Chapter 3 Cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

Cells– C, O, H, N Carry out all chemical activities needed to sustain life. Building blocks of all living things Tissues- groups of cells that are similar in structure and function Structure reflects function Slide 3.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Anatomy of the Generalized Cell
Cells are not all the same All cells share general structures Three main regions Nucleus Cytoplasm Plasma membrane Figure 3.1a Slide 3.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Nucleus Control center Three regions Genetic material (DNA)
Nuclear membrane Nucleolus Chromatin Figure 3.1b Slide 3.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Nuclear Membrane – double membrane or envelope
Barrier of nucleus Double phospholipid membrane Nuclear pores that allow for exchange of material with the rest of the cell – selectively permeable Slide 3.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Surface of nuclear envelope.
Figure 3.29b The nucleus. Surface of nuclear envelope. Fracture line of outer membrane Nuclear pores Nucleus Nuclear pore complexes. Each pore is ringed by protein particles. Nuclear lamina. The netlike lamina composed of intermediate filaments formed by lamins lines the inner surface of the nuclear envelope. © 2013 Pearson Education, Inc.

Nucleoli 1 or more Sites of ribosome production
Ribosomes then migrate to the cytoplasm through nuclear pores Slide 3.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Chromatin (when not dividing)
Composed of DNA and protein Scattered throughout the nucleus Condenses to form chromosomes when the cell divides Slide 3.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

© 2013 Pearson Education, Inc.
Figure Chromatin and chromosome structure. 1 DNA double helix (2-nm diameter) Histones 2 Chromatin (“beads on a string”) structure with nucleosomes Linker DNA Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix) 3 Tight helical fiber (30-nm diameter) 4 Looped domain structure (300-nm diameter) 5 Chromatid (700-nm diameter) 6 Metaphase chromosome (at midpoint of cell division) consists of two sister chromatids © 2013 Pearson Education, Inc.

Plasma Membrane Barrier for cell contents
Double phospholipid layer (fat – water) Hydrophilic heads Hydrophobic tails Other materials in plasma membrane Protein Cholesterol Glycoproteins Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Plasma Membrane Figure 3.2 Slide 3.7b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Plasma Membrane Lipid bilayer and proteins in constantly changing fluid mosaic Plays dynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) Interstitial fluid (IF) = ECF that surrounds cells Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 3.3 The plasma membrane.
Extracellular fluid (watery environment outside cell) Polar head of phospholipid molecule Cholesterol Glycolipid Glyco- protein Nonpolar tail of phospholipid molecule Glycocalyx (carbohydrates) Lipid bilayer containing proteins Outward-facing layer of phospholipids Inward-facing layer of phospholipids Cytoplasm (watery environment inside cell) Integral proteins Filament of cytoskeleton Peripheral proteins © 2013 Pearson Education, Inc.

Membrane Lipids 75% phospholipids (lipid bilayer)
Phosphate heads: polar and hydrophilic Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b) 5% glycolipids Lipids with polar sugar groups on outer membrane surface 20% cholesterol Increases membrane stability Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Membrane Proteins Allow communication with environment
½ mass of plasma membrane Most specialized membrane functions Some float freely Some tethered to intracellular structures Two types: Integral proteins; peripheral proteins Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 3.3 The plasma membrane.
Extracellular fluid (watery environment outside cell) Polar head of phospholipid molecule Cholesterol Glycolipid Glyco- protein Nonpolar tail of phospholipid molecule Glycocalyx (carbohydrates) Lipid bilayer containing proteins Outward-facing layer of phospholipids Inward-facing layer of phospholipids Cytoplasm (watery environment inside cell) Integral proteins Filament of cytoskeleton Peripheral proteins © 2013 Pearson Education, Inc.

Six functions of Membrane Proteins
Transport Receptors for signal transduction Attachment to cytoskeleton and extracellular matrix Enzymatic activity Intercellular joining Cell-cell recognition Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 3.4a Membrane proteins perform many tasks.
Transport • A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. • Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane. PLAY Animation: Transport Proteins © 2013 Pearson Education, Inc.

