Chapter 13 Early Life Forms and the Viruses - Life originated on earth more than 3.8 billion years ago - Its origin and subsequent evolution have been linked to the physical and chemical evolution of the universe, the stars and our solar system - In the past century, many studies and experiments have provided indirect evidence that life originated under conditions that presumable existed on the early Earth - In comparison to the age of the Earth, humans (Homo Sapiens) have been around for only a very short period of time - Humans are a recent offshoot of the primate group - Human evolution has been marked by trends that involved changes in our bones, muscles, teeth, sensory systems and the brain Taxonomy the science of the naming and categorization of organisms according to their evolutionary similarities - Naturalists and biologists have documented more than 1.4 million species that exist on the Earth today, and perhaps millions more wait to be discovered and classifies. - Classification systems are used to organize species into categories based on the evolutionary relatedness. ***We do not need to memorize dates for major events in the history of life. - be sure to know what conditions were like on the early, primitive Earth and how those conditions (such as the development of the gases in the atmosphere) contributed to the appearance of life. - the evidence is that the first cells to evolve were bacteria that only undertook anaerobic metabolism since there was no free atmospheric oxygen at that time to allow aerobic metabolism. 1
13.2 Before There were cells page 237 hydrothermal vent underwater opening from which mineral rich water heated by geothermal energy streams out iron-sulfur world hypothesis hypothesis that life began in rocks rich in iron sulphide near deep sea hydrothermal vents protocells membranous sac that contains interacting organic molecules; hypothesized to have formed prior to the earliest life forms RNA world hypothesis hypothesis that RNA served as the first material of inheritance 1. Laboratory simulations provide indirect evidence that organic subunits can self-assemble under certain condition. 2. They also show how complex organic compounds and protocells may have formed on the early earth 3. The iron-sulfur world hypothesis holds that these events took place near hydrothermal vents 4. The RNA world hypothesis holds that the first genome was RNA based. Take Home Message What do scientific studies reveal about the origin of life? 1. Small organic subunits could have formed on the early earth, or formed in space and fallen to earth on meteorites 2. Complex organic molecules could have self-assembled from simpler ones. 3. The first genetic material may have been RNA instead of DNA 4. Protocells chemical filled membranous sacs that grow and divide may have been the ancestors of the first cells 2
13.3 Origin of the Three domains page 240 ***know all about endosymbiosis for exam*** endosymbiosis one species lives inside another - Some eukaryotic organelles are though to be descended from bacteria - Mitochondria and chloroplasts resemble bacteria in their structure and genome, so these organelles probably evolved through endosymbiosis. - By this process, one species enters another, then lives and replicates inside it (Endo means within; symbiosis means living together) - Endosymbionts inside a cell can be passed along to the cell s descendants when the cell divides. Ozone layer atmospheric layer with a high concentration of ozone that prevents much UV radiation from reaching Earth s surface Stromatolites Dome-shaped structures composed of layers of prokaryotic cells and sediments; form in shallow seas 1. Fossil stromatolites are evidence of early bacterial life. 2. An early branching separated the bacteria from the archaea. 3. Production of oxygen by some photosynthetic bacteria altered Earth s atmosphere and allowed formation of a protective ozone layer 4. Eukaryotes have a composite ancestry with both bacterial and archaeal genes. 5. ***Know for exam*** Mitochondria and chloroplasts are thought to have evolved from bacteria by endosymbiosis. 3
Take Home Message What was early life like and how did it change Earth? 1. Life arose by 3-4 billion years ago; it was initially anaerobic and prokaryotic 2. An early divergence separated ancestors of modern bacteria from the lineage that would lead to archea and eukaryotic cells 3. Evolution of oxygen producing photosynthesis in bacteria led to formation of the ozone layer, and favoured organisms that carried out aerobic respiration 4
