Molecular Biology of the Cell - Assignment Example

1. You are the biologist in a group of scientists who have traveled to a distant star system and landed on a planet. You see an astounding array of shapes and forms. You have three days to take samples of living things before returning to earth. How do you decide what is alive? The choice on what to bring back to earth as living samples should, in my opinion, be evaluated based on the characteristics and processes associated to the state of being alive. According to Campbell and Reece (2002), life has five unifying properties. First, life exhibits a high level of order. Be it the way the petals of a sunflower are arranged, or the way feathers are organized on a bird’s wings, patterns will be observed. Even at the microscopic level, biological order exists. Organs, for instance, are composed of a single type of tissues. Tissues, on the other hand, are composed of a single type of cells. An organism is not simply a random collection of individual cells (Gerhardt et al., 1994). Rather, it is a product of an ordered grouping of cells. Next, living things demonstrate the ability to reproduce. According to the Cell Theory, only life begets life (Alberts et al., 1994). Only dogs bear pups; only trees give off seedlings; and only bears deliver bear cubs. The third property is growth and development. Over time, multicellular organisms increase in size, as a result to the increase in the number of cells in its body. Among unicellular organisms, growth can be observed as an increase in the size of its population (Beveridge et al., 2007). Development cannot be any simpler than the ones at the cellular level, when DNA replicates and microtubules elongate during the course of mitosis. Fourth, living things respond to stimuli. A Mimosa pudica, for example, will close its leaves if you touch them. A sea squirt will release water from its siphons when disturbed. Organisms, whether sedentary or mobile, respond to their environment. Finally, all organisms utilize energy. A butterfly, for instance, obtains food in the form of nectar and transforms it into energy to power its activities. It might not be possible to capture or observe all of these properties within three days (e.g. giving birth) especially if the organism is sedentary. In such cases, taking a piece from the target sample for further examination might be helpful. If these organisms share resemblance to living creatures on earth, their building blocks are similar to the morphology and properties of cells. 2. What happens if an atom of an element gains or loses electrons? What happens if an atom of an element gains or loses neutrons? What happens if an atom of an element gains or loses protons? When a neutral atom gains or loses electrons, it becomes an ion, a charged atom (Bruice 2001). Each electron has one unit of negative charge. So when a neutral atom loses an electron, the net electrical charge becomes + 1, and the resulting ion is called cation. Meanwhile, if the neutral atom gains an electron, the net electrical charge becomes -1, and the ion is specifically called anion. Thus, a neutral atom that gains an extra electron becomes an anion. If it loses an electron, it becomes a cation. However, when an atom gains or losses neutrons, the net charge of the atom will not be affected. Rather, the mass of the atom will change (Bruice 2001). This is because the total number of neutrons and protons determine the atomic mass. Hence, if an atom gains neutrons through the process of fusion, the atomic mass increases (Campbell and Reece, 2002). On the other hand, if it losses neutrons through fission, the atomic mass decreases. These different atomic forms are called isotopes of an element. For instance, the element carbon , which has the atomic number 6, may exist as carbon-12 isotope (6 neutrons), carbon-13 isotope (7 neutrons), or carbon-14 (8 neutrons) ( Campbell and Reece, 2002). Changing the number of protons of an atom effectively makes it a different element. When the element oxygen for instance (atomic number of 8) losses a proton, it becomes nitrogen (atomic number of 7); when it gains a proton, it becomes fluorine (atomic number of 9) (Bruice 2001). Figure 1. Peptide formation 3. The molecule directly above is a peptide made from monomers of amino acids. The molecule below is a disaccharide made from monomers of simple sugars. Both molecules were synthesized suing a common chemical reaction. What is the chemical reaction that formed these molecules and what is the common by-product of both these reactions? Figure 2. Disaccharide formation The formation of peptide bond as illustrated in Figure 1 and glycosidic bond from simple sugars (Figure 2) both require dehydration reaction, the process of removing water from the reacting molecules ( Mckee and Mckee, 1999). Water is the common by-product of this process, where one of the reactants contains an alcohol functional group. One significant example of dehydration reaction is the dehydration of 2-phosphoglycerate, an important step in carbohydrate metabolism (Mckee and Mckee, 1999). Dehydration reaction is actually a subset of elimination reaction, the process of losing an hydroxyl (-OH) group from one carbon and H from another carbon (Bruice 2001). Dehydration reaction requires an acid catalyst and heat. Among the most commonly used acid catalysts for this purpose are phosphoric acid and sulfuric acid. 4. Compare the cellular organelles and other structures to the parts of a city. For example, the nucleus is city hall and the DNA is all the city’s laws and instructions. The nucleus corresponds to the city hall. Just like the city hall ,which symbolizes authority and power, the nucleus is the repository of genetic material which directs the over-all functional and structural integrity of the cell. On the other hand, the mitochondrion can be considered as the city’s power plant since it supplies energy to every cell in the form of ATP. Meanwhile, the endoplasmic reticulum, which functions in