Figure 3.4b Membrane proteins perform many tasks.
Receptors for signal transduction Signal • A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone. • When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. Receptor PLAY Animation: Receptor Proteins © 2013 Pearson Education, Inc.

Figure 3.4c Membrane proteins perform many tasks.
Attachment to the cytoskeleton and extracellular matrix • Elements of the cytoskeleton (cell's internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps maintain cell shape and fix the location of certain membrane proteins. • Others play a role in cell movement or bind adjacent cells together. © 2013 Pearson Education, Inc.

Figure 3.4d Membrane proteins perform many tasks.
Enzymatic activity Enzymes • A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution. • A team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway as indicated (left to right) here. PLAY Animation: Enzymes © 2013 Pearson Education, Inc. Figure 3.4d

Figure 3.4e Membrane proteins perform many tasks.
Intercellular joining • Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. • Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs © 2013 Pearson Education, Inc.

Figure 3.4f Membrane proteins perform many tasks.
Cell-cell recognition • Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells. Glycoprotein © 2013 Pearson Education, Inc.

Glycocalyx "Sugar covering" at cell surface
Lipids and proteins with attached carbohydrates (sugar groups) Every cell type has different pattern of sugars Specific biological markers for cell to cell recognition Allows immune system to recognize "self" and "non self" Cancerous cells change it continuously Slide 3.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Plasma Membrane Specializations
Microvilli Finger-like projections Increase surface area for absorption Small intestine and nephrons of kidney Figure 3.3 Slide 3.8a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cytoplasm Material outside the nucleus and inside the plasma membrane
Cytosol Fluid that suspends other elements Organelles Metabolic machinery of the cell Inclusions Non-functioning units – fat, pigments….. Slide 3.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cytoplasmic Organelles
Figure 3.4 Slide 3.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Membranous Mitochondria Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Nonmembranous Cytoskeleton Centrioles Ribosomes Membranes allow crucial compartmentalization Slide 3.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Mitochondria “Powerhouses” of the cell Double-membrane structure with inner shelflike cristae: Change shape continuously Carry out reactions where oxygen is used to break down food Provides ATP for cellular energy Contain their own DNA, RNA, ribosomes Similar to bacteria; capable of cell division called fission Slide 3.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Ribosomes Made of protein and RNA Protein synthesis Two locations Free in the cytoplasm Attached to rough endoplasmic reticulum Slide 3.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Endoplasmic reticulum (ER) Fluid-filled tubules for carrying substances Two types of ER Rough Endoplasmic Reticulum Studded with ribosomes Site where building materials of cellular membrane are formed (leave the cell) Smooth Endoplasmic Reticulum Functions in cholesterol synthesis and breakdown, fat metabolism, and detoxification of drugs, glycogen conversion, store and release Ca2+ Slide 3.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Diagrammatic view of smooth and rough ER
Figure The endoplasmic reticulum. Nucleus Smooth ER Nuclear envelope Rough ER Ribosomes Diagrammatic view of smooth and rough ER Electron micrograph of smooth and rough ER (25,000x) © 2013 Pearson Education, Inc. 35

Golgi apparatus Stacked and flattened membranous sacs Modifies, concentrates, and packages proteins and lipids from rough ER Slide 3.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 3.19a Golgi apparatus. Cis face— “receiving” side of Golgi apparatus Transport vesicle from rough ER Cisterns New vesicles forming Transport vesicle from trans face Trans face— “shipping” side of Golgi apparatus Secretory vesicle Many vesicles in the process of pinching off from the Golgi apparatus. © 2013 Pearson Education, Inc.

Figure The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins. Slide 2 Rough ER Protein-containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. 1 ER membrane Plasma membrane Proteins in cisterns Golgi apparatus Extracellular fluid © 2013 Pearson Education, Inc.

Figure The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins. Slide 3 Rough ER Protein-containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. 1 ER membrane Plasma membrane Proteins in cisterns Proteins are modified within the Golgi compartments. 2 Golgi apparatus Extracellular fluid © 2013 Pearson Education, Inc.

