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Copyright © 2010 Pearson Education, Inc. Chapter 3: The Living Parts
Copyright © 2010 Pearson Education, Inc. Cell Theory The cell is the basic living unit Organismal functions depend on individual and collective cell functions Biochemical activities of cells are dictated by their specific subcellular structures Continuity of life has a cellular basis
Copyright © 2010 Pearson Education, Inc. Cell Diversity Over 200 different types of human cells Types differ in size, shape, subcellular components, and functions
Copyright © 2010 Pearson Education, Inc. Generalized Cell All cells have some common structures and functions Human cells have three basic parts: Plasma membrane— flexible outer boundary Cytoplasm— intracellular fluid containing organelles Nucleus—control center
Copyright © 2010 Pearson Education, Inc. Plasma Membrane Also called cell membrane Layer of lipids and proteins in a constantly changing fluid mosaic Plays a dynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) Interstitial fluid (IF) = ECF that surrounds cells
Copyright © 2010 Pearson Education, Inc. Membrane Proteins Integral proteins Firmly inserted into the membrane (most are transmembrane) Functions: Transport proteins (channels and carriers), enzymes, or receptors
Copyright © 2010 Pearson Education, Inc. Membrane Proteins Peripheral proteins Loosely attached to integral proteins Include filaments on intracellular surface and glycoproteins on extracellular surface Functions: Enzymes, motor proteins, cell-to-cell links, provide support on intracellular surface, and form part of glycocalyx
Copyright © 2010 Pearson Education, Inc. Membrane Junctions Three types: Tight junction Prevent fluids and most molecules from moving between cells Desmosome “Rivets” or “spot-welds” that anchor cells together Gap junction Transmembrane proteins form pores that allow small molecules to pass from cell to cell For spread of ions between cardiac or smooth muscle cells
Copyright © 2010 Pearson Education, Inc. Types of Membrane Transport Passive processes No cellular energy (ATP) required Substance moves down its concentration gradient Active processes Energy (ATP) required Occurs only in living cell membranes
Copyright © 2010 Pearson Education, Inc. Passive Processes What determines whether or not a substance can passively permeate a membrane? 1.Lipid solubility of substance 2.Channels of appropriate size 3.Carrier proteins
Copyright © 2010 Pearson Education, Inc. Passive Processes Simple diffusion Carrier-mediated facilitated diffusion Channel-mediated facilitated diffusion Osmosis
Copyright © 2010 Pearson Education, Inc. Tonicity Tonicity: The ability of a solution to cause a cell to shrink or swell Isotonic: A solution with the same solute concentration as that of the cytosol Hypertonic: A solution having greater solute concentration than that of the cytosol Hypotonic: A solution having lesser solute concentration than that of the cytosol
Copyright © 2010 Pearson Education, Inc. Figure 3.9 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). (a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions 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 in cells).
Copyright © 2010 Pearson Education, Inc. Membrane Transport: Active Processes Two types of active processes: Active transport Vesicular transport Three types Both use ATP to move solutes across a living plasma membrane
Copyright © 2010 Pearson Education, Inc. Membrane Potential Separation of oppositely charged particles (ions) across a membrane creates a membrane potential (potential energy measured as voltage) Resting membrane potential (RMP): Voltage measured in resting state in all cells Ranges from –50 to –100 mV in different cells Results from diffusion and active transport of ions (mainly K + )
Copyright © 2010 Pearson Education, Inc. Generation and Maintenance of RMP 1.The Na + -K + pump continuously ejects Na + from cell and carries K + back in 2.K + continually leaks out of cell through K + leakage channels 3.Membrane interior becomes negative (relative to exterior) because of large anions trapped inside cell
Copyright © 2010 Pearson Education, Inc. Generation and Maintenance of RMP 4.Electrochemical gradient begins to attract K + back into cell 5.RMP is established at the point where the electrical gradient balances the K + concentration gradient 6.A steady state is maintained because the rate of active transport is equal to and depends on the rate of Na + diffusion into cell
Copyright © 2010 Pearson Education, Inc. Figure K + diffuse down their steep concentration gradient (out of the cell) via leakage channels. Loss of K + results in a negative charge on the inner plasma membrane face. K + also move into the cell because they are attracted to the negative charge established on the inner plasma membrane face. A negative membrane potential (–90 mV) is established when the movement of K + out of the cell equals K + movement into the cell. At this point, the concentration gradient promoting K + exit exactly opposes the electrical gradient for K + entry. Potassium leakage channels Protein anion (unable to follow K + through the membrane) Cytoplasm Extracellular fluid
