The Cell - PDF

THE CELL DIMARUN HANEF D. MACABUNBUN JR. Overview: The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live  Cell structure is correlated to cellular function Figure 6.1 10 µm  Concept 6.1: To...

THE CELL DIMARUN HANEF D. MACABUNBUN JR. Overview: The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live  Cell structure is correlated to cellular function Figure 6.1 10 µm  Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye  Light microscopes (LMs) (powerful exploratory tools for 300 years  Pass visible light through a specimen  Magnify cellular structures with lenses  10 m Different types of 1m Human height microscopes Unaided eye Light microscope Length of some nerve and muscle cells 0.1 m  Can be used to visualize Chicken egg 1 cm different sized cellular Frog egg structures 1 mm Electron microscope 100 µm Measurements Most plant 1 centimeter (cm) = 102 and Animal cells 10 µ m meter (m) = 0.4 inch Nucleus Most bacteria Mitochondrion Electron microscope 1 millimeter (mm) = 10–3 m 1µm 1 micrometer (µm) = 10–3 100 nm Smallest bacteria mm = 10–6 m Viruses 1 nanometer (nm) = 10–3 10 nm Ribosomes mm = 10–9 m Proteins Lipids 1 nm Small molecules Figure 6.2 0.1 nm Atoms   Use different methods for enhancing visualization of cellular structures TECHNIQUE RESULT (a) Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.] 50 µm (b) Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved). (c) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells. Figure 6.3  (d) Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D. (e) Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery. 50 µm (f) Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. 50 µm  Electron microscopes (EMs)  It employ high voltages to direct a beam of electrons through or at a surface of objects examined.  The wavelength of the electron beam is approximately 0.00001 that of ordinary white light, thus permitting far greater magnification and resolution.  Focus a beam of electrons through a specimen (TEM) or onto its surface (SEM)  Transmission Electron microscope (TEM)  Preparations for viewing: 1.Specimens are cut into extremely thin sections (10nm to 100nm thick) 2.It is treated with electron stains (ions of Osmium, Lead and Uranium) to increase contrast between different structures 3.Electrons pass through a specimen & images are seen on fluorescent screen 4.Photographed  The transmission electron microscope (TEM)  Provides for detailed study of the internal ultrastructure of cells Longitudinal Cross section section of of cilium 1 µm cilium (b) Transmission electron micro- scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections. Figure 6.4 (b)  Scanning Electron microscope (SEM)  Preparations for viewing: 1.Specimens are not sectioned 2.Electrons do not pass through them 3.The whole specimen is coated with an electron- dense material & bombarded with electrons causing some electrons to be reflected back & secondary electrons to be emitted 4.An apparent 3-dimensional image is recorded in the photograph (Magnification is not as great as TEM)  The scanning electron microscope (SEM)  Provides for detailed study of the surface of a specimen TECHNIQUE RESULTS 1 µm Cilia (a) Scanning electron micro- scopy (SEM). Micrographs taken with a scanning electron micro- scope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps move inhaled debris upward toward the throat. Figure 6.4 (a)  X-Ray & Nuclear Magnetic Resonance (NMR) Spectroscopy  With greater level of resolution  These techniques reveal the shapes of biomolecules & the relationships among atoms within them  Both are laborious, but NMR Spectroscopy does not require purification & Crystallization of a substance, & molecules can be observed in solution. CELL – the smallest unit of life. CYTOLOGY – the study of cell  HISTORICAL BACKGROUND In 1600’s, The MICROSCOPE was invented. Hooke’s Microscope  HISTORICAL BACKGROUND ROBERT HOOKE British Scientist In 1665, He first observed mass of tiny cavities from thin slices of cork with his self- made microscope. Demonstrated the microscope to the Royal Society of London in cork 1663.  