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.
Learn Protozoans and Algae - Easy Review
1. Which are the groups of living beings that form the protist kingdom?
The protist kingdom includes protozoans and algae. (Two groups of fungi with similar characteristics to protozoans, myxomycetes and oomycetes, have been classified as protists.)
Unicellular protozoans and algae are unicellular eukaryotes. The pluricellular algae are eukaryotes of simple structure too. It is believed thatprotists are phylogenetic ancestors of living beings of the other eukariotic kingdoms (fungi, animals and plants).
Protists Review - Image Diversity: protozoan algae
2. What is the fundamental difference between protozoans and algae?
The basic difference between protozoans and algae is the fact that protozoans are heterotrophs while algae are photosynthetic autotrophs.
3. What are the characteristics of protozoans that make them resemble animals?
Protozoans are unicellular beings with some similar characteristics to animal cells.
In comparison to pluricellular organisms protozoans are more proximal to the animal kingdom than to plants: they are heterotrophs, they have a rudimentary locomotion system (amoeboid movements, cilia, flagella), they do not have cell wall, some species present structures that resemble structures of a primitive digestive system, with cytostome (mouth) and cytopyge (anus), specialized in digestion and excretion.
The evolutionary hypothesis that animal cells have come from differentiation of protozoans is strong.
4. What is the basic morphology of a protozoan cell?
Protozoans are eukaryotic cells so they have organelles and structures common to this kind of cell: endoplasmic reticula, Golgi apparatus, digestive vesicles, ribosomes, mitochondria, nucleus with genetic material, karyotheca, etc. All these elements are found dispersed throughout the cytoplasm. Protozoans do not have cell walls.
Protozoans from the mastigophora group (like trichomonas) have flagella and others, others from the ciliated group (like paramecium) have cilia.
5. Do protozoans have a cellular nucleus?
All protozoans, as eukaryotes, have nucleus. Some species, like the paramecium, have two nuclei: the macronucleus and the micronucleus.
Protists Review - Image Diversity: paramecium
6. What are the respective functions of the macronucleus and of the micronucleus in the paramecium?
The macronucleus is properly the cell nucleus, it has DNA and RNA and acts as the center of the cellular control and regulation. The micronucleus has reproductive functions and it is related to the conjugation process (sexual reproduction).
7. What do protozoans “eat”? Do they move in search for food?
Protozoans are heterotroph beings, i.e., they do not make their own food and thus they need to search for it in the environment. Protozans have developed several locomotion mechanisms and they actively move towards food.
8. How do amoebae, paramecia and trichomonas respectively move?
Amoebae move by amoeboid movements, small projections and invaginations of their plasma membrane (pseudopods) that alter the external morphology of the cell making it move on surfaces. Paramecia have the outer face of their plasma membrane covered by cilia that flap helping the cell to move.Trichomonas are flagellated protozoans, i.e., they have relatively long filaments outside the cell that beat and make possible active swimming in fluid environments.
Protists Review - Image Diversity: amoeboid movement
9. How is digestion performed in protozoans?
Digestion in protozoans is intracellular digestion: organic material is internalized and degraded inside the cell.
Protozoans get food by phagocytosis and then the food is digested when phagosomes fuse with lisosomes within the cell, forming digestive vacuoles. The digestive vacuoles give origin to residual bodies that are eliminated from the cell by exocytosis.
In the paramecium the entrance of food into the cell and the excretion of digestive residuals occur at specialized regions of the plasma membrane, the cytostom and the cytopyge, respectively.
10. Are protozoans presenting contractile, or pulsatile, vacuoles easily found in fresh or in salt water?
Fresh water is the less concentrated of solutes than sea water and it (fresh water) tends to be less concentrated than the intracellular environment making cells to swell. Sea water, on the other hand, since it is very concentrated tends to dehydrate the cell.
The vacuoles of protozoans are internal structures specialized in water storage that when necessary liberate water to the cytoplasm. Vacuoles thus can dilute the cytoplasm for it to enter into osmotic equilibrium with the environment. Protozoans of fresh water then need vacuoles more since their intracellular is hypertonic in relation to the exterior. Without the dilution mechanism provided by the vacuoles, protozoans of fresh water would absorb too much water and would die.
