BIO 102 Chapter 25 Prokaryotes

BIO 102 CHAPTER 25 PROKARYOTES Reading 1 for next class! (required) Dr. Ivonne Bejarano What are prokaryotes? Living things are made up of cells, and cells can be either classified as prokaryotic or eukaryotic. Prokaryotes do not have a well defined nucleus as they lack a nuclear membrane enclo...

BIO 102 CHAPTER 25 PROKARYOTES Reading 1 for next class! (required) Dr. Ivonne Bejarano What are prokaryotes? Living things are made up of cells, and cells can be either classified as prokaryotic or eukaryotic. Prokaryotes do not have a well defined nucleus as they lack a nuclear membrane enclosing their DNA. Prokaryotes do not have membrane- bound organelles like the endoplasmic reticulum, golgi apparatus, mitochondria, or chloroplasts. What are prokaryotes? Because prokaryotes lack a nucleus, they do not divide by mitosis, but instead divide by binary fission- asexual reproduction. * DNA (circular in prokaryotes) replicates, then the two rings are pulled to opposite sides of the cell. Then the cell membrane pinches in, and new cell wall material is deposited. https://www.youtube.com/watch?v=DY9DNWcqxI4 What are prokaryotes? There are four events involved in cell division: 1. Initiation- A signal initiates cell division. E.g. abundant food supplies. 2. DNA Replication-Genetic material duplicates so that each cell will have a complete, identical set of genes. Prokaryotes: 1 chromosome, 1 molecule of DNA; usually circular. 3. DNA segregation- Daughter DNAs are equally separated to each new cells; guided by ori regions. Two regions in the chromosome: ori—where replication starts ter—where replication ends 4. Cytokinesis- A new cell wall separates two new cells. The major source of genetic variation in prokaryotes is mutations, which are expressed immediately, since prokaryotes are haploid. The three domains of life All living things are organized in 3 domains, 2 of which are prokaryotes: Bacteria, Archaea and Eukarya are all descended from a single, common ancestor (the first living organisms, which were simple prokaryotes and extremophiles). * Archaea are more closely related to eukaryotes than they are What are the features that are common to the 3 domains of life?? Have plasma membranes and ribosomes in abundance. Do glycolysis. Use DNA as genetic material. Produce proteins by transcription and translation. Replicate DNA semi-conservatively. Differences between domains Eukaryotic genes have introns: * DNA sequences that are transcribed into mRNA, but spliced out before translation. Differences between domains Bacteria and Archaea commonly have plasmids: * Small circular DNA distinct from the main chromosome that contain one or more genes that are usually not critical to the cell’s life.  The success of prokaryotes Prokaryotes can be found everywhere; therefore, are the most numerous living group. Prokaryotes generally form diverse communities called biofilms. Should we care about biofilms? Species in biofilms change in response to environmental conditions; they are bioindicators of env. conditions. Everywhere!! Prokaryote biofilms can form on the surface of living and non-living things; also on their inside. e.g. plant roots, vessels, water pipes, etc… In our body? Biofilm infections from implants Dental plaque (tooth decay)  The success of prokaryotes Prokaryotes live in/on other organisms. * Some may engage in beneficial relationships while others are pathogens. Aliivibrio fischeri is a bacterium found globally in marine environments. It has bioluminescent properties, and is found predominantly in symbiosis with various marine animals, such as the Hawaiian bobtail squid. Prokaryotes can communicate with signals (e.g. bioluminescence). Reading 1 assignment for next class (required) Additional optional readings: Video Biol. Shore Reading Biol. Plants Prokaryotes have distinctive modes of locomotion * like for example, flagella. Prokaryotes have diverse metabolic Escherichia coli pathways: - obligate anaerobes: oxygen is poisonous for them. - facultative anaerobes: can shift from fermentation to cellular respiration. - aerotolerant anaerobes: have anaerobic Reading 1 Prokaryotes include two domains  Domain BACTERIA Bacteria can be described according to 3 characteristic forms: *coccus (spherical), bacillus (rod-shaped) and spirillum (spiral). They may live singly or associate as chains or clusters of cells. Bacteria can be grouped as gram- negative or gram-positive based on their cell wall characteristics. Peptidoglycan is a distinctive structural component found only in bacterial cell walls. * peptidoglycan is a polymer made up of… The thickness of the peptidoglycan layer is thick in Gram-positive bacteria, and thin in Gram negative cells. Gram staining uses violet dye to stain cell walls, then alcohol as decolorizing agent, and then red dye that