Amino Acids: Structure and Properties

Amino Acids

• The R group in amino acids can be a hydrogen (glycine), a methyl group (alanine), hydroxy methyl (serine), etc.
• Chemical and physical properties of amino acids are determined by the amino, carboxyl, and R functional groups.
• Amino acids can be classified into acidic (e.g., glutamic acid), basic (lysine), and neutral (valine) based on the number of amino and carboxyl groups.
• Aromatic amino acids include tyrosine, phenylalanine, and tryptophan.
• Amino acids have ionizable –NH2 and –COOH groups, which change structure in solutions of different pH.

Lipids

• Lipids are generally water insoluble.
• Fatty acids have a carboxyl group attached to an R group, which can be a methyl, ethyl, or higher number of –CH2 groups.
• Fatty acids can be saturated (without double bond) or unsaturated (with one or more C=C double bonds).
• Examples of fatty acids include palmitic acid (16 carbons) and arachidonic acid (20 carbons).
• Glycerol is a trihydroxy propane and a simple lipid.
• Lipids can be classified into monoglycerides, diglycerides, and triglycerides based on the number of fatty acids esterified with glycerol.
• Fats and oils are classified based on melting point, with oils having a lower melting point (e.g., gingelly oil).

Phospholipids

• Phospholipids have phosphorus and a phosphorylated organic compound.
• They are found in cell membranes and are examples of lipids with more complex structures.
• Lecithin is a type of phospholipid.

Nucleic Acids

• Nitrogen bases include adenine, guanine, cytosine, uracil, and thymine.
• Nucleosides are formed when nitrogen bases are attached to a sugar.
• Nucleotides are formed when a phosphate group is also esterified to the sugar.
• Examples of nucleosides include adenosine, guanosine, thymidine, uridine, and cytidine.
• Examples of nucleotides include adenylic acid, thymidylic acid, guanylic acid, uridylic acid, and cytidylic acid.
• Nucleic acids like DNA and RNA consist of nucleotides and function as genetic material.

Carbonic Anhydrase

• CO2 reacts with H2O to form H2CO3, a slow reaction that produces about 200 molecules of H2CO3 per hour.
• With the presence of carbonic anhydrase, the reaction rate increases dramatically, forming about 600,000 molecules of H2CO3 per second.
• The enzyme accelerates the reaction rate by about 10 million times.

Metabolic Pathways

• A multistep chemical reaction, where each step is catalysed by the same enzyme complex or different enzymes, is called a metabolic pathway.
• The reaction of glucose becoming pyruvic acid is a metabolic pathway that involves ten different enzyme-catalysed reactions.

Stability and Energy

• Stability is related to the energy status of a molecule or structure.
• The energy level difference between the substrate (S) and product (P) determines if the reaction is exothermic or endothermic.
• Activation energy is the difference in average energy content of the substrate from the transition state.
• Enzymes bring down the energy barrier, making the transition of S to P more easy.

Enzyme Action

• Each enzyme has a substrate binding site, forming a highly reactive enzyme-substrate complex (ES).
• The ES complex is short-lived and dissociates into the product(s) and the unchanged enzyme.
• The formation of the ES complex is essential for catalysis.

Biomolecules

• Biomolecules are thousands of organic compounds, including amino acids, sugars, etc.
• Primary metabolites are found in animal tissues and include categories of compounds shown in Figure 9.1.
• Secondary metabolites are found in plant, fungal, and microbial cells, and include compounds such as alkaloids, flavonoids, rubber, essential oils, antibiotics, and colored pigments.

Secondary Metabolites

• Examples of secondary metabolites include pigments, alkaloids, terpenoids, essential oils, toxins, lectins, drugs, and polymeric substances.
• Secondary metabolites may have ecological importance or be useful to human welfare.
• The role or functions of all secondary metabolites in host organisms are not yet fully understood.

Learn about the structure and properties of amino acids, including their functional groups and classification into acidic, basic, and neutral categories.