Copyright © 2010 Pearson Education, Inc. Cell-Environment Interactions Involves glycoproteins and proteins of glycocalyx Cell adhesion molecules (CAMs) Membrane receptors
Copyright © 2010 Pearson Education, Inc. Roles of Cell Adhesion Molecules Anchor cells to extracellular matrix or to each other Assist in movement of cells past one another CAMs of blood vessel lining attract white blood cells to injured or infected areas Stimulate synthesis or degradation of adhesive membrane junctions Transmit intracellular signals to direct cell migration, proliferation, and specialization
Copyright © 2010 Pearson Education, Inc. Roles of Membrane Receptors Contact signaling—touching and recognition of cells; e.g., in normal development and immunity Chemical signaling—interaction between receptors and ligands (neurotransmitters, hormones and paracrines) to alter activity of cell proteins (e.g., enzymes or chemically gated ion channels) G protein–linked receptors—binding activates a G protein, affecting an ion channel or enzyme or causing the release of an internal second messenger
Copyright © 2010 Pearson Education, Inc. Second Messenger System
Copyright © 2010 Pearson Education, Inc. Cytoplasm Located between plasma membrane and nucleus Cytosol Water with solutes (protein, salts, sugars, etc.) Cytoplasmic organelles Metabolic machinery of cell Inclusions Granules of glycogen or pigments, lipid droplets, vacuoles, and crystals
Copyright © 2010 Pearson Education, Inc. Cytoplasmic Organelles Membranous Mitochondria Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Nonmembranous Cytoskeleton Centrioles Ribosomes
Copyright © 2010 Pearson Education, Inc. Mitochondria Double-membrane structure with shelflike cristae Provide most of cell’s ATP via aerobic cellular respiration Contain their own DNA and RNA
Copyright © 2010 Pearson Education, Inc. Ribosomes Granules containing protein and rRNA Site of protein synthesis Free ribosomes synthesize soluble proteins Membrane-bound ribosomes (on rough ER) synthesize proteins to be incorporated into membranes or exported from the cell
Copyright © 2010 Pearson Education, Inc. Endoplasmic Reticulum (ER) Interconnected tubes and parallel membranes enclosing cisternae Continuous with nuclear membrane Two varieties: Rough ER Smooth ER
Copyright © 2010 Pearson Education, Inc. Golgi Apparatus Stacked and flattened membranous sacs Modifies, concentrates, and packages proteins and lipids Secretory vesicles leave trans face of Golgi stack and move to designated parts of cell
Copyright © 2010 Pearson Education, Inc. Lysosomes Spherical membranous bags containing digestive enzymes (acid hydrolases) Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Break down and release glycogen Break down bone to release Ca2 + Destroy cells in injured or nonuseful tissue (autolysis)
Copyright © 2010 Pearson Education, Inc. Endomembrane System Overall function Produce, store, and export biological molecules Degrade potentially harmful substances
Copyright © 2010 Pearson Education, Inc. Peroxisomes Membranous sacs containing powerful oxidases and catalases Detoxify harmful or toxic substances Neutralize dangerous free radicals (highly reactive chemicals with unpaired electrons)
Copyright © 2010 Pearson Education, Inc. Cytoskeleton Elaborate series of rods throughout cytosol Microtubules Determine overall shape of cell and distribution of organelles Microfilaments Involved in cell motility, change in shape, endocytosis and exocytosis Intermediate filaments Resist pulling forces on the cell and attach to desmosomes
Copyright © 2010 Pearson Education, Inc. Centrosome “Cell center” near nucleus Generates microtubules; organizes mitotic spindle Contains centrioles: Small tube formed by microtubules
Copyright © 2010 Pearson Education, Inc. Cellular Extensions Cilia and flagella Whiplike, motile extensions on surfaces of certain cells Contain microtubules and motor molecules Cilia move substances across cell surfaces Longer flagella propel whole cells (tail of sperm)
Copyright © 2010 Pearson Education, Inc. Cellular Extensions Microvilli Fingerlike extensions of plasma membrane Increase surface area for absorption Core of actin filaments for stiffening
Copyright © 2010 Pearson Education, Inc. Nucleus Cellular control center Most cells are uninucleate Red blood cells are anucleate Skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate
Copyright © 2010 Pearson Education, Inc. Nuclear Envelope Double-membrane barrier containing pores Outer layer is continuous with rough ER and bears ribosomes Inner lining (nuclear lamina) maintains shape of nucleus Pore complex regulates transport of large molecules into and out of nucleus
Copyright © 2010 Pearson Education, Inc. Nucleoli Dark-staining spherical bodies within nucleus Involved in rRNA synthesis and ribosome subunit assembly
Copyright © 2010 Pearson Education, Inc. Chromatin Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%) Arranged in fundamental units called nucleosomes Condense into barlike bodies called chromosomes when the cell starts to divide
Copyright © 2010 Pearson Education, Inc. Cell Cycle Defines changes from formation of the cell until it reproduces Includes: Interphase Cell division (mitotic phase)