HISTORICAL BACKGROUND ANTONI VAN LEEUWENHOEK Dutch Scientist In 1674, He first observed Diatoms living cells in a pond of water. Sperm Cells Paramecium RBC’s  HISTORICAL BACKGROUND ROBERT BROWN (1831) British botanist observed plant cells with a distinct central part (nucleus); he described the streaming movement of the cytoplasm (Brownian movement) FELIX DUJARDIN (1835) French Biologist observed that cells were not empty but filled with thick, jelly-like fluids (protoplasm)  HISTORICAL BACKGROUND MATTHIAS JACOB SCHLEIDEN German Botanist In 1838, he concluded that all plant tissue was composed of cells are made of cells. plant cells  HISTORICAL BACKGROUND THEODOR SCHWANN German Biologist In 1839, he stated that all animals are made of cells. animal cells  HISTORICAL BACKGROUND RUDOLF VIRCHOW German Physician In 1858, he concluded that all cells came from pre-existing cells.  HISTORICAL BACKGROUND J. PURKINJE In 1840, he introduced the term PROTOPLASM to describe cell contents. PROTOPLASM  thought to be a granular, gel- like mixture with special elusive life properties of its own.  HISTORICAL BACKGROUND MAX KNOLL and ERNST RUSKA (1932) German engineers built the first transmission electron microscope JAMES WATSON (American biochemist) and FRANCIS CRICK (British biophysicist) (1953) discovered the structure of DNA that ushered in the era of molecular biology  CELL THEORY 1. All living things are made of one or more cells. unicellular multicellular Paramecium Epithelial Tissue Amoeba Nervous Tissue  CELL THEORY 2. Cells are the basic unit of structure and function in living things.  CELL THEORY 3. All cells come from pre-existing cells.  I - CELL CHARACTERSITICS Cell size varies from a size of a bird’s egg to a bacterium (200 – 250 mu) Cell shape varies and is usually related to its function. Cell exhibits motility, irritability, growth and reproduction, metabolism and repair.  CELL SIZE Varies from 2 meters long (nerve cells in giraffe legs) to.2 microns (the smallest bacteria) Nerve cell Egg cell Bacterial cells  10 m Human height 1m CELL SIZE Length of some Light microscope nerve and muscle cells 0.1 m Chicken egg 1 cm Different types of Frog egg microscopes 1 mm  Can be used to visualize Electron microscope 100 µm different sized cellular Most plant and Animal cells structures 10 µ m Nucleus Most bacteria Mitochondrion Electron microscope 1µm 100 nm Smallest bacteria Measurements Viruses 1 centimeter (cm) = 102 meter (m) = 0.4 inch 10 nm Ribosomes 1 millimeter (mm) = 10–3 m Proteins 1 micrometer (µm) = 10–3 mm = 10–6 m Lipids 1 nanometer (nm) = 10–3 mm = 10–9 m 1 nm Small molecules Figure 6.2 0.1 nm Atoms  A smaller cell Surface area increases while total volume remains constant  Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cell 5 1 1 Total surface area (height  width  6 150 750 number of sides  number of boxes) Total volume (height  width  length 1 125 125  number of boxes) Surface-to-volume ratio 6 12 6 (surface area  volume) Figure 6.7  CELL SHAPE Varies from 2 meters long (nerve cells in giraffe legs) to.2 microns (the smallest bacteria) Bacterial cells Egg cell Nerve cell WBC and RBC’s Sperm cell  II – FUNCTIONS OF THE CELL Mechanical function – exhibited by the contraction of the muscle cells. Chemical function – such as the synthesis of proteins, DNA, and RNA. Osmotic function – uptake of materials by cell from their environment. Specialized functions:  II – FUNCTIONS OF THE CELL Specialized functions:  conduction of impulse by nerve cell  increase cell surface area for absorption as exhibited by microvilli  protoplasmic and amoeboid movement that enable the organism to propel food material.  