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Unformatted text preview: Chapter 3 Cell Biology Introduc5on to Cells
- ~0.1mm diameter - Can't be seen well without a microscope - 1665 Robert Hooke examined cork cells - They consisted of millions of irregular units - Named them for rooms or "cells" - Hooke saw only outlines Introduc5on to Cells
- Hooke's research led to Cell Theory - Cells are the building blocks of all plants and animals - All cells come from the division of preexis5ng cells - Cells are the smallest units that perform all vital physiological func5ons - Each cell maintains homeostasis at the cellular level Introduc5on to Cells
- Two types of cells - Sex cells (germ cells) - Sperm - Oocytes (eggs) - Soma5c cells (soma means body) Introduc5on to Cells
- Typical cell - Only a model of "the average" cell - Surrounded by extracellular fluid called intersi5al fluid - Cell contents called Cytoplasm Organelles - Cytoplasm separated from extracellular fluid by cell membrane Cell Membrane
- Also called plasma membrane - General func5ons - Physical isola5on - Separates fluids inside of cell from fluids out side of cell - Keeps enzymes and structural proteins in - Maintains homeostasis Cell Membrane
- Also called plasma membrane - General func5ons - Physical isola5on - Regula5on of exchange with the environment - Controls entry of ions and nutrients - Controls elimina5on of wastes - Controls release of secre5ons Cell Membrane
- Also called plasma membrane - General func5ons - Physical isola5on - Regula5on of exchange with the environment - Sensi5vity to the environment - First part of cell affected by composi5on, concentra5on and pH of extracellular material - Contains variety of receptors - Allow cell to recognize and respond to specific molecules - Trigger ac5va5on or deac5va5on of enzymes Cell Membrane
- Also called plasma membrane - General func5ons - - - - Physical isola5on Regula5on of exchange with the environment Sensi5vity to the environment Structural Support - Specialized connec5ons between - cell membranes of adjacent cells - Cell membranes and extracellular materials Cell Membrane
- Also called plasma membrane - General func5ons - - - - - Physical isola5on Regula5on of exchange with the environment Sensi5vity to the environment Structural Support Very thin containing lipids proteins and carbohydrates Cell Membrane Cell Membrane Membrane Lipids Form most of the surface area of the membrane Phospholipid bilayer (oreo) Membrane Proteins Integral proteins Peripheral proteins Membrane Carbohydrates Components of complex molecules Carbohydrate por5ons extend beyond the outer surface of membrane glycocalyx Cell Membrane Membrane Lipids Membrane Proteins Membrane Carbohydrates Selec5ve Permeability Cell membrane is selec5vely permeable: allows some materials to move freely restricts other materials The cell membrane is a barrier, but: nutrients must get in products and wastes must get out Permeability of cells depends upon their func5on (i.e. diges5ve vs. muscle, etc) Restricted Materials Selec5ve permeability restricts materials based on: size electrical charge molecular shape lipid solubility Transport Transport through a cell membrane can be: ac5ve (requiring energy and ATP) passive (no energy required) Diffusion (passive) Carrier-mediated transport (passive or ac5ve) Vesicular transport (ac5ve) Modes of passive transport Simple Diffusion Osmosis Filtra5on Facilitated diffusion Modes of passive transport Diffusion molecules mix randomly solute spreads through solvent eliminates concentra5on gradient net movement of molecules from region of high concentra5on to that of low concentra5on Diffusion Factors influencing diffusion rate: Distance (greater means slower) Gradient size (greater means faster) Size (smaller means faster) Temperature (increased temp means faster) Electrical forces (i.e., +, -) Diffusion and the Cell Membrane Diffusion can be simple or channel-mediated Figure 315 Passive Transport Simple Diffusion Materials which diffuse through cell membrane: lipid-soluble compounds (alcohols, fady acids, and steroids) dissolved gases (oxygen and carbon dioxide) Passive Transport Channel-Mediated Diffusion Materials which pass