various metabolic processes, is similar in function to a factory complex. It is in the smooth endoplasmic reticulum, for instance, where steroids and phospholipids are produced. The rough endoplasmic reticulum synthesizes secretory proteins. The golgi apparatus is akin to a post office. Here in the golgi apparatus, products of the ER are sorted and shipped to other destinations. The vesicles are the postmen, which specifically transports the cellular products to other sites within and even outside the cell. Moreover, the lysosomes act as law enforcers. They phagocytose and eliminate harmful invaders like bacteria and viruses. The roads are represented by the cytoskeleton, which provides cellular organelles with tracks for them to move around. They could also be considered as the skeletal foundation of buildings and other infrastructures in the city because the cytoskeleton offers support and structural stability. Finally, the ribosomes could be analogous to manufacturing company that specializes in only one product. In the cell, the ribosome is the sole organelle that exclusively manufactures proteins. The fact that it is possible to compare cellular organelles to the different parts of a city just proves that the cell is the simplest collection of matter that can live. 5. Why do you need enzymes to help your cells do their jobs? Enzymes are proteins that act as biological catalysts, molecules that speed up chemical reactions without being consumed in the process (Creighton 1993). The roles enzymes play in maintaining body function are indispensable because living processes consist entirely of biochemical reactions. Without enzymes to serve as catalysts, these reactions will not be fast enough to sustain life’s functions (Mckee and Mckee, 1999). In order to proceed at perceptible rate, chemical reactions require an initial input of energy, called activation energy (Mckee and Mckee, 1999). Under laboratory conditions, this activation energy is usually increased with the application of heat. As heat increases, the tendency by which molecules vibrate and collide with each other also increases, resulting to chemical reactions. Another way to enhance the frequency and intensity of molecular collision is to increase the concentration of reactants. However, in biological environments, the concentration of reactants is usually low and elevated temperatures may destroy the integrity of biological structures. By using enzymes, chemical reactions speed up without increasing the reaction temperature and at minute concentrations of the starting materials. Enzymes possess several significant characteristics. First, enzymes are highly specific to the reactions they catalyze (Campbell and Reece, 2002). So even at low concentrations, the efficiency by which enzymes catalyzed reactions is not affected. Second, the rate of reactions catalyzed by enzymes may increase as much as 106 times (Campbell and Reece, 2002). Third, the production of enzymes is a highly regulated process. (Campbell and Reece, 2002).This means to imply that the body produces them only if they are needed. 6 Explain how photosynthesis and respiration complement each other. The interdependence of photosynthesis and cellular respiration is highlighted by the fact that photosynthesis produces the starting materials for cellular respiration and vice versa (Alberts et al., 2004). The photosynthetic pathway is specifically composed of 2 stages which occur in the chloroplasts: light reactions and Calvin cycle. In the light reactions, light absorbed by the chlorophyll induces the transfer of electrons from water to NADP+, an electron acceptor. Upon taking in electrons, NADP+ is reduced to NADPH, an energized molecule. Also, ATP is generated through the addition of a phosphate group to ADP in a process called photophosphorylation. It is during the process of light reaction that water is split, releasing oxygen. Meanwhile, in the Calvin cycle, carbon from CO2 is incorporated into already existing organic compounds in the chloroplast. After which, the incorporated carbons are reduced to carbohydrates (sugar) by NADPH and ATP generated by the light reactions. By coordinating the two stages of photosynthesis, oxygen and sugar is produced from water and carbon dioxide (Campbell and Reece, 2002). Meanwhile, cellular respiration starts off in the cytosol by virtue of glycolysis. During glycolysis, each glucose molecule is broken down into two molecules of the compound pyruvate. Then, the pyruvate traverses the membrane of the mitochondrion to enter the matrix, where the Krebs cycle decomposes it into carbon dioxide. Electron carriers in the form of NADH and FADH transfer electrons produced during glycolysis and Krebs cycle to the electron transport chain, where oxidative phosphorylation occurs. Electrons moving along the chain end up with oxygen, as the final electron acceptor, giving off water in the process. Hence, cellular respiration produces water and carbon dioxide, which are the starting materials in photosynthesis, from sugar and oxygen (Campbell and Reece, 2002). References 1. Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., and Watson, J. 2004. Molecular biology of the cell. 3rd edition. Garland Publishing, Inc. New York. 2. Beveridge, T., Breznak, J., Marzluf, G., Schmidt, T., amd Snyder, L. 2007. Methods for general and molecular microbiology. 3rd edition. ASM Press. Washington,DC. 3. Bruice, P. 2001.Organic chemistry. 3rd edition. Prentice Hall Inc. Upper Saddle River, New Jersey 4. Campbell, N., and Reece, J. 2002. Biology. 6th edition. Benjamin Cummings. San Francisco, California. 5. Creighton, T. 1993. Proteins: structures and molecular properties. Second edition. W.H. Freemand and Company, New York. 6. Gerhardt, P., Murray, R., Wood, W., and krieg, H. 1994. Methods for general and molecular bacteriology. American Society for Microbiology Press. Washington, DC. 7. McKee, T., and Mckee, J. 1999. Biochemistry: an introduction. Second edition. McGraw-Hill Companies, USA. Read More