Movement of sperm cell by means of a flagellum  III – TYPES OF CELL PROKARYOTIC  Greek word “pro” or before, and “karyon” means kernel or nucleus.  lacking an organized nucleus or membrane-bound organelles  have their DNA located in a region called the nucleoid EUKARYOTIC  Greek word “eu” means true, and “karyon” means kernel or nucleus  with true nucleus PROKARYOTIC vs. EUKARYOTIC Eukaryotic cell Prokaryotic cell  PROKARYOTIC CELL Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating Bacterial of many prokaryotes chromosome 0.5 µm (a) A typical Flagella: locomotion (b) A thin section through the rod-shaped bacterium organelles of bacterium Bacillus coagulans some bacteria (TEM) Figure 6.6 A, B  PROKARYOTIC vs. EUKARYOTIC Feature Prokaryote Eukaryote Size Mostly large (10 – 100 µm) Mostly small (1 – 10 µm) Genetic DNA with some DNA-binding DNA complexed with DNA- System protein; simple, circular DNA binding proteins in complex molecule in nucleoid; linear chromosomes within Nucleoid is not mmbrane nucleus with membranous bound envelope; circular mitochondrial and chloroplast DNA Cell Direct by binary fission or Some form of mitosis; centrioles division budding; no mitosis in many; mitotic spindle present Absent in most; highly Present in most; male & female Sexual modified if present partners; gametes that fuse to form System zygote  PROKARYOTIC vs. EUKARYOTIC Feature Prokaryote Eukaryote Nutrition Absorption by most; Absorption, ingestion, photosynthesis photosynthesis by some by some Energy No mitochondria, oxidative Mitochondria present; Metabolism enzymes bound to cell oxidative enzymes packaged membrane, not packaged therein; more unified pattern separately; great variation in of oxidative metabolism metabolic pattern Intracellular None Cytoplasmic streaming, phagocytosis, pinocytosis movement Flagella/ If present, not with “9 + 2” With “9 + 2” microtubular pattern Cilia microtubular pattern If present, not with Cell wall Contains disaccharide chains disaccharide polymers linked cross-linked with peptides with peptides EVOLUTION OF EUKARYOTIC CELL EVOLUTION OF EUKARYOTIC CELL  THE CELL STRUCTURES & FUNCTIONS REGIONS OF THE CELL Cytoplasm Nucleus  CYTOPLASM the entire region between the nucleus and the membrane bounding the cell. it is where most cell’s activities occur. CYTOSOL – is a semi-fluid medium in the cytoplasm. it serves as the basic structural medium of the cell.  CYTOPLASM FUNCTIONS Brings the following processes: cyclosis, ameboid movement, cell cleavage. Its components carry out the biosynthetic functions of the Cytoplasm Nucleus cell.  NUCLEUS dark staining usually spherical structure located at the central portion of the cell contains most of genes that controls and regulates the functions of other organelles CHROMATIN in the nucleus consists of DNA which carries genes, along with protein synthesis in the cytoplasm present only in eukaryotic cell  NUCLEUS FUNCTIONS Directs work of the cytoplasm necessary to life, growth, differentiation and reproduction. Its DNA instructs RNA and protein synthesis. Nucleus  NUCLEUS Chromatin: DNA and proteins Nucleolus: Chromatin and ribosomal subunits Nuclear envelope: Double membrane with pores Nucleoplasm: semifluid medium inside the nucleus. Inside the Nucleus - The genetic material (DNA) is found DNA is spread out DNA is condensed & And appears as wrapped around CHROMATIN proteins forming in non-dividing cells as CHROMOSOMES copyright cmassengale in dividing cells 48 What Does DNA do? DNA is the hereditary material of the cell Genes that make up the DNA molecule code for different proteins copyright cmassengale 49 NUCLEUS NUCLEOLUS  NUCLEOLUS dark spherical body inside the nucleus, bounded by a nuclear membrane rich in RNA (ribonucleic acid) FUNCTION Manufacture ribosomes  THE CELL STRUCTURES & FUNCTIONS OUTER BOUNDARIES OF THE CELL Cell Membrane Cell Wall (plant)  CELL MEMBRANE a selective barrier that allow sufficient passage of oxygen, nutrients and water very thin, about 0.008 microns and a few molecules thick CELL MEMBRANE  CELL MEMBRANE FUNCTIONS Semi-permeable Gives mechanical Carries out strength and phagocytosis and protection pinocytosis Controls the entrance Establishes cell surface and exit of molecules contact and ions (outside Contains the energy- boundary) generating respiratory Confers cell shape chains in prokaryotes.  