Tree of Life BIOA01

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University of Toronto Scarborough
Biological Sciences
Bebhinn Treanor

Prokaryotes - Thrive almost everywhere, including extreme habitats hostile for most organisms - Remarkable diversity - Simple in structure compared to eukaryotes - Greatest metabolic diversity of all organisms - Classified into 2 domains  Bacteria and Archaea - Unicellular with 3 common cell shapes: sphere (coccus), rod (bacillus), spiral (spirillus) - Diameter of 1-10 um Cell Structure External: - Cell wall (peptidoglycan layer, outer membrane & plasma membrane) - Cell membrane - Capsule - Pili - Flagella Internal: - No internal membrane bound organelles - DNA compacted in nucleoid region - Plasmids- replicate independently - Ribosomes - Semblance of cytoskeleton Genome - Ring of DNA - Singular, circular DNA molecule (=chromosome) - Packed into nucleoid region - No nucleus - Plasmid: resistance to antibiotics - Replicate independently of chromosome Ribosomes - Smaller than eukaryotic ribosomes - Similar function - Archaeal ribosomes share some similarities with eukaryotic ribosomes Reproduction - Binary fission (plasma membrane and chromosome) - Asexual - Exact copies of parent cell - Rapid population growth Metabolic Diversity - Autotrophs self feeding inorganic carbon - Heterotrophs other feeding organic carbon - Chemoautotrophs - Photoautotrophs - Chemoheterotrophs - Photoheterotrophs - Bacteria fall into all types of metabolisms Bacteria - Some essential to health and food productions - Bacterial cell wall maintains shape of cell and protects cell from environment/ bursting ina hypotonic environment - Most contain peptidoglycan (polymer of modified sugars cross-linked by short peptides) - Some contain outer membranes which contain lipopolysaccharide (LPS) - Immune recognition binds to LPS when pathogen detected Gram Stain - Cells stained with crystal violet, then iodine - Rinsed with ethanol, counter rinses safranin - Positive (purple) negative (iodine washed away with ethanol, pink) - Not useful for archaea Sticky Capsule - Layer that lays outside of cell wall - Consists of polysaccharides - Protects cell from environment, antibiotics, viruses - Helps evade detection by immune cells (virulence factor) immune calls cannot recognize bacterial cell Pili and Fimbriae - Hair-like appendage found of surface of bacteria - Aids in attachment of bacteria to host surfaces - Required for colonization during infection - Initiates formation of biofilm - Sex pili allows transfer of plasmids Flagella - Cell surface appendage used for locomotion - Sensory organelle; sensitive to external chemicals and temperature - Whip-like propulsion Methods in promoting diversity 1. Rapid reproduction and Mutation - New mutations can increase diversity quickly in fast reproducing species 2. Genetic recombination (combining DNA from 2 sources) - Conjugation (DNA transferred via pilus), transformation (uptake of foreign DNA from surroundings), transduction (bacteriophages) Antibiotic resistance - Antibiotics shut down protein synthesis or removing cell-wall bonds, causing cell to lyse - Antibiotic binds to enzyme used in bacteria pathway mutation causes bacteria to produce enzyme without this binding site antibiotic resistance - Mutations causing resistance is more prevalent Biofilms - Prokaryotic cells live in communities form on initial attachment of bacteria due to pili (provided there are nutrients and pili on this surface) - Communication begins, gene expression alters, secretion of extracellular polymer (sticky) which isolates and protects bacteria - Communicate by quorum sensing What is a virus? - Nonliving infective agent - A virus particle (virion) consists of a nucleic acid genome in a protein coat/capsod - The viral genome is made of double/single stranded RNA or DNA (few genes) - Reproduce by entering host cell and directing cellular machinery to make new particles of themselves Structure Types: 1) Helical - Proteins assemble into rodlike spiral around the genome - Common plant virus 2) Polyhedral virus - Protein form triangular units, fit together like a geodesic sphere - Some have spikes for recognition & cell binding - Infect plants, animals and bacteria 3) Enveloped virus - Helical or polyhedral covered by membrane derived from host cell - Protein spikes extend through membrane for host cell recognition and adhesion - HIV 4) Complex Polyhedral - Polyhedral head PLUS tail - Genome in head and injected into host cell through sheath - Bacteriophage - Virulent bacteriophages kill host bacteria during each infection cycle - Temperate bacteriophafes have inactive phase of DNA replication within host cells - T-even (T2, T4, T6) are most valuable in E coli studies Infection of Bacteria Lytic Cyle: - Viral event ultimately release viral progeny 1) Phage attaches to host cell 2) Lysozyme digests cell wall to make a hole 3) Phage DNA enters bacterium 4) Phage genes are expressed to control phage replication * Phage proteins synthesized * Phage DNA replicated * Progent phage particles assemble 5) Lysozyme lyses the host cell to release progeny Generalized Transduction - All donor genes are equally likely to be transferred - Virulent bacteriophages kill host cells during each infection (lytic cycle) - Host bacterial chromosome is degraded to provide raw materials for new phage chromosomes - Sometimes bacteria DNA is not digested and infects another cell recombination Lysogenic Cycle: - Integrates the L chromosome into the host (in lytic cycle L goes directly from infection to progeny virus release) - Integrated viral DNA (prophage) is replicated during cell division and is inactive until trigger (certain environmental factors trigger the prophage to loop out of the chromosome) - Latent phase: similar; viruses remain inactive until triggered to become active Specialized Transduction - Lamba apporoves healthy host cell and integrates into host chromosomal DNA and is called a prophage - Prophage is replicated and passed to daughter cells (lysogenic cycle) - Transfer of host genes near L genome Infection of Animals: Unenveloped viruses - No membrane surrounding capsid - Virus binds to host using recognition proteins (adenovirus and polivirus) - Whole virus taken into host cell by endocytosis - Virus directs synthesis of new viruses and kills host when cell ruptured - Snot is dead cells Infection of Animals: Enveloped viruses - Virus binds to host using recognition proteins - Whole virus is taken into host (envelope fuses with membrane) - Virus directs synthesis of new viruses - New viruses acquire membranes as they leave (don’t injure or kill host) - Example: herpes, influenza - H1N1= variations in virus recognit
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