The Prokaryotic-and-Eukaryotic-Cells.pptx

Prokaryotic and Eukaryotic Cells: A Comprehensive Description
Cells are the basic structural and functional units of life. Every living organism, from microscopic bacteria to complex human beings, is made up of cells. The study of cells provides insight into the fundamental processes of life, helping scientists understand how organisms grow, reproduce, and interact with their environment. Cells can be broadly classified into two main types: prokaryotic cells and eukaryotic cells. These two cell types differ in their complexity, structure, and function, yet they share some fundamental similarities that underscore the unity of life. This detailed description explores the characteristics, differences, and significance of prokaryotic and eukaryotic cells, offering an in-depth understanding of these essential biological entities.

The history of cell discovery dates back to the 17th century when Robert Hooke first observed the microscopic structure of cork using an early compound microscope. He coined the term "cell" to describe the tiny, box-like compartments he saw. Around the same time, Anton van Leeuwenhoek made further advancements in microscopy, leading to the discovery of microscopic organisms, including bacteria and protozoa. These early discoveries laid the foundation for modern cell biology and the classification of cells into prokaryotic and eukaryotic categories. Over time, with the development of more sophisticated microscopes, scientists were able to study cells in greater detail, leading to the formulation of the Cell Theory by Schleiden, Schwann, and Virchow. This theory states that all living organisms are composed of one or more cells, that the cell is the fundamental unit of life, and that all cells arise from pre-existing cells.

Prokaryotic cells are the simplest and most ancient forms of life. These cells lack a true nucleus and membrane-bound organelles, making them structurally less complex than eukaryotic cells. Prokaryotes belong to two distinct domains of life: Bacteria and Archaea. While bacteria are found in nearly every environment on Earth, archaea are often found in extreme conditions, such as hot springs, salt lakes, and deep-sea hydrothermal vents. Despite their simplicity, prokaryotic cells have evolved remarkable adaptations that enable them to survive in diverse and sometimes hostile environments.

The structure of prokaryotic cells is relatively simple but highly efficient. The cell membrane, composed of a phospholipid bilayer, regulates the movement of substances in and out of the cell. Surrounding the membrane is the cell wall, a rigid structure that provides protection and maintains the shape of the cell. In bacteria, the cell wall is composed of peptidoglycan, while archaea have cell walls made of different molecules that provide similar structural support. The cytoplasm of a prokaryotic cell contains essential molecules, enzymes, and ribosomes, which are responsible for protein synthesis.

1. Prokaryotic and Eukaryotic Cells

2. Living Cells Can be classified into two general categories – prokaryotes and eukaryotes. Prokaryotes are organisms that do not possess a true nucleus and membrane-bound organelles (e.g., bacteria). Eukaryotic organisms are those that possess a true nucleus and membrane-bound organelles. They are usually multicellular organisms and include plants, animals, fungi, parasites, and algae. Viruses are acellular organisms that possess only DNA or RNA. They are dependent on host cells for their replication and are considered as obligate intracellular parasites.

3. Comparison between Prokaryotes and Eukaryotes

4. Comparison between Prokaryotes and Eukaryotes

5. Comparison between Prokaryotes and Eukaryotes

6. Comparison between Prokaryotes and Eukaryotes

7. Medically Important Microorganisms Organisms that are considered medically important are those that have the potential or the ability to produce significant clinical disease in humans. They may be part of the normal flora of the body or are true pathogenic organisms. These may be categorized into bacteria, viruses, fungi, algae, and parasites (protozoa and helminths). Viruses are acellular organisms. Their outer surface is called capsid, which is composed of repeating sub-units called capsomeres. Viruses possess only a single nucleic acid, either DNA or RNA, but never both. In addition, viruses lack the necessary cellular parts that can allow them to replicate independent of the host cell. They also lack the genes and enzymes that are necessary for energy production. They rely on the cellular machinery of the host cell for protein and energy production. Hence, viruses are considered obligate intracellular parasites.

8. Viruses are classified based on the following: type of nucleic acid they possess; (2) shape of the capsid (icosahedral, helical, polyhedral, or complex); (3) number of capsomeres; (4) size of the capsid; (5) presence or absence of an envelope; (6) type of host they infect (humans, plants, or animals); (7) type of disease they produce; (8) target cell or tropism (e.g.., T helper cells for HIV); and (9) immunologic or antigenic properties.

9. Medically Important Microorganisms Bacteriophages are a special type of viruses that primarily infect bacteria. They are similar to other viruses in that: They are obligate intracellular parasites; They are similarly shaped like other viruses; and They may also be classified based on the type of nucleic acid they possess. They play a role in the acquisition of virulence factors of certain bacteria (e.g., diphtheria toxin of Corynebacterium diphtheriae), as well as in the transfer of genetic material from one bacterium to another (as in transduction)

10. Medically Important Microorganisms Bacteria are prokaryotic cells with majority having an outer covering called the cell wall that is composed mainly of peptidoglycan. Unlike viruses, they possess both DNA and RNA. Unlike eukaryotic organisms, bacteria possess a nucleoid instead of a true nucleus, smaller ribosomes, and lack mitochondria. Based on their physical characteristics, bacteria may be broadly categorized into: gram-negative bacteria with cell wall (e.g., Escherichia coli); gram-positive bacteria with cell wall (e.g., Staphylococcus aureus ); acid-fast bacteria with lipid-rich cell wall (e.g., Mycobacterium tuberculosis ); and, bacteria without cell wall (e.g., Mycoplasma )

11. Medically Important Microorganisms Fungi are eukaryotic cells with an outer surface composed mainly of chitin. Their cell membrane is made up mostly of ergosterol. Like bacteria, fungi possess both DNA and RNA. Unlike bacteria, they possess a true nucleus that is enclosed by a nuclear membrane and mitochondria that function for ATP production. Fungal ribosomes are also larger than bacterial ribosomes (80 Svedberg units).

12. Medically Important Microorganisms Protozoa are the representatives for parasites. Like bacteria and fungi, these are also eukaryotic cells that have an outer surface called a pellicle. These are unicellular organisms that usually divide through binary fission, similar to bacteria. Majority exist in two morphologic forms-cysts and trophozoites. The infective stage is the cyst while the pathogenic stage is the trophozoite. Protozoa possess both DNA and RNA as well as other cellular features seen in typical eukaryotic cells.

13. Medically Important Microorganisms Algae are eukaryotic organisms whose outer surface consists primarily of cellulose. They are described as plant-like organisms because most of them have chlorophyll and are thus capable of photosynthesis. Unlike plants, they do not possess true roots, stems, and leaves. Algae do not produce significant disease in humans. Most algae are beneficial in that they are important sources of food, iodine, and other minerals. They may also be used as fertilizers, emulsifies for puddings, and stabilizers for ice cream and salad dressings.

14. Medically Important Microorganisms Diatoms are unicellular algae that inhibit both fresh- and saltwater. Their cell wall contains silicone dioxide that may be utilized in filtration systems, insulations, and as abrasives. Dinoflagellates are also unicellular algae that are important members of the phytoplankton group. They contribute greatly to the oxygen in the atmosphere and serve as important links in the food chain. On the other hand, they are also responsible for what is known as “red tide.” These small organisms produce a powerful neurotoxin which, when ingested in significant amounts, is responsible for the potentially fatal disease called paralytic shellfish poisoning.

15. Cyanobacteria Diatom Dinoflagellate Green algae Coccolithophore Figure 2.3 Various structure of phytoplankton's that are usually found on water.

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