma membrane that carry solutes from one side of the membrane to the other Specificity Transport proteins specific for a certain ligand Solute binds to a specific receptor site on carrier protein Differs from membrane enzymes because carriers do not chemically change their ligand Simply picks them up on one side of the membrane, and releases them, unchanged, on the other Saturation As the solute concentration rises, the rate of transport rises, but only to a point—transport maximum (Tm) Two types of carrier-mediated transport Facilitated diffusion and active transport
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Carrier-Mediated Transport
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transport maximum (Tm) through plasma membrane) Rate of solute transport (molecules/sec passing Figure 3.17 Concentration of solute Transport maximum—transport rate when all carriers are occupied
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Carrier-Mediated Transport
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Each pump cycle consumes one ATP and exchanges three Na+ for two K+ Keeps the K+ concentration higher and the Na+ concentration lower within the cell than in ECF Necessary because Na+ and K+ constantly leak through membrane Half of daily calories utilized for Na+−K+ pump Glucose Na+ Apical surface SGLT Cytoplasm Replace this photo with Figure 3.19 in the text page 96 Na+– K+ ATP pump ADP + Pi Basal surface Na+
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The Cell Interior Structures in the cytoplasm
Organelles, cytoskeleton, and inclusions All embedded in a clear gelatinous cytosol
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The Cytoskeleton 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
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Cytoskeleton Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microvilli Microfilaments Secretory vesicle in transport T erminal web Desmosome L ysosome Kinesin Microtubule Intermediate filaments Intermediate filaments Centrosome Microtubule in the process of assembly Microtubule undergoing disassembly Nucleus Mitochondrion (a) Basement membrane Hemidesmosome Figure 3.25a
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Organelles 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
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The Nucleus Nucleus—largest organelle (5 m in diameter)
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
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The Nucleus Cont. Nucleoplasm—material in nucleus
Supported by nuclear lamina Web of protein filaments Supports nuclear envelope and pores Provides points of attachment and organization for chromatin Plays role in regulation of the cell life cycle Nucleoplasm—material in nucleus Chromatin (threadlike matter) composed of DNA and protein Nucleoli—one or more dark masses where ribosomes are produced
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Endoplasmic Reticulum
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
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Endoplasmic Reticulum
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
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Smooth and Rough ER Figure 3.28c Rough endoplasmic reticulum Ribosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rough endoplasmic reticulum Ribosomes Cisternae (c) Smooth endoplasmic reticulum Figure 3.28c
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Ribosomes 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
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Golgi Complex 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
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Golgi Complex Figure 3.29 Golgi vesicles Golgi complex 600 n m
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Golgi vesicles Golgi complex Figure 3.29 600 n m Visuals Unlimited
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Lysosomes 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
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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 (H2O2) Catalase breaks down excess peroxide to H2O and O2 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
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Lysosome and Peroxisomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondria Peroxisomes Lysosomes Smooth ER Golgi complex (a) Lysosomes 1 mm (b) Peroxisomes 0.3 mm © Don Fawcett/Photo Researchers, Inc. Figure 3.30a Figure 3.30b
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Mitochondria 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Matrix Outer membrane Inner membrane Mitochondrial ribosome Intermembrane space Crista Figure 3.31
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Mitochondrial ribosome
Mitochondrion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Matrix Outer membrane Inner membrane Figure 3.31 Mitochondrial ribosome Intermembrane space Crista 1 m (Left): Dr. Donald Fawcett & Dr. Porter/Visuals Unlimited
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Inclusions Two kinds of inclusions Never enclosed in a unit membrane
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
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Inclusions
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