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Bacterial Cell Review from
Biology Questions and Answers
The Bacterial Cell - Questions and Answers
1. What are bacteria?
Bacteria are prokaryotic and unicellular beings. Bacteria have simple organization, they present an external cell wall, plasma membrane, circular DNA within the cytoplasm and ribosomes for protein synthesis. Some bacteria are encapsulated, i.e., they have a polysaccharide capsule outside the cell wall.
Bacterial Cell Review - Image Diversity: bacteria
2. Are bacteria the only prokaryotic beings?
Prokaryotic beings are classified into two big groups: archaebacteria and bacteria (this last also known as eubacteria).
Compared to bacteria, archaebacteria have basic differences, like the chemical compositions of their plasma membrane and cell wall and different enzymes related to DNA and RNA metabolism.
Bacterial Cell Review - Image Diversity: bacteria cell
3. What are halophile, thermoacidophile and methanogen archaebacteria?
There are three peculiar types of archaebacteria. The halophile archaebacteria only survive in salt-rich environments (even salinity of the sea is not enough for them). Thermoacidophile archaebacteria are characterized by living under high temperatures and low pH. The methanogen archaebacteria are those that liberate methane gas (CH4), they are found in swamps.
4. What are the main ecological roles of bacteria?
Bacteria are responsible for the decomposition process at the end of food chains and food webs; in this process, they also liberate utile gases and nutrients for other living beings. Bacteria that live within the digestive tube of ruminants and of some insects digest cellulose for these animals. Some bacteria also participate in the nitrogen cycle, making fixation of nitrogen, nitrification and denitrification, almost always in mutualist ecological interaction with plants. Bacteria present within living beings, for example, some that live inside the bowels, compete with other pathogenic bacteria so controlling the population of noxious agents. There are also bacteria that cause diseases and bacteria used in the production of medical drugs.
Excessive proliferation or mass destruction of bacteria can impact entire ecosystems. For example, when a river is polluted by organic material the population of aerobic bacteria increases since the organic material is food for them; the great number of bacteria then exhausts the oxygen dissolved in water and other aerobic beings (like fishes) undergo mass death.
5. What are examples of human diseases caused by bacteria?
Some human diseases caused by bacteria are tuberculosis, pertussis, diphtheria, bacterial meningitis, gonorrhea, syphilis, bubonic plague, leptospirosis, cholera, typhoid fever, Hansen’s disease, trachoma, tetanus, anthrax.
6. What are some industrial processes that use bacteria?
Bacteria are used by industry in various ways. There are vaccines made of attenuated pathogenic bacteria or of antigens present in bacteria. One of the most ancient uses of bacteria is the fermentation of milk to produce yogurt, cheese and curd (even before the knowledge of the existence of bacteria these microorganisms were already used in the making of those products). Some methods of antibiotic production involve bacteria. The recombinant DNA technology (genetic engineering) allows the industrial production and commercialization of human proteins, like insulin for diabetics, synthesized by mutant bacteria. Some bacteria can produce fuel, like methane gas.
7. What are some mechanisms by which pathogenic bacteria cause diseases? Why is this knowledge important?
Pathogenic bacteria have characteristics known as virulence factors that help them to parasite their host. Some bacteria have fimbriae, cilium-like structures that attach the bacterial cell to the host tissue. There are bacteria specialized in intracellular parasitism. Other bacteria secrete toxins, molecules that cause disease; in some cases, the bacterial population growth causes food contamination by toxins. Generally, bacterial disease is caused by bacterial population growth with invasion and destruction of tissues or by bacterial toxins that contaminate the organism.
Bacterial Cell Review - Image Diversity: bacterial virulence factors
8. In which environments do bacteria live?
Bacteria can be found in various environments throughout the planet. There are bacteria in the air, in fresh water, on the surface, in the intermediate depth and on the bottom of the sea, in soils, in our skin and practically in all terrestrial environments through which air circulates freely. Some bacteria can be found in volcanic craters under extremely high temperatures.
9. How are bacteria classified according to the production of organic material for the energetic metabolism?
Most bacteria are heterotroph, they do not produce their own food. There are also autotroph bacteria: chemosynthetic bacteria or photosynthetic bacteria.
Some photosynthetic bacteria, like cyanobacteria, make photosynthesis like plants do, using water. Others, the sulfur photosynthetic bacteria, use hydrogen sulfide (H2S) instead of water.
10. How are bacteria classified according to their need for oxygen?
According to their necessity of oxygen bacteria are classified into anaerobic (those that survive without oxygen) and aerobic (those that do not survive without oxygen).
11. What is meant when it is said that a bacteria is an obligate anaerobe?
Obligate anaerobes are those living beings that do not survive in the presence of oxygen. For example, the bacteria Clostridium tetani, agent of tetanus, is an obligate anaerobe.
In superficial wounds, it is commom to use hydrogen peroxide to expose anaerobic microorganisms to oxygen and kill them.
12. According to their morphology how are bacteria classified?
Bacteria present different morphological patterns. A bacterium can be classified into coccus, bacillus, vibrion or spirochete.
Bacterial Cell Review - Image Diversity: coccus bacillus vibrion spirochete
13. What is the main constituent of the cell wall of bacteria?
The bacterial cell wall is made of peptidoglycans.
Bacterial Cell Review - Image Diversity: bacterial cell wall
14. Which are the intracellular organelles present in bacteria?
Considering typical eukaryotic cell organelles, heterotrophic bacteria have ribosomes, essential for protein synthesis.
15. What are plasmids? What is the importance of plasmids for the recombinant DNA technology?
Plasmids are circular fragments of DNA that are accessories to the main bacterial DNA. Plasmids are important for genetic engineering because genes from other organisms are inserted into them to produce recombinant beings, for example, mutant bacteria. These bacteria are made, for example, to produce utile proteins for humans on an industrial scale.
Bacterial Cell Review - Image Diversity: plasmid
16. How do bacteria reproduce?
Bacteria reproduce by binary fission (scissiparity). Some bacteria however present a kind of sexual reproduction (transformation, transduction or conjugation) with a combination of genetic material from different individuals.
Bacterial Cell Review - Image Diversity: binary fission bacterial cell reproduction
17. How does sexual reproduction occur in bacteria? How different are the modalities of bacterial sexual reproduction?
Sexual reproduction occurs when bacteria incorporate genetic material into other bacteria of the same species; the inserted genetic fragment then becomes part of the genetic material of the second bacteria. This kind of reproduction can happen by means of transformation, transduction or conjugation.
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