Figure The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins. Slide 4 Rough ER Phagosome Protein-containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. 1 ER membrane Plasma membrane Proteins in cisterns Pathway C: Lysosome containing acid hydrolase enzymes Proteins are modified within the Golgi compartments. 2 Vesicle becomes lysosome Proteins are then packaged within different vesicle types, depending on their ultimate destination. 3 Secretory vesicle Golgi apparatus Pathway B: Vesicle membrane to be incorporated into plasma membrane Pathway A: Vesicle contents destined for exocytosis Secretion by exocytosis Extracellular fluid © 2013 Pearson Education, Inc.

Lysosomes Contain enzymes that digest non-usable materials within the cell or “foreign” or toxic materials Peroxisomes Membranous sacs of oxidase and catalase enzymes Detoxify harmful substances Break down free radicals (highly reactive chemicals) Catalyze and synthesize fatty acids Replicate by pinching in half Slide 3.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cytoskeleton Network of protein structures that extend throughout the cytoplasm Provides the cell with an internal framework Slide 3.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Gives strength, compression resistance
Figure 3.23a Cytoskeletal elements support the cell and help to generate movement. Microfilaments Tough, insoluble protein fibers constructed like woven ropes composed of tetramer (4) fibrils Gives strength, compression resistance Involved in cell motility, change in shape, endocytosis and exocytosis Tetramer subunits 10 nm Microfilaments form the blue batlike network in this photo. © 2013 Pearson Education, Inc.

Resist pulling forces on cell; attach to desmosomes
Figure 3.23b Cytoskeletal elements support the cell and help to generate movement. Intermediate filaments Strands made of spherical protein subunits called actins Resist pulling forces on cell; attach to desmosomes E.g., neurofilaments in nerve cells; keratin filaments in epithelial cells Actin subunit 7 nm Intermediate filaments form the purple network surrounding the pink nucleus in this photo. © 2013 Pearson Education, Inc.

Determine overall shape of cell and distribution of organelles
Figure 3.23c Cytoskeletal elements support the cell and help to generate movement. Microtubules Hollow tubes of spherical protein subunits called tubulins Determine overall shape of cell and distribution of organelles Mitochondria, lysosomes, secretory vesicles attach to microtubules; moved throughout cell by motor proteins Tubulin subunits 25 nm Microtubules appear as gold networks surrounding the cells’ pink nuclei in this photo. © 2013 Pearson Education, Inc.

Figure Microtubules and microfilaments function in cell motility by interacting with motor molecules powered by ATP. Vesicle Receptor for motor molecule Motor molecule (ATP powered) Microtubule of cytoskeleton Motor molecules can attach to receptors on vesicles or organelles, and carry the organelles along the microtubule “tracks” of the cytoskeleton. Motor molecule (ATP powered) Cytoskeletal elements (microtubules or microfilaments) In some types of cell motility, motor molecules attached to one element of the cytoskeleton can cause it to slide over another element, which the motor molecules grip, release, and grip at a new site. Muscle contraction and cilia movement work this way. © 2013 Pearson Education, Inc.

Centrosome Contains paired Centrioles Rod-shaped bodies made of microtubules Direct formation of mitotic spindle during cell division Centrioles form basis of cilia and flagella Slide 3.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cellular Projections Not found in all cells Used for movement
Cilia moves materials across the cell surface Flagellum propels the cell Slide 3.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cell Diversity Figure 3.7; 1, 2 Slide 3.19a

Cell Diversity Figure 3.7; 3 Slide 3.19b

Cell Diversity Figure 3.7; 4, 5 Slide 3.19c

Cell- Size range Diameter: 10 µm to 100 µm Length: 5 µm to 1 meter
How big is a micrometer?? µm = micrometer = 10^-6 meters µm = 1 thousandth of a millimeter

Variety of cell shapes Spherical fat cells Disk-shaped RBC’s Branched
Nerve Cells Cube-like Epithelial cells

