Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Spring Williams Enduring Understanding Due Thursday, August 16, 2007 Post-course evidence essay: Living organisms are complex systems composed of interdependent chemical structures and processes, and therefore can be understood at a molecular level using the same chemical principles that apply to non-living objects. Two examples of chemical principles of nonliving objects that can be used to explain the complexity of living organisms are polarity and bonding. The chemical principle of polarity in hydrophobic and hydrophilic molecules can be used to explain a cell and its environment. The chemical principle of molecular bonding can be used to explain the protein of hair with and without a permanent. A molecule has polar bonds if the difference in electronegativity between the central atom and the atom attached is greater than .5. However, a molecule can have both polar and nonpolar bonds; depending on the difference in electronegative of each atom that is attached to the central atom. In contrast, a nonpolar bond would have a difference in electronegativity of less than .5. To determine if a molecule is polar, the type of bonds, electronegativity and lone pairs must be considered. A polar molecule must have polar bonds and/or lone pairs. A molecule is nonpolar if it contains all nonpolar bonds. The degree of molecular polarity depends on the relative number of polar groups compared to the size of nonpolar areas. If two molecules with the same polar region and different nonpolar regions were compared, the molecule with the largest nonpolar region would be considered less polar. In Ingrid’s Biology class, we learned about the structure of the cell membrane. The cell membrane in an animal cell is the barrier that separates the inside of the cell from its environment. Both the inside of the cell and its environment are composed mostly of water. The cell membrane is composed of two layers of phospholipids which have polar and nonpolar regions. The polar region is hydrophilic and is called the head. The nonpolar region is hydrophobic and is called the tail. The phospholipids arrange themselves so that one layer of phospholipids has its head facing the environment and the other layer has its head facing the inside of the cell. This arrangement allows the hydrophobic tails of each layer to be facing one another. This lipid bilayer forms because the hydrophobic tails are repelled by water in the intracellular and extracellular matrix. The amoeba is a unicellular organism that obtains food by the process of engulfing. The organism is able to wrap its cell membrane around a food particle, until it uses the cell membrane to bring the food inside of the organism and form a food vacuole. The lipids from the cell membrane are able to arrange themselves into a vacuole because the nonpolar tails face inside and the polar heads face the watery environment inside of the cell and the vacuole. The remaining lipids in the cell membrane reassemble to form a closed cell membrane. Amoeba eating a paramecium (taken from encarta.msn.com/media_461532743_761557743_-1) An example of an organism’s molecular polarity discussed in class can be observed in the DNA extraction lab. The purpose of the lab was to isolate DNA from a plant cell. To reach the DNA, barriers such as membranes needed to be destroyed. Because the nonpolar region of lipids is significantly larger than the polar region, they are considered to be nonpolar molecules. In the DNA lab, a nonpolar substance needed to be used to dissolve the cell membrane. The substance that we used was Edward’s buffer, a detergent with polar and nonpolar region. The polar region remained in water while the nonpolar region dissolved the lipids making up the cell and nuclear membranes. Examples of bonds that were studied in class include but are not limited to peptide (amide bonds), ionic, and disulfide bonds. Intermolecular forces (IMF’s) are bonds that work between molecules to hold them together. The three types of IMF’s that we learned about in class are London forces, dipole-dipole, and hydrogen bonding. Molecules may be bonded by more than one type of IMF. London forces work between all molecules but are the only force between nonpolar molecules. Because they are the weakest force, they are easy to break. Dipole-dipole forces are only between polar molecules. Hydrogen bonding is found between molecules bonding a Hydrogen atom bonded to Nitrogen, Oxygen, or Fluorine. They are a strong version of dipole-dipole force. In class bonds in living organisms were studied in our learning of amino acids. Amino acids are molecules that join to form protein in an organism. It has specific characteristics based on its functional group. Amino acid monomers join together by forming covalent peptide bonds. The peptide bond forms as water is removed when the amine group from one amino acid bonds with the carboxyl group of the other. This joining is known as the formation of the amino acid’s primary structure. A protein’s primary structure is controlled by genes. If there is a gene mutation, a person will have an incorrect sequence of amino acids (primary structure). The other structures that result from bonding within and/or between amino acids are secondary, tertiary, and quaternary. Secondary structures are formed when amino acids are linked together, and within the chain of amino acids, the backbone of individual amino acids hydrogen bonds with the backbone of another amino acid. Two examples of the repeated structure that may form are the alpha helix or the beta sheet. Tertiary structures form when the side chains of amino acids (within a chain) bond by ionic, disulfide, hydrogen, or dipole-dipole bonds. Quaternary structures form when there is ionic, hydrogen, dipole-dipole, or disulfide bonds between subunits of amino acids. An example of a protein that I thought of during our discussion of protein structure was keratin. Keratin is a protein that is found in our hair. This protein has many alpha helixes and disulfide bonds. If a person uses a permanent to get wavy hair, a reducing agent is used to break some of the disulfide bonds, resulting in a change in the tertiary structure. Next, the hair may be put on rollers and a neutralizer may be added to reform disulfide bonds forming the desired tertiary structure (Ophardt, 2003).