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Cellular Chemistry Help

By — McGraw-Hill Professional
Updated on Apr 25, 2014

Cellular Chemistry

All matter, living and nonliving, consists of building units called chemical elements. Ninety-six percent of the human body is composed of the chemicals Carbon (C), Nitrogen (N), Oxygen (O), and Hydrogen (H). Calcium (Ca), Phosphorus (P), Potassium (K), and Sulfur (S) make up 3 percent of the body. The remainder of the body is composed of small quantities of Iron (Fe), Chlorine (Cl), Iodine (I), Sodium (Na), Magnesium (Mg), Copper (Cu), Manganese (Mn), Cobalt (O), Zinc (Zn), Chromium (Cr), Florine (F), Molybdenum (Mo), Silicon (Si), and Tin (Sn) referred to as trace elements.

Atoms

An atom is the smallest unit of an element that retains its chemical properties. Every pure element is composed of only one kind of atom.

An atom is composed of three kinds of elementary particles:

  • protons: Charge of +1, mass of 1.
  • neutrons: No electrical charge, mass of 1.
  • electrons: Charge of -1, very small mass.

Protons and neutrons are bound in the nucleus of the atom.

The atomic number is the same for all atoms of a given chemical element. Surrounding the nucleus are precisely Z electrons, making the atom as a whole electrically neutral. Electrons orbit the nucleus, much as the planets of the solar system orbit the sun. The distribution of electrons is organized into energy levels (shells). The electrons are distributed among the shells. The capacities of the first four shells are 2, 8, 8, and 18 electrons. The atom is built by one electron at a time, with a given shell entered only if all interior shells are full.

Molecules and Chemical Bonds

A molecule is a combination of two or more atoms, joined by chemical bonds. Just as atoms are the smallest units of a chemical element, molecules are the smallest unit of a chemical compound. Water is a chemical compound that is essential for life. It consists of molecules, each containing one oxygen atom and two hydrogen atoms (H2O). In chemical notation, subscripts denote how many atoms of each element are in one molecule of the compound.

Molecules are held together by attractive forces called bonds. Ionic bonds form when atoms give up or gain electrons and become either positively or negatively charged. The charged atoms are called ions, and those with negative charges are attracted strongly to those with positive charges (Figure 2-1). Covalent bonds form when atoms share electrons (Figure 2-2). A hydrogen bond is a weak bond between molecules that forms when hydrogen forms a covalent bond with another atom, or example oxygen. The hydrogen atom gains a slight positive charge and has an affinity for the slightly negatively charged oxygen of other molecules. Chemical reactions occur when molecules form, are broken, or rearrange their component atoms.

Cellular Chemistry

Many of the unique properties of water, freezing and boiling points, surface tension, adhesion, cohesion, and capillary action are due to the hydrogen bonding between water molecules.

Solutions and Properties of Solutions

When two or more substances combine without forming bonds with each other, the result is a mixture. Solutions are mixtures in which the molecules of all the combined substances are distributed homogeneously throughout the mixture. Solutions include solids (the solute) dissolved in liquid (the solvent) as with salt water. The concentration of solute in a solution may be measured in many ways such as the percentage of the solutes in the solution, or the molarity of the solution, a measure of the moles of solute per liter of solution (1 mole = 6.022 ×1023 molecules).

One important property of solutions is the acidity or basicity (alkalinity) of the solution. This property is measured by the pH of the solution. In any sample of water, a certain proportion of water molecules exits in an ionized form as H+ (hydrogen ions) and OH- (hydroxide ions). In pure water the number of H+ equals the number of OH-, and the solution is referred to as neutral, with a pH of 7.

The lower the pH number, the greater the acidity, the higher the number, and the greater the alkalinity of the solution.

A salt is an ionic compound formed from the residue of an acid and the residue of a base. When an acid loses its proton (H+) and a base loses a hydroxyl group (OH-) the remaining ions of the molecules will sometimes bind together forming a salt. For example, the formation of table salt is represented below:

A buffer is a combination of a weak acid and its salt in a solution that has the effect of stabilizing the pH of the solution. If a solution contains a buffer, its pH will not change dramatically even when strong acids or bases are added. When acid is added to the solution, it is neutralized by the salt of the weak acid. When a base is added to the solution it is neutralized by the weak acid itself. Three important buffer systems found in the body are the bicarbonate buffer found in the blood and the extracellular fluid, the phosphate buffer in the kidneys and the intracellular fluid, and the protein buffer found in all tissues.

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