(a) What type of interaction holds DNA’s double-helical strands together?

(b) Why would it not be good for DNA’s double-helical strands to be held together by covalent bonds?

In the process of respiration

C$_6$H$_{12}$O$_6$(s) + 6 O$_2$(g) $\rightarrow$ 6 CO$_2$(g) + 6 H$_2$O(l)

which molecule undergoes oxidation? Which molecule undergoes reduction?

There are 4$^1$ = 4 mononucleotides of DNA, there are 4$^2$ = 16 possible dinucleotides, and so on. If a segment of DNA were completely random, how many nucleotides long would it need to be in order to have one possible sequence for each person on Earth (currently about 7.5 billion people)?

How many codons are possible? All of these codons are used in molecules of mRNA and there are only 20 amino acids normally encoded (plus start codons and stop codons). Is there exactly one codon per amino acid, must some codons select for more than one amino acid, or must there be some amino acids for which there is more than one codon?

(a) According to the genetic code in Table 24.1, which amino acid is selected by the mRNA codon GAA?

(b) What is the sequence in the original DNA that led to this codon being present in the mRNA?

(c) If a mutation occurs in the DNA in which a G is substituted for the nucleotide at the second position of this coding region in the DNA, which amino acid will now be selected?

Consider the amino acids alanine, leucine, serine, phenylalanine, lysine, and aspartic acid. Which have polar R groups, and which have nonpolar R groups?

Determine the molecular geometry around the phosphorus atom in the phosphorothioate group.

(a) Determine the enthalpy change for the production of one mole of glucose by the process of photosynthesis at $25^{\circ} {C} . \Delta_f H^{\circ}$ [glucose $({s})]=-1273.3 {~kJ} / {mol}$

$$6 {CO}_2({~g})+6 {H}_2 {O}(\ell) \rightarrow {C}_6 {H}_{12} {O}_6({~s})+6 {O}_2({~g})$$

(b) What is the enthalpy change involved in producing one molecule of glucose by this process?

(c) Chlorophyll molecules absorb light of various wavelengths. One wavelength absorbed is 650 nm. Determine the energy of a photon of light having this wavelength.

(d) Supposing that all of this energy goes toward providing the energy needed for the photosynthetic reaction, can the absorption of one photon at 650 nm lead to the production of one molecule of glucose, or should multiple photons be absorbed?

Care should be exercised in selecting good primers to use in PCR.

a. Why are primers often chosen that have a high number of cytosines and guanines in their sequences?

b. Why would a primer sequence of CCCCCCCCCCGGGGGGGGGG not be a good choice?

c. Why is a vast excess of primer used for the amount of DNA to be amplified?

What is the equilibrium constant for the conversion of $\alpha$-D-glucose to $\beta$-D-glucose in water at room temperature (assume that there is no glucose present in the open-chain structure)?

Draw two Lewis structures for the dipeptide alanineisoleucine that show the resonance structures of the amide linkage.

The body processes ethanol by first converting it to acetaldehyde in a reaction catalyzed by the enzyme alcohol dehydrogenase.

$${CH}_3 {CH}_2 {OH}+{NAD}^{+} \stackrel{\text { alcohol dehydrogenase }}{\longrightarrow} {CH}_3 {CHO}+{NADH}+{H}^{+}$$

Acetaldehyde can cause headaches and nausea in the body and is one of the causes of hangovers. Eventually, the acetaldehyde is oxidized to the acetate ion and then converted to carbon dioxide and water. In the reaction of ethanol with ${NAD}^{+}$, which species (ethanol or ${NAD}^{+}$) undergoes oxidation? Which species undergoes reduction?

Consider the following reaction:

$${NADH}+{H}^{+}+1 / 2 {O}_2 \rightarrow {NAD}^{+}+{H}_2 {O}$$

(a) Which species ( ${NADH}, {H}^{+}$, or ${O}_2$ ) undergoes oxidation?

(b) Which species undergoes reduction?

(c) Which species is the oxidizing agent?

(d) Which species is the reducing agent?

The chemical equation for the fermentation of glucose into ethanol is

$${C}_6 {H}_{12} {O}_6({~s}) \rightarrow 2 {C}_2 {H}_5 {OH}(\ell)+2 {CO}_2({~g})$$

Using $\Delta_f H^{\circ}$ values at $25^{\circ} {C}$, determine $\Delta_r H^{\circ}$ for this reaction.