13.4 The Viruses page 244 bacteriophage virus that infects bacteria disease vector organism that carries a pathogen from one host to the next viral envelope a layer of cell membrane derived from the host cell in which an enveloped virus was produced virus a noncellular infectious particle with a protein coat and a genome of RNA or DNA; replicates only in living cells *** Concentrate on being able to identify the general structural features of all viruses at a minimum know: - a virus consists of nucleic acid (either RNA or DNA but never both) held inside a protein based shell called a protein coat (Capsid) - The viral coat consists of many protein subunits that bond together in a repeating pattern, producing a helical rod or polyhedral shape. - In many viruses that infect animals the protein coat is enclosed within a viral envelope - Viruses do not have cytoplasm, at most will contain only one or two enzymes that have a specialized purpose in their infection process and are absolute obligate parasites of cells. - 1. Viruses consist of RNA or DNA inside a protein coat (capsid) 2. Some also have a viral envelope 3. Viruses replicate only in living cells, as when bacteriophages multiply in bacteria 4. Mutation and viral reassortment produce new types of viruses 5. Insects serve as disease vectors that spread some viral diseases of plants. 6. HIV infects human cells. It began as an epidemic and now is a pandemic. HIV is an enveloped RNA virus. Pg. 246 animated 5
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Take Home Message What are viruses and how do they affect us? 1. Viruses are noncellular particles that consist of genetic material wrapped in a protein coat (capsid). They replicate only within living cells. 2. Viral structure varies. Each type of virus infects and replicates inside a specific type of host 3. A virus harms and eventually kills a host cell. Viral genes direct the host cell s metabolic machinery to produce new viral particles 4. Viral genomes can be altered by mutation. Viruses with new combinations of genes also arise as a result of viral reassortment. 7
13.5 Bacteria and Archaea page 248 archaea prokaryotes most closely related to eukaryotes; many live in extreme environments autotroph organism that uses carbon dioxide as its carbon source; obtains energy from light or breakdown of minerals heterotroph organism that obtains both carbon and energy by breaking down organic compounds. bacteria most diverse and well known lineage of single elled organisms that lack a nucleus (prokaryote) binary fission method of asexual reproduction in which a prokaryote divides into two identical descendant cells conjugation one bacterium transfers a plasmid to another decomposer organism that breaks down organic material into its inorganic subunits plasmid of many prokaryotes, a small ring of non chromosomal DNA replicated independently of the chromosome extreme halophile organism that lives where the salt concentration is high extreme thermophile organism that lives where the temperature is very high methanogen organism that produces methane gas as a metabolic by-product nitrogen fixation process of combining nitrogen gas with hydrogen to form ammonia normal flora collection of microorganisms that normally live in or on a health animal or person 8
1. Archaea and bacteria were historically lumped together as prokaryotes They lack a nucleus, reproduce asexually by binary fission, and swap plasmids by conjugation 2. Bacteria and archaea may be aerobic or anaerobic and they show great metabolic diversity. 3. Autotrophs use carbon dioxide as their carbon source. They include photoautotrophs such as cyanobacteria and chemoautotrophs such as the archaea that are methanogens. 4. By contrast heterotrophs obtain carbon from organic compounds. Chemoheterotrophs that serve decomposers and pathogens obtain energy by breaking down organic compounds. 5. Bacteria serve as decomposers, release oxygen into the air and carry out nitrogen fixation. Many are part of our normal flora, but others are human pathogens. 6. Archaea include heat-loving extreme thermophiles or saltloving extreme halophiles. 7. Others live in less extreme environments Take Home Message What are prokaryotes? 1. prokaryotes are cells that do not have a nucleus. They reproduce mainly by binary fission and they swap genes by conjugation and other processes. Pg. 248 2. Collectively prokaryotes are the most metabolically diverse organisms. They live almost anywhere there is carbon and energy 3. Archaea are the most recently discovered domain of life. Many archaea live in extremely hot or salty habitats. 4. Bacteria include species that play important roles in nutrient cycles. Some live in or on the human body, either as normal flora or as pathogens. 9
