The Chemical Level of Organization

Carbon-Based Molecular Diversity

Carbon is the foundational element for organic compounds, which are the diverse molecules found in cells. By sharing electrons, carbon can form four covalent bonds, allowing it to branch in multiple directions and create complex molecular structures.

• Organic compounds: Molecules containing carbon bonded to other elements.

• Carbon's bonding ability: Enables the formation of large, diverse molecules essential for life.

Chemical Groups and Functional Groups

The properties of organic compounds are determined by their size, shape, and the functional groups attached to them. Functional groups are specific clusters of atoms that influence the chemical behavior of molecules.

• Functional groups: Affect biological molecule function and are often hydrophilic, making them soluble in water.

• Examples of functional groups: Hydroxyl, carbonyl, carboxyl, amino, phosphate, and methyl groups.

Functional Groups and Biological Function

Functional groups can cause similar compounds to have different biological effects. For example, sex hormones differ only in their functional groups, resulting in distinct physiological features in males and females.

• Estradiol vs. Testosterone: Small changes in functional groups lead to major differences in biological activity.

Macromolecules and Polymers

Classes of Biological Molecules

Cells synthesize a vast array of large molecules from a small set of monomers. The four main classes of biological macromolecules are carbohydrates, proteins, lipids, and nucleic acids.

• Macromolecules: Large molecules essential for cell structure and function.

• Polymers: Chains of monomers linked together.

• Monomers: Universal building blocks (e.g., amino acids for proteins, nucleotides for DNA).

Polymer Formation and Breakdown

Monomers are joined to form polymers through dehydration reactions, which remove water. Polymers are broken down by hydrolysis, which adds water. Enzymes catalyze these reactions in cells.

• Dehydration reaction: Builds polymers by removing water.

• Hydrolysis: Breaks polymers by adding water.

Carbohydrates

Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as the main fuel for cellular work. Their carbon skeletons vary in length, typically from three to seven carbons.

• Examples: Glucose (an aldose), fructose (a ketose).

• Function: Energy source and raw material for other organic molecules.

Disaccharides

Disaccharides are formed when two monosaccharides join via a dehydration reaction. Sucrose (table sugar) is a common example.

• Formation: Dehydration reaction between glucose and fructose.

Polysaccharides

Polysaccharides are long chains of monosaccharides and serve as storage or structural molecules. They are hydrophilic and absorb water.

• Starch: Storage polysaccharide in plants.

• Glycogen: Storage polysaccharide in animals.

• Cellulose: Structural component of plant cell walls.

• Chitin: Structural component in exoskeletons of insects and crustaceans.

Lipids

Fats and Energy Storage

Lipids are hydrophobic molecules important for energy storage. Fats are made from glycerol and fatty acids, and contain twice as much energy as polysaccharides.

• Structure: One glycerol linked to three fatty acids (triglyceride).

• Formation: Dehydration reaction links fatty acids to glycerol.

Saturated vs. Unsaturated Fats

Fatty acids may contain double bonds, causing kinks in the carbon chain. Unsaturated fats have fewer hydrogen atoms, while saturated fats have the maximum number.

• Saturated fats: Promote higher cholesterol levels and risk of atherosclerosis.

• Unsaturated fats: Healthier due to fewer hydrogen atoms.

Phospholipids and Steroids

Phospholipids are major components of cell membranes, forming a bilayer with hydrophilic heads and hydrophobic tails. Steroids, such as cholesterol, have fused ring structures and are precursors to sex hormones.

• Phospholipids: Essential for membrane structure.

• Steroids: Cholesterol and sex hormones.

Proteins

Structure and Function

Proteins are polymers of 20 amino acids and have unique structures directly related to their functions. They serve as enzymes, structural components, contractile elements, defensive molecules, signal transmitters, receptors, and transporters.

• Enzymes: Catalyze metabolic reactions.

• Structural proteins: Provide support.

• Contractile proteins: Enable movement.

• Defensive proteins: Antibodies.

• Signal proteins: Hormones.

• Receptor proteins: Receive signals.

• Transport proteins: Move substances.

Amino Acids and Peptide Bonds

Amino acids have an amino group, a carboxyl group, a hydrogen atom, and an R group attached to a central carbon. They are classified as hydrophobic or hydrophilic. Peptide bonds link amino acids via dehydration reactions.

• Peptide bond: Covalent linkage between amino acids.

Protein Structure Levels

Protein function depends on its shape, which is determined by four structural levels:

• Primary structure: Unique amino acid sequence.

• Secondary structure: Coiling (alpha helix) or folding (pleated sheet) due to hydrogen bonding.

• Tertiary structure: Three-dimensional shape from R group interactions and disulfide bridges.

• Quaternary structure: Association of multiple polypeptide chains (e.g., collagen).

Nucleic Acids

Structure and Function

DNA and RNA are polymers of nucleotides, each consisting of a 5-carbon sugar, a phosphate group, and a nitrogenous base. DNA contains adenine, thymine, cytosine, and guanine; RNA contains adenine, cytosine, guanine, and uracil.

• Polynucleotide formation: Phosphate of one nucleotide bonds to the sugar of the next, creating a sugar-phosphate backbone.

DNA Double Helix and Genes

DNA consists of two polynucleotide strands forming a double helix, with base pairs held together by hydrogen bonds. Genes are sequences of nucleotides that instruct the formation of polypeptides.

• Base pairing: A-T and C-G in DNA; A-U and C-G in RNA.

• Mutations: Changes in nucleotide sequence can alter gene function.

Mutations and Carcinogenesis

Mutations can be spontaneous or induced by mutagens (radiation, chemicals). They may cause cancer by altering gene expression. Carcinogenesis can be environmental, viral, or genetic.

• Oncogenes: Cancer-causing genes.

• Tumor suppressor genes: Prevent cancer by aiding DNA repair and immune response.

• Malignant cells: Unregulated mitosis, avoidance of apoptosis, metastasis.

Summary Table: Functional Groups of Organic Compounds

Additional info: This study guide covers the chemical level of organization, focusing on molecular diversity, functional groups, macromolecules, and their relevance to cell structure and function. It also addresses mutations and their role in carcinogenesis, linking molecular biology to health and disease.