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The Cell Structures and Its Functions

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The Cell Structures and Its Functions THE CELL STRUCTURES AND ITS FUNCTIONS Prepared by: NR-NUR 102 TEAM 2018-2019 1665: Robert Hooke, “Father of Microscopy,” coined the term “cells” 1838-1839: Matthias Schleiden and Theodore Schwann concluded that all plant and animal tissues are made up of cells. 1858: Rudolf Virchow proposed the “Theory of Biogenesis” EUKARYOTIC CELLS ALGAE FUNGI PROTOZOA PLANTS ANIMALS PROKARYOTIC CELLS BACTERIA ARCHAEA Eucaryotes: “eu” = true “caryo” = nut or nucleus Size: 10 to 30 µm in diameter Cell Structures Common to Most Eukaryotes Glycocalyx Cell Membrane Nucleus Vacuoles Mitochondria Endoplasmic Reticulum Ribosomes Golgi Complex Cytoplasm Cytoskeleton GLYCOCALYX The outermost boundary of most eukaryotic cells Functions: protection adherence reception of chemical signals Supported by either a cell wall or a cell membrane GLYCOCALYX GLYCOCALYX Usually composed of polysaccharides Appears as a network of fibers, a slime layer, or a capsule The layer beneath the glycocalyx varies among eukaryotes. Fungi and most algae have a thick, rigid cell wall Protozoa and animal cells do not have cell wall GLYCOCALYX CYTOPLASMIC MEMBRANE Bilayer of phospholipids with protein molecules embedded Also contain sterols Gives stability Especially important in cells without a cell wall Selectively permeable Cell Membrane NUCLEUS Distinguishing characteristic between a eukaryotic and prokaryotic cell “The command center” Three components: Nucleoplasm Chromosomes Nucleolus Nuclear Membrane CHROMOSOMES consist of linear DNA molecules and proteins (histones and nonhistones) Genes as “beads on a string” RIBOSOMES Consists of rRNA and CHON Primarily for CHON synthesis Each eucaryotic (80S) ribosome consist of the ff: Large subunit (60S subunit) Small subunit (40S subunit) CHON released are mostly immature Cell Structures Present in Some Eukaryotes Cell Wall Chloroplasts Locomotor organs CELL WALL Provides rigidity, shape and protection May contain the ff: Cellulose, pectin and lignin in plant cells Chitin or cellulose, and mixed glycans in fungi Some minerals, pectin, and mannans in algae Cellulose can also be found in ALGAE Chitin is also present in the exoskeleton of beetles and crabs PLASTIDS An energy producing organelle Contains numerous photosynthetic pigments A type of plastid, chloroplasts contains chlorophyll PHOTOSYNTHESIS – process by which light energy is used to convert carbon dioxide and H20 into CHO and O2 PLANT CELL STRUCTURE FLAGELLA AND CILIA Flagella – long, thin, whiplike structures that serve as organelles of locomotion Cilia – hairlike structures shorter than flagella that also serves for locomotion in a coordinated and rhythmic manner COMPARISON BETWEEN ANIMAL AND PLANT CELLS CATEGORY PLANT CELL ANIMAL CELL Biologic All plants, fungi All animals and Distribution and algae protozoa Nuclear Membrane Present Present Membranous structures other Present Present than cell membranes Vacuole Size Larger Smaller COMPARISON BETWEEN ANIMAL AND PLANT CELLS CATEGORY PLANT CELL ANIMAL CELL Microtubules Present Present Cytoplasmic Ribosomes 80S 80S (Density) Composed of DNA Composed of DNA Chromosomes and CHON and CHON When present, have When present, have Flagella or Cilia a complex structure a complex structure Present, usually Cell Wall Absent contains cellulose Photosynthesis (Chlorophyll) Present Absent A prokaryote can be distinguished from the other type of cell (a eukaryote) because of certain characteristics it possesses: The way its DNA is packaged The makeup of its cell wall Its internal structures Prokaryotic Form and Function CELL STRUCTURES COMMON TO ALL BACTERIAL CELLS Cell membrane Cytoplasm Ribosomes One (or a few) chromosomes CELL STRUCTURES FOUND IN MOST BACTERIAL CELLS Bacterial Cell Wall Glycocalyx CELL STRUCTURES FOUND IN SOME BACTERIAL CELLS Flagella Pili Fimbriae Capsules Slime layers Inclusions Actin cytoskeleton Endospores EXTERNAL STRUCTURES • APPENDAGES – FLAGELLA – AXIAL FILAMENTS – FIMBRIAE / PILI • GLYCOCALYX EXTERNAL STRUCTURES Appendages: Cell extensions Common but not present on all species Can provide motility (flagella and axial filaments) Can be used for attachment and mating (pili and fimbriae) FLAGELLA • Long filamentous appendages • Propels bacteria • Functions – Chemotaxis- positive and negative – Move by runs and tumbles Figure 4.2 FLAGELLA ARRANGEMENT AXIAL FILAMENTS a.k.a. Periplasmic flagella or Endoflagella In spirochetes Bundle of fibrils Rotation causes cell to move. FIMBRIAE Small, bristlelike fibers Most contain protein Allow attachment Tend to stick to each other and to surfaces Mostly responsible for microbial colonization in inanimate objects PILI