Instructor Bertha EscobarPoni MD Associate Professor Chapter 3

Instructor: Bertha Escobar-Poni, MD Associate Professor

Chapter 3 Outline • Introduction • Eukaryotic Cell Structure • Prokaryotic Cell Structure • Summary of Structural Differences Between Prokaryotic and Eukaryotic Cells • Reproduction of Organisms and Their Cells • Taxonomy • Determining Relatedness Among Organisms GLBH 205 - Fundamentals of Microbiology 2

Q&A • Penicillin was called a “miracle drug” because it doesn’t harm human cells. Why doesn’t it? GLBH 205 - Fundamentals of Microbiology 3

Introduction • The cell is the fundamental unit of any living organism because it exhibits the basic characteristics of life. • There are two categories of cells: 1. Prokaryotic • bacteria and archaea 2. Eukaryotic • algae, protozoa, fungi • Some are not composed of cells • viruses, prions, viroids GLBH 205 - Fundamentals of Microbiology 4

Acellular and Cellular Microbes http: //www. learner. org/vod_window. html? pid=1369 GLBH 205 - Fundamentals of Microbiology 5

Prokaryotic Cells • Do not contain a nucleus • Prokaryotic cells do not possess a complex system of membranes and membrane-bound organelles. Eukaryotic Cells • Contain a “true” nucleus, • A true nucleus consists of nucleoplasm, chromosomes, and a nuclear membrane. • Possess a complex system of membranes and membrane-bound organelles • Both eukaryotic and prokaryotic cells possess a cell membrane. Cell membranes have selective permeability, allowing only certain substances to pass through them. GLBH 205 - Fundamentals of Microbiology 6

The Eukaryotic Nucleus • The “command center” of the cell. • 3 components: nucleoplasm, chromosomes, and nuclear membrane. • Chromosomes are embedded in the nucleoplasm. • Eukaryotic chromosomes consist of linear DNA molecules and proteins. GLBH 205 - Fundamentals of Microbiology 7

The Eukaryotic Nucleus • Genes are located along chromosomes. • 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). GLBH 205 - Fundamentals of Microbiology 8

The Eukaryotic Nucleus, cont. • Types of ribonucleic acid (RNA) 1. Ribosomal ribonucleic acid (r. RNA) 2. Transfer ribonucleic acid (t. RNA) • Characteristic of a particular species • The number and composition of chromosomes • The number of genes on each chromosome • Human diploid cells: 46 chromosomes (23 pairs). • It has been estimated that the human genome consists of between 20, 000 and 30, 000 genes. GLBH 205 - Fundamentals of Microbiology 9

Eukaryotic Cell Structures • Cytoplasm • Endoplasmic Reticulum (ER) • Lysosomes & Peroxisomes • RER • Mitochondria • SER • Plastids • Ribosomes • Cytoskeleton • Golgi Complex • Cell Wall GLBH 205 - Fundamentals of Microbiology 10

Cell Walls – Some eukaryotic cells contain cell walls – an 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 GLBH 205 - Fundamentals of Microbiology 11

Other Eukaryotic Cell Structures • Flagella and Cilia (contain microtubules) – Flagella: long, thin, whiplike organelles of locomotion – Flagellated cells may possess one or more flagella. – Cilia: Some cells move by this mean – shorter, thinner, and more numerous than flagella; described as being “hair-like. ” – Cilia can be found on some species of protozoa and certain types of cells in our bodies (e. g. , ciliated epithelial cells in the respiratory tract). GLBH 205 - Fundamentals of Microbiology 12

Cilia Cross sections of cilia showing the 9 + 2 arrangement of microtubules. GLBH 205 - Fundamentals of Microbiology 13

Prokaryotic Cell • Compared to eukaryotic cells: 10 X smaller and simpler • Reproduce by binary fission. • All bacteria are prokaryotes, also all archaea. • The cytoplasm of prokaryotic cells • Not filled with membranous structures (organelles) • Surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer. GLBH 205 - Fundamentals of Microbiology 14

