Chemical Elements

Topic 3.1

3.1.1: Chemistry of Life

Living organisms are composed of many chemical elements but the most frequently occurring elements are carbon, hydrogen, oxygen and nitrogen. As shown in Figure 1 below these four elements make up a majority of the human body, as well as most other living organisms. These are the four main elements of biological molecules such as carbohydrates (examples shown below in Figure 2), proteins, fats, and nucleic acids. Outlined in Table 1 are the roles of the elements sulfur, calcium, phosphorus, iron and sodium which are involved in important functions of animals, plants and prokaryotes. These other elements are only required in minute quantities.

Figure 1: Most frequently occuring chemical elements in living organisms


3.1.2 & 3.1.3: The roles of the other elements.

The table below outlines one of the many roles of sulphur, calcium, phosphorus, iron and sodium in plants, animals and prokaryotes.

Element Plants Animals Prokaryotes
sulphur Found in the amino acids cysteine and methionine contain sulfur. Thus the element is present in all polypeptides, proteins, and enzymes that contain these amino acids. Found in the amino acids cysteine and methionine contain sulfur. Thus the element is present in all polypeptides, proteins, and enzymes that contain these amino acids. Energy source in chemical reactions.
calcium Ca2+ ions are an essential component of plant cell walls and cell membranes. Functions in muscle contraction by binding proteins that are necessary for promoting muscle contraction. Used in signal transduction by calcium-binding proteins.
phosphorus Being a component of ATP, phosphorus is needed for the conversion of light energy to chemical energy (ATP) during photosynthesis. Found in hydroxyapatite which is the main component of bones. A component of nucleic acids.
iron Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron required for many enzymes, and for hemoglobin. Used in energy generation by transforming Fe(II) into Fe(III).
sodium Is involved in the regeneration of phosphoenolpyruvate in CAM and C4 plants. A common electrolyte, is important in nerve transmission. Used in moving the flagellum.

3.1.4: The importance of water

The oxygen and hydrogen atoms that make up the water molecule have different pulling properties on the electrons that are shared in their covalent bonds. This pulling property is known as electronegativity. The oxygen atom has a negative charge because it pulls the shared pair of electrons closer to its nucleus. Therefore, the hydrogen atom has a positive charge because ithas the shared pair of electrons pulled farther away from its nucleus. The water molecule is polar because of this unequal sharing of electrons between the atoms (known as a polar covalent bond). Figure 3 outlines the polarilty in water.

Figure 2: Polarity in a water molecule


3.1.5 & 3.1.6: Hydrogen Bonding

The thermal and cohesive properties of water (outlined in Figure 4 below) can be attributed to its ability to form hydrogen bonds between water molecules. a hydrogen bond is formed when when an H atom (positive end) of one water molecule is attracted to an O atom (negative end) of another water molecule. Although this is considered a weak bond, the hydrogen is considered important in the chemistry of life. Water's ability to act as a solvent (outlined in Figure 4 below)results from the polarity of its molecules. It can dissolve ionic compounds because the negative end of the molecule is attracted to positive ions while the positive end is attracted to negative ions. Polar molecules, which contain positive and negative charges are dissolved in water because become surrounded by polar water molecules. the figure below outlines these properties and gives an example of each property.

Figure 3: Properties of water


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