Chemistry Lecture 2: Chemical Organization

Water Properties

• Water exhibits cohesion, allowing molecules to stick together.
• Water moderates temperature, absorbing significant energy before increasing in temperature.
• Water absorbs heat during the day and releases it at night, aiding in temperature control.
• Ice expands upon freezing, creating a lattice structure that makes it less dense than liquid water, enabling it to float.
• Water is a polar solvent, dissolving hydrophilic substances easily while repelling hydrophobic substances like oils.
• Buffers in the body maintain pH within the narrow range of 7.35-7.45, crucial for physiological functions.

Organic Molecules

• Organic molecules contain carbon and consist of carbon skeletons connected by covalent bonds.
• Molecules exclusively made of carbon and hydrogen are termed hydrocarbons.
• Functional groups attached to carbon skeletons determine the chemical properties and functions of organic molecules.
• Biological molecules often exist as polymers composed of repeating monomers, including carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Composed of carbon, hydrogen, and oxygen, carbohydrates make up 2-3% of total body mass.
• Monosaccharides are the simplest form of carbohydrates, serving as their building blocks.
• Dehydration synthesis links monosaccharides to form complex carbohydrates like disaccharides.

Proteins

• Proteins are polymers formed from amino acid monomers, linked by peptide bonds via dehydration synthesis.
• Peptides consist of a few amino acids, while polypeptides can range from 10 to 2000 amino acids.
• The primary structure of proteins is defined by the amino acid sequence determined by genes.
• Secondary structures include repeated folds (α-helices or β-sheets), stabilized by hydrogen bonds.
• Tertiary structure refers to the three-dimensional conformation, influenced by various bonds and interactions.
• Quaternary structure describes the arrangement of multiple polypeptide chains in proteins that have this complexity.
• Proteins can be classified as fibrous (insoluble, e.g., keratin) or globular (soluble, e.g., enzymes, antibodies).
• Denaturation refers to loss of structure in proteins, rendering them biologically inactive.

Enzymes

• Enzymes act as biological catalysts, speeding up chemical reactions without being consumed.
• Cofactors and coenzymes assist enzyme activity, enhancing catalysis.
• Enzymes exhibit high specificity, interacting with substrates at active sites through a "lock and key" mechanism.
• They improve reaction rates by lowering activation energy, critical for metabolic processes.
• Regulation of enzyme synthesis and activity is vital for cellular function.

Nucleic Acids

• Nucleic acids consist of carbon, hydrogen, oxygen, nitrogen, and phosphorus, mainly forming DNA and RNA.
• Genes are segments of DNA encoding specific proteins, with DNA transcribed to RNA, which is then translated to proteins by ribosomes.
• Nucleotides, the monomers of nucleic acids, comprise nitrogenous bases, a pentose sugar, and a phosphate group.
• DNA consists of deoxyribose sugar and bases A, G, C, T; RNA contains ribose sugar and bases A, G, C, U.
• DNA forms a double helix structure, with base pairs consisting of one purine and one pyrimidine.
• Three major types of RNA: mRNA (messenger), rRNA (ribosomal), tRNA (transfer), each serving specific roles in protein synthesis.
• DNA replication creates a new copy of the double helix using one strand as a template; mutations occur through changes in nucleotide sequences.