Biomolecules: Diversity and Composition

Study Notes

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.