TRANSPORT OF MATERIALS Transport of Materials Across the Membrane 1. DIFFUSION the net movement of particles from a region of greater concentration to a region of lesser concentration. It occurs because of the kinetic energy of the particles in order to attain equalization of concentration and maintain equilibrium TRANSPORT OF MATERIALS  TRANSPORT OF MATERIALS Transport of Materials Across the Membrane 2. OSMOSIS the diffusion of water or solvents through a semi-permeable membrane from lower osmotic pressure to greater osmotic pressure It depends on the amount of solutes; when then concentration of solutes is higher than the solvent, the greater osmotic pressure and vice versa. OSMOSIS SEMI-PERMEABLE MEMBRANE  TRANSPORT MECHANISM 1. PASSIVE TRANSPORT a. SIMPLE DIFFUSION The particle is transported through the permease of the membrane without the aid of the permease and without expenditure of energy by the cell b. FACILITATED DIFFUSION the particle is transported through the permease of the membrane but without expenditure of energy by the cell TRANSPORT MECHANISM b. FACILITATED DIFFUSION  TRANSPORT MECHANISM 2. ACTIVE TRANSPORT the particle is transported through the permease of the membrane and with the expenditure of energy by the cell 3. BULK TRANSPORT particles are transported in large amounts or in bulk without actually passing or crossing the membrane but through endocytosis (inward) or exocytosis (outward) 2. ACTIVE TRANSPORT  3. BULK TRANSPORT A. PHAGOCYTOSIS – the particle to be engulfed is in solid form or chunks of matter, commonly called “cell eating” B. PINOCYTOSIS – the particle to be engulfed is in liquid form or very small, commonly called as “cell drinking” ENDOCYTOSIS & EXOCYTOSIS EXOCYTOSIS ENDOCYTOSIS  Golgi Animation Materials are transported from Rough ER to Golgi to the cell membrane by VESICLES copyright cmassengale 69 ENDOCYTOSIS in ANIMAL CELLS RECEPTOR- MEDIATED PINOCYTOSIS PHAGOCYTOSIS  CELL SURFACE CONTACT Gap Junction Desmosome Tight Junction  CELL SURFACE CONTACT Inanimals, there are three types of intercellular junctions Tight junctions Desmosomes Gap junctions  CELL SURFACE CONTACT TIGHT JUNCTIONS Tight junction At tight junctions, the membranes of Tight junctions prevent neighboring cells are very tightly pressed fluid from moving against each other, bound together by across a layer of cells specific proteins (purple). Forming continu- ous seals around the cells, tight junctions prevent leakage of extracellular fluid across A layer of epithelial cells. 0.5 µm DESMOSOMES Desmosomes (also called anchoring Tight junctions junctions) function like rivets, fastening cells Intermediate Together into strong sheets. Intermediate Filaments made of sturdy keratin proteins filaments Anchor desmosomes in the cytoplasm. Desmosome Gap 1 µm junctions GAP JUNCTIONS Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to an adjacent cell. Gap junctions Extracellular consist of special membrane proteins that matrix surround a pore through which ions, sugars, Space between Gap junction amino acids, and other small molecules may Plasma membranes pass. Gap junctions are necessary for commu- cells of adjacent cells nication between cells in many types of tissues, including heart muscle and animal embryos. Figure 6.31 0.1 µm  CELL SURFACE CONTACT: Tight Junctions At tight junctions, the membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins (purple). Forming continuous seals around the cells, tight junctions prevent leakage of extracellular fluid across. A layer of epithelial cells.  