through transmembrane proteins (channels): water soluble compounds ions Passage depends on: size charge interac5on with the channel Passive Transport Osmosis diffusion of water molecules across a membrane Water will always move to area of higher solute concentra5on. How Osmosis Works More solute molecules, lower concentra5on of water molecules Membrane must be freely permeable to water, selec5vely permeable to solutes Osmosis Osmosis Water Movement Water molecules diffuse across membrane toward solu5on with more solutes Volume increases on the side with more solutes Osmosis Osmo5c Pressure Is the force of a concentra5on gradient of water Equals the force (hydrosta5c pressure) needed to block osmosis Osmosis Isotonic Solu5ons A solu5on that does not cause osmo5c flow of water in or out of a cell iso = same, tonos = tension Hypotonic Solu5ons hypo = below Has less solutes Loses water through osmosis A cell in a hypotonic solu5on: gains water ruptures (hemolysis of red blood cells) Hypertonic Solu5ons hyper = above Has more solutes Gains water through osmosis A cell in a hypertonic solu5on: loses water shrinks (crena5on of red blood cells) Passive Transport Filtra5on water moving through porous substances that behave as filter very small solutes pushed across membrane with water Kidneys Carrier-Mediated Transport Passive transport facilitated diffusion Ac5ve transport Characteris5cs of Carrier-Mediated Transport Specificity: 1 transport protein, 1 set of substrates Satura5on limits: rate depends on transport proteins, not substrate Regula5on: cofactors such as hormones Facilitated Diffusion Passive Carrier mediated Figure 318 How Facilitated Diffusion Works Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids): molecule binds to receptor site on carrier protein protein changes shape, molecules pass through receptor site is specific to certain molecules Ac5ve Transport Ac5ve transport proteins: move substrates against concentra5on gradient require energy, such as ATP ion pumps move ions (Na+, K+, Ca+, Mg2+) exchange pump counter transports 2 ions at the same 5me Sodium-Potassium Exchange Pump Figure 319 Sodium-Potassium Exchange Pump Ac5ve transport, carrier mediated: sodium ions (Na+) out, potassium ions (K+) in 1 ATP moves 3 Na+ Secondary Ac5ve Transport Na+ concentra5on gradient drives glucose transport ATP energy pumps Na+ back out Figure 320 Transport Vesicles Also called bulk transport Vesicles: endocytosis (endo = into) ac5ve transport using ATP: receptor-mediated pinocytosis phagocytosis exocytosis (exo = out of) Receptor-Mediated Endocytosis Figure 321 Receptor-Mediated Endocytosis Receptors (glycoproteins) bind target molecules (ligands) Coated vesicle (endosome) carries ligands and receptors into the cell Pinocytosis Pinocytosis cell drinking Endosomes "drink" extracellular fluid Figure 322a Phagocytosis Phagocytosis (cell ea9ng) pseudopodia (psuedo = false, podia = feet) engulf large objects in phagosomes Figure 322b Exocytosis Is the reverse of endocytosis Figure 37b Cytoplasm Between cell membrane and nuclear membrane Two main parts Cytosol intracellular fluid Organelles structures suspended within the cytosol Membranous Non-membranous Cytoplasm Organelles Nonmembranous Organelles Microvilli Centrioles Cilia Proteosomes Cytoskeleton Ribosomes Cytoplasm
Cytoskeleton cell skeleton; give strength and flexibility Microfilaments ac5n Intermediate Filaments Thick Filaments myosin Microtubules tubulin Cytoplasm Non-membranous Organelles Ribosomes responsible for protein synthesis 2 subunits small and large fixed vs free Cytoplasm Organelles Membranous Organelles Endoplasmic re5culum Golgi apparatus Lysosomes Membrane flow Mitochondria Cytoplasm Membranous Organelles Endoplasmic re5culum Synthesis produc5on of protein, carbohydrates and lipids Storage stores molecules synthesized in the cell or absorbed from the cytoplasm Transport materials can travel from place to place within the ER Cytoplasm Membranous Organelles Endoplasmic re5culum Smooth ER no ribosomes lipids and carbohydrates (especially for membranes cell, nuclear, and ER) involved in steroid synthesis (testosterone and estrogen) involved in glycogen produc5on and storage Cytoplasm Membranous