11. Do protozoans have sexual or asexual reproduction?
In protozoans reproduction is sexual or asexual. The most frequent form of sexual reproduction is binary division, or scissiparity, in which the cell divides itself by mitosis originating two daughter cells. Some species, like the plasmodium, agent of malaria, reproduce asexually by schizogony (multiple fission); in this form of reproduction the cell becomes multinucleated, generally inside a host cell, and each nucleus is expelled out together with cytoplasm portions giving rise to new protozoans.
The sexual reproduction in protozoans can happen by conjugation, with incorporation of genetic material from one cell into another, or by gametes that fecundate others and form zygotes. In the plasmodium sexual reproduction happens in the mosquito, the definitive host, and the zygote undergoes mitosis (sporogony) creating many sporozoites.
12. Which is the form of protozoan reproduction that generates more variability?
Sexual reproduction always generates more genetic variability than asexual reproduction. That is because in sexual reproduction the fusion ofgenetic material from different individuals occurs and so the offspring is not genetically identical to the parent cell.
If the hypothesis that protozoans originated multicellular animals is strong, other hypotheses may be even stronger: that these protozoans were able to reproduce sexually, since only genetic variation can produce biological differentiation to the point of creating new types of living beings.
13. What are the four groups of protozoans?
The four main groups of protozoans are the sarcodines (that form pseudopods, like amoebae), the mastigophores (flagellated, like the trypanosome that causes Chagas’ disease), the ciliated (like paramecia) and the sporozoans (spore-forming, like plasmodia).
Protists Review - Image Diversity: sarcodines mastigophores ciliated protozoans sporozoans
14. Why are euglenas involved in polemics related to their taxonomic classification?
Euglenas are involved in taxonomic polemics because they tend to be classified sometimes as protozoans and sometimes as algae. Although they have chloroplasts and they are photosynthetic autotrophic beings, euglenas do not have a cell wall and they can survive by “eating” substances from the environment when light is not available for photosynthesis. Curiously euglenas also have a photosensitive structure called stigma that orients the movement of the cell towards light. Nowadays euglenas are classified as algae, but it is suspected that they are common ancestors of algae and protozoans.
Protists Review - Image Diversity: euglena
15. Do algae reproduce sexually or asexually?
There are algae that reproduce sexually and there are algae that reproduce asexually.
In unicellular algae reproduction is generally asexual by binary division.
In pluricellular algae asexual reproduction can occur by fragmentation or by sporulation.
In sexual reproduction of algae, uni or pluricellular, there is fusion of gametes (syngamy). There are algae in which all cells can become gametes and there are algae in which only some cells can play that role. Some species may present alternation of generations, forming gametophytes and sporophytes with different ploidies.
16. What is the commercial importance of algae?
Many algae have high nutritional value and are commercialized and consumed as human food, they are very popular food in the oriental world. Jelly compounds are extracted from some algae, like glues and pastes for industrial and commercial use.
The agar-agar, used as a medium for biological culture in laboratories and in medicines, and the substance known as carrageenin, a component of tooth pastes, cosmetics, paint and hygienic products, are extracted from rhodophyte algae. Diatom algae deposited on the bottom of the sea form diatomites, used in the production of filters, refractories, thermal isolation and cement. Some algae are used as agricultural fertilizers.
17. What is the phenomenon known as “red tide”? Which ambiental harms can it cause?
Red tide is a phenomenon that occurs when dinoflagellates (algae from the pyrrophyte group) proliferate excessively in the ocean. These algae liberate toxins that affect the nervous system and can cause death when ingested by marine animals and by humans that eat contaminated animals.
Protists Review - Image Diversity: red tide
Learn the Facts About the Fungi Kingdom
1. What are the main cellular features of fungi?
There are unicellular and pluricellular fungi. All fungi are eukaryotes and heterotrophs.
Fungi have cells with cell wall made of chitin, the same substance that constitutes the exoskeleton of arthropods. Fungi, likewise animals, characterize for storing glucose in the form of its polymer glycogen.
Fungi Kingdom Review - Image Diversity: fungi
2. Are there photosynthetic fungi? How do fungi nourish themselves?
All fungi are heterotrophs (so, they do not perform photosynthesis). Fungi are typical decomposers, they eat and degrade organic material.
3. Fungi are classified in their own kingdom. Into which phyla is the fungi kingdom divided? Into which of those phyla are mushrooms classified?
The kingdom fungi is divided into four phyla: ascomycetes, basidiomycetes, zygomycetes and deuteromycetes.
