Chapter 2

Chemistry

 

1.  Describe background terminology.

 

matter – anything that occupies space and has mass

states of matter – solid, liquid, gas

  • solid – has definite shape and volume
  • liquid – has no definite shape and definite volume
  • gas – has no definite shape and no definite volume

 

energy – the capacity to do work or put matter into motion

  • kinetic energy – energy in action
  • potential energy – stored energy; has the capability to do work but is not now doing so

 

forms of energy

  • chemical – stored in the bonds of chemical substances (food molecules, ATP)
  • electrical – movement of charged particles
  • mechanical – energy directly involved in moving matter
  • radiant – energy that travels in waves (electromagnetic spectrum)

 

2.  Describe basic atomic structure.

 

            All matter is composed of elements, unique substances that cannot be broken down by ordinary chemical methods.  The elements are listed in the periodic table. Each element is known by an atomic symbol.

            Each element is composed of particles called atoms that display the characteristic properties of that element. Physical properties are things that can be detected with our senses or measured (color, texture, boiling point). Chemical properties describe how atoms react with other atoms.

            An atom has three subatomic particles – protons, neutrons, and electrons. The central nucleus of an atom is composed of protons and neutrons. Protons are positively charged; neutrons are neutral (no charge). The nucleus is surrounded by negatively charged electrons orbiting in an electron cloud. An atom has an overall neutral charge because there are equal numbers of protons and electrons.

            Elements can be identified by their atomic numbers. The atomic number is the number of protons in an element. It is written as a subscript to the left of the atomic symbol.

 

3.  List the four major elements of the body and the major minerals and trace elements.

 

The elements carbon, oxygen, hydrogen, and nitrogen make up around 96% of body weight. Some elements necessary for the body are referred to as minerals. The most important minerals are calcium, chlorine, sulfur, potassium, sodium, magnesium, and phosphorus. Several other elements are needed in small amounts, and are known as trace minerals:  fluorine, cobalt, chromium, copper, iodine, iron, manganese, selenium, and zinc. (See Table 24.3.)

 

4.  Define the terms molecule, compound, mixture, solution, solvent, and solute and give examples of each.

 

molecule - combination of two or more atoms held together by chemical bonds

When the two atoms are identical the resulting substance is called a molecule of that element (H2 is a molecule of hydrogen gas).

 

compound – when two or more different kinds of atoms bind they form molecules of a compound; chemically pure; all molecules identical (H2O is a compound – it is a molecule of water).

 

mixtures – substances composed of two or more substances physically intermixed.

 

solutions – homogeneous mixtures of components that may be gases, liquids, or solids. [air, seawater]

solvent – substance in a solution present in the greatest amount (dissolving medium) [water]

solute – substance in a solution present in smaller amounts (thing that is dissolved) [salt]

 

5.  Describe and give examples of ionic, covalent (nonpolar and polar), and hydrogen bonding.

 

            The electrons in an atom are arranged in energy levels (or electron shells) that increase in capacity the farther away they get from the nucleus. The outermost energy level (called the valence shell) is the most important in determining how atoms react with other atoms. Atoms are most stable when the outermost shell has 8 electrons in it and will react with other atoms to try to reach this level of stability. (The exception to this is hydrogen and helium, which only have one energy level that is filled to capacity and is stable with only 2 electrons.)

 

            Atoms are neutral, but they can gain or lose electrons. When this happens an atom becomes an ion, which will have a charge – either positive or negative depending upon whether electrons were lost or gained. An ionic bond is a chemical bond between atoms formed by the transfer of one or more electrons from one atom to another. An example is sodium chloride (NaCl), table salt.

 

            Atoms can also achieve stability by sharing electrons. This means that electrons are not transferred from one atom to the other, but spend time orbiting both nuclei. A covalent bond is a chemical bond formed between two atoms that are sharing a pair of electrons, each atom contributing one electron to the shared pair. If the atoms are shared equally then the resulting molecule is nonpolar (hydrogen gas). If one atom has a greater attraction for electrons (a property known as electronegativitiy), the electrons may be shared unequally, resulting in a polar molecule (water).

 

            Hydrogen bonds form when a hydrogen atom, already covalently linked with one electronegative atom (like oxygen or nitrogen), is attracted by another electronegative atom and forms a bridge between them. These bonds are too weak to bind atoms together to form molecules, but they are important in attracting water molecules to each other and as intramolecular bonds in large biological molecules (proteins, DNA) where the hydrogen bonds stabilize the overall structure.