Organelles Endoplasmic re5culum Rough ER fixed ribosomes synthesis of proteins transport vesicles Cytoplasm Membranous Organelles Golgi apparatus Secretory vesicles discharge contents via cell membrane (exocytosis) Membrane renewal vesicles exchange of materials Lysosomes remain in cytoplasm containing diges5ve enzymes Cytoplasm Membranous Organelles Lysosomes Primary lysosomes inac5ve enzymes Secondary lysosomes ac5vated enzymes absorb damaged organelles absorb nutrients Autolysis Cytoplasm Membranous Organelles Membrane Flow Constant exchange of materials within cell Replacement of membrane Interconnectedness Cytoplasm Membranous Organelles Mitochondria Responsible for energy produc5on Double membrane (cristae) Fluid contents (matrix) contain enzymes for catalyzing energy reac5ons Glycolysis The Nucleus Is the cell's control center Figure 310a Structure of the Nucleus Nucleus: largest organelle Nuclear envelope: double membrane around the nucleus Perinuclear space: between 2 layers of nuclear envelope Nuclear pores: communica5on passages Within the Nucleus DNA: all informa5on to build and run organisms Nucleoplasm: fluid containing ions, enzymes, nucleo5des, and some RNA Nuclear matrix: support filaments Nucleus Controls Cell Structure and Func5on Direct control through synthesis of: structural proteins secre5ons (environmental response) Indirect control over metabolism through enzymes HOW DO THEY DO IT? Gene5c code informa5on stored in the sequence of DNA nucleo5des (A, C, G, and T) Triplet Code 3 base sequence specify the iden5ty of one amino acid. Genes Sequences of triplets that determine protein structures. DNA and Genes Gene: DNA instruc5ons for 1 protein DNA: instruc5ons for every protein in the body Organiza5on of DNA Nucleosomes: DNA coiled around histones Chroma5n: loosely coiled DNA (cells not dividing) Chromosomes: 5ghtly coiled DNA (cells dividing) KEY CONCEPT The nucleus contains chromosomes Chromosomes contain DNA DNA stores gene5c instruc5ons for proteins Proteins determine cell structure and func5on Protein Synthesis Transcrip5on: copies instruc5ons from DNA to mRNA (in nucleus) Transla5on: ribosome reads code from mRNA (in cytoplasm) assembles amino acids into polypep5de chain mRNA Transcrip5on A gene is transcribed to mRNA in 3 steps: gene ac5va5on DNA to mRNA RNA processing Step 1: Gene Ac5va5on Uncoils DNA, removes histones Start (promoter) and stop codes on DNA mark loca5on of gene: coding strand is code for protein template strand used by RNA polymerase molecule Step 2: DNA to mRNA Enzyme RNA polymerase transcribes DNA: binds to promoter (start) sequence reads DNA code for gene binds nucleo5des to form messenger RNA (mRNA) mRNA duplicates DNA coding strand, uracil replaces thymine Step 3: RNA Processing At stop signal, mRNA detaches from DNA molecule: code is edited (RNA processing) unnecessary codes (introns) removed good codes (exons) spliced together triplet of 3 nucleo5des (codon) represents one amino acid Codons Table 32 Protein synthesis
Transcription Formation of mRNA from DNA mRNA carries instructions from the nucleus to the cytoplasm Translation Formation of protein from mRNA Transcription is process of messenger RNA (mRNA) formation using the information stored in DNA. Transcription is process of messenger RNA (mRNA) formation using the information stored in DNA. Transcription is process of messenger RNA (mRNA) formation using the information stored in DNA. Transcription is process of messenger RNA (mRNA) formation using the information stored in DNA. Transla5on is the forma5on of a protein A func5onal polypep5de is constructed using mRNA codons Sequence of codons determines the sequence of amino acids Complementary base pairing of an5codons (tRNA) provides the amino acids in sequence Ribosomes are necessary for transla5on to occur Transla5on (1 of 6) mRNA moves: from the nucleus through a nuclear pore Figure 313 Transla5on (2 of 6) mRNA moves: to a ribosome in cytoplasm surrounded by amino acids Figure 313 (Step 1) Transla5on (3 of 6) mRNA binds to ribosomal subunits tRNA delivers amino acids to mRNA Figure 313 (Step 2) Transla5on (4 of 6) tRNA an5codon binds to mRNA codon 1 mRNA codon translates to 1 amino acid