Biomolecules: Amino Acids, Lipids, and Nucleic Acids

Proteinaceous Amino Acids: Structure and Diversity

• General Composition: Proteinaceous amino acids are organic compounds containing an amino group and an acidic carboxyl group. The specific identity of an amino acid is determined by the functional group designated as the R group.
• The R Group Variation: The R group in proteinaceous amino acids determines the specific type of amino acid:
  • Glycine: The R group is a hydrogen atom ($H$).
  • Alanine: The R group is a methyl group ($CH_3$).
  • Serine: The R group is a hydroxy methyl group ($CH_2OH$).
• Total Variety: There are twenty different amino acids commonly found in proteins, three of which are illustrated as primary examples in biochemical studies (Glycine, Alanine, and Serine).

Chemical and Physical Properties of Amino Acids

• Functional Groups: The chemical and physical properties of amino acids are primarily due to the amino ($NH_2$), carboxyl ($COOH$), and the R functional groups.
• Classification Based on Acidity and Basicity: Based on the relative number of amino and carboxyl groups, amino acids are categorized as:
  • Acidic: For example, glutamic acid.
  • Basic: For example, lysine.
  • Neutral: For example, valine.
• Aromatic Amino Acids: Some amino acids possess aromatic rings in their structure (e.g., Tyrosine, Phenylalanine, Tryptophan).
• Ionization and Zwitterionic Form: A unique property of amino acids is the ionizable nature of $-NH_2$ and $-COOH$ groups. Because of this, the structure of amino acids changes in solutions of different $pH$ levels.
  • Zwitterion (Form B): At a specific $pH$, the amino acid exists in a form where both the amino group is protonated and the carboxyl group is deprotonated, resulting in a net neutral charge despite carrying both positive and negative charges.
  • The transition is typically represented as:
    • (A): $H_3\text{N}^+ - CH(R) - COOH$
    • (B): $H_3\text{N}^+ - CH(R) - COO^-$ (Zwitterionic form)
    • (C): $H_2\text{N} - CH(R) - COO^-$

Lipids: Structure, Fatty Acids, and Glycerol

• General Nature: Lipids are generally water-insoluble biomolecules.
• Fatty Acids: A fatty acid consists of a carboxyl group attached to an R group.
  • R Group Composition: The R group can be a methyl ($-CH_3$), ethyl ($-C_2H_5$), or a higher number of carbon groups ranging from $1$ to $19$ carbons.
  • Palmitic Acid: Contains a total of $16$ carbons, including the carboxyl carbon.
  • Arachidonic Acid: Contains a total of $20$ carbon atoms, including the carboxyl carbon.
• Saturation Levels:
  • Saturated Fatty Acids: Lack double bonds between carbon atoms.
  • Unsaturated Fatty Acids: Contain one or more $C=C$ double bonds.
• Glycerol: A simple lipid identified as trihydroxy propane.

Complex Lipids, Fats, and Oils

• Esterification: Many lipids contain both glycerol and fatty acids, where the fatty acids are found esterified with glycerol.
  • Monoglycerides: One fatty acid attached to glycerol.
  • Diglycerides: Two fatty acids attached to glycerol.
  • Triglycerides: Three fatty acids attached to glycerol.
• Fats vs. Oils: These are classified based on their melting points:
  • Oils: Have lower melting points (e.g., gingelly oil) and remain in liquid state during winters.
  • Fats: Have higher melting points and may solidify at lower temperatures.
• Phospholipids: Some lipids contain phosphorus and a phosphorylated organic compound.
  • Function: They are vital components of the cell membrane.
  • Example: Lecithin.
• Neural Tissues: Certain tissues, particularly neural tissues, possess lipids with significantly more complex structures.

Sugars and Carbon Compounds

• Glucose: A common simple sugar with the chemical formula $C_6H_{12}O_6$.
• Heterocyclic Rings: Living organisms contain various carbon compounds that feature heterocyclic rings, notably nitrogen bases.

Nucleosides, Nucleotides, and Nucleic Acids

• Nitrogen Bases: These include Adenine (A), Guanine (G), Cytosine (C), Uracil (U), and Thymine (T).
• Nucleosides: Formed when a nitrogen base is attached to a sugar.
  • Examples: Adenosine, guanosine, thymidine, uridine, and cytidine.
• Nucleotides: Formed when a phosphate group is esterified to the sugar of a nucleoside.
  • Examples: Adenylic acid, thymidylic acid, guanylic acid, uridylic acid, and cytidylic acid.
• Nucleic Acids: High-molecular-weight compounds like DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) that consist solely of nucleotides.
  • Biological Function: DNA and RNA function as the genetic material for living organisms.