CELL SURFACE CONTACT: Desmosomes Desmosomes (also called anchoring junctions) function like rivets, fastening cells Together into strong sheets. Intermediate Filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm.  CELL SURFACE CONTACT: Gap Junctions Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to an adjacent cell. Gap junctions consist of special membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissues, including heart muscle and animal embryos.  Plants: Plasmodesmata Plasmodesmata  Are channels that perforate plant cell walls Cell walls Interior of cell Interior of cell Figure 6.30 0.5 µm Plasmodesmata Plasma membranes CELL MEMBRANE  CELL WALL a rigid structure and a protective layer external to the plasma membrane contain cellulose, pectin and lignin in plant cells; murein in bacteria, and chitin or cellulose or both in fungal cells not part of the cellular material but is a product of the cell present only in prokaryotic cells (except in cell wall-less bacteria) and fungal cells and plant cells CELL WALL  CELL WALL Permits cell to withstand very dilute (hypotonic) external media without bursting Helps support and gives shape to individual cells  THE CELL STRUCTURES & FUNCTIONS MEMBRANE- BOUND ORGANELLES Nucleolus Golgi Apparatus Ribosome Lysosome  Bound Ribosome Vacuole  Free Ribosome Mitochondria Endoplasmic Reticulum Peroxisome  Smooth ER Cytoskeleton  Rough ER Cilia and Flagellum  RIBOSOME small granular bodies which are rich in RNA with smaller and larger subunits maybe assembled into polysomes in prokaryotes 2 types: FREE RIBOSOMES  suspended in the cytosol  makes protein for the functions within the cytosol ATTACHED or BOUND RIBOSOMES  attached to the outside of the membranous network called the ER  makes protein for inclusion into membranes for packaging  e.g. cells in pancreas (has millions of bound ribosomes that secrete digestive enzymes)  RIBOSOME Attached Free Ribosome Ribosome RIBOSOME  ENDOPLASMIC RETICULUM “Endoplasmic” means within the cytoplasm; “reticulum” means network complex system of membrane forming a canal which extends from the nuclear membrane to the plasma membrane Functions:  Passageway of materials  Involved in protein synthesis  Involved in the synthesis of certain hormones and enzymes of carbohydrate metabolism and lipid synthesis  ENDOPLASMIC RETICULUM Smooth ER Nuclear pore Nuclear envelope Rough ER  ENDOPLASMIC RETICULUM 2 types: 1. AGRANULAR/ SMOOTH ER  diverse metabolic processes including synthesis of lipids  metabolism of carbohydrates, detoxification of drugs and poison  produce sex hormones/ thyroid 2. GRANULAR/ ROUGH ER  synthesis of secretory proteins, secretes proteins produced by ribosomes attached to rough ER ENDOPLASMIC RETICULUM Rough ER Smooth ER ENDOPLASMIC RETICULUM  Golgi Animation Materials are transported from Rough ER to Golgi to the cell membrane by VESICLES copyright cmassengale 91  GOLGI APPARATUS system of membrane consisting of 3 to 20 parallel flattened sacs stacked together present only in eukaryotes Functions: 1. It acts as a collection and processing center 2. It is involved in cellular secretion of enzymes and hormones  GOLGI APPARATUS Incoming Vesicle Outgoing Vesicle GOLGI APPARATUS  GOLGI APPARATUS Look like a stack of pancakes Modify, sort, & package molecules from ER for storage or transport out of cell copyright cmassengale 95  LYSOSOME small membrane enclosed sacs which contain hydrolytic enzymes that the cell uses to digest macro-molecules such as proteins, polysaccharides, fats, and nucleic acids may fuse with pinocytic/ phagocytic vesicles containing foreign materials carry HYDROLASES that degade nucleotides, proteins, lipids, phospholipids, and also remove carbohydrate, sulfate, or phosphate groups from molecules.  