Literally meaning to possess a “true nucleus,” eukaryotes consist of animals and plants.
Clearly seen under a microscope, the enclosed nucleus separates these cells from prokaryotes; in addition, eukaryotic cells also contain organelles.
Whether prokaryotes, eukaryotes or protists, four points apply to all types of cells:
German scientists Matthias Schleiden and Theodor Schwann are accredited with the basics of cell theory, which was later expanded by Rudolf Virchow; many other scientists have offered contributions, refining cell theory as the instruments used to study cells advanced over the decades.
Prokaryotic and Eukaryotic cells differ structurally as well as in the way they replicate. However, it’s important to note the chemical similarities – reactions that enable cell life.
Both types of cells use and/or contain:
All types of cells must make and store energy to survive. Chemical reactions aid in the ability to metabolize food and build proteins; whether autotrophic or heterotrophic, cells need amino acids (proteins) and energy (glucose/ATP) to maintain structure and carry out a range of functions that include cell replication.
Even though at a most elemental level, all cells require the same functions to survive, the significant differences between prokaryotes and eukaryotes include structure and replication process.
Most noteworthy is the lack of nucleus in bacteria and archaean – the two types of prokaryote cells; prokaryotes:
In addition, the presence of rods, spheres or spirals aid in the identification of the three main types of prokaryotic bacteria.
A circular, easily identifiable dark object in the center of a cell, the nucleus is the first and most important characteristic of a eukaryotic cell. Encompassing three kingdoms: plants, animals and protists; plants and animals are multi-cellular, while protists consist of mostly unicellular plant-like, animal-like and fungus-like cells.
Eukaryotes contain many organelles – structures within the cell – including:
Nucleus – the defining structure, often likened to the “brain” or control center of the cell; the nucleus contains genetic material (DNA and RNA) and also manages the activities of the other organelles within the cell; other aspects include:
Cytoplasm – contained within the plasma membrane of the cell, but outside the nucleus; microfilaments and microtubules aid in the formation of the cytoskeleton
Cytoskeleton – provides shape to the cell through a “criss-cross” arrangement of protein-based filaments secured to the cell membrane; changes in filament tension lend to cell movement; certain cells move via the attachment of microtubules, cilia and flagella to the outer cytoskeleton; also plays a role in the separation of chromosomes during the process of mitosis
Cell Wall – most prominent in plant cells and commonly made of cellulose or chitin; glycocalyx in animal cells make the thin wall more durable and provides a means for cells to connect to each other
Mitochondria – a powerful part of a cell located in sphere-shaped double membrane structures throughout the cytoplasm; the outer layer is smooth, while the inner membrane contains cristae -- a progression of “folds” along the sphere that allow for an incredibly large surface area, while the small inner space (matrix) contains fluid; converts food into energy via aerobic respiration; essential to the production of ATP (energy)
Chloroplast – the plant version of mitochondria; contains chlorophyll and enzymes required for photosynthesis; like mitochondria, chloroplasts possess their own DNA, which it replicates on its own
Ribosome – manufactures protein in eukaryotes
Endoplasmic Reticulum (ER) – called the “intercellular highway,” the ER transports material around the cell; located between the pores of the nuclear envelope, the ER allows for the transfer of compounds in and out of the cell; two types:
Golgi Apparatus/Complex – responsible for preparing or “packaging” items, such as enzymes or proteins, within cisterns transported outside the cell through a vacuole or to another area of the cell like a lysosome; also produces/modifies proteins
Lysosome – uses an enzyme to break down food sources into usable forms such as amino acids (proteins) or energy (glucose); also ingests bacteria, protecting the cell from harmful intruders
Vacuole – storage facility for food and water; can be very large in plant cells and, in addition to storing nutrients and water, plant vacuoles can store metabolic waste and other harmful substances, keeping them away from the cytoplasm so the plant remains healthy
In advanced multi-cellular eukaryotes, cells communicate intrinsically and extrinsically. Specific organs might contain cells with a predominant organelle; for example, the liver contains a higher percentage of lysosomes, ridding the body of poisonous substances.
As whole entities, the survival of plants and animals comes down to the function and interaction of individual cells. Exposure to free radicals, disease, viruses, and parasites can cause damage to multiple cells; while a nutritious diet, aerobic exercise and limiting stress creates a positive effect on a cellular level.
When viewing eukaryotes under a microscope, organelles are most visible in the moments before, during, and after mitosis or cell division. Tissue specimens often contain multiple cells on a slide. Although cells from different organs or species may look different, eukaryotes all contain the same organelles.
Microscopic studies show the miniscule differences that exist between species and phylum – even where external variations seem much more than one or two chromosomal differences.
A background in histology and/or pathology aids in the recognition of cell anomalies. In addition, the ability to recognize organelles under different microscopic instruments lends to learning more and more information regarding the function of eukaryotes on a cellular level.
Techniques such as dark field, phase contrast, and DIC, the use of different dyes, utilizing photomicrography and computers are some of the ways hobbyists, students, teachers, medical professionals and researchers can use to explore eukaryotes on a cellular level. In addition, possessing the skills to identify different organelles found in eukaryotes under a variety of environments or circumstances yields numerous research possibilities.
Beginning with the nucleus, eukaryotes are significantly different from prokaryotes – although many of the chemical processes are similar such as those involving proteins, lipids, nucleic acids and carbohydrates.
Understanding that organelles become clearer before, during, and after cell division helps the recognition of parts of a cell in different states. This can decrease mistakenly calling something an artifact.
The amount of knowledge associated with studying various states of eukaryotic cells, the cellular differences between species and even the disparities that occur in different organs of the same species is exciting.
Each microscopic cell, imprinted with a genetic code and micromanaged by the nucleus, reveals a story; with the right instruments and techniques, we can observe the stages and functions of each organelle within a eukaryotic cell.
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