Prokaryotic Cell GLBH 205 - Fundamentals of Microbiology 15

Prokaryotic Cell membrane Chromosome – Similar in structure and function to the eukaryotic cell membrane – Prokaryotic chromosome usually consists of a single, long, supercoiled, circular DNA molecule – serves as the control center of the cell – Selectively permeable – Many enzymes are attached to the cell membrane and metabolic reactions take place there Plasmids are small circular molecules of DNA that are not part of the chromosome (extra-chromosomal) GLBH 205 - Fundamentals of Microbiology 16

Typical Bacterial Genome • Chromosome with 3000 genes • Plasmid with 5 – 100 genes GLBH 205 - Fundamentals of Microbiology 17

Prokaryotic Cell Structure, cont. • Cytoplasm – Semi-liquid that consists of water, enzymes, waste products, nutrients, proteins, carbohydrates and lipids – materials required for metabolic functions • Cytoplasmic particles – Most are ribosomes, some of which occur in clusters – Eukaryotic ribosomes are smaller than prokaryotic ribosomes, but their function is the same – they are the sites of protein synthesis GLBH 205 - Fundamentals of Microbiology 18

The Cell Wall • Prevents osmotic lysis • Made of peptidoglycan (in bacteria) GLBH 205 - Fundamentals of Microbiology 19

Prokaryotic Cell Structure, cont. • Bacterial Cell Wall – A rigid exterior that defines the shape of bacterial cells – chemically complex – Main constituent of most bacterial cell walls is peptidoglycan (only found 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 GLBH 205 - Fundamentals of Microbiology 20

Gram-negative and Gram-positive Cell Walls GLBH 205 - Fundamentals of Microbiology 21

Gram-Positive Bacterial Cell Wall Linked by polypeptides GLBH 205 - Fundamentals of Microbiology 22 Figure 4. 13 b

Gram-Positive Cell Walls • Teichoic acids – Lipoteichoic acid links to plasma membrane – Wall teichoic acid links to peptidoglycan • May regulate movement of cations • Polysaccharides provide antigenic variation GLBH 205 - Fundamentals of Microbiology 23 Figure 4. 13 b

Gram-Negative Bacterial Cell Wall GLBH 205 - Fundamentals of Microbiology 24 Figure 4. 13 c

Gram-Negative Cell Wall GLBH 205 - Fundamentals of Microbiology 25 Figure 4. 13 c

Gram-positive Cell Wall Gram-negative Cell Wall § Thin peptidoglycan • Thick peptidoglycan § Outer membrane § Periplasmic space • Teichoic acids GLBH 205 - Fundamentals of Microbiology 26 Figure 4. 13 b–c

Bacterial Cell Walls A. Gram-positive bacterium B. Gram-negative bacterium GLBH 205 - Fundamentals of Microbiology 27

Glycocalyx • Outside cell wall • Usually sticky • Capsule: neatly organized § Slime layer: unorganized and loose § Extracellular polysaccharide allows cell to attach § Capsules prevent phagocytosis GLBH 205 - Fundamentals of Microbiology 28

Prokaryotic Cell Structure, cont. • Glycocalyx (Slime Layers and Capsules) – Some bacteria possess glycocalyx, a slimy, gelatinous material produced by the cell membrane and secreted outside the cell wall – 2 types of glycocalyx – slime layer (loosely connected to the cell wall) and capsule (highly organized and firmly connected) • Pseudomonas spp. produces a slime layer • K. pneumoniae, N. meningitidis and S. pneumoniae possess a capsule, which serves as anti-phagocytic function GLBH 205 - Fundamentals of Microbiology 29

Capsule Stain (Example of a negative staining technique) GLBH 205 - Fundamentals of Microbiology 30

Flagella in G+ Bacterium • • Outside cell wall Made of chains of flagellin Attached to a protein hook Anchored to the wall and membrane by the basal body GLBH 205 - Fundamentals of Microbiology 31

