Bonds, Alleles, and Polymers: Key Concepts

Bond types: Covalent vs Ionic

Covalent bonds: strong associations between atoms that result from sharing valence electrons.
Ionic bonds: weaker bonds; electrostatic attractions between ions.

In our cells, we have at least two copies of each gene; these copies are called alleles.
When genes are expressed, the information in DNA is used to produce a functional product (protein or RNA).
This aligns with the central dogma: DNA → RNA → Protein.
Allelic variation can influence expression and phenotype.

Cysteine amino acids contain a sulfhydryl group (-SH).
Disulfide bonds form between two cysteine residues (S-S), helping stabilize protein structure.
Curly hair is associated with abundant cysteine/disulfide cross-links; hair texture is influenced by these bonds.
Hair straightening with heat breaks disulfide bonds temporarily; heat provides energy to break the sulfur-sulfur bonds.
When two cysteines come into contact, they can form a disulfide cross-link; with enough heat, these bonds can be temporarily broken to allow rearrangement.
Disulfide bond formation (conceptual chemical representation):

2 R{-}SH \rightarrow R{-}S{-}S{-}R + 2 H^+ + 2 e^-.

The monomers of large biomolecules are similar in structure and size but have subtle differences.
Most large molecules are polymers, composed of repeating subunits called monomers.
A polymer consisting of n repeating units can be represented as (\text{monomer})_n.

Links between molecular bonds and observable traits (e.g., hair) and to core biology (gene expression and protein folding).
Polymer concept underpins biomolecules such as proteins, nucleic acids, and polysaccharides.
Practical implications: understanding bond breakage (via heat) informs cosmetics and protein chemistry.
Ethical/practical implications: gene alleles contribute to health and disease risk; knowledge of polymers informs technology and materials.