Biology - Cell Organization (PDF)

BIOLOGY tenth edition Topic 3 Organization of the Cell © Cengage Learning 2015 SOLOMON MARTIN MARTIN BERG  4.1 The Cell: Basic Unit of Life The cell is the smallest unit that c...

BIOLOGY tenth edition Topic 3 Organization of the Cell © Cengage Learning 2015 SOLOMON MARTIN MARTIN BERG  4.1 The Cell: Basic Unit of Life The cell is the smallest unit that can carry out all activities associated with life – Most prokaryotes and many protists and fungi consist of a single cell, while most plants and animals are composed of millions of cells Cells are: – Building blocks of complex multicellular organisms – Extraordinarily diverse and versatile © Cengage Learning 2015  Cell Theory: A Unifying Concept Cells are the basic living units of organization and function in all organisms All cells come from other cells All living cells have a common origin, provided by basic similarities in their structures and molecules of which they are made © Cengage Learning 2015  The Organization and Basic Functions of All Cells Are Similar Cells are able to maintain homeostasis – Plasma membrane acts as a selective barrier between cell contents and the environment to support homeostasis Most cells have specialized organelles that carry out metabolic activities Each cell has genetic instructions coded in DNA © Cengage Learning 2015  Cell Size is Limited Most cell components are measured in nanometers (nm) Everything that enters or leaves a cell must pass through its plasma membrane – Ratio of surface area to volume is critical Some variations in cell shape represent a strategy for increasing the ratio of surface area to volume – Example: microvilli © Cengage Learning 2015  Cell Size and Shape Are Adapted to Function Amoebas and white blood cells change shape as they move – Sperm cells have long, whiplike tails (flagella) for locomotion Nerve cells have long, thin extensions that enable them to transmit messages over great distances Rectangular epithelial cells and stack like building blocks to form sheet-like tissues © Cengage Learning 2015  4.2 Methods For Studying Cells Robert Hooke first described cells in 1665, using a microscope that he had made Antonie van Leeuwenhoek discovered bacteria, protists, blood cells, and sperm cells with small lenses that he made In the late 19th century, microscopes were sufficiently developed for biologists to seriously study cells © Cengage Learning 2015  Light Microscopes Are Used to Study Stained or Living Cells A light microscope consists of a tube with glass lenses at each end in which visible light passes through stained or living cells – Lenses refract light and magnify the image © Cengage Learning 2015  Light microscope Light beam Ocular lens Objective lens Specimen Condenser lens Light source © Cengage Learning 2015  Light Microscopes (cont’d.) Magnification: ratio of the size of the image seen with the microscope to actual size of the object – Light microscopes magnify an object no more than 2000X – Resolving power: minimum distance between two points at which they can both be seen separately Depends on lens quality and wavelength; increases as wavelength decreases © Cengage Learning 2015  Light Microscopes (cont’d.) Five different optical systems help biologists study living cells – Bright-field microscopy – Dark-field microscopy – Phase contrast microscopy and Nomarski differential-interference-contrast microscopy – Fluorescence microscope – Confocal microscopy © Cengage Learning 2015  Using Light Microscopy b c d f © Cengage Learning 2015  Electron Microscopes Provide a High-Resolution Image The electron microscope is used to study the ultrastructure of cells – Some electron microscopes have resolving powers less than 1 nm – The electron beam consists of energized electrons, focused by electromagnets Two types: – Transmission electron microscope – Scanning electron microscope © Cengage Learning 2015  Biologists Use Biochemical and Genetic Methods Cell fractionation is a technique for separating parts of cells for studying – Cells broken apart are spun in a centrifuge, separating the extract into a pellet and a supernatant The supernatant can be centrifuged again into another pellet, called differential centrifugation – Pellets can be resuspended or components further purified by density gradient centrifugation © Cengage Learning 2015  4.3 Prokaryotic and Eukaryotic Cells © Cengage Learning 2015  Organelles of Prokaryotic Cells Are Not Surrounded by Membranes Bacteria and Archaea are prokaryotic cells – DNA is located in a nucleoid – No membrane-enclosed internal organelles – Most have cell walls outside the plasma membrane – Many have prokaryotic flagella for movement – Interior contains ribosomes and storage granules © Cengage Learning 2015  Structure of a Prokaryotic Cell Fimbriae Storage granule Capsule Flagellum Ribosome Cell wall Plasma