The Structure of a Prokaryotic Flagellum GLBH 205 - Fundamentals of Microbiology 32

Prokaryotic Cell Structure, cont. • Flagella – Motile bacteria possess flagella – whiplike appendages composed of threads of protein called flagellin – Number and arrangement of flagella are characteristic of a particular species: • Peritrichous bacteria – flagella over entire surface • Lophotrichous bacteria – flagella at one end • Amphitrichous bacteria – flagella at both ends • Monotrichous bacteria – single polar flagellum GLBH 205 - Fundamentals of Microbiology 33

Four Basic Types of Flagella Arrangement on Bacteria Motile bacteria possess flagella – whiplike appendages composed of threads of protein called flagellin GLBH 205 - Fundamentals of Microbiology 34

Arrangements of Bacterial Flagella GLBH 205 - Fundamentals of Microbiology 35

A Peritrichous Salmonella Cell GLBH 205 - Fundamentals of Microbiology 36

Motile Cells • Rotate flagella to run or tumble • Move toward or away from stimuli (taxis) • Flagella proteins are H antigens (e. g. , E. coli O 157: H 7) GLBH 205 - Fundamentals of Microbiology 37

Motile Cells Figure 4. 9 a GLBH 205 - Fundamentals of Microbiology 38

Axial Filaments • Also called endoflagella • In spirochetes • Anchored at one end of a cell • Rotation causes cell to move GLBH 205 - Fundamentals of Microbiology 39 Figure 4. 10 a

Fimbriae and Pili • Fimbriae allow attachment GLBH 205 - Fundamentals of Microbiology 40 Figure 4. 11

Prokaryotic Cell Structure (continued) • Pili (also called fimbriae) – Hair-like structures, most often observed on Gramnegative bacteria – Composed of polymerized protein molecules called pilin – Pili are thinner than flagella, have a rigid structure and are not associated with motility – Pili enable bacteria to anchor themselves to surfaces – Some bacteria possess a sex pilus for conjugation GLBH 205 - Fundamentals of Microbiology 41

Proteus vulgaris cell, showing pili and several flagella Pili Flagella Copyright © 2011 Wolters

Prokaryotic Cell Structure, cont. • Spores (Endospores) – A few genera (e. g. , Bacillus and Clostridium) are capable of forming thick-walled spores as a means of survival – The process of spore formation is called sporulation – it is not reproduction – Spores have been shown to survive for many years and are resistant to heat, cold, drying, and most chemicals – Usually one spore is produced in a bacterial cell and generates into one vegetative bacterium – Endospores can be visualized using a spore stain GLBH 205 - Fundamentals of Microbiology 43

A Bacillus Cell With a Well-Defined Endospore Copyright © 2011 Wolters Kluwer Health |

Recap of Structural Differences Between Prokaryotic and Eukaryotic Cells • Eukaryotic cells contain a true nucleus; prokaryotic cells do not. • Eukaryotic cells are divided into plant and animal types – Animal cells do not have a cell wall, plant cells have a simple cell wall. • Eukaryotic cells contain membranous structures and many membrane-bound organelles; prokaryotic cells possess no membranes other than the cell membrane that encloses the cytoplasm GLBH 205 - Fundamentals of Microbiology 45

Recap of Structural Differences Between Prokaryotic and Eukaryotic Cells EUCARYOTIC PROCARYOTIC contain a true nucleus with linear chromosomes No nuclear membrane with one circular chromosome Animal cell do not have wall. Plant cells have a simple cell wall. Nucleus divides by mitosis Divides by binary fission Sex cells are haploid in diploid Always haploid Cell membrane capable of endocytosis and exocytosis Cell membrane incapable of endocytosis and exocytosis Cell wall does not have peptidoglycan. Animals cells lack cell walls Cell walls with peptidoglycan May have flagella and cilia Have flagella. No cilia GLBH 205 - Fundamentals of Microbiology 46