Membrane Transport How do substances enter and exit the cell?
Slide 3.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cellular Physiology: Membrane Transport
Membrane Transport – movement of substance into and out of the cell Two basic methods Passive transport No energy required (diffusion, osmosis, filtration) Active transport (solute pumping, bulk) Uses metabolic energy Slide 3.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Selective Permeability
Plasma membrane allows some materials to pass while excluding others Includes movement into and out of the cell Slide 3.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Passive Transport Processes
Diffusion Particles distribute themselves evenly Movement from high to low concentration Types Osmosis (water) Facilitated (proteins) Figure 3.8 Slide 3.23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Diffusion through the Plasma Membrane
Slide 3.25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Tonicity Tonicity: Ability of solution to alter cell's water volume
Isotonic: Solution with same non-penetrating solute concentration as cytosol Hypertonic: Solution with higher non-penetrating solute concentration than cytosol Hypotonic: Solution with lower non-penetrating solute concentration than cytosol © 2013 Pearson Education, Inc.

Figure 3.9 The effect of solutions of varying tonicities on living red blood cells. Isotonic solutions Hypertonic solutions Hypotonic solutions Cells retain their normal size and shape in isotonic solutions (same solute/water concentration as inside cells; water moves in and out). Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of solutes than are present inside the cells). Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (contains a lower concentration of solutes than are present inside cells). © 2013 Pearson Education, Inc.

Passive Transport Processes
Filtration Water and solutes are forced through a membrane by fluid, or hydrostatic pressure A pressure gradient must exist Slide 3.26 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes
Solute Pumping Against concentration gradient Sodium-Potassium Pump Slide 3.30a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Bulk transport (vesicles) Exocytosis Moves material out of cell Endocytosis Bringing material into cell Phagocytosis – cell eating Pinocytosis – cell drinking Slide 3.30a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 3.13a Comparison of three types of endocytosis.
Phagocytosis The cell engulfs a large particle by forming projecting pseudopods ("false feet") around it and enclosing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein coated but has receptors capable of binding to microorganisms or solid particles. Receptors Phagosome © 2013 Pearson Education, Inc.

Figure 3.13b Comparison of three types of endocytosis.
Pinocytosis The cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated. Vesicle © 2013 Pearson Education, Inc.

Figure Exocytosis. Slide 1 The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Fusion pore formed 3 The vesicle and plasma membrane fuse and a pore opens up. Secretory vesicle Vesicle SNARE (v-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Molecule to be secreted Cytoplasm 4 Vesicle contents are released to the cell exterior. 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). Fused v- and t-SNAREs © 2013 Pearson Education, Inc.

Cell Life Cycle How do cells reproduce? Slide 3.31

Figure The cell cycle. G1 checkpoint (restriction point) Interphase S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M Mitosis Cytokinesis Prophase Metaphase Telophase Anaphase Mitotic phase (M) G2 checkpoint © 2013 Pearson Education, Inc.

Cell Life Cycle Cells have two major periods Interphase Cell grows
Cell carries on metabolic processes Cell division Cell replicates itself Function is to produce more cells for growth and repair processes Slide 3.31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Interphase Period from cell formation to cell division
Nuclear material called chromatin Three subphases: G1 (gap 1)—vigorous growth and metabolism Cells that permanently cease dividing said to be in G0 phase S (synthetic)—DNA replication occurs G2 (gap 2)—preparation for division Slide 3.31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Events of Cell Division
Mitosis (PMAT) Division of the nucleus Results in the formation of two daughter nuclei Cytokinesis Division of the cytoplasm Results in the formation of two daughter cells Slide 3.33 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Stages of Mitosis Figure 3.15, step 1 Centrioles Plasma membrane
Interphase Nucleolus Nuclear envelope Chromatin Figure 3.15, step 1

Interphase Early prophase Nucleolus Nuclear envelope Chromatin Forming mitotic spindle Centromere Chromosome, consisting of two sister chromatids Figure 3.15, step 2

Interphase Early prophase Late prophase Nucleolus Nuclear envelope Spindle pole Chromatin Forming mitotic spindle Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Spindle microtubules Figure 3.15, step 3

