The last two centuries present significant advancement in the study of cell development in biological science since the term was first coined by Robert Hooke in 1665. Although Hooke first observed the presence of cells in matters it was Jean Baptiste De Lamarck (1744 – 1829), a French scientist, who initiated early steps in recognizing the concept of the cell as a biological element in living things while carrying out extensive works in evolution and classifications in the animal kingdom.
This is similar to the Rene Dutrochet’s pronouncement in 1824 that the structure of a living body’s fundamental elements is the cell, created through the process called juxtaposition or combination, producing both animals and plant forms. Several assumptions followed which serves as basis for the modern cell theory including Ludolph Christian Treviranus’s (1779-1864) proposition that a cell can be further separated into even smaller components by its intracellular space or individual units comprising the cell itself particularly in plants.
Building on this concept, Robert Brown (1773-1858) published a paper naming one of these units “cell nucleus” in 1883. Although scientifically accepted as fact today, Brown together with Bauer, at that time, never thought the idea of cell nucleus to be universally present in all living things and limit the concept to monocotyledons (also called monocots), one of the major groups of angiosperms or flowering plants. Amidst the numerous assumptions and differing opinions of their times three names excel in the field of cell science: Theodor Schwann (1810-1882), Matthias Jakob Schleiden (1804-1881) and Rudolf Virchow (1821-1902).
Schwann discovered what is called Schwann cell or neurolemnocytes, glial cells supplying vitality to peripheral nerve fibers. Together with Schleiden they concluded that all living things are composed of cells and published their findings in a paper called Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals. Almost their contemporary, Virchow further improved the idea into a wider and more scientific scale stating that cells come from cells of the same kind, refuting the theory of Spontaneous Generation.
Virchow was also one of the very first scientists to apply existing cell theories together with findings he himself formulated in medicine that led to the discovery of leukemia cells and a deeper understanding of lung cancer and other deceases related to cell formation and their behavior. In 1855, Virchow states that cells replicate through the process called “cell division”. Together, Schwann, Schleiden and Virchow are the three considered to be the key figures and originator of the basis for the concepts of modern Cell Theory.
Development in the Cell Theory in the 1900’s is not as numerous as that of the 1700’s and 1800’s. One discovery, however, worth mentioning is the finding made by James D. Watson and Francis Crick regarding the double-helix structure for DNA in the 1953. 2. Membranous Organelles of Eukaryotic Cells • Chloroplast (plastid). Chloroplasts are present in eukaryotic a cell which main function is to capture light energy to conserve free energy in the form of ATP moderating Nicotinamide Adenine Dinucleotide Phosphate (NADP) and requires NADPH as a reductant in a reduction-oxidation (redox) reaction.
• Endoplasmic Reticulum (ER) forms the network of tubules, vesicles and cisternae in cells necessary for protein synthesis ( the process where cells proteins), protein folding and transport, secretion or exocytosed, and manufacture and storage of glycogen, steroids and macromolecules. • Golgi Apparatus or Golgi Complex deals with the processing of proteins and lipids after synthesis before transporting (e. g. secretion) • Mitochondrion generates the cell’s energy (i. e. chemical energy) and produce majority of its Adenosine Triphosphate (ATP)
• Vacuole is an enclosed water filled compartment within a cell containing enzymes and various natural and inorganic molecules. • Nucleus contains majority of the cell’s genetic materials organized in a multiple long linear Deoxyribonucleic acid (DNA). It is considered to be the cell’s control center. 3. Methods in Molecular Exchange • Diffusion. Diffusion balances the degree of concentration of molecules from a region with higher concentration to a region with lower concentration as a reaction to thermal motion.
It plays a vital role in the distribution of oxygen, nutrients and other molecules across the capillary walls and across membranes. An diffusion equilibrium is said to be attained when the amount of molecule between two regions are equal and no diffusion movement occurs, or the net flux is at zero rate. The degree of concentration, temperature, and room affects the direction and extent of net flux related to the process. • Endocytosis. Endocytosis takes place when cells suck up molecules from the outside of the cell by swallowing it up using their cell membrane.
