1. Discuss and decide upon characteristics that define each of the following bro
ID: 253964 • Letter: 1
Question
1. Discuss and decide upon characteristics that define each of the following broad groups
(domains, kingdoms) of organisms in order to attempt to define these major groups of life
on the planet. Although many characteristics may overlap from one group to the next,
attempt to define some traits that could be used to definitively (exclusively) place an
organism into a specific group. Finally, for each, what would the small subunit ribosomal
rRNA gene sequence tell us?
Viruses
Bacteria
Archaea
Protists (algae, protozoa)
Fungi
Animals
Plants
2. For the previous groups, which include representatives of ones that live as part of the
“human ecosystem”? Provide some examples of each and where they can be found,
including both those that are part of our normal microbiota (i.e., not pathogens) and some
that are.
3. Considering the above and what we’ve covered about these groups of organisms,
identify some structures/processes that hypothetically could be used to inhibit or kill
different types of pathogens without (hypothetically, at least) harming the human host.
4. Consider the microbial world. Which has a greater impact or importance – pathogens,
or benign microbes? Explain, giving examples.
5. A number of antibiotics target the bacterial 70S ribosome, exploiting structural
differences from the 80S ribosome found in humans and other eukaryotes. Although
effective at killing bacteria, these drugs can still have some toxicity to humans. In the
context of the endosymbiotic theory of evolution, provide a hypothesis as to why this
might be.
Explanation / Answer
The life on earth is vast and diverse. We have classified the organisms based on different traits for the ease of study. There are several major groups of organisms as details below:
1. Viruses: They are like boundary between living and non living entities. They have their genetic material surrounded by protein coat. They use host system to replicate and express their proteins. They lie lifeless when outside the host. Thus show exclusive reliance on host. 16s rRNA gene sequence of viruses is not possible, since it has no ribosomes.
2. Bacteria: The bacteria are ubiquitous oranisms on earth. They are microscopic and unicelllular in nature. They have a cell wall which surrounds cell membrane. They do not have true nucleus and have no major organelles in the cytoplasm. They divide or replicate by fission process.
3. Archea: They resemble bacteria in many cases but have distinct features. They are extreme stress tolerant organsims. They have different cell wall and cell membrane structure compared to bacteria. They also divide by fission.
4.Protists: They comprise of both multicellular abnd unicellular organisms. They can be photosynthetic or chemosynthetic. They can be autotrophic or heterotrophic. They are eukaryotes, meaning have true nucleus which habours the genetic material. They possess all major cellular organelles. They can divide by fission or vegetative propagation.
5. Fungi: They are also eukaryotes and unicellular. They can reproduce by budding or by mitosis. They have thick cell wall and produce reproductive spores. Spores germinate to give rise to new hyphae.
6. Animals: They are multicellular larger organisms. They are eukaryotes with all cellular organelles and do not have cell wall. They have distinct male and female bodies which will reproduce sexually. They have locomotary organs and are highly adpated to the habitat. They are heterotrophic and aerobic in nature.
7. Plants: Plants are also eukaryotes and multicellular in nature. They are autotrophic and can photosynthesize in the presence of sunlight. They do not move as animals, but respond to all the environmental changes. They have thick cell wall made up of cellulose, lignin and pectin.
2. Out of the above groups, the bacteria live as a part of human ecosystem. They are found on our skin and in intestine. Human hut habours diverse groups of bacteria which aid in digestion. One group of such benificial bacteria are lactobacilli and byphedobacteria. This is present in diatery products and help in digestion. Some bacteria can cause diseases and we call them as pathogens. Most common human pathogens are Salmonella, e.coli, V. cholerae...etc.
3. Inhibitory compounds are used to kill the target organisms without affecting the human.
Viruses can be targeted and only be killed by drugs that target the viral surface proteins.
Bacteria can be target using antibiotics which target only the bacterial ribosomes or cell wall.
Archea can be targeted using the altered cell membrane lipid compounds present on the archea.
Protists can be targeted to their cell wall and selectively inhibit the DNA replication.
Fungi. Fungi can be blocekd by targeting their cell wall. This will inhibit the cell division process.
Animals. This is very difficult to treat as animals share maximum similarity with humans. We can use certain medicines to block the anerobic respiration of worms inside the human body.
Plants. Plant pollen can enter human lungs and cause hypersensitive reactions. The drugs can be designed to target pollen cell walls and target them to immune clearance.
5. Endosymbiotic hypothesis states that in the course of evolution, human cells have aquired certain bacterial cells and have retained them inside. These internalised bacterial cells are faithfully dividing along with the host and in the long run of evolution, lost their ability to infect and escape. One of the common example is mitochondria. This has structues similar to bacteria and has its own genetic material. The drugs which target the bacteria can affect the mitochondrial function. This can cause unwanted side effects and in some cases serious health issues.
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