Mushrooms are basidiomycetes.
Fungi Kingdom Review - Image Diversity: ascomycetes basidiomycetes zygomycetes deuteromycetes
4. What are the hyphae and the mycelium of pluricellular fungi?
The main structures of pluricellular fungi are the hyphae (threadlike filaments made of contiguous uni or multinucleated cells) and the mycelium (a set of hyphae).
Fungi Kingdom Review - Image Diversity: hyphae mycellium
5. What are the types of reproduction that occur in fungi?
In fungi there are asexual and sexual reproduction. Fungi reproduce asexually by fragmentation, gemmation and sporulation. Some species can reproduce sexually by fusion of hyphae from different individuals, even with metagenesis (alternation of generations).
6. What are the fruiting bodies present in some fungi?
Fruiting bodies are structures made of hyphae that project radially from the superior portion of the peduncle of some fungi. These structures contain the reproductive cells of the individual. They form the umbrella-like cap in mushrooms (basidiocarp) or the ascocarp in ascomycetes.
Fungi Kingdom Review - Image Diversity: basidiocarp
7. What is the ecological importance of fungi?
Fungi are heterotrophs and decomposers (they break down dead beings) and they actively participate in the recycling of organic material in ecosystems. Somefungi keep mutualist ecological interaction with algae or cyanobacteria, forming lichen, and with plant roots, forming mycorrhizas.
8. What is the utility of fungi for some industries?
Fungi are industrially used in the production of fermented beverage, bread, cheese, etc. Some fungi are very important for the production of medical drugs. There are fungi processed to serve as food for humans, like eatable mushrooms.
9. What are lichens? How do fungi participate in this ecological interaction?
Lichens are formed by mutualist ecological interaction between fungi and algae or between fungi and cyanobacteria. In this ecological interaction, the fungi absorb water that is then used by algae (or cyanobacteria), and algae (or cyanobacteria), as autotrophs, produce organic material in excess to serve as food for thefungi.
Fungi Kingdom Review - Image Diversity: lichens
10. What are mycorrhizas? How does each participant benefit in this ecological interaction?
Mycorrhizas are mutualist ecological interactions between fungi and some plants roots. Fungi provide to the plant more water and mineral salts and obtain organic material from the vegetable.
11. What are the main human diseases caused by fungi?
The main human diseases caused by fungi are coccidioidomycosis, histoplasmosis, blastomycosis, paracoccidioidomycosis, or South American blastomycosis, sporotrichosis, aspergillosis and systemic candidiasis.
Fungi are also responsible for many dermatologic diseases (dermatomycosis) that affect the skin, the nails, the scalp, etc.
On the other hand, many fungi are able to produce antibacterial substances that combat diseases. In the second world war, in German jails, Russian prisoners that accepted to eat moldy bread had less skin infection than those that refused the food. In China, moldy soy sauce has millennial past use against infections. Penicillin, a potent antibiotic, was discovered in 1928 by Alexander Fleming when he observed the antibacterial activity offungi from the genus Penicillium.
12. What is cyclosporin? How are fungi related to this substance?
Cyclosporin is a drug discovered in the 1970’s that revolutionized organ transplantation in Medicine. It is a powerful immunosuppressor and so it lessens the immune activity of the receptor and reduces the risk of rejection of the transplanted organ.
Cyclosporin is a protein produced by the fungus Tolypocladyum inflatum.
Easily Understand Viral Microbiology
1. Are viruses cellular beings?
Viruses are considered living beings but they do not have cellular structure.
There is some controversy regarding their classification as living beings. Their characteristics of self-reproduction and of having genetic material however reinforce that classification.
2. What is the basic structure of a virus?
Viruses are constituted of genetic material (DNA or RNA) covered by a protein capsule also known as a capsid. Some viruses, like HIV, have in addition an external envelope derived from the plasma membrane of the host cell from which it came.
Virus Review - Image Diversity: virus structure
3. Are there non-parasitic viruses?
All viruses are obligate intracellular parasites, i.e., they depend on the host cell to complete their life cycle. A virus does not have its own metabolism.
4. Why is it a strong evolutionary hypothesis that although viruses are the structurally simplest beings they were not the first living beings?
The fact that viruses are obligate intracellular parasites makes very weak the hypothesis that virus appeared before cellular beings in the evolution of life.