 

 

6.  Describe water as an inorganic compound and universal solvent.

 

Water has several important properties:

  • high heat capacity – absorbs and releases large amounts of heat before changing appreciably in temperature itself. This prevents sudden, severe changes in body temperature from vigorous activity.
  • high heat of vaporization – large amounts of heat are needed to break water’s hydrogen bonds and allow it to change from a liquid to a gas (evaporation). This makes perspiration and effective cooling mechanism.
  • polar solvent properties – the universal solvent. The chemical reactions of the body depend on the reactants being dissolved in water. Since water molecules are polar, ionic compounds and other small reactive molecules dissociate in water, causing the substance to dissolve. Water also forms hydration layers around large charged molecules, such as proteins.
  • reactivity – decomposition reactions by hydrolysis; large molecule assembly by dehydration synthesis

 

7.  Describe pH scale, buffers, acids and bases.

 

Acids are substances that release hydrogen ions (H+) in detectable amounts. Hydrochloric acid (HCl) is found in the stomach. Bases take up hydrogen ions in detectable amounts and are characterized by the presence of hydroxyl ions (OH-). Bicarbonate ion is an important base in the body. The more hydrogen ions present, the more acidic a solution is; the more hydroxyl ions present, the more basic a solution is.

 

The relative concentration of hydrogen ions in body fluids is measured in concentration units called pH. The pH scale runs from 0 – 14 and is logarithmic, i.e. each unit represents a ten-fold change. At a pH of 7, a solution is neutral with equal amounts of hydrogen and hydroxyl ions. Below 7 is acidic; above 7 is basic. The farther away from 7 a substance is in pH, the more it dissociates in solution and the stronger a substance it is. For example, something with  pH of 1 or 2 is a strong acid; something with a pH of 13 or 14 is a strong base. Closer to 7, something is a weak acid or weak base.

 

Blood must maintain a pH in the range of 7.35 – 7.45. Buffers are present in the blood to prevent big shifts in pH. A buffer does this by releasing hydrogen ions when the pH rises and binding hydrogen ions when the pH drops.

 

8.  Discuss and give examples of the most important carbohydrates, proteins, lipids and nucleic acids found in the body and relate these substances to specific body structures or functions.

 

Carbohydrates include sugars and starches. They are composed of carbon, hydrogen, and oxygen. Monosaccharides are simple sugars, example glucose (the major fuel source for the body). Disaccharides are composed of two sugar units, for example table sugar or sucrose (glucose + fructose). Polysaccharides are composed of many sugar units, for example starch (the storage carbohydrate of plant tissues) and glycogen (the storage carbohydrate of animal tissues). The primary function of carbohydrates in the body is to serve as a source of cellular fuel.

 

Lipids are insoluble in water, but dissolve readily in other lipids and organic solvents like alcohol. Lipids include neutral fats, phospholipids, and steroids. Tryglycerides are neutral fats, composed of a backbone of glycerol with three attached fatty acid chains. Neutral fats provide the body’s most efficient and compact form for storing usable energy fuel. Phospholipids are similar to triglycerides except one fatty acid chain is replaced by a phosphate group. Phospholipids compose a large part of cellular membranes. Steroids are flat molecules made of interlocking hydrocarbon rings. An example of cholesterol which is a building block of Vitamin D, steroid hormones, and bile salts.

 

Proteins are composed of building blocks called amino acids joined by peptide bonds. There are 20 different amino acids in biological proteins. Proteins serve as the major structural material in the body and also as enzymes. Proteins may fold up into distinct shapes via intramolecular hydrogen bonding. The protein usually must maintain its proper three-dimensional shape in order to function. Fibrous proteins such as collagen make up a large part of connective tissue. Globular proteins include hormones and enzymes. Enzymes are biological catalysts – substances that regulate and accelerate the rate of biochemical reactions but are not used up or changed in those reactions. Basically enzymes help the biochemical reactions of our body to proceed at a rate that supports life.

 

Nucleic acids such as DNA and RNA are composed of chains of nucleotides made up of a phosphate, sugar, and nitrogen-containing base. DNA (deoxyribonucleic acid) is the genetic material. A chromosome consists of a molecule of DNA. Certain segments of DNA are known as genes. A gene provides the instructions for how to make a single protein chain. RNA (ribonucleic acid) assists in gene expression by carrying the code for a protein to the place in the cell that proteins are manufactured. ATP (adenosine triphosphate) is a nucleotide which serves as the energy carrier molecule in the cell.