Chapter 5 Cell Biology of Bacteria and Eukaryotes Notes PDF

Cell biology of bacteria and eukaryotes Chapter 5 Chapter Objectives **Describe** the key parts of a bacterial cell. **Explain** the importance of a bacterial cell's parts for the function of antibiotics. **Describe** the key parts of a eukaryotic cell, and explain how pathogens take advantage...

Cell biology of bacteria and eukaryotes Chapter 5 Chapter Objectives **Describe** the key parts of a bacterial cell. **Explain** the importance of a bacterial cell's parts for the function of antibiotics. **Describe** the key parts of a eukaryotic cell, and explain how pathogens take advantage of these to infect a eukaryotic host. The Bacterial Cell: An Overview Two major classifications of cells with different forms: - Prokaryotic - Bacteria and archaea - Lack nuclear membrane - Eukaryotic - All other cells - DNA found in nucleus - The Bacterial Cell: An Overview A Model of the Bacterial Cell ([Review Chapter 4 for more information about structure]) The cell envelope is made up of: - Cell membrane -- surrounds the cytoplasm of the cell - Cell wall -- rigid, mesh-like structure that encloses the cell body - Composed of peptidoglycan - Periplasm - Some bacteria have an **outer membrane** - The Bacterial Cell: An Overview Within the **cytoplasm**: - Chromosome organized into the nucleoid region -- no membrane - As DNA is copied loops are transcribed into RNA by RNA polymerase - mRNA is translated to proteins by ribosomes in the cytoplasm Biochemical Composition of Bacteria: - Water - Inorganic ions - K^+^, Cl^-^ - Small organic ions - Lipids and sugars - Macromolecules - Nucleic acids, proteins - Bacterial Membranes and Transport Within the cell membrane there are proteins that serve a variety of functions: - **Structural support:** anchor layers of membrane together, form the base of other structures - **Detecting environmental signals:** sense environmental triggers that can activate expression of virulence factors - **Secreting virulence factors and communication signals:** export toxins, send signals to host to do something - **Transport across the cell membrane:** determine what substance move through membrane - **Energy storage and transfer:** maintain concentration gradients - Bacterial Membranes and Transport Transport of Nutrients - Some, like oxygen, passively diffuse across membranes - Others use a **permease** - Sugars and peptides may cross through a **protein channel** - Organisms often utilize **concentration gradients** of nutrients when transporting - Transport of Nutrients - **Passive Transport** - Moves from higher to lower concentration - **Facilitated diffusion** from a membrane protein can speed rate of transport - **Active Transport:** - Moves from lower to higher concentration gradient - Energy required (ATP or proton motive force)! - **Coupled transport** - Symport vs. Antiport - Transport of Nutrients - Transport of Nutrients Transport Powered by ATP - ATP binding cassette, known as ABC transporters, are energy driven transport systems - Two proteins form a membrane channel and cytoplasmic proteins bind ATP - Substrate-binding protein binds substrate - They may take up nutrients - Efflux transporters expel waste - Multidrug efflux pump - Transport of Nutrients Proton Motive Force - Energy stored in form of **potential energy** across membrane - Generated when protons are pumped outside the cell - H+ concentration increases outside the cell - Make ATP, move nutrients into cell, drive motors - Bacterial Cell Wall & Outer layers - Bacterial cell walls usually composed of **peptidoglycan** - Single molecule composed of parallel polymers of disaccharides called **glycan chains** - Cross linked with peptides of 4 amino acids - Glycan chains contain: **N-acetylglucosamine (NAG)** and **N-acetylmuramic acid (NAM)** - Glycan strands linked by **peptide bridges** composed of 4-6 amino acid residues - L-alanine, D-glutamic acid, m-daminopimelic acid (DAP), and D-alanine (maybe two of these) - Two in the unusual D mirror form - Peptidoglycan Synthesis as a Target for Antibiotics - Building the peptidoglycan requires the many different genes that encode a variety of enzymes - Make sugars and peptides - Seal the cross-bridges - These enzymes make great antibiotic targets - Penicillin targets transpeptidase - Vancomycin binds the terminal D-alanine - Widespread, indiscriminate use of antibiotics is allowing for growing bacterial resistance - Gram-Positive Cell Envelope - Teichoic acids enforce peptidoglycan - Help attach to host cells - Recognized by the immune system - Capsule may be present - Surface layer, or S-layer virulence factor for pathogens - Crystalline layer with thick subunits of protein or glycoprotein - May