Cell Types & Structures - Lecture Notes PDF

Cell types & structures Lecture outline Prokaryotic & eukaryotic domains Prokaryotic general characteristics Bacteria specific structures & functions Bacterial behaviors Helpful & harmful bacteria Shape & arrangement of bacteria Archean specific structures & functions...

Cell types & structures Lecture outline Prokaryotic & eukaryotic domains Prokaryotic general characteristics Bacteria specific structures & functions Bacterial behaviors Helpful & harmful bacteria Shape & arrangement of bacteria Archean specific structures & functions Eukaryote general characteristics Origins of eukaryotes Review of prokaryotes & eukaryotes prokaryotes single celled bacteria single celled archaeans eukaryotes single celled protists single & multicellular fungi multicellular plants multicellular animals Prokaryotes in general asexual, single celled organisms with no nucleus or other membrane-bound organelles, & circular DNA can live independently or in colonies, but do not build bodies diverse & widespread found on & in multicellular organisms found in habitats too extreme for eukaryotes to survive Domains Bacteria & Archaea General bacterial cell structures & functions of components cell wall acts as protective armor; maintains cellular morphology plasma membrane separates cell innards from environment; controls traffic in/out What’s it made of? DNA encodes proteins; singular & circular chromosomal & plasmids What’s it made of? Molecular shape? ribosomes sites of protein synthesis may have inclusions storage structures may have flagellum/a for locomotion in aqueous solutions (like an outboard motor) may have pili (singular: pilus) grab on to things/adhesive may have a slippery capsule; makes cell hard to catch Cell wall: peptidoglycan only bacteria make peptidoglycan & nearly every other organism can recognize it (!!!) a meshwork of crosslinked alternating molecules provide significant strength 2 types of cell wall, use gram stain to identify type gram positive simpler wall with think layer of peptidoglycan protect the cell from drying, crushing & heat gram negative more complex wall with thinner peptidoglycan & an outer layer of glycolipids resistant to detergents & other chemicals Compari ng Gram + to Gram - Cell wall: peptidoglycan gram staining used to identify cell wall structure cover cells in purple dye (crystal violet) wash away excess dye, add counterstain (pink dye safranin) if cells stay purple, they’re “gram +” crystal violet binds to peptidoglycan; cells that stay purple have a lot; cells that don’t stay purple have a little gram positive stain purple gram negative stain pink (the natural color of cells is unrelated to gram stain results!) Cell wall: peptidoglycan Gram stain can indicate relatedness gram + cluster in a super family gram – cluster in a super family there are completely harmless & deadly examples in both families, but gram – are more likely to be antibiotic resistant & the lipids are often toxic gram – are more likely to induce fever b/c they are less resistant to heat than gram + there are a few species that are neither called “weakly gram +” or “gram indeterminant” ex.: Mycobacterium tuberculosis (called acid-fast positive) it is unknown if gram + or gram – evolved first Gram stain can indicate relatedness Inclusions storage structures for excess nutrients or specific resources; may be... polymerized nutrients (also help reduce buildup of osmotic pressure that occurs as a cell accumulates solutes) Inclusions of polyhydroxybutyrate (PBH) glycogen & starches are produced by some species of Bacillus & Pseudomonas. Industrially inorganic phosphate, sulfur or lipid have been used as a source of biodegradable polymers for bioplastics. storage gas vacuoles (cells can alter buoyancy in water column) magnetic iron oxide (cells can align along magnetic field, aiding in movement) Bacterial flagellum complex structure made from elongated tubes of proteins that are attached to the plasma membrane & cell wall various arrangements flagella spin & propel bacteria forward; reverse spin, bacterium tumbles about randomly until it faces the direction it wants to go! (run & tumble) for their size, they are very powerful! of interest to physicists... Pili (aka fimbriae) made of interlocking proteins stick to surfaces or other cells for pathogenic bacteria, important for colonization & virulence play a role in biofilm formation A few species make a capsule bacteria & background stained, capsule remains colorless exterior to the cell wall made of polysaccharides, proteins &/or glycolipids makes cells slippery & difficult for phagocytosis by WBC protect cells from dehydration & environmental hazards can also play a role in biofilm formation Bacterial behaviors aid in the survivorship of bacteria (& aid in disease) quorum sensing biofilm formation endospore formation Bacterial behavior: quorum sensing how bacteria communicate with each other they measure levels of hormone-like molecules based on how many of their relatives are present, they may change behavior ex. need a minimum #, need more than 1 or 2 bacteria to make a biofilm a form of coordinated of gene expression (!!) this “behavior” can include making toxins, making a biofilm, or invading tissues Bacterial behavior: biofilms a “biofilm” is a thick layer of microbes, AND a sticky extracellular matrix that is made by & houses bacteria often display increased antibiotic resistance bacteria protected from immune system – white blood cells can’t attack or engulf bacteria