Nuclear membrane DNA area © Cengage Learning 2015  Membranes Divide the Eukaryotic Cell Into Compartments Eukaryotic cells: characterized by highly organized and specialized membrane- enclosed organelles – Nucleus contains DNA – Cytoplasm: part of the cell outside the nucleus – Cytoskeleton: allows a larger size than prokaryotes – Some organelles present only in specific cells © Cengage Learning 2015  Membranes Allow Eukaryotic Cells to Carry on Many Diverse Functions Membrane-enclosed compartments allow for different cell activities to go on simultaneously – Chemical reactions in cells are carried out by enzymes that are bound to membranes – Membranes allow cells to store energy As particles of a substance move from an area of higher concentration to lower concentration, the cell can convert some of potential energy to ATP © Cengage Learning 2015  4.4 The Cell Nucleus The nucleus is the control center of the cell – Nuclear envelope: double membrane that separates nuclear contents from the cytoplasm – Nuclear pores: regulate passage of materials between nucleoplasm and cytoplasm – Nuclear lamina: helps organize nuclear contents, DNA duplication and regulating the cell cycle © Cengage Learning 2015  The Cell Nucleus (cont’d.) DNA replication occurs during cell division, when DNA is reproduced and passed on to two daughter cells – DNA molecules include genes that contain coded instructions for protein production – The nucleus transcribes information from DNA to messenger RNA (mRNA) molecules mRNA moves into the cytoplasm, where proteins are manufactured © Cengage Learning 2015  The Cell Nucleus (cont’d.) Chromatin: DNA associates with RNA and certain proteins – Helps DNA molecules pack inside the nucleus as chromosomes The nucleus of each human cell has 46 chromosomes (23 pairs), containing 2 meters of DNA © Cengage Learning 2015  The Cell Nucleus (cont’d.) Most nuclei have one or more nucleoli (nucleolus), which synthesizes ribosomal RNA (rRNA) – Proteins needed to make ribosomes are synthesized in the cytoplasm and imported into the nucleolus – rRNA and proteins are assembled into ribosomal subunits that leave the nucleus through nuclear pores © Cengage Learning 2015  The Cell Nucleus (cont’d.) Nucleus Nucleolus © Cengage Learning 2015  Ribosomes Manufacture Proteins in the Cytoplasm Ribosomes: organelles found free in the cytoplasm or attached to certain membranes – Contain the enzyme that forms peptide bonds, which join amino acids into polypeptides – Each ribosome has a large subunit and a small subunit that join to assemble polypeptides – Cell can change the number of ribosomes present to meet its metabolic needs © Cengage Learning 2015  4.5 Membranous Organelles In The Cytoplasm Endomembrane system: a network of organelles that exchange materials through small membrane-enclosed transport vesicles – Each vesicle has proteins embedded in its membrane that serve as specific routing signals for its destination organelle © Cengage Learning 2015  The Endoplasmic Reticulum is a Network of Membranes ER makes up a significant part of the total volume of the cytoplasm Smooth ER synthesizes lipids, breaks down toxins and might store Ca 2+ – Synthesizes phospholipids and cholesterol to make cell membranes Rough ER synthesizes secreted and membrane proteins © Cengage Learning 2015  Endoplasmic Reticulum (ER) Smooth ER Rough ER Ribosomes © Cengage Learning 2015  The Golgi Complex Consists of stacks of flattened membranous sacs called cisternae Processes, sorts, and modifies proteins Each Golgi stack has three areas – The cis face: entry surface – The trans face: exit surface – The medial region: in between © Cengage Learning 2015  The Golgi Complex (cont’d.) © Cengage Learning 2015  The Golgi Complex (cont’d.) A typical sequence followed by a glycoprotein destined for secretion from the cell © Cengage Learning 2015  Lysosomes Are Compartments For Digestion Small sacs of digestive enzymes dispersed in the cytoplasm of animal cells – Contain about 40 different digestive enzymes – Maintain an interior pH of about 5 – Primary lysosomes bud from the Golgi complex – One or more primary lysosomes fuse with a vesicle to form a secondary lysosome © Cengage Learning 2015  Lysosomes Are Compartments For Digestion © Cengage Learning 2015  Lysosomes (cont’d.) Primary lysosomes contain hydrolytic enzymes synthesized in rough ER – Sugars attached to each molecule direct the Golgi complex to sort the enzyme to lysosomes One or more primary lysosomes fuse with a vesicle when bacteria or debris is engulfed by a cell, forming a secondary lysosome: help in cell digestion © Cengage Learning 2015  Vacuoles Are Large, Fluid-Filled Sacs With a Variety of Functions Large, single, membrane-enclosed sacs – Tonoplast: membrane of the vacuole – Play a significant role in plant growth and development (the central vacuole) – Plant vacuoles