Copyright © 2010 Pearson Education, Inc. Interphase Period from cell formation to cell division Nuclear material called chromatin Four subphases: G 1 (gap 1)—vigorous growth and metabolism G 0 —gap phase in cells that permanently cease dividing S (synthetic)—DNA replication G 2 (gap 2)—preparation for division
Copyright © 2010 Pearson Education, Inc. DNA Replication DNA helices begin unwinding from the nucleosomes Helicase untwists the double helix and exposes complementary chains The Y-shaped site of replication is the replication fork Each nucleotide strand serves as a template for building a new complementary strand
Copyright © 2010 Pearson Education, Inc. DNA Replication DNA polymerase only works in one direction Continuous leading strand is synthesized Discontinuous lagging strand is synthesized in segments DNA ligase splices together short segments of discontinuous strand
Copyright © 2010 Pearson Education, Inc. DNA Replication End result: two DNA molecules formed from the original This process is called semiconservative replication
Copyright © 2010 Pearson Education, Inc. Cell Division Mitotic (M) phase of the cell cycle Essential for body growth and tissue repair Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle
Copyright © 2010 Pearson Education, Inc. Cell Division Includes two distinct events: 1.Mitosis—four stages of nuclear division: Prophase Metaphase Anaphase Telophase 2.Cytokinesis—division of cytoplasm by cleavage furrow
Copyright © 2010 Pearson Education, Inc. Cytokinesis Begins during late anaphase Ring of actin microfilaments contracts to form a cleavage furrow Two daughter cells are pinched apart, each containing a nucleus identical to the original
Copyright © 2010 Pearson Education, Inc. Figure 3.33 Contractile ring at cleavage furrow Nuclear envelope forming Nucleolus forming Telophase Telophase and Cytokinesis
Copyright © 2010 Pearson Education, Inc. Control of Cell Division “Go” signals: Critical volume of cell when area of membrane is inadequate for exchange Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks))
Copyright © 2010 Pearson Education, Inc. Control of Cell Division “Stop” signals: Contact inhibition Growth-inhibiting factors produced by repressor genes
Copyright © 2010 Pearson Education, Inc. Protein Synthesis DNA is the master blueprint for protein synthesis Gene: Segment of DNA with blueprint for one polypeptide Triplets of nucleotide bases form genetic library Each triplet specifies coding for an amino acid
Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA Messenger RNA (mRNA) Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm Ribosomal RNA (rRNA) A structural component of ribosomes that, along with tRNA, helps translate message from mRNA Transfer RNAs (tRNAs) Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis
Copyright © 2010 Pearson Education, Inc. Transcription Transfers DNA gene base sequence to a complementary base sequence of an mRNA Steps DNA unwound and RNA polymerase attaches to begin copy Two strands of mRNA are generated and sent from nucleus to ribosome for translation
Copyright © 2010 Pearson Education, Inc. Translation Steps mRNA passes through ribosome where is will be met by tRNA. Anticodon on tRNA matches codon on mRNA for transfer of amino acid. Amino acid strings generate a polypeptide which ultimately generate a protein.
Copyright © 2010 Pearson Education, Inc. Genetic Code Each three-base sequence on DNA is represented by a codon Codon—complementary three-base sequence on mRNA
Copyright © 2010 Pearson Education, Inc. Figure 3.36 SECOND BASE UUG UUA UUC UUU Phe Leu CUG CUA CUC CUU Leu AUA AUC AUU Ile GUG GUA GUC GUU Val UCG UCA UCC UCU Ser CCG CCA CCC CCU Pro ACG ACA ACC ACU Thr GCG GCA GCC GCU Ala UAC UAU Tyr CAG CAA CAC CAU His Gln AAG AAA AAC AAU Asn Lys GAG GAA GAC GAU Asp Glu UGC UGU Cys Trp CGG CGA CGC CGU Arg AGG AGA AGC AGU Ser Arg GGG GGA GGC GGU Gly UAAStopUGAStop AUG Met or Start UAGStopUGG UCAG G A C U G A C U G A C U G A C U U C A G
Copyright © 2010 Pearson Education, Inc. Other Roles of DNA Intron (“junk”) regions of DNA code for other types of RNA: Antisense RNA Prevents protein-coding RNA from being translated MicroRNA Small RNAs that interfere with mRNAs made by certain exons Riboswitches Folded RNAs that act as switches regulating protein synthesis in response to environmental conditions
Copyright © 2010 Pearson Education, Inc. Extracellular Materials Body fluids (interstitial fluid, blood plasma, and cerebrospinal fluid) Cellular secretions (intestinal and gastric fluids, saliva, mucus, and serous fluids) Extracellular matrix (abundant jellylike mesh containing proteins and polysaccharides in contact with cells)
Copyright © 2010 Pearson Education, Inc. Theories of Cell Aging Wear and tear theory: Little chemical insults and free radicals have cumulative effects Immune system disorders: Autoimmune responses and progressive weakening of the immune response Genetic theory: Cessation of mitosis and cell aging are programmed into genes. Telomeres (strings of nucleotides on the ends of chromosomes) may determine the number of times a cell can divide.
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