Nucleic Acids and Carbohydrates: Structure, Function, and Key Concepts

Polymers

Formation and Breakdown of Polymers

Polymers are large molecules composed of repeating subunits called monomers. Their synthesis and degradation involve specific chemical reactions that are fundamental to biological processes.

• Dehydration Reaction: The process by which monomers are joined to form polymers, releasing water molecules. For example, when a polymer of 4 subunits is made, 3 molecules of water are released.

• Hydrolysis Reaction: The process by which polymers are broken down into monomers, consuming water molecules.

• Key Terms:

  • Dehydration: Leads to production of polymers.

  • Hydrolysis: Leads to breakdown of polymers.

• Example: Formation of proteins from amino acids or polysaccharides from monosaccharides.

Carbohydrates

Structure and Classification

Carbohydrates are organic molecules consisting of carbon, hydrogen, and oxygen. They serve as energy sources and structural components in cells.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

• Glycosidic Bond: The covalent bond connecting monosaccharides in carbohydrates.

• Atoms in Carbohydrates: Typically contain carbon, hydrogen, and oxygen. Nitrogen is not found in standard carbohydrates.

Types of Monosaccharides

• Aldose: Monosaccharide with an aldehyde group.

• Ketose: Monosaccharide with a ketone group (e.g., fructose).

• Hexose: Six-carbon sugar (e.g., glucose, fructose).

• Pentose: Five-carbon sugar (e.g., ribose).

• Example: The molecule shown is a ketose and a hexose.

Ring Formation and Anomeric Carbon

Monosaccharides can exist in linear or ring forms. The conversion involves specific carbons:

• Carbonyl Carbon (C1): Always involved in ring formation.

• Oxygen on C5: Participates in forming the ring structure.

• Anomeric Carbon: The carbon that becomes chiral upon ring formation (usually C1 in glucose).

• Alpha/Beta Anomers: Determined by the orientation of groups attached to the anomeric carbon.

Polysaccharides: Structure and Function

• Glycogen: Storage polysaccharide in animals; monomer is glucose.

• Amylopectin: Type of starch most similar to glycogen (branched structure).

• Cellulose vs. Starch:

  • Cellulose uses glucose β-anomers.

  • Starch uses glucose α-anomers.

Nucleic Acids

Structure and Monomers

Nucleic acids (DNA and RNA) are polymers of nucleotides, which consist of a pentose sugar, a phosphate group, and a nitrogenous base.

• Nucleotide: Monomer of nucleic acids.

• Pentose Sugar: Ribose in RNA, deoxyribose in DNA.

• Phosphate Group: Attached to the 5' carbon of the sugar.

• Key Carbons:

  • 5' carbon: Bound to phosphate group.

  • 2' carbon: Determines DNA (no OH) or RNA (has OH).

  • 1' carbon: Covalently binds to nitrogenous base (e.g., adenine).

  • 3' and 5' carbons: Involved in phosphodiester bond formation between nucleotides.

Nitrogenous Bases and Nucleotide Classification

• Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA).

• Purines: Adenine, Guanine.

• Uracil: Only found in RNA.

• Thymine: Only found in DNA.

Phosphodiester Bond

The covalent bond that connects nucleotides together in a nucleic acid strand is the phosphodiester bond.

• Formation: Between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of the next.

• Equation: $\text{Nucleotide}_1\ (3'\text{-OH}) + \text{Nucleotide}_2\ (5'\text{-phosphate}) \rightarrow \text{Nucleotide}_1\text{-phosphodiester-}\text{Nucleotide}_2$

DNA Structure and Complementarity

• Double Helix: DNA consists of two strands held together by hydrogen bonds between complementary bases.

• Base Pairing:

  • Adenine (A) pairs with Thymine (T).

  • Guanine (G) pairs with Cytosine (C).

• Reverse Complementary: The two strands run in opposite directions (5' to 3' and 3' to 5').

• Denaturation: DNA strands with more A-T pairs denature at lower temperatures than those with more G-C pairs (G-C pairs have three hydrogen bonds, A-T have two).

RNA Structure and Function

• Single-Stranded: RNA is typically single-stranded, allowing for a greater variety of structures and functions.

• Variety: RNA can form complex secondary structures and has more functions than DNA (e.g., mRNA, tRNA, rRNA).

DNA Sequence Complementarity

Given a DNA sequence, the complementary strand is determined by base pairing rules and the antiparallel orientation.

• Example: The complementary strand to 3' AGCCTT 5' is 5' TCGGAA 3'.

Summary Table: Key Bonds in Biological Macromolecules

Macromolecule	Monomer	Covalent Bond Type
Carbohydrates	Monosaccharide	Glycosidic bond
Nucleic Acids	Nucleotide	Phosphodiester bond
Proteins	Amino acid	Peptide bond

Additional info:

• Some explanations and definitions have been expanded for clarity and completeness.

• Images referenced in the original file have been described and their academic context inferred.