General Biology Study Notes: Biological Importance of Carbon and Biological Macromolecules

Biological Importance of Carbon

Introduction to Carbon

Carbon is a fundamental element in biological systems due to its unique chemical properties. Its ability to form stable covalent bonds with many elements, including itself, allows for the complexity and diversity of organic molecules essential for life.

• Organic compounds are primarily composed of carbon (C) and hydrogen (H).

• The study of carbon compounds is central to the chemistry of life.

• Cells are composed of approximately 70-90% water; the remainder consists mainly of carbon-based compounds.

• Carbon can form four covalent bonds, enabling the formation of complex molecules.

Hydrocarbons

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. They serve as the backbone for more complex organic molecules.

• Example: Methane (CH4).

• Hydrocarbons are generally nonpolar and hydrophobic (do not mix with water).

• They can contain functional groups that replace one or more hydrogen atoms, altering their chemical properties.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They play a key role in molecular function and reactivity.

• Functional groups can replace hydrogen atoms in hydrocarbons.

• They affect the chemical properties and solubility of molecules.

• Examples include estradiol and testosterone, which differ in their functional groups.

Key Functional Groups

Functional Group	Structure	Properties	Example
Hydroxyl Group (-OH)	Oxygen bound to hydrogen	Polar, hydrophilic, neutral	Alcohols, e.g., ethanol
Carbonyl Group (C=O)	Carbon double-bonded to oxygen	Polar, hydrophilic	Aldehydes, ketones
Carboxyl Group (-COOH)	Carbon double-bonded to oxygen and single-bonded to OH	Polar, hydrophilic, acidic	Carboxylic acids, amino acids
Amino Group (-NH2)	N bound to 2 H	Polar, hydrophilic, basic	Amino acids
Sulfhydryl Group (-SH)	Sulfur bound to hydrogen	Polar, hydrophilic, weakly acidic	Proteins (cysteine)
Phosphate Group (-PO4H2)	P bound to 4 O (one double bond), 2 OH	Polar, acidic, hydrophilic	Phospholipids, nucleic acids
Methyl Group (-CH3)	C bound to 3 H	Nonpolar, hydrophobic	Methylated DNA

Biological Macromolecules

Macromolecules Overview

Biological macromolecules are large molecules composed of thousands of atoms. Most are polymers, built by linking monomers through chemical reactions. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

• Polymers: Large molecules made by joining monomers.

• Monomers: Identical or similar building blocks.

Polymerization Reactions

• Dehydration Reaction (Synthesis): Monomers are joined by removing a molecule of water, forming a new covalent bond. Enzyme: Dehydrogenases. $\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration}} \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: Polymers are broken down by adding water, splitting the covalent bond. Enzyme: Hydrolases. $\text{Polymer} + \text{H}_2\text{O} \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates

Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen, typically with a ratio of CH2O. They serve as fuel and structural components in cells.

• Monomers are sugars.

• Very hydrophilic due to multiple hydroxyl groups.

• Names often end with "-ose" (e.g., glucose).

Types of Carbohydrates

Type	Description	Example
Monosaccharides	Single sugars, classified by number of carbons and location of carbonyl group	Glucose (C6H12O6), fructose
Disaccharides	Formed by linking two monosaccharides via glycosidic linkage	Sucrose, lactose
Polysaccharides	Polymers of hundreds to thousands of monosaccharides; function in storage and structure	Starch, glycogen, cellulose, chitin

• Isomers: Monosaccharides can form isomers (e.g., α and β glucose).

• Glycosidic linkage: Covalent bond formed during dehydration synthesis between sugars.

Lipids

Lipids are hydrophobic molecules that do not form polymers. They include fats, phospholipids, and steroids, and serve as energy storage, structural components, and signaling molecules.

• Dissolve in nonpolar solvents (e.g., chloroform).

• Three main types: fats, phospholipids, steroids.

Types of Lipids

Type	Description	Structure
Fats	Energy storage; composed of glycerol and 1-3 fatty acids	Connected via ester linkage
Saturated Fatty Acids	No double bonds; saturated with hydrogen	Solid at room temperature
Unsaturated Fatty Acids	One or more double bonds; less dense packing	Liquid at room temperature
Phospholipids	Glycerol + 2 fatty acids + phosphate group; amphipathic	Forms cell membranes
Steroids	Four fused rings; differ in functional groups	Cholesterol, hormones

Proteins

Proteins are polymers made of amino acids. They perform a vast array of functions in cells, including catalysis, structure, signaling, and transport.

• Monomers: Amino acids (AAs).

• All amino acids share a central carbon, hydrogen atom, amino group, carboxyl group, and a variable side chain (R group).

Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary structure: Large-scale folding due to interactions among side chains.

• Quaternary structure: Assembly of multiple polypeptide chains.

Protein Functions

• Structure

• Signaling

• Enzymes

• Defense

• Transport

Nucleic Acids

Nucleic acids are polymers that store and transmit genetic information. The two main types are DNA and RNA.

• DNA: Deoxyribonucleic acid

• RNA: Ribonucleic acid

Will be discussed in more detail later in the semester.

Summary Table: Macromolecules

Macromolecule	Monomer	Polymer	Main Function
Carbohydrates	Sugars (monosaccharides)	Polysaccharides	Energy, structure
Lipids	Fatty acids, glycerol	Not true polymers	Energy storage, membranes, signaling
Proteins	Amino acids	Polypeptides	Catalysis, structure, transport, signaling
Nucleic Acids	Nucleotides	DNA, RNA	Genetic information

Practice Question

Compare and contrast macromolecules. Which of the following macromolecules involves monomers that are sugars?

• a. starch (Correct answer)

• b. protein

• c. phospholipids

• d. fatty acids

All macromolecules are polymers except lipids.

Additional info: These notes are expanded and clarified for academic completeness, including definitions, examples, and summary tables for exam preparation.