3.6 The Protists page 252 Contractile vacuole in freshwater protists, an organelle that collects and expels excess water Flagellated protozoan member of a heterotrophic lineage of protists that have one or more flagella Foraminiferan heterotrophic protest that secretes a calcium carbonate shell Pellicle layer of proteins that gives shape to many nwalled single celled protists Plankton community of mostly microscopic drifting or swimming organisms Algal bloom population explosion of single celled aquatic organisms such as dinoflagellates Apicomplexan parasitic protest that enters and lives inside the cells of its host Bioluminescent able to use ATP to produce light Ciliate single celled, heterotrophic protest with many cilia Dinoflagellates single-celled aquatic protest typically with cellulose plates and two flagella; may be heterotrophic or photosynthetic Amoeba solitary heterotrophic protis that feeds and moves by extending pseudopods Cellular slime mold heterotrophic protest that usually lives as a single celled, amoeba like predator. When conditions are unfavourable, cells aggregate into a cohesive group that can form a fruiting body Choanoflagellates heterotrophic protists with a collared flagellum; protest group most closely related to animals 10
Plasmodial slime mold heterotrophic protest that moves and feeds as a multinucleated mass; forms a fruiting body when conditions are unfavourable. 11
Take Home message? What are the protists? 1. The protists are a diverse collection of eukaryotic lineages, some of which are only distantly related to one another 2. Most protists live as single cells, but there are colonial and multicelled species 3. We find protists that are photosynthesizers, predators and decomposers in lakes, seas and damp places on land. Protists also live inside the bodies of other eukaryotes, including humans. Some of these protists are helpful, but others are parasites and pathogens 4. Green algae are the closes protest relatives of land plants and choanoflagellates are the closest protest relatives to animals *** Know for exam Define Protist: a eukaryote whose cells have a nucleus that is not a fungus, plant or animal: - Protists are the most like the first eukaryotic cells - Unlike prokaryotes, protist cells have a nucleus and cytoskeleton that includes microtubules - Most protists also have mitochondria, endoplasmic reticulum and golgi bodies. - All protists have multiple chromosomes, each consisting of DNA with proteins attached. - Most protists live in water or moist habitats including host tissues - Protists reproduce asexually by mitosis, sexually by meiosis or both - Most protists are single celled species, but there are also colonial forms and multi celled species. - Many protists are photoautotrophs that have chloroplasts. - Others are predators, parasites or decomposers 12
Types of Protists 1. protozoans (Protazoa) member of a heterotrophic lineage of protists that have one or more flagella protozoa grouped together because of their animal like behaviour (of course they are not animals because they consist only of one cell) 2. Foraminifera - single celled animal like protists who build pretty shells out of calcium carbonate - they have pseudopods like an amoeba which they use to move anchor themselves and capture their food - most of them live in the sea, but a few species inhabit freshwater and damp rainforest soil 3. Ciliates - single celled animal like protists that move using cilia, special hair like structures n the outside of their bodies - they live in fresh and salt water, as well as in the soil example paramecium 4. Dinoflagellates (whirling flagellate) - single celled protists that live in water, mostly in the sea - Some prey on bacteria, some are parasites and, - Some of them are photosynthetic they can make their own food from sunlight and they are an important part of the mix of creatures which make up plankton. - They move around using flagella. - When certain types of dinoflagellates populations get out of control they can cause red tides which turn the sea red and make most shellfish poisonous to humans 13
5. Apicomplexans - parasitic protists that spend part of their life inside cells of their hosts. - Such as the species that cause malaria, are parasites that spend part of their life in cells of their host - Single celled and have no way of moving on their own 6. Water molds (plant destroyers) oomocytes - form a mesh of nutrient absorbing filaments - most help decompose organic debree and dead organisms in aquatic habitats - a few are parasites - some destroy crops and forests cause $5 billion in crop losses each year - closest relatives of water molds are two photosynthetic groups diatoms and brown alage 7. Algae, brown algae, Diatoms, Red algae, green algae - are photosynthesizing organisms that range in size from single cells to multicellular seaweed (red algae) - can be of various pigmentations - can live in fresh water or sea water 8. Amoebas and Slime Mold (amoebozoans) - most amoebas are predators in freshwater habitats - others live inside animals and some cause human disease - most are single celled and move using pseudopods, extensions which ooze out of their bodies - they use the pseudopods to hunt for food like bacteria and algae 9.Choanoflagellates - these are the protest group with genes most similar to those of animals - look like feeding cells of sponges, which are among the simplest animals - not considered ancestors of animals, but a group that shared a common single-celled ancestor with animals 14
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