Elongate, rigid tubular structures Made of the protein pilin Used in conjugation – sex pilus Most often observed in Gram (-) bacteria Figure 4.8 GLYCOCALYX composed of repeating polysaccharide units, polypeptide (protein) or both Protects the cell A capsule is neatly organized, bound more tightly and is denser and thicker. A slime layer is unorganized & loose, protects some bacteria from loss of water and nutrients GLYCOCALYX Extracellular polysaccharide (EPS) allows cell to attach on various surfaces: (rocks, plant roots, human teeth, medical implants, water pipes & even bacteria) The Cell Envelope: The Boundary layer of Bacteria Majority of bacteria have a cell envelope Lies outside of the cytoplasm Composed of two or three basic layers Cell wall Cell membrane In some bacteria, the outer membrane Differences in Cell Envelope Structure The differences between gram-positive and gram-negative bacteria lie in the cell envelope Gram-positive Two layers Thick cell wall and cytoplasmic membrane Gram-negative Three layers Outer membrane, thin cell wall, and cytoplasmic membrane Figure 4.12 CELL WALL • Made of peptidoglycan (murein), NAM (N- acetylglucosamine), NAG (N-acetylmuramic acid) • Prevents osmotic lysis • Anchorage for flagella CELL WALL contributes to pathogenicity site of action of some antibiotics GRAM-POSITIVE CELL WALL Thick layer of peptidoglycan (60-100% murein) Contain teichoic and lipoteichoic acids acidic charge on the cell surface for antigenic specificity GRAM-NEGATIVE CELL WALL Thin layer of peptidoglycan (10-20% murein) more susceptible to mechanical breakage Periplasmic space surrounds peptidoglycan important reaction site for a large and varied pool of substances that enter and leave the cell Figure 4.14 Nontypical Cell Walls Some aren’t characterized as either gram- positive or gram-negative Some don’t have a cell wall at all For example, Mycobacterium and Nocardia- unique types of lipids The Gram-Negative Outer Membrane Similar to the cell membrane, except it contains specialized polysaccharides and proteins Uppermost layer- contains lipopolysaccharide O polysaccharides – antigens and receptors Innermost layer- phospholipid layer anchored by lipoproteins to the peptidoglycan layer below lipid A – Endotoxin causes fever and shock reactions such as meningitis and typhoid fever. The negative charge produced is vital The Gram-Negative Outer Membrane Serves as a partial chemical sieve Only relatively small molecules can penetrate Access provided by special membrane channels formed by porin proteins block the entrance of certain antibiotics such as penicillin, digestive enzymes such as lysozyme, detergents, heavy metals, bile salts, and certain dyes. Figure 4.14 PLASMA MEMBRANE PLASMA (CELL) MEMBRANE Also known as the cytoplasmic membrane Very thin (5-10 nm) Contain primarily proteins and phospholipids Functions: Provides a site for functions such as energy reactions, nutrient processing, and synthesis Regulates transport (selectively permeable membrane) Secretion Practical Considerations of Differences in Cell Envelope Structure Outer membrane- an extra barrier in gram- negative bacteria Makes them impervious to some antimicrobial chemicals Generally more difficult to inhibit or kill than gram- positive bacteria Cell envelope can interact with human tissues and cause disease Corynebacterium diphtheriae Streptococcus pyogenes Mycobacterium species INTERNAL STRUCTURE – CYTOPLASM – NUCLEOID • Chromosomes and Plasmids – RIBOSOMES – INCLUSIONS – ACTIN CYTOSKELETON – ENDOSPORES CYTOPLASM Internal matrix Contains CHON enzymes, CHO, lipids, inorganic ions, ribosomes, and inclusions NUCLEAR AREA (NUCLEOID) Contains a single long circular molecule of double stranded DNA called: BACTERIAL CHROMOSOMES There could also be plasmids. No histones and nuclear envelope RIBOSOMES CHON synthesis • Some antibiotics work to inhibit protein synthesis like: ERYTHROMYCIN CHLORAMPHENICOL Bacterial Inclusions Metachromatic Granules - volutin (synthesis of ATP) – found in algae, fungi, protozoa & bacteria Polysaccharide Granules Lipid Inclusions Figure 4.19 The Actin Cytoskeleton Long polymers of actin Arranged in helical ribbons around the cell just under the cell membrane Contribute to cell shape Figure 4.20 ENDOSPORES Usually found in gram (+) bacteria Dormant bodies produced by Bacillus, Clostridium, and Sporosarcina Specialized resting cells Capable of sporulation and germination Highly durable and dessicated cells with thick walls & additional layers Endospore-Forming Bacteria two-phase life cycle Phase One- Vegetative cell Metabolically active and growing Can be induced by the environment to undergo spore formation (sporulation) Phase Two: Endospore Stimulus for sporulation- the depletion of nutrients Vegetative
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