effectively common sites are wounds, catheters, surgical implants, your teeth, rocks in streams, your dog’s water bowl... biofilms have been known for decades but no one could really describe now realize they are relatively common & how they work new research in medicine to develop “biofilm disrupters” Bacterial behavior: endospore formation bacteria in hibernation (when essential nutrient is scarce) allow a bacterium to survive adverse conditions most bacteria cannot do this bacteria make 6-7 layers of walls around DNA cell takes in no food, makes no waste VERY difficult to destroy ex.: Bacillus subtilis extremely resistant to desiccation, temperature extremes, UV & ionizing radiation has been intensely studied in space also resists acid, boiling, our immune system, etc. ex.: 70-80 year old Bacillus anthracis endospores emerged to live & be happy! Some bacteria help humans: our microbiome! all the microbes that live on & in our bodies bacteria, fungi & viruses; also called microbiota in the human body, there are ~ 1000 species aids in digestion of food synthesizes vitamins B & K defends us against pathogens prevents their growth plays a role in “training” our immune system on which foreign invaders to attach & which to leave alone helps certain medications work better Human Microbiome Project studies the composition of a typical microbiome & how changes in it are related to disease (our microbiome becomes a necrobiome after death!) Some bacteria help humans elsewhere fix nitrogen for plants/crops major decomposers production of foods sauerkraut, yogurt, cheese & more synthesize useful chemicals antibiotics, insulin, plastics, preservatives, etc. fuels for energy production & cars National Microbiome Initiative studies the role of microbes in different ecosystems, including soil, plants, aquatic environments & the human body A few bacteria cause disease bacteria cause ½ of all human disease BUT only 1% of bacteria are pathogenic! some well known examples Streptococcus pyogenes Enterics: Salmonella, Campylobacter, E. coli Chlamydia Mycobacterium tuberculosis (now with extra drug-resistance!) Clostridium difficile How does causing disease benefit bacteria? they eat us as food, we’re tasty & easy to digest! we provide a place to reproduce signs/symptoms of disease may spread microbes around (ex.: sneezing) people travel & interact with others to spread microbes they don’t have to compete with other bacteria once they’re in our tissues We’re cozy! We provide a constant temperature Shape of bacterial cells cocci (round) bacilli (rod) spirochete (spiral)  in addition to cell shape, cells of the same species may group together in distinctive arrangements depending on plane of cell division staining reveals both shape & arrangement Review of prokaryotes & eukaryotes prokaryotes single celled bacteria single celled archaeans eukaryotes single celled protists single & multicellular fungi multicellular plants multicellular animals Domain Archaea were classified as bacteria until molecular analysis showed they are vastly different differences in composition of plasma membranes, cells walls & flagella cell walls not made of peptidoglycans cell walls contain polysaccharides not found in bacteria or eukaryotes some enzymes & ribosomes similar to eukaryotes antibiotics have no effect on growth no known species pathogenic habitats help classify can thrive in extreme temperatures, salt, pH, pressure (extremophiles) can live in not-so extreme habitats too, including in humans Eukaryotic cell structure: a brief review plasma membrane (phospholipid- based) nucleus & other membrane-bound organelles including chloroplasts & mitochondria ribosomes & other structures cytoskeleton DNA is linear & paired chromosomes may have: cell wall appendages flagella & cilia Where did eukaryotes come from? Dr. Lynn Margulis (1938 – 2011), biologist proposed the endosymbiosis theory in her first book, Origins of Eukaryotic Cells (1970) at the time, her ideas were considered far-fetched but now are widely accepted Where did eukaryotes come from? endosymbiosis theory mitochondria & chloroplasts were once small prokaryotes that began living in larger prokaryotes over time, the endosymbiont & the host both benefited from the relationship eventually, they grew increasingly dependent on each other until they could not live w/o each other became a single, more complex organism Evidence of endosymbiosis theory: mitochondria & chloroplasts are both... similar in size to prokaryotes surrounded by a double membrane inner membrane has many similarities to prokaryotic membranes contain their own DNA DNA is circular like prokaryotic DNA contain their own ribosomes more similar to prokaryotic ribosomes than to eukaryotic ribosomes reproduce by a splitting process similar to some prokaryotes Summary prokaryotes are unicellular organisms; domains bacteria & archaea; there are characteristics shared by all prokaryotes, but some specific to each domain there are prokaryotic-specific structures & functions/behaviors that can be used to help ID them there are both harmful & helpful bacteria; no known harmful archeans the shape & arrangement of bacteria can help ID them eukaryotes are larger & more complex than prokaryotes; can be unicellular or multicellular organisms; domain eukarya; all eukaryotic cells contain membrane-bound organelles; some eukaryotes cause disease eukaryotes evolved from prokaryotes living in close association with each other & growing more dependent upon each other; endosymbiosis theory