5. What is the genetic material of a virus? How does that material act in viral reproduction?
There are DNA viruses (double strand or single strand DNA) and RNA viruses (double strand or single strand RNA too). Viruses inoculate their DNA or RNA molecules into cells and these cells (by means of transcription or reverse transcription and translation) synthesize proteins for the assembling of a new virus. This synthesis is commanded by the viral DNA or RNA molecules.
6. What is the typical reproduction cycle of a DNA virus?
A typical virus has proteins on its capsid that bind to the outer membrane of the host cell. In the place where the virus adhered viral proteins act to break the cell membrane and then the virus injects its DNA molecules into the host cell.
Within the host cell the viral DNA is transcripted and thus messenger RNA is produced. Viral mRNA then is translated and viral proteins are made.
Viral polypeptides made within the host cell are cut by enzymes called proteases and then copies of the virus are assembled with the newly formed proteins. When the assemblage of new viruses is completed the cell membrane breaks and the viruses are released to the outside. One sole infected cell can produce hundreds of viruses.
Virus Review - Image Diversity: viral life cycle
7. What are retroviruses? How do they reproduce and what is the role of the enzyme reverse transcriptase?
Retroviruses are viruses whose genetic material is RNA. HIV and the virus of SARS (severe acute respiratory syndrome) are examples of retrovirus.
These viruses inoculate their RNA into the host cell and within the cell the viral RNA is reversely transcripted into DNA. DNA made from the viral RNA then commands the synthesis of viral proteins for the assemblage of new viruses and the breaking of the host cell to liberate them outside.
The enzyme reverse transcriptase is the catalyst of the reverse transcription of RNA into DNA. The enzyme is part of the virus and it is also inoculated into the host cell.
Virus Review - Image Diversity: retrovirus
8. What is the basic structure of the HIV virus? What is the function of the glycoproteins of its envelope?
HIV is an RNA virus. In its core there are two strands of RNA and reverse transcriptase molecules. The core is covered by a capsid, a layer of proteins. The capsid then is covered by an envelope having glycoproteins and lipids.
The glycoproteins of the HIV envelope are located on the outer surface of the virus and they are responsible for the recognition of the cells to be infected (the HIV host cell is the CD4 lymphocyte) and for the adhesion ofthe virus to the cell membrane. (CD4 is a receptor glycoprotein of the outer membrane of some lymphocytes).
Virus Review - Image Diversity: viral envelope
9. What are bacteriophages?
Bacteriophages are viruses specialized in parasitism of bacteria. They are used in genetic engineering as molecular cloning vehicles to insert recombinant DNA into bacteria. They were also used in the former Soviet Union to treat bacterial infections.
Bacteriophages have a polyhedron-like capsid and DNA as genetic material. The “head” of the virus is connected to a tail that ends in small fibers that help the virus to attach to the bacterial cell wall and to inject its genetic material into the host.
Virus Review - Image Diversity: bacteriophage
10. What is meant when it is said that a virus is in an inactive state?
Viruses considered in inactive state are those whose genetic material is within host cells without synthesis of viral proteins and assemblage of new virus. The life cycle of these viruses can be activated under certain conditions and then synthesis of viral proteins begins and new copies are made.
The virus that causes herpes (herpes virus) is an example of a virus that stays in an inactive state and is sometimes activated.
11. What are the main human diseases caused by virus?
Among diseases caused by virus are common cold, flu, mumps, variola (considered eradicated nowadays), rubella, measles, AIDS, the viral hepatitis, human papillomatosis (HPV infection), rabies, dengue fever, yellow fever, poliomyelitis (an almost eradicated disease in developed countries), hemorrhagic fever from Ebola virus, SARS (severe acute respiratory syndrome).
Viruses also cause many other diseases in animals and plants.
12. SARS is a disease that appeared in 2003 with epidemic features in the province of Guangdong, in east China. What type of agent causes SARS?
SARS is caused by a virus from the coronavirus group, a RNA virus (retrovirus). SARS can be fatal.
13. What is crystallization of a virus? What is the importance of this process?
Crystallization is the process of transformation of viral components into organized solid particles.
Crystallization of biological macromolecules, including viral components, is used to study structural characteristics, for example, through X-rays, laser beams, etc.
Virus Review - Image Diversity: viral crystallization
ليست هناك تعليقات:
إرسال تعليق