are like lysosomes They break down wastes © Cengage Learning 2015  Vacuoles (cont’d.) Food vacuoles fuse with lysosomes to digest food Contractile vacuoles remove excess water from the cell © Cengage Learning 2015  Peroxisomes Metabolize Small Organic Compounds Contain enzymes that help transfer hydrogen from other compounds to oxygen – Break down fatty acid molecules – Synthesize phospholipids – Degrade alcohol in yeast cells; detoxify toxic compounds in human liver and kidney cells, – Can convert stored fats to sugars in plant seeds © Cengage Learning 2015  Mitochondria and Chloroplasts Are Energy Converting Organelles Specialized to facilitate conversion of energy from one form to another – Chemical energy or light energy must be converted into more convenient forms, such as ATP Have their own ribosomes and DNA molecules – Theory of serial endosymbiosis © Cengage Learning 2015  Mitochondria and Chloroplasts (cont’d.) Aerobic respiration Photosynthesis Mitochondria Chloroplasts (most eukaryotic cells) (some plant and algal cells) © Cengage Learning 2015  Figure 4-19 Aerobic respiration and photosynthesis Aerobic respiration takes place in the mitochondria of virtually all eukaryotic cells. In this process, some of the chemical energy in glucose is transferred to ATP. Photosynthesis, which is carried out in chloroplasts in some plant and algal cells, converts light energy to ATP and to other forms of chemical energy. This energy is used to synthesize glucose from carbon dioxide and water. © Cengage Learning 2015  Mitochondria Make ATP Through Aerobic Respiration Aerobic respiration converts the chemical energy in certain foods to ATP A double membrane forms two compartments: intermembrane space and matrix – Outer mitochondrial membrane is smooth, allowing small molecules to pass through it – Inner mitochondrial membrane strictly regulates molecules that move across it © Cengage Learning 2015  Folds in the inner membrane (cristae) extend into the matrix and increase surface area for chemical reactions The inner membrane contains enzymes and other proteins needed to synthesize ATP © Cengage Learning 2015  Mitochondria Make ATP (cont’d.) Important in apoptosis, a normal part of development and maintenance – Example: The hand of a human embryo is webbed until apoptosis destroys the tissue between the fingers – Can initiate apoptosis by interfering with energy metabolism or by activating destructive enzymes Example: Cytochrome c activates caspases, which cut up vital compounds in the cell © Cengage Learning 2015  Mitochondria Make ATP (cont’d.) Inappropriate inhibition of apoptosis may contribute to a variety of diseases Mutations in mitochondrial DNA are associated with certain genetic diseases Mitochondria also affect health and aging by leaking electrons, forming free radicals: toxic, highly reactive compounds with unpaired electrons © Cengage Learning 2015  Chloroplasts Convert Light Energy to Chemical Energy via Photosynthesis Chlorophyll: a green pigment that traps light energy for photosynthesis – Also contain light-absorbing yellow and orange pigments – Disc-shaped structures with a system of folded membranes – The inner membrane encloses a fluid-filled stroma that contains enzymes that produce carbohydrates from CO2 and H2O © Cengage Learning 2015  Chloroplasts (cont’d.) Chloroplasts also have: – An interconnected set of thylakoids arranged in stacks, suspended in the stroma – Thylakoid membrane that encloses the thylakoid lumen, in which chlorophyll molecules absorb energy from sunlight A type of plastids: organelles that produce and store food materials in cells of plants © Cengage Learning 2015  Chloroplasts (cont’d.) All plastids develop from proplastids Chromoplasts contain pigments that give flowers and fruits characteristic colors that attract animals that serve as pollinators or as seed dispersers Leukoplasts include amyloplasts: store starch in many seeds, roots, and tubers © Cengage Learning 2015  Inner Stroma membrane Outer membrane Granum (stack of Thylakoid thylakoids) Intermembrane lumen space Thylakoid membrane  Figure 4-21 A chloroplast, the organelle of photosynthesis This TEM shows part of a chloroplast from a corn leaf cell. Chlorophyll and other photosynthetic pigments are in the thylakoid membranes. One granum is cut open to show the thylakoid lumen. The inner chloroplast membrane may or may not be continuous with the thylakoid membrane (as shown).  