A) i. State the Chargaff's rule. ii. Provide the complementary sequence for 5'-CCTAGTAAG-3'. b) i. Give three (3) structural differences between DNA and RNA.

Here's the answer to question 6:

6. a) i. State the Chargaff's rule.
Chargaff's rule states that in a double-stranded DNA molecule, the total amount of adenine ($\text{A}$) is approximately equal to the total amount of thymine ($\text{T}$), and the total amount of guanine ($\text{G}$) is approximately equal to the total amount of cytosine ($\text{C}$). Consequently, the sum of purines ($\text{A} + \text{G}$) equals the sum of pyrimidines ($\text{T} + \text{C}$), and the ratio of $(\text{A} + \text{T})$ to $(\text{G} + \text{C})$ varies among different species.

6. a) ii. Provide the complementary sequence for 5'-CCTAGTAAG-3'.
To find the complementary sequence, we pair C with G, and A with T, and reverse the direction.
Given sequence: $5'-\text{CCTAGTAAG}-3'$
Complementary sequence: $3'-\text{GGATCATTC}-5'$ or written in the standard $5' \to 3'$ direction: $\boxed{5'-\text{CTTAATGG}-3'}$

6. b) i. Give three (3) structural differences between DNA and RNA.

• Sugar: DNA contains deoxyribose sugar, which lacks a hydroxyl group at the 2' carbon. RNA contains ribose sugar, which has a hydroxyl group at the 2' carbon.
• Nitrogenous Bases: DNA contains the bases adenine ($\text{A}$), guanine ($\text{G}$), cytosine ($\text{C}$), and thymine ($\text{T}$). RNA contains adenine ($\text{A}$), guanine ($\text{G}$), cytosine ($\text{C}$), and uracil ($\text{U}$) instead of thymine.
• Strandedness: DNA is typically a double-stranded molecule, forming a double helix. RNA is typically a single-stranded molecule, though it can fold into complex secondary and tertiary structures.

6. b) ii. Differentiate between nucleotides and nucleosides.

• Nucleotide: A nucleotide is the basic building block of nucleic acids (DNA and RNA). It consists of three components: a nitrogenous base (purine or pyrimidine), a five-carbon sugar (ribose or deoxyribose), and one or more phosphate groups.
• Nucleoside: A nucleoside consists of only two components: a nitrogenous base and a five-carbon sugar. It lacks the phosphate group(s) that are present in a nucleotide.

6. c) Outline the properties of DNA double helix.

• Antiparallel Strands: The two polynucleotide strands run in opposite directions; one strand runs $5' \to 3'$, and the complementary strand runs $3' \to 5'$.
• Right-Handed Helix: The two strands are coiled around a central axis in a right-handed helical fashion.
• Base Pairing: Specific hydrogen bonding occurs between complementary bases: adenine ($\text{A}$) always pairs with thymine ($\text{T}$) via two hydrogen bonds, and guanine ($\text{G}$) always pairs with cytosine ($\text{C}$) via three hydrogen bonds.
• Sugar-Phosphate Backbone: The backbone of each strand is composed of alternating sugar and phosphate groups, which are hydrophilic and located on the exterior of the helix.
• Hydrophobic Base Stacking: The nitrogenous bases are stacked in the interior of the helix, perpendicular to the helical axis, and are stabilized by hydrophobic interactions and van der Waals forces.
• Major and Minor Grooves: The helical structure creates two unequal grooves on the surface: a wider major groove and a narrower minor groove, which are important for protein binding.