lecture 2

Water Properties

• Cohesion allows water molecules to stick together, enhancing surface tension.
• Water moderates temperature, absorbing significant energy before warming; it helps maintain stable environmental temperatures and plays a role in sweating.
• Water expands upon freezing due to hydrogen bonds forming a lattice structure, causing ice to float and providing insulation for aquatic life during winter.
• Being a polar molecule, water effectively dissolves polar and charged substances, known as hydrophilic; oils and lipids are examples of hydrophobic substances.
• Buffers maintain pH levels, crucial for blood, which must remain between 7.35-7.45. Water composes over 90% of blood.

Organic Molecules and Functional Groups

• All matter, including living organisms, follows chemical and physical laws, leading to complex molecules known as organic compounds, primarily made of carbon.
• Organic molecules consist of carbon skeletons connected by covalent bonds, forming hydrocarbons when only carbon and hydrogen are present.
• Functional groups attached to carbon skeletons dictate unique chemical properties, influencing cellular function such as those in steroid hormones.
• Biological molecules are complex with many composed of polymers formed from monomers, categorized into four classes: carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Composed of carbon, hydrogen, and oxygen, making up 2-3% of total body mass.
• Monosaccharides are the simplest sugars and serve as monomers for carbohydrates, linked by dehydration synthesis to form more complex forms like disaccharides and polysaccharides.
• Glycogen serves as the primary storage polysaccharide in animals, while starches serve this role in plants; cellulose is indigestible in humans due to lack of the necessary enzyme.

Lipids

• Lipids are hydrophobic molecules primarily made of carbon and hydrogen, representing 18-25% of body mass in humans.
• Types include fatty acids, triglycerides, phospholipids, steroids, eicosanoids, and fat-soluble vitamins.
• Fatty acids vary by saturation: saturated fatty acids have no double bonds, while unsaturated have one or more double bonds.
• Triglycerides are three fatty acids bonded to glycerol; they can be solid (fats) or liquid (oils) at room temperature.
• Phospholipids are amphipathic, essential for biological membranes, with hydrophilic phosphate heads and hydrophobic tails.
• Steroids, built from four fused carbon rings, include cholesterol, which is vital for membrane fluidity.

Proteins

• Proteins are large structures comprising carbon, hydrogen, oxygen, and nitrogen, contributing 12-18% of total body mass and determining tissue structure.
• Amino acids are the building blocks of proteins, linked by peptide bonds formed through dehydration synthesis.
• Protein structure is hierarchical: primary (amino acid sequence), secondary (folds formed by hydrogen bonding), tertiary (three-dimensional shape), and quaternary (arrangement of multiple polypeptides).
• Denaturation leads to loss of structure and function.
• Enzymes act as biological catalysts, enhancing reaction rates without consumption and requiring specific substrates.

Nucleic Acids

• Composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus, existing as DNA or RNA.
• DNA contains genes, which are regions specifying proteins, and undergoes transcription to form RNA, which is then translated into proteins.
• Nucleotides are the monomers, consisting of nitrogenous bases (A, T, C, G for DNA and A, U, C, G for RNA), a pentose sugar, and a phosphate group.
• DNA forms a double helix due to base pairing, with mutations arising from sequence changes.
• RNA plays various roles in cellular processes, including mRNA, rRNA, and tRNA.
• ATP serves as the energy currency in cells, generated through cellular respiration and hydrolysis, releasing energy when phosphate bonds are broken.