• Exocytosis. Exocytosis is the reverse process of endocytosis where a cell releases the contents accumulated by the secretory vesicles out of the cell membrane. 4. Catalyst and Enzyme Catalysts are substances that make a chemical reaction faster than its normal rate. Catalysts inhibit changes in matters acted upon (substrate) but remain unchanged on the final output of the reaction (end product). Enzymes are types of catalyst that are almost always in protein form and are used in biochemical (living) reactions. 5. Enzyme-Controlled Reaction
During an enzyme-controlled reaction, the enzyme’s key portion called “active site” interacts with the substrate. The substrate begins reacting to the enzyme entering a stress state. Upon reaching the necessary stress rate, the substrate changes in form or state (or both) producing the end product. The resulting end product is said to “drift away” and the enzyme is then free to perform the same procedure in the chemical reaction until no reactible substance is left, concluding the process. 6. Enzymes, Coenzymes and Vitamins
The primary function of vitamins in living organisms is to serve as cofactors for chemical reactions involving enzymes. Although a cofactor is a non-protein chemical compound, cofactors are tied to a protein and is necessary for proteins to perform its biological functions. These types of proteins are almost always a kind of enzyme and cofactors can be thought as of “helpers” in performing its transformation. Vitamins or derivatives of vitamins make up an organic cofactor. 7. Chemosynthesis is the process by which organisms generate their own energy through chemical reaction rather than sunlight.
This process converts carbon substances and nutrients into organic form (hydrocarbon) by oxidation as an energy source. 8. In the process called Glycolysis, requires two ATP’s to break down glucose into phosphoglyceraldehyde (2 PGAL). In the 2nd stage of glycolysis, the 2 PGAL’s are then broken into 2 pyruvates. This stage produces 4 ATP’s and 2 NADH’s. The net ATP production is 2 ATP’s as in the same case with the Krebs Cycle. 9. Stages in Photosynthesis The process of photosynthesis starts with the accumulation of substances needed by the process.
These substances are carbon dioxide (CO2), water (H2O) and, of course, sunlight to be processed in the leaf’s chloroplasts. Sunlight then is converted into an energy form called ATP and NADPH. The sunlight absorbed through the stomata follows as certain chain of processing and results in the production of ATP, NADPH and oxygen. This process is called light reaction. Utilizing the ATP and NADPH, carbon dioxide is then converted into sugar. The resulting sugar is then broken down into two molecules called glucose and fructose, molecules that make up sucrose and sugar.
The process is called dark reaction. 10. Assuming Photosynthesis I and Photosynthesis II refers to Light Reaction and Dark reactions: During light reactions electrons react as light strikes the chlorophyll. This results to the formation of ATP and NADPH. Also, water undergoes chemical reaction splitting oxygen and hydrogen. Carbon dioxide is accumulated from the atmosphere, hydrogen is added producing carbohydrates. This process is called carbon fixation. In the case of dark reactions, carbon dioxide is accumulated by a 5-C chemical called ribulose biphosphate (RuBP).
Six molecules of carbon dioxide go in the Calvin Cycle, creating a glucose molecule. TP and NADPH created is used to attach phosphates into the PGA. Residual PGAL molecules are converted to reform 6 molecules of RuBP repeating the cycle again. REFERENCES Enger, E. D. , Ross, F. C. , & Bailey, D. B. (2009). Concepts in biology (13th ed. ). New York: McGraw-Hill. Turner W. (January 1890). “The Cell Theory, Past and Present BIOS 100 Lecture Material Online. Fall 2004. Glycolysis, Krebs Cycle, and other Energy-Releasing Pathways. May 15, 2009. http://www. bio. miami. edu/~cmallery/255/255hist/cell_theory. htm