Chapter 25: Bacteria and Archaea (Biology Eighth Edition) PDF

Chapter 25 Bacteria and Archaea Delivered by Dr. Salamah Alwahsh Medi...

Chapter 25 Bacteria and Archaea Delivered by Dr. Salamah Alwahsh Medicine Program PowerPoint® Lecture Presentations for PPU Biology Date: Nov 2024 Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structural and functional Prokaryotes are divided into two domains: bacteria and archaea. Most prokaryotes are unicellular, although some species form colonies Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Some bacteria are pathogens, causing disease, but most bacteria on our bodies are benign or beneficial Prokaryotic cells three most common shapes are spheres (cocci), rods (bacilli), and spirals. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings External features contribute to the success of prokaryotes ▪ Prokaryotic cells have three common cell shapes. Cocci are spherical prokaryotic cells. They sometimes occur in chains that are called streptococci. Bacilli are rod-shaped prokaryotes. Bacilli may also be threadlike, or filamentous, E. coli A curved rod, called vibrio: Cholera Spiral prokaryotes are like a corkscrew. – Short and rigid prokaryotes are called spirilla. – Longer, more flexible cells are called spirochetes, Treponema pallidum causes syphilis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prokaryotic Shapes 1 µm 2 µm 5 µm (a) Spherical (b) Rod-shaped (c) Spiral (cocci) (bacilli) Prokaryotes are diverse and widespread ▪ Several hundred species of bacteria live in and on our bodies, decomposing dead skin cells, supplying essential vitamins, and guarding against pathogenic organisms ▪ Prokaryotes in soil decompose dead organisms, sustaining chemical cycles. Prokaryotes Cell-Surface Structures An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment Eukaryote cell walls are made of cellulose or chitin Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram- negative groups based on cell wall composition Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant Many antibiotics target peptidoglycan and damage bacterial cell walls… (often causing cell lysis). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Bacteria: Cell Wall Composition: Gram Stain Carbohydrate portion of lipopolysaccharide Outer Peptidoglycan Cell Cell membrane layer wall wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- Gram- positive negative bacteria bacteria 20 µm (a) Gram-positive: peptidoglycan traps crystal violet. (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. toxic bacteria The genome of a prokaryote typically has about one- thousandth as much DNA as a eukaryotic genome and  A polysaccharide or protein layer called a capsule covers many prokaryotes Some prokaryotes have fimbriae, which allow them to stick (attach) to their substrate Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA by conjugation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria Fimbriae -- allow bacteria to adhere to each other and substrates Fimbriae 200 nm Motility / Internal Organization Most motile bacteria propel themselves by flagella that are different from eukaryotic flagella Many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Prokaryotic cells lack complex compartmentalization Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria flagellum - Structurally different from Eukaryotic flagella Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane Bacteria often have Specialized Internal Membranes 0.2 µm 1 µm Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote  Prokaryotic Genome - No Nucleus The prokaryotic genome has less DNA than the eukaryotic genome. Most of the genome consists of a circular chromosome. Some species of bacteria also have smaller rings of DNA called plasmids The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Single Circular Chromosome Plasmids smaller DNA rings 1 µm Reproduction and endospores Prokaryotes reproduce asexually quickly by binary fission and can clone / divide every 1– 3 hours Many prokaryotes form metabolically inactive endospores, which can remain dormant and viable in harsh conditions for centuries. Endospore Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Binary fission Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Factors promote genetic diversity Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity in prokaryotes: – Rapid reproduction – Mutation – Genetic recombination Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Genetic Recombination Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation Transduction is the movement of genes between bacteria by bacteriophages (viruses) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Phage virus DNA Transduction By bacteriophage A+ B+ A+ B+ Bacteria Donor Cell A+ Recombination A+ A– B– Bacteria Recipient Cell A+ B– Recombinant cell Conjugation and Plasmids Conjugation is the process where genetic material is transferred between bacterial cells Sex pili allow cells to connect and pull together for DNA transfer A piece of DNA called the F factor is required for the production of sex pili The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome and is transferable during conjugation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Conjugation Sex pilus 1 µm F factor allows genes to be transferred from one bacterium carrying the factor to another bacterium lacking the factor by conjugation R Plasmids and Antibiotic Resistance R plasmids carry genes for antibiotic resistance Antibiotic resistant strains of bacteria are becoming more common Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Diverse nutritional and metabolic adaptations have evolved in prokaryotes Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs require CO2 as a carbon source Heterotrophs require an organic nutrient to make organic compounds These factors can be combined to give the four major modes of nutrition: photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prokaryotic Nutritional Diversity The electrons required for this are obtained from minerals such as iron.  The role of oxygen in metabolism Prokaryotic metabolism varies with respect to O2 – Obligate aerobes require O2 for cellular respiration – Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration – Facultative anaerobes can survive with or without O2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Root nodules on a soybean plant Shoot In nitrogen fixation, some prokaryotes Nodules convert atmospheric Rhizobium bacteria within vesicle in an Roots nitrogen (N2) to infected cell ammonia (NH3) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Streptomyces bacteria, the source of many antibiotics Streptomyces is cultured by pharmaceutical companies as a source of many antibiotics, antifungal and anti-parasitic drugs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Staphylococcus aureus, an exotoxin producer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prokaryotes play crucial roles in the biosphere. Chemical Cycling Prokaryotes play a major role in the recycling of chemical elements Chemoheterotrophic prokaryotes function as decomposers (saphrophytes) breaking down corpses, dead vegetation, and waste products. Nitrogen-fixing prokaryotes add usable nitrogen to the environment Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ecological Interactions Symbiosis ‫ تكافل‬is an ecological relationship in which two different species live in close contact: a larger host and smaller symbiont. In mutualism, + + both symbiotic organisms benefit. In commensalism, + 0 one organism benefits while neither harming nor helping the other ‫تعايش‬ In parasitism, + - an organism called a parasite harms but does not kill its host. Parasites that cause disease are called pathogens, E.g., tapeworm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Pathogenic prokaryotes typically cause disease by releasing toxins Exotoxins cause disease even if the prokaryotes that produce them are not present Endotoxins are released only when bacteria die and their cell walls break down Many pathogenic bacteria are potential weapons of bioterrorism. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Exotoxin Endotoxin Component of gram- negative Secreted by cell plasma membrane Staphylococcus aureus Salmonella enteritidis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria Structure Review Fimbriae Cell wall Single, circular, closed chromosome in a nucleoid Additional circular DNA (plasmids) Capsule Sex pilus Internal Ribosomes for protein organization synthesis An outer cell wall reinforced with Flagella peptidoglycan For some bacteria, a flagella for locomotion Capsule Tonsil cell Capsule Bacterium