Structure and Function of Large Biological Molecules

Overview of Biological Macromolecules

Biological macromolecules are essential components of living cells, responsible for a wide range of structural and functional roles. The four major classes are carbohydrates, lipids, proteins, and nucleic acids. Three of these (carbohydrates, proteins, nucleic acids) are polymers, composed of repeating monomer subunits, while lipids are not true polymers.

• Carbohydrates: Provide energy and structural support.

• Proteins: Perform diverse functions including catalysis, transport, and signaling.

• Nucleic acids: Store and transmit genetic information.

• Lipids: Serve as energy storage, insulation, and form biological membranes.

Learning Objectives

• Explain how polymers are assembled and disassembled.

• Describe the structures and functions of simple and complex carbohydrates.

• Describe the structures and functions of three kinds of lipids.

• List the main functions of proteins and describe the structures of amino acids and proteins.

• Compare and contrast the structures of DNA and RNA and their component nucleotides.

• Explain the impact of DNA sequencing on biological inquiry and applications.

Carbohydrates

Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They exist as monosaccharides (simple sugars), disaccharides, and polysaccharides (complex carbohydrates).

• Monosaccharides: The simplest carbohydrates, such as glucose, serve as immediate energy sources.

• Disaccharides: Formed by joining two monosaccharides (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides; examples include starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (structural support in plant cell walls).

General Formula:

• Monosaccharides: (e.g., glucose: )

Functions:

• Fast release energy

• Structural support

Sources:

• Fruits, vegetables, grains, sugars

Lipids

Structure and Function

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids. Unlike other macromolecules, lipids are not polymers.

• Fats: Composed of glycerol and fatty acids; function as long-term energy storage and insulation.

• Phospholipids: Consist of a glycerol backbone, two fatty acids, and a phosphate group; major component of cell membranes.

• Steroids: Characterized by four fused carbon rings; include hormones like cholesterol.

General Structure:

• Phospholipid: Hydrophilic head (phosphate group) and hydrophobic tails (fatty acids)

Functions:

• Protection

• Insulation

• Slow release energy

• Cell membrane structure

Sources:

• Fats, oils

Nucleic Acids

Structure and Function

Nucleic acids are polymers made of nucleotide monomers. The two main types are DNA and RNA.

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

• DNA: Double-stranded helix; stores genetic information.

• RNA: Single-stranded; involved in protein synthesis and gene regulation.

General Structure:

• Nucleotide:

Functions:

• Encoding genetic information

• Gene expression

Sources:

• Whole foods (all living cells contain nucleic acids)

Proteins

Structure and Function

Proteins are polymers of amino acids, folded into specific three-dimensional shapes that determine their function. They are the most diverse macromolecules in terms of function.

• Amino Acid: Contains a central carbon (alpha carbon), amino group, carboxyl group, hydrogen atom, and variable R group (side chain).

• Polypeptide: Linear chain of amino acids linked by peptide bonds.

• Protein: One or more polypeptides folded into a functional shape.

Functions:

• Speeding up chemical reactions (enzymes)

• Structural support

• Transport

• Signaling

• Defense (antibodies)

Sources:

• Meats, beans, dairy

Protein Structure Levels

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (alpha helices, beta sheets) stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape due to interactions among R groups.

• Quaternary Structure: Association of multiple polypeptide chains.

Summary Table: Biological Macromolecules

Example: Alcohol Dehydrogenase

Alcohol dehydrogenase is a protein enzyme that catalyzes the breakdown of alcohol in the body. Its three-dimensional structure determines its function and efficiency, which can vary among individuals.

Additional info:

• DNA sequencing technologies have revolutionized biological research and medical diagnostics by enabling rapid analysis of genetic information.

• Proteins can be denatured by changes in temperature or pH, leading to loss of function.