Macromolecules and Carbon Compounds in Biology: Structure, Function, and Diversity

Learning Goals and Outcomes

Overview of Biological Macromolecules

Biological macromolecules are large, complex molecules essential for life. They include carbohydrates, lipids, proteins, and nucleic acids. Understanding their structure and function is fundamental to studying biology.

• Polymers are large molecules made by joining many smaller units called monomers.

• Key learning goals include recognizing the structure, composition, and function of each macromolecule type, and understanding how they are synthesized and broken down.

• Students should be able to identify examples, compare types, and predict how molecular composition affects function.

Carbon Compounds and Life

The Importance of Carbon

Carbon is the backbone of biological molecules due to its ability to form four covalent bonds, allowing for a diversity of stable structures.

• Carbon skeletons can vary in length, branching, double bond position, and ring structure, leading to molecular diversity.

• Common variations include straight chains (e.g., ethane, propane), branched chains (e.g., isobutane), and rings (e.g., cyclohexane, benzene).

• Carbon bonds play a crucial role in energy transformation (metabolism) by storing and releasing energy during chemical reactions.

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

Chemical Group	Compound Name	Examples
Hydroxyl (–OH)	Alcohol	Ethanol
Carbonyl (C=O)	Ketone, Aldehyde	Acetone, Propanal
Carboxyl (–COOH)	Carboxylic acid	Acetic acid
Amino (–NH2)	Amine	Glycine
Sulfhydryl (–SH)	Thiol	Cysteine
Phosphate (–OPO32–)	Organic phosphate	Glycerol phosphate
Methyl (–CH3)	Methylated compound	5-Methyl cytosine

Function: The presence and arrangement of functional groups affect molecular reactivity and biological function.

Hydrocarbons

Structure and Properties

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. They are nonpolar and hydrophobic, making them important in the structure of lipids.

• Hydrocarbons can undergo reactions that release large amounts of energy, such as in the metabolism of fats.

• Examples include methane (CH4), ethane (C2H6), and benzene (C6H6).

Macromolecule Synthesis and Breakdown

Polymerization and Depolymerization

Macromolecules are formed and broken down by specific chemical reactions:

• Dehydration reaction (condensation): Joins monomers by removing a water molecule, forming a covalent bond.

• Hydrolysis: Breaks covalent bonds between monomers by adding a water molecule.

Example: The synthesis of a polysaccharide from monosaccharides involves repeated dehydration reactions.

Carbohydrates

Structure and Function

Carbohydrates are sugars and their polymers. They serve as energy sources and structural materials.

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., sucrose = glucose + fructose; lactose = glucose + galactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Example: Lactose is a disaccharide composed of glucose and galactose. In Galactosemia, the enzyme to convert galactose to glucose is non-functional, leading to toxic accumulation.

Lipids

Types and Biological Roles

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They are not true polymers but are essential for energy storage, membrane structure, and signaling.

Type	Components	Examples	Function
Fats (triglycerides)	Glycerol + 3 fatty acids	Butter, oils	Energy storage
Phospholipids	Glycerol + 2 fatty acids + phosphate group	Cell membrane bilayer	Membrane structure
Steroids	Four fused carbon rings	Cholesterol, hormones	Membrane component, signaling

• Saturated fats: No double bonds in fatty acid tails; solid at room temperature.

• Unsaturated fats: One or more double bonds; liquid at room temperature due to kinks in tails.

• Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails, forming bilayers in water.

Proteins

Structure and Levels of Organization

Proteins are polymers of amino acids, folded into specific three-dimensional shapes that determine their function.

• Primary structure: Linear sequence of amino acids.

• Secondary structure: Local folding into α-helices and β-pleated sheets, stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape due to interactions among R groups (side chains), including hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

• Quaternary structure: Association of multiple polypeptide chains.

Example: Hemoglobin has quaternary structure, consisting of four polypeptide subunits.

Enzymes are proteins that catalyze biochemical reactions, such as the breakdown of galactose in metabolism.

Nucleic Acids

DNA and RNA Structure and Function

Nucleic acids store and transmit genetic information. They are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

Type	Sugar	Nitrogenous Bases	Strands	Function
DNA	Deoxyribose	A, T, C, G	Double-stranded	Stores hereditary information
RNA	Ribose	A, U, C, G	Single-stranded	Gene expression, protein synthesis

• Base pairing: In DNA, A pairs with T, and C pairs with G via hydrogen bonds.

• Polarity: Nucleic acid strands have directionality (5' to 3').

Example: mRNA carries genetic instructions from DNA in the nucleus to ribosomes in the cytoplasm for protein synthesis.

Additional info:

• Understanding the structure and function of macromolecules is foundational for topics such as metabolism, genetics, and cell biology.

• Model systems and simulations are used to predict and evaluate biological processes.