Biological Molecules

Organic Molecules and Carbon

Organic molecules are the foundation of biological chemistry, consisting primarily of carbon atoms. The versatility of carbon allows for the formation of a wide variety of molecular structures essential for life.

• Organic molecules: Molecules containing carbon, except for simple carbon compounds like graphite, diamonds, carbon dioxide, and carbon monoxide

• Carbon atoms: Have a valence of 4, allowing them to form up to four covalent bonds, which makes them highly versatile building blocks.

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms attached to the carbon skeleton of organic molecules, conferring distinct chemical properties and reactivity.

• Functional groups: Small characteristic groups of atoms that determine the chemical properties and reactivity of organic molecules.

• Common functional groups include:

Synthesizing Organic Molecules: A Modular Approach

Monomers and Polymers

Biological molecules are often assembled from smaller units called monomers, which join to form polymers through specific chemical reactions.

• Monomers: Simple building blocks (e.g., amino acids, monosaccharides).

• Polymers: Chains of monomers linked together (e.g., proteins, polysaccharides).

Polymerization Reactions

• Dehydration synthesis (condensation reaction): Covalent linkage of monomers accompanied by the removal of a water molecule.

• Hydrolysis: Breaking of covalent bonds between monomers by the addition of water.

Principle Types of Biological Molecules

Classes of Macromolecules

There are four major classes of biological macromolecules, each with distinct monomers, polymers, and functions.

Carbohydrates

Monosaccharides

Monosaccharides are simple sugars that serve as major sources of nutrients and energy for cells.

• General formula:

• Glucose is the most common monosaccharide.

• Produced by photosynthetic organisms from CO2, H2O, and light.

Disaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage (dehydration synthesis).

Polysaccharides

Polysaccharides are large polymers of monosaccharides, serving storage and structural functions.

• Starch: Storage polysaccharide in plants.

• Glycogen: Storage polysaccharide in animals (muscle and liver).

• Cellulose: Structural polysaccharide in plant cell walls; unbranched polymer of glucose.

• Chitin: Structural polysaccharide in exoskeletons of arthropods and cell walls of fungi; polymer of an amino sugar.

Proteins

Structure and Function

Proteins are polymers of amino acids, essential for most cellular functions. They are linked by peptide bonds and have diverse roles.

• Functions: Structural support, catalysis (enzymes), storage, transport, movement, hormones, immune defense, and more.

• Proteins can range from a few to thousands of amino acids in length.

Amino Acids

Amino acids are the monomeric building blocks of proteins, each with a central carbon attached to four groups:

1. Hydrogen atom

2. Carboxyl group (-COOH)

3. Amino group (-NH2)

4. R group (side chain, variable)

• Classified as hydrophobic (nonpolar) or hydrophilic (polar).

Peptide Bonds

Peptide bonds are covalent bonds formed by dehydration synthesis between the carboxyl group of one amino acid and the amino group of another.

Levels of Protein Structure

1. Primary structure: Linear sequence of amino acids, determined by genes.

2. Secondary structure: Regular coiling and folding stabilized by hydrogen bonds; includes alpha helices and beta pleated sheets.

3. Tertiary structure: Irregular folding due to interactions among side chains (R groups), including covalent linkages (disulfide bridges), hydrogen bonds, ionic bonds, and hydrophobic interactions.

4. Quaternary structure: Association of multiple polypeptide chains into a single protein complex.

Protein Conformation and Denaturation

Protein conformation is determined by its primary structure and the resulting higher-order structures. Denaturation is the loss of native structure due to environmental changes, disrupting weak interactions and potentially leading to loss of function.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) are polymers of nucleotides, responsible for information storage and transmission in cells.

• Nucleotide structure: Composed of a five-carbon sugar, a phosphate group, and a nitrogenous base.

• DNA: Contains deoxyribose sugar; stores genetic information.

• RNA: Contains ribose sugar; involved in protein synthesis and gene regulation.

• Phosphate groups link nucleotides, forming the backbone of nucleic acids.

• ATP (adenosine triphosphate) is a nucleotide important for cellular energy transfer.

Lipids

Structure and Types

Lipids are hydrophobic molecules composed mainly of carbon and hydrogen. They include fats, phospholipids, steroids, and waxes.

• Fats and oils: Constructed from fatty acids and glycerol; serve as energy storage.

• Fatty acids: Hydrocarbon chains with a carboxyl group; can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Triglycerides: Composed of three fatty acids bonded to glycerol.

• Phospholipids: Major component of cell membranes; contain two fatty acids, a phosphate group, and glycerol.

• Steroids: Lipids with a characteristic four-ring structure; include cholesterol and hormones.

• Waxes: Protective coatings (e.g., plant cuticle).

Properties and Functions

• Fats store energy more compactly than carbohydrates.

• Phospholipids form bilayers in cell membranes due to their amphipathic nature (hydrophilic head, hydrophobic tails).

• Steroids act as hormones and structural components.

Additional info: The notes provide foundational knowledge for understanding the chemistry and biology of macromolecules, their structure, and their function in living organisms.