BSci106: MICROBIOLOGY & PARASITOLOGY Unit 2 Introduction to Microbes and Cellular Biology Copyright © 2015 W olters Kluwer • All Rights Reserved Outline • Eukaryotic Cell Structure • Prokaryotic Cell Structure • Summary of Structural Differences between Prokaryotic and Eukaryotic Cells • Prokaryotic Cell Reproduction • Taxonomy • Determining Relatedness among Organisms Copyright © 2015 W olters Kluwer • All Rights Reserved • The cell is the fundamental unit of any living organism because it exhibits the basic characteristics of life. • two categories of cells: eukaryotic and prokaryotic • some microbes are prokaryotes (bacteria and archaea), some are eukaryotes (algae, protozoa, fungi), and some are not composed of cells (viruses, prions, viroids) Copyright © 2015 W olters Kluwer • All Rights Reserved Acellular and Cellular Microbes Copyright © 2015 W olters Kluwer • All Rights Reserved Eukaryotic Cell Structure Copyright © 2015 W olters Kluwer • All Rights Reserved EUKARYOTES • Eukaryotic cells contain a “true” nucleus, whereas prokaryotic cells do not. • Eukaryotic cells possess a complex system of membranes and membrane-bound organelles, whereas prokaryotic cells do not. • Both eukaryotic and prokaryotic cells possess a cell membrane. Cell membranes have selective permeability, allowing only certain substances to pass through them. Copyright © 2015 W olters Kluwer • All Rights Reserved Eukaryotic Nucleus • “command center” of the cell as it controls the function of the entire cell • three components: nucleoplasm, chromosomes, and nuclear membrane • chromosomes are embedded in the nucleoplasm • eukaryotic chromosomes consist of linear deoxyribonucleic acid (DNA) molecules and proteins • genes are located along DNA molecules. An organism’s complete collection of genes is referred to as its genotype or genome. • each gene contains the information to produce one or more gene products (usually proteins). Copyright © 2015 W olters Kluwer • All Rights Reserved Eukaryotic Nucleus (cont.) • Although most genes code for proteins, some code for two types of ribonucleic acid (RNA) – Ribosomal ribonucleic acid (rRNA) – Transfer ribonucleic acid (tRNA) • The number and composition of chromosomes and the number of genes on each chromosome are characteristic of the particular species of organism. • Human diploid cells have 46 chromosomes (23 pairs). • It has been estimated that the human genome consists of between 20,000 and 25,000 genes. Nucleolus - appears as dark (electron dense) area in the nucleus; where rRNA molecules are manufactured Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures Endoplasmic reticulum (ER) Cytoplasm - a semifluid, gelatinous, nutrient matrix - contains storage granules and a variety of organelles - each organelle has a specific function - where most metabolic reactions occur – a highly convoluted system of membranes arranged to form a transport network in the cytoplasm – rough ER has ribosomes attached to it, whereas smooth ER does not Ribosomes – Consist of ribosomal RNA and protein – sites of protein synthesis Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) Golgi complex – also called the Golgi apparatus or Golgi body – connects or communicates with ER – completes the transformation of newly synthesized proteins and packages them for storage or export (“packaging plants”) Lysosomes and peroxisomes – originate in the Golgi complex – lysosomes contain lysozyme and other digestive enzymes – peroxisomes are membrane-bound vesicles where H2O2 is generated and broken down Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) • Plastids • Mitochondria – “power plants,” “powerhouses,” or “energy factories” – ATP molecules are produced within mitochondria by cellular respiration – number of mitochondria varies depending on the activities of the cell – Membrane-bound structures containing photosynthetic pigments – sites of photosynthesis – Chloroplasts are a type of plastid; they contain chlorophyll Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) • Cytoskeleton – A system of fibers throughout the cytoplasm – Three types of fibers: microtubules, microfilaments, and intermediate filaments – Microtubules and microfilaments are essential for a variety of activities Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) • Cell wall – Some eukaryotic cells contain cell wallsan external structure to provide shape, protection, and rigidity – Simpler in structure than prokaryotic cell walls – Chitin found in cell walls of fungi; cellulose in cell walls of algae and plants Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) Copyright © 2015 W olters Kluwer • All Rights Reserved Other Eukaryotic Cell Structures (cont.) • Flagella and cilia (contain microtubules) – Some eukaryotic cells (e.g., spermatozoa and certain protozoa) possess long, thin, whiplike organelles of locomotion called flagella. – Flagellated cells may possess one or more flagella. – Some cells move by means of cilia, which are shorter, thinner, and more numerous than flagella, and described as being “hair-like.” – Cilia can be found on some species of protozoa and certain types of cells in bodies (e.g., ciliated epithelial the respiratory tract). Copyright © 2015 W olters Kluwer • All Rights Reserved our cells in Prokaryotic Cell Structure • Prokaryotic cells are about 10 times smaller than eukaryotic cells. • Prokaryotic cells are simple compared to eukaryotic cells. • Prokaryotic cells reproduce by binary fission. • All bacteria are prokaryotes, as are archaea. • Unlike eukaryotic cells, the cytoplasm of prokaryotic cells is not filled with internal membranes. • The cytoplasm of prokaryotic cells is surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer. Copyright © 2015 W olters Kluwer • All Rights Reserved A typical prokaryotic cell Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) • Cell membrane – Similar in structure and function to the eukaryotic cell membrane – Selectively permeable – Many enzymes are attached to the cell membrane where metabolic reactions take place Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) • Chromosome – Prokaryotic chromosome usually consists of a single, long, supercoiled, circular DNA molecule and serves as the control center of the cell – Plasmids are small, circular molecules of double stranded DNA that are not part of the chromosome (extra-chromosomal) Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) • Cytoplasm – It is a semiliquid that consists of water, enzymes, waste products, nutrients, proteins, carbohydrates, and lipidsmaterials required for metabolic functions. • Cytoplasmic particles – Most are ribosomes, some of which occur in clusters. – Prokaryotic ribosomes are smaller than eukaryotic ribosomes, but their function is the samethey are the sites of protein synthesis Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) • Bacterial cell wall – A rigid exterior that defines the shape of bacterial cellschemically complex – Main constituent of most bacterial cell walls is peptidoglycan (found only in bacteria) – Gram-positive bacteria have a thick layer of peptidoglycan; Gram-negative bacteria have a much thinner layer. – Mycoplasma spp. do not have a cell wall; they are pleomorphic; peptidoglycan is absent – Archaea have cell walls, but their cell walls do not contain peptidoglycan Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Glycocalyx (Slime Layers and Capsules) - bacterial cells may or may not be surrounded by glycocalyx - slimy, gelatinous material produced by the cell membrane and secreted outside the cell wall - two types of glycocalyx - slime layers and capsules - slime layer - not highly organized, not firmly attached to the cell wall; enable certain bacteria to glide or slide along solid surfaces; Pseudomonas produce a slime layer Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Glycocalyx (Slime Layers and Capsules) - capsules - highly organized and firmly attached to the cell wall; consist of polysaccharides, which may be combined with lipids and proteins - serve an antiphagocytic function, protecting the encapsulated bacteria from being phagocytized Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Flagellum/Flagella - threadlike, protein appendages that enable bacteria to move - about 10 to 20 nm thick; too thin to be seen with the compound light microscope - number and arrangement of flagella possessed by a certain species of bacterium be used for classification and identification purposes Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Pili/Pilus (Fimbriae/Fimbrius) - hairlike structures, most often observed on Gram-negative bacteria - composed of polymerized protein molecules called pilin - have a rigid structure, and are not associated with motility - one type merely enables bacteria to adhere or attach to surfaces; the other type (called a sex pilus) enables transfer of genetic material from one bacterial cell to another following attachment of the cells to each other Copyright © 2015 W olters Kluwer • All Rights Reserved Prokaryotic Cell Structure (cont.) Spores (Endospores) - some bacteria (e.g., Bacillus, Clostridium) are capable of forming thick-walled spores as a means of survival when their moisture or nutrient supply is low - Endospores enable bacteria to survive adverse conditions, such as temperature extremes, desiccation, and lack of nutrients. Copyright © 2015 W olters Kluwer • All Rights Reserved Copyright © 2015 W olters Kluwer • All Rights Reserved REPRODUCTION OF ORGANISMS AND THEIR CELLS Procaryotic Cell Reproduction - Bacterial cells reproduce by binary fission—one cell splits in half to become two cells - length of time it takes for one bacterial cell to split into two cells is referred to as the organism’s generation time - generation time varies from one bacterial species to another and also depends on the growth conditions (e.g., pH, temperature, availability of nutrients) Copyright © 2015 W olters Kluwer • All Rights Reserved TAXONOMY • • science of classification of living organisms consists of three separate but interrelated areas: classification, nomenclature, and identification 1. Classification - arrangement of organisms into taxonomic groups (known as taxa [sing., taxon]) on the basis of similarities or relationships Taxa - include kingdoms or domains, divisions or phyla, classes, orders, families, genera, and species • Closely related organisms (i.e., organisms having similar characteristics) are placed into the same taxon Copyright © 2015 W olters Kluwer • All Rights Reserved TAXONOMY 2. Nomenclature is the assignment of names to the various taxa according to international rules 3. Identification is the process of determining whether an isolate belongs to one of the established, named taxa or represents a previously unidentified species. Copyright © 2015 W olters Kluwer • All Rights Reserved TAXONOMY - An organism’s complete collection of genes is referred to as the organism’s genotype or genome. - An organism’s complete collection of physical characteristics is known as the organism’s phenotype. Copyright © 2015 W olters Kluwer • All Rights Reserved TAXONOMY Microbial Classification - In the binomial system of nomenclature, the first name (e.g., Escherichia) is the genus (plural-genera), and the second name (e.g., coli) is the specific epithet - When used together, the first and second names (e.g., Escherichia coli) are referred to as a species Copyright © 2015 W olters Kluwer • All Rights Reserved DETERMINING RELATEDNESS AMONG ORGANISMS - relatedness among organisms is determined by analysis of genes that code for small subunit ribosomal RNA (SSUrRNA) - most widely used technique for gauging diversity or relatedness is called rRNA sequencing - ribosomes are made up of two subunits: a small subunit and a large subunit - small subunit contains only one RNA molecule, which is referred to as the “small subunit rRNA” or SSUrRNA. Copyright © 2015 W olters Kluwer • All Rights Reserved Copyright © 2015 W olters Kluwer • All Rights Reserved Structure of Peptidoglycan Copyright © 2015 W olters Kluwer • All Rights Reserved Cilia Copyright © 2015 W olters Kluwer • All Rights Reserved
