Macromolecules and Functional Groups in General Biology

Carbon and Its Importance in Biology

Carbon: Properties and Bonding

Carbon is a fundamental element in biological molecules due to its versatile bonding properties. Its ability to form four covalent bonds allows for the creation of complex and diverse organic molecules.

• Valence Electrons: Carbon has four valence electrons, enabling it to form four covalent bonds with various atoms, especially hydrogen and oxygen.

• Large Molecules: Carbon's bonding versatility allows for the formation of large, complex molecules essential for life.

Carbon Skeletons

Carbon atoms can bond to other carbon atoms, forming the backbone of most organic molecules.

• Carbon skeletons vary in length and shape.

• They can be straight, branched, or arranged in rings.

• Branching, double bonding, and presence of rings contribute to molecular diversity.

Isomers

Isomers are molecules with the same chemical formula but different structures, resulting in different properties.

• Structural Isomers: Atoms are bonded differently.

• Geometric (cis-trans) Isomers: Differ in spatial arrangement around a double bond.

• Enantiomers: Mirror images of each other, often with different biological activities.

Macromolecules and Functional Groups

Functional Groups

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

• Hydroxyl Group (-OH): Polar, forms hydrogen bonds with water. Example: Alcohols.

• Carbonyl Group (C=O): Polar, found in ketones (within carbon skeleton) and aldehydes (at end of skeleton).

• Carboxyl Group (-COOH): Acts as an acid, can donate a hydrogen ion. Found in amino acids and fatty acids.

• Amino Group (-NH2): Acts as a base, can pick up a hydrogen ion. Found in amino acids.

• Sulfhydryl Group (-SH): Forms disulfide bonds, important in protein structure. Example: Cysteine.

• Phosphate Group (-PO4): Contributes negative charge, important in energy transfer (e.g., ATP).

• Methyl Group (-CH3): Nonpolar, affects gene expression.

Macromolecules

Macromolecules are large molecules composed of repeating subunits called monomers. The four major classes are carbohydrates, proteins, lipids, and nucleic acids.

Monomers	Polymers	Covalent Bond Type
Amino Acids	Proteins (Polypeptides)	Peptide linkage
Monosaccharides	Carbohydrates (Polysaccharides)	Glycosidic linkage
Nucleotides	Nucleic Acids (DNA & RNA)	Phosphodiester linkage

Monomers and Polymers

• Monomers are linked by dehydration synthesis (removal of water).

• Polymers are broken down by hydrolysis (addition of water).

Carbohydrates (C, H, O)

Monosaccharides

Monosaccharides are the simplest carbohydrates, serving as monomers for more complex carbohydrates and as energy sources.

• General formula: (CH2O)n

• Examples: Glucose, fructose, galactose

• Classified by number of carbons: trioses (3), pentoses (5), hexoses (6)

• Can exist as straight chains or rings (alpha and beta forms)

Disaccharides

Disaccharides are formed by covalent (glycosidic) bonds between two monosaccharides via dehydration synthesis.

• Examples: Maltose (glucose + glucose), Sucrose (glucose + fructose), Lactose (glucose + galactose)

Oligosaccharides

Oligosaccharides consist of 3–20 monosaccharides and play roles in cell recognition and membrane binding.

Polysaccharides

Polysaccharides are large polymers of monosaccharides joined by glycosidic linkages.

• Cellulose: Structural component of plant cell walls

• Starch: Energy storage in plants (amylose and amylopectin)

• Glycogen: Energy storage in animals (highly branched)

• Chitin: Structural component in fungi and arthropod exoskeletons

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store, transmit, and use genetic information. They are polymers of nucleotides.

• Nucleotide: Composed of a pentose sugar, phosphate group, and nitrogenous base

• Linked by phosphodiester bonds

DNA Structure

• Double helix: Two strands held together by hydrogen bonds between nitrogenous bases

• Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

• Base pairing: A-T, C-G

RNA Structure

• Single-stranded

• Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

• Types: mRNA, tRNA, rRNA

Lipids

Fatty Acids

Fatty acids are nonpolar hydrocarbon chains with a polar carboxyl group. They are major components of lipids.

• Saturated fatty acids: No double bonds, straight chains

• Unsaturated fatty acids: One or more double bonds, bent chains

Types of Lipids

• Fats and Oils: Glycerol + 3 fatty acids (triglycerides), energy storage

• Phospholipids: Glycerol + 2 fatty acids + phosphate group, form cell membranes

• Steroids: Four fused carbon rings, include cholesterol and hormones

• Vitamins: Fat-soluble (A, D, E, K), must be acquired from diet

• Waxes: Fatty acid + alcohol, waterproofing

Proteins

Structure and Function

Proteins are polymers of amino acids and are the most abundant macromolecules in cells. They perform a wide range of functions.

• Enzymatic proteins: Catalyze chemical reactions

• Defensive proteins: Protect against disease

• Transport proteins: Move substances across membranes

• Signal proteins: Coordinate cellular activities

• Contractile proteins: Movement (e.g., actin, myosin)

• Structural proteins: Support (e.g., collagen, keratin)

Protein Structure

Proteins have four levels of structure:

1. Primary Structure: Linear sequence of amino acids

2. Secondary Structure: Local folding (alpha helix, beta sheet) stabilized by hydrogen bonds

3. Tertiary Structure: 3D shape determined by interactions among R-groups (side chains)

4. Quaternary Structure: Association of multiple polypeptide chains

• R-group interactions include disulfide bridges, hydrophobic interactions, and ionic interactions.

Example: Hemoglobin

Hemoglobin is a quaternary protein composed of four polypeptide subunits, each with a heme group that binds oxygen.

Additional info: The notes above are expanded with standard academic context to ensure completeness and clarity for exam preparation.