Biomolecules, Hydrocarbons, and Oxidation Concepts

Overview: hydrocarbons vs polar biomolecules

Hydrocarbons are organic compounds composed only of carbon (C) and hydrogen (H). They are nonpolar and covalent in nature, which makes them poorly soluble in water and relatively unreactive under many biological conditions. They burn well, providing energy, but themselves are not highly reactive. In contrast, the four major biomolecule families we focus on—carbohydrates, lipids, proteins, and nucleic acids—are polar and contain elements in addition to carbon and hydrogen. These molecules are reactive and are tied to their specific functions in biology. They generally have lower energy per bond than hydrocarbons and are built for reactivity, signaling, and information storage, not just simple energy release. An activity mentioned during the instruction is to build some of these molecules, highlighting hands-on practice with their structures and functional groups.

Major biomolecule families and their general notes

• Carbohydrates, Lipids, Proteins, and Nucleic Acids (to be discussed in more detail): these are polar biomolecules containing more than C and H, making them chemically reactive and functionally versatile.
• The emphasis in this unit is on understanding the structure–function relationship: the biomolecules are closely tied to their roles, enabling them to perform specific tasks in organisms.
• There is a practical emphasis on energy storage and metabolism: lipids (fats) are highlighted as long-term energy storage, with a side note that they also contribute to taste and palatability; carbohydrates and other biomolecules contribute to energy transduction, signaling, and information storage.
• Foundational idea: moving from simple hydrocarbons toward more complex, functional biomolecules involves introducing polarity, functional groups, and reactivity, enabling biological activity beyond mere combustion.

Carbohydrates

• Base unit: monosaccharide. Monosaccharides are the building blocks of carbohydrates.
• Carbon skeleton size: there are common 5-carbon and 6-carbon sugars; pentoses (5C) and hexoses (6C) are typical examples.
• Polarity and reactivity: carbohydrates are polar and contain functional groups beyond carbon and hydrogen, making them reactive in biological contexts.

Lipids

• Base unit: fatty acid. Fatty acids are the core components of lipids, though the lipid class is broader than just fats.
• Common terminology: lipids are often referred to as fats, but that is a subset of lipids; lipids include other types such as phospholipids and steroid derivatives.
• Function: primary role is long-term energy storage, providing a dense energy reservoir for organisms.
• Additional note: lipids are also described as having a palatable aspect in some contexts, which can influence dietary intake and metabolism.

Proteins

• Proteins are one of the four major biomolecule groups and, like carbohydrates and lipids, are polar and contain elements beyond carbon and hydrogen.
• They are highly reactive and versatile, enabling catalysis (enzymes), structure, signaling, transport, and other cellular functions.

Nucleic Acids

• Nucleic acids (DNA and RNA) are the fourth major biomolecule group to be discussed in this sequence, with essential roles in information storage, transmission, and expression.

Oxidation concepts and functional group interconversions

• Oxidation by adding oxygen is described as raising the oxidation state of the molecule. A simplifying teaching cue used is that adding O often corresponds to oxidation, while removing hydrogen is another way to represent oxidation.
• When oxidation occurs by removing hydrogen to form a double bond, the molecule becomes more oxidized. A generalized idea: introducing a double bond (unsaturation) often requires removal of two hydrogens.
• Resulting functional groups from oxidation include aldehydes (terminal) and ketones (internal):
  • Terminal double-bond formation or oxidation can yield an aldehyde at the end of a carbon chain.
  • Internal double-bond formation yields a ketone in the middle of the chain.
  • Concept summary: dehydrogenation (removing hydrogens) can lead to unsaturation and the appearance of aldehyde or ketone functionalities depending on the position.
• Carboxylic acids and aldehydes: carboxylic acids are described as more oxidized than aldehydes in the oxidation hierarchy. This reflects a higher oxidation state due to the extra oxygen (in the form of the –COOH group).
• Hydrogen acceptors (bases) and pH: species that can accept hydrogen ions (H+) raise the pH of the solution. Examples given include water (H₂O) and ammonia (NH₃). These bases can accept protons to form conjugate acids, thereby increasing pH when they participate in equilibria.
• pH concept: pH is a measure of hydrogen ion concentration, defined as $ext{pH} = -<br />\nabla ext{log}_{10} [H^+] ag{1}$
  作为 a practical guide to understanding how bases affect acidity in biological contexts.
• Practical note on oxidation and hydrogen removal: a double bond formation involves the removal of two hydrogens, which is described as an oxidation step. In this teaching context, aldehyde formation is described as terminal, and ketone formation is described as internal.

Summary of key concepts and connections

• Hydrocarbons form the nonpolar, relatively unreactive, carbon-and-hydrogen world, largely used for energy production through combustion but not suitable for the nuanced chemistry of living systems.
• Biomolecules introduce polarity, diverse functional groups, and reactivity, enabling biological roles such as energy storage (lipids), information storage and transfer (nucleic acids), catalysis and structure (proteins), and energy transduction and signaling (carbohydrates).
• Monosaccharides as the basic carbohydrate units can be 5- or 6-carbon structures, which, through polymerization, form the larger carbohydrate polymers (not detailed here but foundational for understanding energy storage and structure).
• Lipids store energy in a highly reduced form (fatty acids are long hydrocarbon chains with carboxyl groups) and provide long-term energy storage, insulation, and other functional roles.
• Oxidation concepts tie into how biomolecules undergo structural changes: removing hydrogen to form double bonds leads to aldehydes and ketones; oxidation states progress from aldehydes to carboxylic acids.
• Bases like water and ammonia illustrate how hydrogen acceptance modulates proton concentration, thereby influencing pH and biochemical environments.
• The interplay between redox chemistry (oxidation/reduction), functional group formation (aldehydes, ketones, carboxylic acids), and biomolecule function underpins much of metabolism and biosynthesis in living systems.

Illustrative reactions and relationships (LaTeX-formatted)

• General oxidation of a primary alcohol to an aldehyde (simplified representation):
  $$ R-CH2OH ightarrow R-CHO + H2O \