Molecules of Life Molecules of Life Molecules of life are synthesized by living cells • • • • Carbohydrates Lipids Proteins Nucleic acids Organic Compounds Consist primarily of carbon and hydrogen atoms • Carbon atoms bond covalently with up to four other atoms, often in long chains or rings Functional groups attach to a carbon backbone • Influence organic compound’s properties An Organic Compound: Glucose Four models Functional Groups: The Importance of Position Processes of Metabolism Cells use energy to grow and maintain themselves Enzyme-driven reactions build, rearrange, and split organic molecules Building Organic Compounds Cells form complex organic molecules • • • • Simple sugars → carbohydrates Fatty acids → lipids Amino acids → proteins Nucleotides → nucleic acids Dehydration synthesis combines monomers to form polymers Dehydration synthesis and Hydrolysis Carbohydrates – The Most Abundant Ones Three main types of carbohydrates • Monosaccharides (simple sugars) • Oligosaccharides (short chains) • Polysaccharides (complex carbohydrates) Carbohydrate functions • Instant energy sources • Transportable or storable forms of energy • Structural materials Oligosaccharides: Sucrose Complex Carbohydrates: Starch, Cellulose, and Glycogen Structure of cellulose c Glycogen. In animals, this polysaccharide is a storage form for excess glucose. It is especially abundant in the liver and muscles of highly active animals, including fishes and people. Greasy, Oily – Must Be Lipids Lipids • Fats, phospholipids, waxes, and sterols • Don’t dissolve in water • Dissolve in nonpolar substances (other lipids) Lipid functions • Major sources of energy • Structural materials • Used in cell membranes Fats Lipids with one, two, or three fatty acid tails • Saturated Triglycerides (neutral fats ) • Three fatty acid tails • Most abundant animal fat (body fat) • Major energy reserves Triglyceride Formation Phospholipids Main component of cell membranes • Hydrophilic head, hydrophobic tails Waxes Firm, pliable, water repelling, lubricating Steroids: Cholesterol Membrane components; precursors of other molecules (steroid hormones) Protein Structure Built from 20 kinds of amino acids Four Levels of Protein Structure 1. Primary structure • Amino acids joined by peptide bonds form a linear polypeptide chain 2. Secondary structure • Polypeptide chains form sheets and coils 3. Tertiary structure • Sheets and coils pack into functional domains Four Levels of Protein Structure 4. Quaternary structure • Many proteins (e.g. enzymes) consist of two or more chains Levels of Protein Structure Levels of Protein Structure Levels of Protein Structure Levels of Protein Structure Why is Protein Structure So Important? Protein structure dictates function Sometimes a mutation in DNA results in an amino acid substitution that alters a protein’s structure and compromises its function • Example: Hemoglobin and sickle-cell anemia Normal Hemoglobin Structure VALINE HISTIDINE LEUCINE THREONINE PROLINE b One amino acid substitution results in the abnormal beta chain in HbS molecules. Instead of glutamate, valine was added at the sixth position of the polypeptide chain. c Glutamate has an overall negative charge; valine has no net charge. At low oxygen levels, this difference gives rise to a water-repellent, sticky patch on HbS molecules. They stick together because of that patch, forming rod shaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.) VALINE sickle cell normal cell GLUTAMATE Clumping of cells in bloodstream Circulatory problems, damage to brain, lungs, heart, skeletal muscles, gut, and kidneys Heart failure, paralysis, pneumonia, rheumatism, gut pain, kidney failure Spleen concentrates sickle cells Spleen enlargement Immune system compromised Rapid destruction of sickle cells d Melba Moore, celebrity spokesperson for sickle-cell anemia organizations. Right, range of symptoms for a person with two mutated genes for hemoglobin’s beta chain. Anemia, causing weakness,fatigue, impaired development,heart chamber dilation Impaired brain function, heart failure Denatured Proteins If a protein unfolds and loses its threedimensional shape (denatures), it also loses its function Caused by shifts in pH or temperature, or exposure to detergent or salts • Disrupts hydrogen bonds and other molecular interactions responsible for protein’s shape Nucleotides, DNA, and RNAs Nucleotide structure, 3 parts: • Sugar • Phosphate group • Nitrogen-containing base Nucleotide Functions: Reproduction, Metabolism, and Survival DNA and RNAs are nucleic acids, each composed of four kinds of nucleotide subunits ATP energizes many kinds of molecules by phosphate-group transfers Nucleotides of DNA DNA, RNAs, and Protein Synthesis DNA (double-stranded) • Encodes information about the primary structure of all cell proteins in its nucleotide sequence RNA molecules (usually single stranded) • Different kinds interact with DNA and one another during protein synthesis covalent bonding in carbon backbone hydrogen bonding between bases