4.6 The Cytoskeleton Plasma membrane Microfilament Intermediate filament Microtubule © Cengage Learning 2015  Figure 4-22 The cytoskeleton The cytoskeleton of eukaryotic cells consists of networks of several types of fibers, including microtubules, microfilaments, and intermediate filaments. The cytoskeleton contributes to the shape of the cell, anchors organelles, and sometimes rapidly changes shape during cell locomotion. © Cengage Learning 2015  Microtubules Are Hollow Cylinders Rigid, hollow rods about 25 nm in diameter – Function in cytoskeleton structure in movement of chromosomes during cell division – Track for intracellular movement i.e involved in transport of cellular materials by interacting with “motor” molecules to cause the movement of organelles – Structural components of cilia and flagella – Consist of two forms of the protein: α-tubulin and β-tubulin, which combine to form a dimer © Cengage Learning 2015  Microtubules © Cengage Learning 2015  Microtubules (cont’d.) Structural microtubule-associated proteins (MAPs) regulate microtubule assembly, and cross-link microtubules to other cytoskeletal polymers Motor MAPs use ATP energy to produce movement Kinesin moves organelles toward the plus end of a microtubule Dynein moves organelles toward the minus end (retrograde transport) © Cengage Learning 2015  Centrosomes and Centrioles Function in Cell Division Microtubule-organizing centers (MTOCs) anchor minus ends of microtubules to other parts of the cell – In animal cells, the main MTOC is the centrosome, containing two centrioles, which are duplicated before cell division – Microtubules assemble and disassemble rapidly during cell division; tubulin subunits organize into a mitotic spindle, which helps distribute chromosomes © Cengage Learning 2015  Centrioles Anchoring of microtubules to MTOCs typically occurs via their minus-ends, whereas the plus-ends extend away from it and are more dynamic © Cengage Learning 2015 9+0 pattern arrangement  Cilia and Flagella Are Composed of Microtubules Cilia and flagella help unicellular and small multicellular organisms move through a watery environment – Cells use cilia to move liquids and particles across the cell surface – EXAMPLES: Cilia on epithelial cells in respiratory tract Flagella on a sperm © Cengage Learning 2015  Eukaryotic cilia and flagella are structurally alike with a 9 + 2 arrangement of microtubules Each cilium or flagellum is anchored in the cell by a basal body, which has a 9 × 3 structure of microtubules (9+0 pattern arrangement) © Cengage Learning 2015  Cilia and Flagella © Cengage Learning 2015  Microfilaments Consist of Intertwined Strings of Actin Also called actin filaments – Flexible, solid fibers about 7 nm in diameter – Consists of two intertwined polymer chains of beadlike actin molecules – Linked by linker proteins – Bundles to provide support for cell structures – Form the cell cortex, just inside the plasma membrane © Cengage Learning 2015  Microfilaments (cont’d.) Microfilaments generate movement by rapidly assembling and disassembling Muscle cells have two types of specialized filaments: myosin and actin – ATP, actin and myosin help contract muscles – In amoeba and human WBC, actin filaments push the plasma membrane outward Form pseudopodia that adhere to surface while contractions at the opposite end force cytoplasm forward © Cengage Learning 2015  Intermediate Filaments Help Stabilize Cell Shape Tough, flexible fibers about 10 nm in diameter – Provide mechanical strength and help stabilize cell shape – Only some animal groups have intermediate filaments – Include keratins in vertebrate epithelial cells, and neurofilaments in nerve cells – Abnormal neurofilaments associated with several diseases © Cengage Learning 2015  4.7 Cell Coverings Many cells are surrounded by a glycocalyx – Allows cells to recognize one another, make contact, and form adhesive or communicating associations – Contributes to the mechanical strength of multicellular tissues © Cengage Learning 2015  Cell Coverings (cont’d.) Many animal cells secrete an extracellular matrix consisting of a gel of carbohydrates and fibrous proteins (mainly collagen) Fibronectins organize the matrix and help cells attach to it. They are glycoproteins of ECM that bind to integrins, receptor proteins in the plasma membrane. Integrins in the plasma membrane maintain adhesion between ECM and intermediate filaments and microfilaments inside the cell © Cengage Learning 2015  Cell Coverings (cont’d.) The cells of most bacteria, archaea, fungi, and plants are surrounded by a cell wall – Plant cell walls contain cellulose – A growing plant cell secretes a primary cell wall, which either solidifies or replaced by a secondary cell wall with a different chemical composition © Cengage Learning 2015 Cell 1 Middle lamella Primary cell wall Multiple layers of secondary cell wall Cell 2 Figure 4-30 Plant cell walls The cell walls of two adjacent plant cells are labeled in this TEM. The cells are cemented together by the middle lamella, a layer of gluelike polysaccharides called pectins. A growing plant cell first secretes a thin primary wall that is flexible and can stretch as the cell grows. The thicker layers of the secondary wall are secreted inside the primary wall after the cell stops elongating.