Microbiology Chapter 5: Cell Biology of Bacteria and Eukaryotes PDF

CHAPTER 5 Cell Biology of Bacteria and Eukaryotes Copyright © 2021 W. W. Norton & Company, Inc. Cell Biology of Bacteria and Eukaryotes Chapter Objectives ▪ Describe the key parts of a bacterial cell. ▪ Explain the function of a bacterial cell’s parts and their importance for antibiotic th...

CHAPTER 5 Cell Biology of Bacteria and Eukaryotes Copyright © 2021 W. W. Norton & Company, Inc. Cell Biology of Bacteria and Eukaryotes Chapter Objectives ▪ Describe the key parts of a bacterial cell. ▪ Explain the function of a bacterial cell’s parts and their importance for antibiotic therapy. ▪ Describe the key parts of a eukaryotic cell, and explain how pathogens take advantage of these to infect a eukaryotic host. 2 An Upscale Tick Bite – 1 Scenario ▪ Sharon, the CEO of a start-up company, lives in Westchester County, a wooded community north of New York City. She spends her summer weekends emailing her managers from the outdoor deck of her home, shaded by tall oak trees. The acorns from the oak tree provide food for a large population of mice, which in turn are fed upon by an abundant population of ticks (Ixodes scapularis). 3 An Upscale Tick Bite – 2 Signs and Symptoms ▪ One evening, Sharon’s husband noticed a red rash on the back of her arm. Sharon recalled seeing this “bull’s eye” type of rash on the Internet, where it was described as a clinical sign for ___________, a type of borreliosis caused in the United States by the spirochete Borrelia burgdorferi. 4 An Upscale Tick Bite – 3 Signs and Symptoms ▪ Sharon recalled that a neighbor’s child had suffered crippling arthritis caused by an undetected case of Lyme disease. Another neighbor who contracted Lyme disease had experienced neurological symptoms, which ultimately cost him his job and million-dollar home. 5 An Upscale Tick Bite – 4 Diagnosis and Treatment ▪ The next day Sharon went to her doctor. He recognized the rash and prescribed a few weeks of the oral antibiotic doxycycline. For Sharon, the antibiotic cleared up her symptoms. She was fortunate, however, because without the rash, her disease might have gone undiagnosed and untreated, leading to more serious symptoms. 6 5.1 The Bacterial Cell: An Overview – 1 Section Objectives ▪ Describe the structure and function of the bacterial cell and how it differs from the cell of a eukaryote. ▪ Describe the biochemical composition of a bacterial cell. 7 5.1 The Bacterial Cell: An Overview – 2 ▪ Cells are the fundamental unit of life. Prokaryotic cells – Cells without a “true” nucleus (no nuclear membrane) – Bacteria and archaea Eukaryotic cells – Cells with a “true” nucleus and other organelles – All other organisms (animals, plants, fungi, and protists) 8 A Model of the Bacterial Cell – 1 ▪ The cytoplasm of the bacterial cell is a gel-like network of proteins and other macromolecules. It is contained by a cell membrane. ▪ Outside of the membrane the cell body is enclosed by a cell wall. The cell wall is made up of peptidoglycan. ▪ Outside the cell wall, Gram-negative bacteria have an outer membrane. ▪ The cell membrane, cell wall, and outer membrane (for Gram- negative species) constitute the cell envelope. ▪ The chromosome is organized within the cytoplasm as a system of looped coils called the nucleoid. 10 A Model of the Bacterial Cell – 2 ▪ Prokaryotic cell structure 12 A Model of the Bacterial Cell – 3 ▪ The cell wall consists of glycan chains (parallel rings) linked by peptides (arrows). The spaces between links are open, porous to large molecules. 13 A Model of the Bacterial Cell – 4 ▪ The bacterial cell wall acts like a molecular cage, protecting the cell membrane from osmotic shock. 14  A Model of the Bacterial Cell – 5 ▪ The outer membrane consists of phospholipids and lipopolysaccharides (LPS), a class of lipids attached to long polysaccharides (sugar chains). O-Antigen: Extends outward from the core oligosaccharide. Not embedded in the membrane. Core Oligosaccharide: Attached to Lipid A. Extends outward but not embedded in the membrane Lipid A: Embedded in the bacterial outer membrane. Fatty acid chains anchor LPS into the membrane. Responsible for endotoxic effects when killed. A Model of the Bacterial Cell – 6 ▪ Another common external structure is the flagellum (plural, flagella), a helical protein filament whose rotary motor propels the cell in search of a more favorable environment. E. coli the flagella extend freely outside of the cell. Borrelia burgdorferi or Treponema pallidum the flagella wrap around the cell body. From: https://www.cdc.gov/ecoli/about/index.html From: https://www.creative-biolabs.com/vaccine/treponema-pallidum-vaccines.htm 5.2 Bacterial Membranes and Transport – 1 Section Objectives ▪ Describe the functions of a cell membrane. ▪ Explain how nutrients are transported and how energy is spent to drive transport. ▪ Describe how pathogens use ion gradients and ATP to obtain nutrients from the host 18 5.2 Bacterial Membranes and Transport – 2 ▪ The cell membrane defines a cell. Cell (plasma) membrane separates the cytoplasm from the outside environment. Phospholipid bilayer with proteins 19 Bacterial Membrane Proteins ▪ Support for structures that protrude from the cell (flagella, pili) ▪ Signaling and communication (ToxR = Cholera toxins) ▪ Export of toxins and other virulence factors ▪ Transport of substances in and out of the cell across the membrane ▪ Establishment of concentration gradients for energy transfer Amin Marashi, et al., (2013). 20 Nina Gubensäk, et al., (2023). Transport of Nutrients – 1 ▪ Microbes must move nutrients across the membrane into the cytoplasm. ▪ Passive transport moves nutrients with the concentration gradient while active transport moves nutrients against the concentration gradient. ▪ The use of energy from one gradient to drive transport up another gradient is called coupled transport. Symport Antiport 22 Transport of Nutrients – 2 23  Transport of Nutrients – 3 ▪ ABC Transporters (ABC (ATP- ▪ Siderophores Binding Cassette) Transporters) 24 5.3 The Bacterial Cell Wall and Outer Layers Section Objectives ▪ Describe the cell wall structure, and explain how it protects bacteria from osmotic shock. ▪ Explain the function of the Gram-positive cell wall and teichoic acids. ▪ Explain the function of the Gram-negative outer membrane, LPS, and periplasm. 25 The Cell Wall Is a Single Molecule – 1 ▪ The cell wall is a single, interlinked molecule that encloses the entire cell. ▪ Peptidoglycan consists of parallel polymers of disaccharides called glycan chains. The glycan chains are cross-linked with short peptides. 26  The Cell Wall Is a Single Molecule – 2 A disaccharide unit of glycan has an attached peptide of four to six amino acids attached to the NAM terminal. On the peptide, the extra amino group of m-diaminopimelic acid can cross-link to the carboxyl terminus of a neighboring peptide. The addition of D-alanine to the peptide is blocked by vancomycin, and the cross-bridge formation by transpeptidase is blocked by penicillin. 27  The Cell Wall Is a Single Molecule – 2 A disaccharide unit of glycan has an attached peptide of four to six amino acids attached to the NAM Penicillin binds to terminal. a bacterial On the peptide, the extra amino enzyme called transpeptidase group of m-diaminopimelic acid can (responsible for cross-link to the carboxyl terminus catalyzing the of a neighboring peptide. formation of peptide cross- bridges). The addition of D-alanine to the peptide is blocked by vancomycin, and the cross-bridge formation by transpeptidase is blocked by penicillin. Vancomycin binds directly to the terminal D-alanine residues of the peptidoglycan chains, blocking the formation of peptide cross-bridges. 28 Gram-Positive and Gram-Negative Outer Layers – 1 ▪ Bacterial cell wall types Gram-positive: thick cell wall, multiple layers of peptidoglycan – Bacillus anthracis, Streptococcus pyogenes Gram-negative: thin cell wall, single layer of peptidoglycan, enclosed by an outer membrane – Escherichia coli, Pseudomonas aeruginosa Gram-Positive and Gram-Negative Outer Layers – 2 ▪ Gram-positive cell wall 30 Gram-Positive and Gram-Negative Outer Layers – 3 ▪ Gram-negative cell wall 31 Gram-Positive and Gram-Negative Outer Layers – 4 ▪ Gram-negative close-up Murein lipoprotein: inner leaflet of the outer membrane that forms a peptide bond with peptidoglycan Lipopolysaccharide (LPS): outer leaflet of the outer membrane; lipid A and polysaccharide chains – Lipid A acts as an endotoxin in lysed cells, so antibiotic treatment can kill cells but can also cause endotoxic shock in patients. 32 The Mycobacterial Envelope ▪ Mycobacteria contain a unique envelope. Complex cell wall with peptidoglycan and mycolic acid Resistant to staining Include human pathogens – Mycobacterium tuberculosis – Mycobacterium leprae 33 Case History: A Rash Reveals an Ancient Disease ▪ Naranjan lives in the Indian state of Bihar. The lesions on his face and lips are the result of leprosy, a bacterial infection caused by Mycobacterium leprae. ▪ The lesions contain the bacteria, which can only be observed in skin scrapings stained with the acid-fast method, which uses heat to allow the stain to penetrate the waxy coating created by the mycolic acid in the cell wall. 34