use to attach to - Gram-Negative Cell Envelope - Inner membrane - Periplasm -- between inner and outer membranes - 1-2 layers of peptidoglycan - Outer membrane - Lipoproteins anchor to peptide bridges of cell wall - Murein lipoprotein - Special membrane lipid called lipopolysaccharide (LPS) - Gram-Negative Cell Envelope LPS composed of three parts: - Lipid A - endotoxin - Core polysaccharide - Five sugars with side chains - O antigen - Polysaccharide chain - Can have as many as 200 sugars - Transporters called **porins** also found - Murein lipoprotein binds to DAP - Mycobacterial Envelope - *Mycobacterium* species - Weakly Gram-positive but cell envelopes have many unique layers - Thick waxy coat slows down nutrient uptake -- slow growth - Benzene like aromatic rings -- extremely hydrophobic - Mycolic acids - Two hydrocarbon chains, one comparable to other membrane lipids, the other threefold longer - The nucleoid and bacterial cell division Bacterial DNA is Organized in a Nucleoid - DNA of bacteria and archaea is usually a single circular chromosome - DNA is held together by DNA-binding proteins in the nucleoid - Loops all connect to **origin of replication (*ori*)** attached to cell envelope at cell's "equator" - Chromosome has extra twists called supercoils - Allow for compaction - Caused by DNA gyrase - The nucleoid and bacterial cell division Bacterial Cell Division - DNA replication begins at origin and proceeds **bidirectionally** around the circle - DNA double helix unzips at origin -\> replication forks - DNA polymerase synthesizes DNA - Replicate DNA continuously as they grow - Cell expands cytoplasm simultaneously - **Septation** occurs as the termination site is replicated - Septum forms to result in two identical daughter cells - Specialized Structures of Bacteria Certain structures allow bacteria to adhere to substrates - **Adherence** allows microbes to attach to a substrate using structures - Pili, fimbrae, and Stalks Flagella provide **motility** to some - Number and arrangement of flagella can vary - Flagella enhance virulence - *Proteus* - Specialized Structures of Bacteria Bacterial Structures for Different Habitats - **Thylakoids** - Extensively folded intracellular membranes that conduct photosynthesis - **Gas vesicles** - Collect gases produced by organisms metabolism (Hydrogen or CO~2~) to become buoyant and stay near the top of the water column where sunlight is present - **Storage granules** - Store energy in polymers - **Sulfur granules** - Granules of solid sulfur stored in cytoplasm or globules outside of cell; avoid predation - **Magnetosomes** - Magnetic mineral magnetite allow some pond-dwelling bacteria to swim along magnetic filed - The Eukaryotic Cell - Eukaryotic cells include cells of the human body, plants, fungi, and single celled parasites - Range in size from as small as a bacterium to large enough to be seen with the naked eye - The Eukaryotic Cell Organelles of the Eukaryotic Cell - Eukaryotes posses many different organelles: - Endoplasmic reticulum - Mitochondria - Golgi apparatus - Most prominent difference between eukaryotes and prokaryotes: presence of a true nucleus - Contains nuclear pore complexes for movement of material into and out of the nucleus - The Eukaryotic Cell Mitochondria and chloroplasts generate energy for the cell. - **Mitochondria**: conduct oxidative phosphorylation and make ATP - **Chloroplasts**: perform photosynthesis - Evolved via **endosymbiosis** -- one cell is engulfed by larger cell but not digested - Mutualistic relationship develops - Mitochondria and Chloroplasts Yield Energy Mitochondria - **Inner and outer membrane** - Inner membrane has cristae to increase surface area, ATP synthase located here, resembles ancestral bacterial membrane - Outer membrane composition is similar to eukaryotic membrane - **Two different compartments** - Intermembrane space -- between inner and outer membranes - Matrix -- enclosed by inner membrane - These combined compartments are where oxidative respiration occurs - Cytoskeleton Maintains Shape figure 5.29 **Cytoskeleton** -- network of proteins that determine shape of cell; Involved in cell movement and movement of substances - **Microfilaments**: - Actin - Dynamic -- grow and shrink - **Intermediate filaments:** - Form meshwork under cell to maintain shape and resist tension - **Microtubules:** - Tubulin - Dynamic - Can forms parts of cilia and flagella - Move substances in the cell - Specialized Structures - **Flagella and cilia** - Bundles of microtubules - Usually only one or two - Cilia may capture food - **Pellicle** - Protists - Membranous layers reinforced by microtubules - **Contractile vacuole** - Removes excess water from the cytoplasm by expelling through a pore