Reproduction of Organisms and Their Cells • Prokaryotic Cell Reproduction – Prokaryotic cells reproduce by a process known as binary fission – one cell splits in half to become two daughter cells. • Before a prokaryotic cell divides in half, the chromosome must be duplicated. – The time it takes for binary fission to occur is called the generation time. • Generation time varies from one species to another and depends on growth conditions (under ideal conditions, E. coli has a generation time of about 20 minutes). GLBH 205 - Fundamentals of Microbiology 47

GLBH 205 - Fundamentals of Microbiology 48

Binary Fission of a Bacterial Cell GLBH 205 - Fundamentals of Microbiology 49

Taxonomy • Taxonomy is the science of classification of living organisms. • Taxonomy consists of 1. classification, 2. nomenclature, and 3. identification. GLBH 205 - Fundamentals of Microbiology 50

Taxonomy 1. Classification • the arrangement of organisms into taxonomic groups (known as taxa). 2. Nomenclature • The assignment of names to the various taxa according to international rules 3. Identification. • Process of determining whether an isolated belongs to one of the established, named taxa or represents a previously unidentified species. GLBH 205 - Fundamentals of Microbiology 51

Taxonomy Tool for remembering the sequence of Taxa “King David Came Over for Good Spaghetti” KDCOFGS K for Kingdom D for Division (Phylum) C for Class O for Order F for Family G for Genus and S for Species GLBH 205 - Fundamentals of Microbiology 52

Microbial Classification • Organisms are categorized into larger groups based on their similarities and differences. • The Five-Kingdom (Domain) System of microbial classification • Viruses are not included because they are acellular. • Three-Domain System (more popular). GLBH 205 - Fundamentals of Microbiology 53

Five-Kingdom System Categories based on similarities & differences 1. Prokaryote (Monera) – Bacteria and Archae 2. 3. 4. 5. Protista (protists) = algae & protozoa Fungi Plantae Animalia (other than humans) GLBH 205 - Fundamentals of Microbiology 54

Three Domain System [Gaining popularity] Based on differences in ribosomal RNA structure 1. Archaea Domain • Archaebacteria Kingdom 2. Bacteria Domain • Eubacteria Kingdom 3. Eukarya Domain • Protista Kingdom, Fungi Kingdom, Plantae Kingdom and Animalia Kingdom GLBH 205 - Fundamentals of Microbiology 55

Microbial Classification Nomenclature • Binomial System of nomenclature. • each organism is given 2 names – • genus and the specific epithet • taken together, both names constitute the species. – For example, Escherichia coli; Escherichia is the genus and coli is the specific epithet. • The genus is frequently abbreviated with just a single letter, (e. g. , E for Escherichia). • The abbreviation “sp. ” is used to designate a single species and “spp. ” for more than one species. GLBH 205 - Fundamentals of Microbiology 56

Microbial Classification (continued) • The Three-Domain System of Classification 1. Archaea (prokaryotic) 2. Bacteria (prokaryotic) 3. Eukarya (all eukaryotic organisms) • The Three-Domain System is based on differences in the structure of certain ribosomal RNA (r. RNA) molecules among organisms in the 3 domains. GLBH 205 - Fundamentals of Microbiology 57

Determining Relatedness Among Organisms • Which is the most widely technique used to determine diversity or “relatedness” of organisms? • The ribosomal RNA (r. RNA) sequencing. • How Ribosomes looks like? • They are composed of two subunits; a small subunit and a large subunit. • The small subunit is composed of only one r. RNA molecule, which is coded for by a gene called the 16 S r. RNA gene in prokaryotes and the 18 S r. RNA gene in eukaryotes. GLBH 205 - Fundamentals of Microbiology 58

Determining Relatedness Among Organisms, cont. • How scientist determine how closely related one prokaryotic organism is to another? • They compare the sequence of nucleotide base pairs in the 16 S r. RNA gene from one of the organisms to the sequence of base pairs in the 16 S r. RNA gene from the other organisms. • The more similar the sequence of base pairs, the more closely related are the organisms. GLBH 205 - Fundamentals of Microbiology 59