Hydrolases – active at an acid pH found only in eukaryotic cells LYSOSOME  LYSOSOME Functions: 1. Digestive organ of the cell 2. Provides a mechanism for ridding the body of dead and degenerating cells thus they are called “suicide bags” 3. handle the products of receptor-mediated endocytosis such as the receptor, and associated membrane  LYSOSOME Nucleus 1 µm Lysosomes carry out intracellular digestion by  Phagocytosis Lysosome Lysosome contains Food vacuole Hydrolytic active hydrolytic fuses with enzymes digest enzymes lysosome food particles Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole Figure 6.14 A (a) Phagocytosis: lysosome digesting food LYSOSOME  LYSOSOME Lysosome containing 1µm two damaged organelles Autophagy Mitochondrion fragment Peroxisome fragment Lysosome fuses with Hydrolytic enzymes vesicle containing digest organelle damaged organelle components Lysosome Digestion Figure 6.14 B Vesicle containing damaged mitochondrion (b) Autophagy: lysosome breaking down damaged organelle  VACUOLE diverse functions in cell maintenance a membrane-enclosed fluid-filled space a membrane enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development larger in plant cells containing cell sap; smaller in animal cells it is rich in pigments and absorb water that elongate the cell found in eukaryotic cells VACUOLE  VACUOLE Types: 1. FOOD VACUOLES – formed by phagocytosis 2. CONTRACTILE VACUOLES – pump excess water out of the cell 3. CENTRAL VACUOLE – found in mature plant Functions: 1. Dumping sites of noxious wastes 2. Stores concentration of amino acids, sugars, organic acids and some proteins Contractile Vacuole Found in unicellular protists like paramecia Regulate water intake by pumping out excess (homeostasis) Keeps the cell from lysing (bursting) Contractile vacuole animation copyright cmassengale 105  Relationships among organelles of the endomembrane system 1 Nuclear envelope is Nucleus connected to rough ER, which is also continuous with smooth ER Rough ER 2 Membranes and proteins produced by the ER flow in Smooth ER the form of transport vesicles cis Golgi to the Golgi Nuclear envelop 3 Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles Plasma membrane trans Golgi Figure 6.16 4 Lysosome available 5 Transport vesicle carries 6 Plasma membrane expands for fusion with another proteins to plasma by fusion of vesicles; proteins vesicle for digestion membrane for secretion are secreted from cell  MITOCHONDRIA a spherical to rod-shaped filamentous organelle concerned with cell respiration and energy production generates ATP by extracting energy from sugars, fats, and other fuels with the help of O2 formed by 2 membranes made of free ribosomes, has DNA with own ribosomes can shift to places in the cytoplasm where energy is needed it is where catabolic process occurs the “powerhouse of the cell” MITOCHONDRIA  MITOCHONDRIA Functions: 1. Extract energy from foodstuffs and make it available to the cell 2. Site of cellular respiration 3. Site of oxidation reactions and the electron transport chain MITOCHONDRIA… Interesting fact… Mitochondria Come from cytoplasm in the EGG cell during fertilization Therefore … You inherit your mitochondria from your 110 mother!copyright cmassengale  PLASTIDS large organelles bound by a double –membrane layer found in plants and eukaryotic algae, site of photosynthesis present in plant cells and plant-like protists Functions:  1. Stores starch, oils, proteins, or other materials  2. Carries out photosynthesis  PLASTIDS CHLOROPLAST  PLASTIDS Types: 1. LEUCOPLAST – white or colorless plastids e.g. amyloplast (colorless plastids - roots and tubers) 2. CHROMOPLAST – colored plastids e.g. chloroplast (colored containing the green pigment chlorophyll, DNA is present, and site of photosynthesis)  PEROXISOME contain enzymes that transfer hydrogen from various substances to oxygen, producing hydrogen peroxide organelles that contain oxidative enzymes, such as D-amino acid oxidase, ureate oxidase, and catalase distinguished by a crystalline structure inside a sac which also contains amorphous gray material. self replicating, like the mitochondria. PEROXISOME  PEROXISOME Function:  1. To rid the body of toxic substances like hydrogen peroxide, or other metabolites.  