stain only decolorized cells. Gram-positive cells retain the violet stain due to their thick peptidoglycan layer, whereas Gram-negative cells, with a Antibiotics exploit differences between prokaryotes and eukaryotes Penicillin and ampicillin interfere with the formation of peptidoglycan cell walls, so they harm bacteria but not our cells. Other antibiotics interfere with the smaller, 70s bacterial ribosome, but do not affect the larger 80s eukaryotic ribosome. Most bacteria are harmless to humans and other animals, and some are very useful to us, but certain bacteria cause some of the most feared diseases. Groups of bacteria, with examples: Spirochetes Cell body is like a helix. Can live in humans as parasites. A few are pathogens (e.g. syphilis, Lyme disease). Syphilis: A sexually transmitted disease. Caused by the spirochete Treponema pallidum. Can cause paralysis, blindness, dementia and death. Only leaves in human cells. Chlamydias Very small parasites. Can take up ATP from host cell. Can cause sexually transmitted diseases, among others. High GC Gram-Positives High ratio of guanine and cytosine to A-T nucleotide pairs. They develop a branched system of filaments to access nutrients and water and increase their surface-area. Actinobacteria (summary video). Low GC Gram-Positives Low ratio of G+C to A+T nucleotide pairs. Some produce endospores: heat resistant resting structures that survive harsh conditions and become active and divide when conditions improve. Clostridium tetani Proteobacteria- Purple bacteria Huge group. Includes pathogenic bacteria like: E.coli and Vibrio cholerae (gastrointestinal disease). Also includes nitrogen-fixing bacteria. Cholera Caused by Vibrio cholera Kills more than 150,000 people every year. The bacteria releases a toxin that causes severe diarrhea, and people die of dehydration and loss of critical body salts. Most people get it through contaminated water. https://www.youtube.com/watch?v=Ji3WiF 6tldw “The black death”; bubonic plague Caused by the bacteria Yersinia pestis. Killed 25-45% of the population of Europe in the 14th century. It was transmitted by fleabite, often of fleas associated with rats. Cyanobacteria Also called blue-green bacteria Are phototrophs that use chlorophyll a for photosynthesis and release oxygen gas; many species fix nitrogen. Form filamentous colonies with 3 cell types: 1. vegetative cells- photosynthesize 2. spores- resting stages 3. heterocysts-for nitrogen fixation.  The nitrogen cycle Bacteria play a key role in the cycling of nutrients through the environment. * As an example, in the cycling of nitrogen. Nitrogen is essential for life as it is part of proteins, nucleic acids, and ATP. Nitrogen is abundant in the atmosphere (78%), but plants and animals cannot use atmospheric N2, but other forms. The nitrogen cycle There are five major steps in the nitrogen cycle: 1. Fixation- Fixing bacteria and some leguminous take molecular N2 and turn it into ammonia (NH3). 2. Assimilation- NH3 and nitrates (NO3) are absorbed by plants. By eating the plants, animals obtain N into their systems. 3. Ammonification- organic N2 from death tissues pass to NH3 by bacteria and fungi. 4. Nitrification- NH3 is then transformed by bacteria into nitrites (NO2) and to nitrates (NO3). 5. Denitrification- And then denitrifying bacteria  Bacteria good for our health Many bacteria are very important for humans. Bacteria in our large intestine produce vitamin K (help blood clotting) and vitamin Biotin (help cell growth, metabolism of fats and amino acids). Vaginally born babies are exposed to the protective film of microbes that builds their initial immune system as they exit the mother's vaginal canal. * Bacterial baptism Bacteria living on our skin may outcompete harmful bacteria and help prevent infection. Bacteria can be used to create different foods. Bacteria are used in sewage waste treatment: * the soluble organic matter is digested by aerobic bacteria. Some bacteria can naturally consume the hydrocarbons in oil spills and convert it to carbon dioxide. * bioremediation Prokaryotes include two domains  Domain Archaea Archeobacteria, or archaeans, live in extreme environments, e.g. high salinity, low oxygen, high temperatures, high or low pH, but also in habitats that are not extreme. They live for example in hot springs, salt lakes, swamps, ocean.  Archaea Archaeans do not have peptidoglycan in their cell walls. Their cell membranes are distinctive: The fatty-acids are branched chains Membranes can be more rigid and resistant to harsh conditions because can form monolayers (instead of bilayers). The tails fuse.  Archaea Two main groups: 1. Euryarchaeota- Includes some extreme halophiles (salt lovers). 2. Crenarchaeota- Includes thermophiles and acidophiles (acid-loving). * Sulfolobus lives in hot sulfur springs (70–75°C, pH 2 to 3).