Guided Study for BSC 2010 Exam 4: Carry-Over Concepts

Q1. How much does one molecule or one mole of adenine weigh (in grams or Daltons)?

Background

Topic: Units of Molecular Weight

This question tests your understanding of how to determine the mass of a molecule or a mole of molecules, and the difference between units like grams and Daltons (atomic mass units).

Key Terms and Formulas:

• Dalton (Da): A unit of mass equal to 1/12 the mass of a carbon-12 atom (also called atomic mass unit, amu).

• Mole: Avogadro's number ($6.022 \times 10^{23}$) of particles (atoms, molecules, etc.).

• Molecular Weight: The sum of the atomic masses of all atoms in a molecule (in Daltons or grams per mole).

• Key Formula:

  $\text{Molecular weight (g/mol)} = \sum (\text{number of each atom} \times \text{atomic mass of atom})$

• 1 Dalton = $1.66054 \times 10^{-24}$ grams

Step-by-Step Guidance

1. Determine the molecular formula of adenine (C5H5N5).

2. Find the atomic masses for carbon (C), hydrogen (H), and nitrogen (N):

   • C: ~12 Da

   • H: ~1 Da

   • N: ~14 Da

3. Calculate the total molecular weight in Daltons by multiplying the number of each atom by its atomic mass and summing:

   $\text{Molecular weight} = (5 \times 12) + (5 \times 1) + (5 \times 14)$

4. To find the weight of one mole of adenine, use the molecular weight in grams per mole (g/mol). To find the weight of one molecule, convert Daltons to grams using the conversion factor above.

Try solving on your own before revealing the answer!

Q2. How many atoms and covalent bonds are found in one molecule of adenine?

Background

Topic: Covalent Bonding and Molecular Structure

This question tests your ability to analyze a molecular structure and count the number of atoms and covalent bonds present.

Key Terms and Formulas:

• Atom: The basic unit of a chemical element.

• Covalent Bond: A chemical bond formed when two atoms share electrons.

• Each line in a structural formula represents a covalent bond; double bonds count as two covalent bonds.

Step-by-Step Guidance

1. Write out or visualize the structure of adenine (C5H5N5).

2. Count the total number of atoms by adding the number of C, H, and N atoms.

3. Identify all single and double bonds in the structure. Remember, each double bond counts as two covalent bonds.

4. Add up all the covalent bonds (single and double) present in the molecule.

Try solving on your own before revealing the answer!

Q3. How many polar covalent bonds and nonpolar covalent bonds does adenine contain? (Count double bonds as TWO covalent bonds.)

Background

Topic: Covalent Bond Polarity

This question tests your understanding of the difference between polar and nonpolar covalent bonds, and how to identify them in a molecule.

Key Terms and Formulas:

• Polar Covalent Bond: A bond where electrons are shared unequally due to a difference in electronegativity between atoms (e.g., C-N, N-H).

• Nonpolar Covalent Bond: A bond where electrons are shared equally (e.g., C-H, C-C, N-N).

• Double bonds count as two covalent bonds for this question.

Step-by-Step Guidance

1. Draw or refer to the structure of adenine.

2. Identify all the covalent bonds in the molecule, noting which atoms are involved in each bond.

3. Classify each bond as polar or nonpolar based on the difference in electronegativity between the bonded atoms.

4. Count the total number of polar covalent bonds and nonpolar covalent bonds, remembering to count double bonds as two.

Try solving on your own before revealing the answer!

Q4. How many atoms in adenine have undergone sp3 hybridization?

Background

Topic: Covalent Bonding and Hybridization

This question tests your understanding of orbital hybridization, specifically sp3 hybridization, and how to identify which atoms in a molecule have this geometry.

Key Terms and Formulas:

• sp3 Hybridization: Occurs when an atom forms four sigma bonds (single bonds), resulting in a tetrahedral geometry.

• Atoms with sp3 hybridization typically have four groups (atoms or lone pairs) attached.

Step-by-Step Guidance

1. Draw the structure of adenine and identify all the atoms (C, N, H).

2. For each atom, count the number of sigma bonds and lone pairs attached to it.

3. Determine which atoms have four groups (bonds or lone pairs) around them, indicating sp3 hybridization.

4. Count the total number of atoms in adenine that are sp3 hybridized.

Try solving on your own before revealing the answer!

Q5. Which functional group found in nucleotides, DNA, or RNA is acidic at cellular pH?

Background

Topic: Acidic and Basic Functional Groups in Nucleic Acids

This question tests your knowledge of the functional groups present in nucleotides, DNA, and RNA, and which of these groups can donate a proton (H+) at physiological pH (~7.4).

Key Terms and Formulas:

• Functional Group: A specific group of atoms within a molecule that is responsible for characteristic chemical reactions.

• Acidic Group: A group that can donate a proton (H+) at physiological pH.

• Common functional groups in nucleotides: phosphate, hydroxyl, amino, carbonyl.

Step-by-Step Guidance

1. List the functional groups present in nucleotides, DNA, and RNA (e.g., phosphate, hydroxyl, amino, carbonyl).

2. Recall which of these groups can act as an acid at cellular pH (i.e., can lose a proton).

3. Identify the group that is deprotonated and negatively charged at physiological pH.

Try solving on your own before revealing the answer!