Stages of Mitosis Figure 3.15, step 4 Spindle Metaphase plate
Sister chromatids Spindle Metaphase plate Figure 3.15, step 4

Stages of Mitosis Figure 3.15, step 5 Metaphase Anaphase
Daughter chromosomes Sister chromatids Spindle Metaphase plate Figure 3.15, step 5

Stages of Mitosis Figure 3.15, step 6 Metaphase Anaphase
Telophase and cytokinesis Daughter chromosomes Sister chromatids Nuclear envelope forming Nucleolus forming Spindle Metaphase plate Cleavage furrow Figure 3.15, step 6

Figure Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (2 of 6) Early mitotic spindle Early Prophase Aster Centromere Chromosome consisting of two sister chromatids © 2013 Pearson Education, Inc.

Figure Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (3 of 6) Spindle pole Polar microtubule Late Prophase Fragments of nuclear envelope Kinetochore Kinetochore microtubule © 2013 Pearson Education, Inc.

Figure Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (6 of 6) Nuclear envelope forming Nucleolus forming Contractile ring at cleavage furrow Telophase Cytokinesis © 2013 Pearson Education, Inc.

Protein Synthesis Gene – DNA segment that carries a blueprint for building one protein Proteins have many functions Building materials for cells Act as enzymes (biological catalysts) RNA is essential for protein synthesis Slide 3.37 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Role of RNA Transfer RNA (tRNA) Ribosomal RNA (rRNA) Messenger RNA
Transfers appropriate amino acids to the ribosome for building the protein Ribosomal RNA (rRNA) Helps form the ribosomes where proteins are built Messenger RNA Carries the instructions for building a protein from the nucleus to the ribosome Slide 3.38 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Transcription and Translation
Transfer of information from DNA’s base sequence to the complimentary base sequence of mRNA Translation Base sequence of nucleic acid is translated to an amino acid sequence Amino acids are the building blocks of proteins Slide 3.39 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Protein Synthesis Figure 3.15 Slide 3.40

Extracellular Materials
Body fluids—interstitial fluid, blood plasma, and cerebrospinal fluid Cellular secretions—intestinal and gastric fluids, saliva, mucus, and serous fluids Extracellular matrix—most abundant extracellular material Jellylike mesh of proteins and polysaccharides secreted by cells; acts as "glue" to hold cells together © 2013 Pearson Education, Inc.

Developmental Aspects of Cells
All cells of body contain same DNA but cells not identical Chemical signals in embryo channel cells into specific developmental pathways by turning some genes on and others off Development of specific and distinctive features in cells called cell differentiation © 2013 Pearson Education, Inc.

Apoptosis and Modified Rates of Cell Division
During development more cells than needed produced (e.g., in nervous system) Eliminated later by programmed cell death (apoptosis) Mitochondrial membranes leak chemicals that activate caspases  DNA, cytoskeleton degradation  cell death Dead cell shrinks and is phagocytized © 2013 Pearson Education, Inc.

Apoptosis and Modified Rates of Cell Division
Organs well formed and functional before birth Cell division in adults to replace short-lived cells and repair wounds Hyperplasia increases cell numbers when needed Atrophy (decreased size) results from loss of stimulation or use © 2013 Pearson Education, Inc.

Theories of Cell Aging Wear and tear theory—Little chemical insults and free radicals have cumulative effects Mitochondrial theory of aging—free radicals in mitochondria diminish energy production Immune system disorders—autoimmune responses; progressive weakening of immune response; C- reactive protein of acute inflammation causes cell aging © 2013 Pearson Education, Inc.

Theories of Cell Aging Most widely accepted theory
Genetic theory—cessation of mitosis and cell aging programmed into genes Telomeres (strings of nucleotides protecting ends of chromosomes) may determine number of times a cell can divide Telomerase lengthens telomeres Found in germ cells; ~ absent in adult cells © 2013 Pearson Education, Inc.

Chapter 3 Cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

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Chapter 3 Cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

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