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Biological Sciences

Bio Lecture 2: 1/27/14 Overview: Master of Adaptation a. Utah’s Great Salt Lake salt concentration of 32% provides a home for living prokaryotes that it its pink color b. Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms c. Are microscopic, but what they lack in size they make up for in numbers d. There are more in a handful of fertile soil tan the number of people who have ever lived e. Prokaryotes are divided into two domains: bacteria and archaea Concept 27:1: Structural and Functional adaptations contribute to prokaryotic success a. Earth’s fist organisms were likely prokaryotes 1. Most prokaryotes are unicellular, some species form colonies 2. Most prokaryotic cells are 0.5-5 nanometers, smaller than the 10-100nanometer of many eukaryotic cells with a variety of shapes 3. The three most common shapes: spheres (cocci), rods (bacilli), and spirals Cell-Surface Structures a. Important feature: cell wall wich maintains shape, protects cells and prevents it from bursting in a hypertonic environment b. While eukaryote cell walls are made of cellulose or chitin c. Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides d. Archaea contain polysaccharides and proteins but lack peptidoglycan e. Scientists use gram stain to classify bacteria by cell composition 1. Gram-positive: bacteria have simple cell walls made up of peptidoglycan (Staphylococcus aureus) 2. Gram-negative: bacteria call walls have thinner layer of peptidoglycan and an outer membrane that can be toxic (E. Coli and Salmonella) f. Many antibiotics taget paptidoglycan to damage bacterial cell walls (penicillin) g. Gram-negative bacteria, however, are more likely to be resistant to antibiotics that target only peptidoglycan h. In addition a polysaccharide or protein layer called a capsule covers many prokaryotes 1. Often enabling them to attach to other cells (Steptococcus in the throat) i. Surviving harsh conditions is often accomplished through an endospore stage, sometimes for a number of years 1. Coating of dipioclinic acid provides heat resistance j. Some prokaryotes have fimbrae which allow them to stick to their substrate or each other in a colony k. Pilli (or sex pilli) are longer than fimbrae and allow prokaryotes to exchange DNA Motility a. In a heterogeneous env., many bacteria exhibit taxis 1. Chemotaxis is the movement toward or away from a chemical stimulus b. Most motile bacteria are propelled by flagella scattered about the surface or at one or both ends c. Bacterial flagella are composed of a motor, hook, and filament (flagelin) d. Diffusion of protons back and forth across cell membrane cause filament to rotate Evolutionary Origins of Bacterial Flagella a. Flagella of bacteria, archea, and eukaryotes are composed of different proteins and likely evolved independently 1. Many of the flagella’s proteins are modified version of proteins that perform other tasks in bacteria 2. Flagella probably evolved as existing proteins were added to an ancestral secretory system 3. This is an example of adaptation, where existing structures take on new function through descent with modification Internal Organization and DNA a. Prokaryotic cells usually lack complex compartmentalization 1. Some prokaryotes do have specialized membranes that perform metabolic function, but these are usually in-folding of the plasma membrane b. The prokaryotic genome has less DNA than the eukaryotic genome 1. Most of the genome consists of a circular chromosome 2. The chromosome is not surrounded by a membrane, it is located in the nucleoid region 3. Some species of bacteria also have smaller rings of DNA called plasmids that often play a role in antibiotic resistance c. There are some differences between prokaryotes and eukaryotes in DNA replication, transcription and translation 1. Ex: ribosomes of prokaryotes are smaller, contain different protein and RNA composition d. These differences allow people to use some antibiotics to inhibit bacterial growth without harming eukaryotic cells: 1. Certain antibiotics like eythrmycin and tetracycline bind to prokaryotic ribosomes, blocking tRNA translocation and terminating prokaryotic synthesis 2. But have no effect on eukaryotic processes Reproduction and Adaptation a. Key features of prokaryotic reproduction: 1. They are small, and reproduce quickly 2. They reproduce by binary fission, identical progeny 3. They have short generation times, divide ever 1-3 hour allowing prokaryotes to evolve quickly b. So prokaryotes are not “primitive” they are simply highly ev
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