2. Major site of oxygen utilization and are numerous in the liver where toxic byproducts are going to accumulate.  3. The breakdown of fatty acid molecules, in a process called beta-oxidation  4. It is involved in lipid biosynthesis.  5. It is involved in the synthesis of bile acids, which are derived from cholesterol.  CYTOSKELETON A animal cell ENDOPLASMIC RETICULUM (ER) Nuclear envelope Nucleolus NUCLEUS Rough ER Smooth ER Chromatin Flagelium Plasma membrane Centrosome CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Lysosome Figure 6.9 Mitochondrion  CYTOSKELETON The eukaryotic cytoskeleton is a network of filaments and tubules that extends from the nucleus to the plasma membrane. The cytoskeleton contains three types of elements responsible for cell shape, movement within the cell, and movement of the cell: Types:  Actin filaments  Microtubules  Intermediate filaments Function: Gives mechanical support to the cell  CYTOSKELETON: Actin Filaments Are built from molecules of the protein actin Actin filaments occur in bundles or mesh-like networks. Actin filaments play a structural role and interact with motor molecules, such as myosin. 3-119  CYTOSKELETON: Actin Filaments 3-120  Are found in microvilli Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments Figure 6.26 0.25 µm  Microfilaments that function in cellular motility  Contain the protein myosin in addition to actin Muscle cell Actin filament Myosin filament Myosin arm Figure 6.27 A (a) Myosin motors in muscle cell contraction.  Amoeboid movement  Involves the contraction of actin and myosin filaments Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Figure 6.27 B  Cytoplasmic streaming  Is another form of locomotion created by microfilaments Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Parallel actin filaments Cell wall (b) Cytoplasmic streaming in plant cells Figure 6.27 C  CYTOSKELETON: Microtubule small,hollow cylinders. Functions: 1) help maintain the shape of the cell 2) act as tracks along which organelles and chromosomes can move. 3-125  CYTOSKELETON: Microtubule 3-126 CYTOSKELETON: Intermediate Filaments Intermediate filaments -ropelike assemblies of fibrous polypeptides 1) support the plasma membrane 2) support the nuclear envelope. 3) Fix organelles in place 3-127 CYTOSKELETON:Intermediate Filaments 3-128 Table 6.1  CENTRIOLE small dark rod-like bodies outside the nucleus of most animal cells it organizes microtubule assembly Function: Associated with spindle formation in dividing animal cells CENTRIOLE  CENTROSOME considered to be a “microtubule-organizing center” Contains a pair of centrioles  CENTROSOME Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules Cross section Figure 6.22 of one centriole of the other centriole  CILIA & FLAGELLA Containspecialized arrangements of microtubule locomotor appendages of some cells  CILIA & FLAGELLA Flagellum Cilia  CILIA & FLAGELLA Flagella beating pattern Direction of swimming 1 µm Figure 6.23 A (a) Motion of flagella. A flagellum usually undulates, its snakelike motion driving a cell in the same direction as the axis of the flagellum. Propulsion of a human sperm cell is an example of flagellatel ocomotion (LM).  CILIA & FLAGELLA Ciliary motion Figure 6.23 B (b) Motion of cilia. Cilia have a back-and-forth motion that 15 µm moves the cell in a direction perpendicular to the axis of the cilium. A dense nap of cilia, beating at a rate of about 40 to 60 strokes a second, covers this Colpidium, freshwater protozoan (SEM). CILIA Figure 23–2