Chapter Summary

Introduction (page 39)

Chemistry deals with the composition of substances and changes in their composition. Biochemistry is the chemistry of living things.

Structure of Matter (page 39)

Matter is anything that has weight and takes up space.

1. Elements and atoms a. Naturally occurring matter on earth is composed of ninety-two elements.

b. Elements occur most frequently in chemical combinations called compounds.

c. Elements are composed of atoms.

d. Atoms of different elements vary in size, weight, and ways of interacting.

2. Atomic structure a. An atom consists of electrons surrounding a nucleus, which contains protons and neutrons. The exception is hydrogen, which contains only a proton in its nucleus.

b. Electrons are negatively charged, protons positively charged, and neutrons uncharged.

c. A complete atom is electrically neutral.

d. The atomic number of an element is equal to the number of protons in each atom; the atomic weight is equal to the number of protons plus the number of neutrons in each atom.

3. Isotopes a. Isotopes are atoms with the same atomic number but different atomic weights (due to differing numbers of neutrons).

b. All the isotopes of an element react chemically in the same manner.

c. Some isotopes are radioactive and release atomic radiation.

4. Molecules and compounds a. Two or more atoms may combine to form a molecule.

b. A molecular formula represents the numbers and kinds of atoms in a molecule.

c. If atoms of the same element combine, they produce molecules of that element.

d. If atoms of different elements combine, they form molecules of substances called compounds.

5. Bonding of atoms a. When atoms combine, they gain, lose, or share electrons.

b. Electrons are arranged in shells around a nucleus.

c. Atoms with completely filled outer shells are inactive, whereas atoms with incompletely filled outer shells tend to gain, lose, or share electrons and thus achieve stable structures.

d. Atoms that lose electrons become positively charged; atoms that gain electrons become negatively charged.

e. Ions with opposite charges attract and join by ionic bonds; atoms that share electrons join by covalent bonds.

f. Polar molecules result from an unequal sharing of electrons.

g. Hydrogen bonds occur between polar molecules.

h. A structural formula represents the arrangement of atoms within a molecule.

6. Chemical reactions a. In a chemical reaction, bonds between atoms, ions, or molecules break or form.

b. Three kinds of chemical reactions are synthesis, in which larger molecules form from smaller particles; decomposition, in which smaller particles form from larger molecules; and exchange reactions, in which parts of two different molecules trade positions.

c. Many reactions are reversible. The direction of a reaction depends upon the proportion of reactants and products, the energy available, and the presence or absence of catalysts.

7. Acids, bases, and salts a. Compounds that ionize when they dissolve in water are electrolytes.

b. Electrolytes that release hydrogen ions are acids, and those that release hydroxyl or other ions that react with hydrogen ions are bases.

c. Acids and bases react together to form water and electrolytes called salts.

8. Acid and base concentrations a. The concentration of hydrogen ions (H+) and hydroxyl ions (OH-) in a solution can be represented by pH.

b. A solution with equal numbers of H+ and OH- is neutral and has a pH of 7.0; a solution with more H+ than OH- is acidic (pH less than 7.0); a solution with fewer H+ than OH- is basic (pH greater than 7.0).

c. There is a tenfold difference in hydrogen ion concentration between each whole number in the pH scale.

Chemical Constituents of Cells (page 49)

Molecules containing carbon and hydrogen atoms are organic and are usually nonelectrolytes; other molecules are inorganic and are usually electrolytes.

1. Inorganic substances a. Water is the most abundant compound in cells. Many chemical reactions take place in water. Water transports chemicals and heat and helps release excess body heat.

b. Oxygen releases energy needed for metabolic activities from glucose and other molecules.

c. Carbon dioxide is produced when energy is released during metabolic processes.

d. Inorganic salts provide ions needed in a variety of metabolic processes.

e. Electrolytes must be present in certain concentrations inside and outside of cells.

2. Organic substances a. Carbohydrates provide much of the energy required by cells; their building blocks are simple sugar molecules.

b. Lipids, such as fats, phospholipids, and steroids, supply energy and are used to build cell parts; their building blocks are molecules of glycerol and fatty acids.

c. Proteins serve as structural materials, energy sources, hormones, cell surface receptors, antibodies, and enzymes.

(1) Enzymes initiate or speed chemical reactions without being consumed themselves.

(2) The building blocks of proteins are amino acids.

(3) Proteins vary in the numbers and kinds of amino acids they contain, the sequences in which these amino acids are arranged, and their three-dimensional structures, or conformations.

(4) The amino acid sequence determines the protein's conformation.

(5) The protein's conformation determines its function.

(6) Protein molecules may be denatured by exposure to excessive heat, radiation, electricity, or certain chemicals.

d. Nucleic acids constitute genes, the instructions that control cell activities, and direct protein synthesis.

(1) The two major kinds are RNA and DNA.

(2) Nucleic acid molecules are composed of building blocks called nucleotides.

(3) DNA molecules store information that is used by cell parts to construct specific kinds of protein molecules.

(4) RNA molecules help synthesize proteins.

(5) DNA molecules are replicated and an exact copy of the original cell's DNA is passed to each of the newly formed cells, resulting from cell division.

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