Biomolecules: Diversity and Composition

Biomolecules

• Biomolecules are organic molecules that contain mainly carbon, which behaves as it always does in organic compounds, forming 4 bonds, usually with a tetrahedral arrangement.
• The carbon skeleton can be linear, branched, cyclic, or aromatic.
• Other important elements in biomolecules are H, O, N, P, and S.

Characteristics of Biomolecules

• Biomolecules are larger than typical organic molecules, with molecular weights in the thousands, millions, or even billions.
• They have specific 3-dimensional shapes, which are maintained by numerous non-covalent bonds between atoms in the molecule.
• Biomolecules exhibit stereochemistry, meaning they can exist in two different isomeric forms that have different configurations in space.

Classes of Biomolecules

• Amino Acids and Proteins:
  • Amino acids are relatively small molecules with molecular weights around 100-200.
  • They are used to produce energy, synthesize other molecules, and make proteins.
  • Proteins are polymers of amino acids, with molecular weights ranging from several thousand to over a million.
  • Proteins function as enzymes, structural elements, transport molecules, antibodies, etc.
• Carbohydrates (Sugars and Starches):
  • The simplest carbohydrates are monosaccharides, with molecular weights of around 100-200.
  • They are a major source of energy for biological systems.
  • Polysaccharides are polymers of monosaccharides, with molecular weights often in the millions.
  • Polysaccharides serve as structural elements or stored metabolic energy.
• Lipids (Fats and Oils):
  • Lipids are relatively small, water-insoluble molecules with molecular weights of up to 750-1500.
  • They are used for energy production and storage, hormones, structural elements of cell membranes, and vitamins.
  • Lipids do not polymerize to form macromolecules, but they can aggregate non-covalently to form large structures.
• Nucleic Acids (DNA and RNA):
  • Nucleotides are relatively small molecules with molecular weights in the hundreds.
  • They function in transferring energy and helping enzymes to catalyze reactions.
  • Nucleic acids are large polymers of nucleotides, with molecular weights up into the billions.
  • They form structures like the double helix and function in storing, transmitting, and utilizing genetic information.

Other Biomolecules

• Small Organic Molecules:
  • In addition to the major classes of biomolecules, there are many relatively small organic molecules required by cells for specific functions.
  • These molecules do not fall neatly into one of the above major categories.
• Inorganic Ions:
  • Though not actually biomolecules, many inorganic ions are required by cells, often in trace amounts.
  • These ions perform a variety of functions, such as structural elements, regulation of osmotic pressure and transport, and components of proteins and enzymes.

Combinations of Biomolecules

• Sometimes, one biomolecule can contain components from two of the major classes, such as a lipoprotein (lipid plus protein) or a glycoprotein (carbohydrate plus protein).### Nucleic Acids Synthesis
• Both DNA and RNA are synthesized by adding new nucleotides to the 3' end of the chain.

Structure of RNA and DNA

• RNA is a single-stranded polymer of nucleotides.
• DNA is a double-stranded molecule, with two strands wrapping around each other as a helix.
• The two strands of DNA run in opposite directions.

Hydrogen Bonds in DNA

• The two strands of DNA are held together by hydrogen bonds between the nitrogenous bases in opposite strands.
• A (adenine) in one strand is opposite T (thymine) in the other.
• G (guanine) in one strand is opposite C (cytosine) in the other.

Other Uses of Nucleotides

• Nucleotides are used in important energy transfer reactions.
• ATP (Adenosine TriPhosphate) is an energy-rich molecule with high-energy bonds between phosphate groups.
• Energy is captured in the synthesis of phosphate bonds of ATP and released in the breakage of those bonds.
• NAD (Nicotinamide Adenine Dinucleotide) is composed of two nucleotides.
• NAD is used in many oxidation-reduction reactions to accept or donate high-energy electrons.