Figure 313 (Step 3) Transla5on (5 of 6) Enzymes join amino acids with pep5de bonds Polypep5de chain has specific sequence of amino acids Figure 313 (Step 4) Transla5on (6 of 6) At stop codon, components separate Figure 313 (Step 5) Summary 1 2 3 KEY CONCEPT Genes: are func5onal units of DNA contain instruc5ons for 1 or more proteins Protein synthesis requires: several enzymes ribosomes 3 types of RNA KEY CONCEPT Muta5on is a change in the nucleo5de sequence of a gene: can change gene func5on Causes: exposure to chemicals exposure to radia5on mistakes during DNA replica5on Cell Life Cycle Cell division is the reproduc5on of cells Mitosis is the nuclear division of soma5c cells Meiosis produces sex cells Most of a cell's life is spent in a nondividing state (interphase) The Cell Life Cycle In cancer cells the cycle time can decrease to as little as 12 hours. Differentiated 3 Stages of Cell Division Body (soma5c) cells divide in 3 stages: DNA replica5on duplicates gene5c material exactly Mitosis divides gene5c material equally Cytokinesis divides cytoplasm and organelles into 2 IDENTICAL daughter cells DNA Replica5on DNA strands unwind DNA polymerase adaches complementary nucleo5des Figure 324 Mitosis Mitosis divides duplicated DNA into 2 sets of chromosomes: DNA coils 5ghtly into chroma5ds chroma5ds connect at a centromere Stage 1: Prophase Figure 325 (Stage 1) Features of Prophase Nucleoli disappear Centriole pairs move to cell poles Microtubules (spindle fibers) extend between centriole pairs Nuclear envelope disappears Spindle fibers adach to kinetochore Stage 2: Features of Metaphase Chromosomes align in a central plane (metaphase plate) Stage 3: Features of Anaphase Microtubules pull chromosomes apart Daughter chromosomes group near centrioles Stage 4: Features of Telophase Nuclear membranes reform Chromosomes uncoil Nucleoli reappear Cell has 2 complete nuclei KEY CONCEPT Mitosis duplicates chromosomes in the nucleus for cell division Stage 4: Features of Cytokinesis Division of the cytoplasm Cleavage furrow around metaphase plate Membrane closes, producing daughter cells During cytokinesis, the cytoplasm divides and cell division ends Figure 325 (Stage 4, 2 of 2) DNA replication Figure 3.29a-d End result of Mitosis/Cytokinesis 2 identical daughter cells Figure 3.29e, f Mito5c Rate and Energy Rate of cell division: slower mito5c rate means longer cell life cell division requires energy (ATP) Telomeres Progeria Rapid shortening of the telomeres Long Life, Short Life Muscle cells, neurons rarely divide Exposed cells (skin and diges5ve tract) live only days or hours Hematopoe5c stem cells live decades Cancer cells are immortal Regula5ng Cell Life Normally, cell division balances cell loss Gene5cally controlled Some5mes cells lose control ("division addicts") Oncogenes: mutated genes that cause cancer Cell Division and Cancer tumor when balance is broken down and cell divides con5nuously benign a tumor which remains confined within a connec5ve 5ssue capsule malignant a tumor which is capable of spreading into nearby 5ssue Cancer: illness that disrupts cellular controls produces malignant cells A Simplistic Model of Cancer You Birth Life Death Cancer Cancer Cell DNALife Birth Mutation Cancer Stages Cancer develops in steps: abnormal cell primary tumor metastasis secondary tumor Primary tumor cells Abnormal cell Growth of blood vessels into the tumor Secondary tumor cells Invasion Cell divisions Penetration Circulation Escape The Development of Cancer KEY CONCEPT Muta5ons disrupt normal controls over cell growth and division Cancers omen begin where stem cells are dividing rapidly More chromosome copies mean greater chance of error Differen5a5on Process of Specializa5on Results from inac5va5on of par5cular genes Reproduces popula5ons of cells with limited capabili5es Differen5ated cells form specific 5ssues All soma5c cells contain the same chromosomes, but some have been "turned off" As more are turned off the cell becomes more specialized KEY CONCEPT All body cells, except sex cells, contain the same 46 chromosomes Differen5a5on depends on which genes are ac5ve and which are inac5ve ...
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- Fall '11