1 - Gavilan College



Review Questions Ch 1-4

Answers for all questions should be full and complete both for credit and for them to be useful preparation for the exam.

1. Define the terms hypothesis, theory, and law.

A hypothesis is an educated guess based on observations. It must make a prediction(s) and it must be falsifiable (disprovable). A hypothesis cannot be proven to be true.

A theory is a hypothesis or related group of hypotheses that have been supported by repeated testing.

A law explains a body of observations where no exceptions have been found to the rule that it states. A law is generally able to be stated as a mathematical equation.

2. Compare and contrast DNA and RNA.

DNA and RNA are both nucleotides made up of a 5 carbon sugar, a phosphate group, and a N containing base, the polymers of both are built by the bonding of the sugar of one nucleotide to the phosphate group of the next, and both play a role in the building of proteins.

DNA differs from RNA in several ways. The sugar found DNA is deoxyribose rather than the ribose found in RNA. DNA carries the genetic information needed for protein construction whereas RNA is directly involved in protein construction. DNA and RNA share four of their four bases. Both have adenine (A), guanine (G), and cytosine (C). The fourth base of DNA is thymine (T) whereas the fourth base in RNA is uracil (U). Each DNA molecule consists of two chains of nucleotides forming a double helix held together by hydrogen bonds. RNA consists of a single strand of nucleotides.

3. Describe the 3 types of molecular bonds. Which is strongest and which is weakest?

The strongest of the molecular bonds is the covalent bond. Covalent bonds are formed by the sharing of outer valence electrons. Two electrons (one from each atom) are shared in a covalent bond. Covalent bonds can share electrons evenly in nonpolar bonds when the nuclei are of similar size or unequally in polar bonds when the nuclei are of very different sizes. Covalent bonds may share also share 4 (2 each) electrons in a double bond or 6 (3 each) in a triple bond. Most biological molecules contain covalent bonds.

Ionic bonds are formed by the electromagnetic attraction of oppositely charged ions. One atom loses one or more electrons creating a positive charge (+1 per electron lost) and emptying its outer valence. The other atom gains one or more electrons creating a negative charge (-1 per electron gained) filling its outer valence. The opposite charges of these ions attract one another binding them together in an ionic bond.

Hydrogen bonds are by far the weakest of the three molecular bonds, though when many of them act in concert the combined effect can be stronger than a single ionic bond. Hydrogen bonds are formed by the weak electromagnetic attraction between the positive end of one polar molecule to the negative end of another polar molecule, for example the weakly negatively charged oxygen end of a water molecule is attracted to one of the weakly positively charged hydrogen ends of another water molecule.

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