Topic 2. The Molecules of Life I. Carbon and the Molecular Diversity of Life September 19, 2005 Biology 1001

Putting Life In Its Chemical Context  96% of living matter is made up of 4 elements – C, O, H, and N

The Importance of Carbon Carbon enters the biosphere by photosynthesis from CO 2 Carbon forms large, complex, and diverse molecules The macromolecules of life - proteins, carbohydrates, lipids, & nucleic acids - are all compounds of carbon bonded to O, H, N, S, P & other elements The versatility of carbon underlies biological diversity The study of the compounds of carbon is called organic chemistry

The Properties of Carbon The carbon atom has 4 electrons in its outermost energy shell, a property called tetravalence  This electron configuration gives carbon covalent compatibility with many different elements

 Carbon forms molecules that can branch in up to four directions  Carbon also forms double and triple covalent bonds A diverse array of molecules is possible - like these hydrocarbons  Carbon’s Versatile Electron Configuration

Isomers – Another Level of Diversity  Molecules with the same molecular formula but different structures and properties  There are structural isomers, geometric isomers, and enantiomers of carbon compounds Structural Geometric Enantiomers

Organic Polymers  Another level in the hierarchy of biological organization is reached when small organic molecules are joined together to form macromolecules Macromolecules are giant molecules composed of 1000’s of atoms covalently bonded together  Most macromolecules are polymers, composed of monomers Three of the classes of organic molecules are polymers – carbohydrates, proteins and nucleic acids The fourth class, lipids, are complex macromolecules but not technically polymers

Carbohydrates The Monomers  Simple sugars or monosaccharides Glucose, fructose, galactose  Double sugars or disaccharides Sucrose, maltose, lactose The Polymers  Polysaccharides Starch, glycogen, cellulose, chitin Functions of Carbohydrates  Fuel for cellular respiration – the mono- and disaccharides  Storage of fuel – Starch (plants) & glycogen (animals)  Structural support – cellulose (plants) & chitin (animals)

The Structure of Carbohydrates Mono- and Disaccharides Polysaccharides

Proteins The Monomers  Amino acids The Polymers  Polypeptides  Proteins

 Protein Functions  Enzymes, support, transport, storage, hormones, cell receptors, movement, antibodies Eg. Transport - Hemoglobin Eg. Enzyme - Lysozyme Eg. Structural protein – Spider silk

Nucleic Acids  The Monomers The nucleotides – Adenine, Guanine, Cytosine & Thymine or Uracil  The Polymers The polynucleotides - Deoxyribonucleic Acid (DNA) & Ribonucleic Acid (RNA)  Functions DNA stores & transmit hereditary information DNA & RNA are required for protein synthesis

The Structure of Nucleic Acids

Lipids  Large hydrophobic molecules with diverse functions  Three biologically important groups: the fats, the phospholipids, and the steroids  The functions of lipids Long-term energy storage (fats) Components of cell membranes (phospholipids & the steroid cholesterol) Hormones (steroids)

The Structure of Lipids FATS Phospholipids Cholesterol

Topic 2. The Molecules of Life II. The Origin of Life September 21, 2005 Biology 1001

A Four-Stage Hypothesis Scientists hypothesize that chemical and physical processes on the early Earth led to the formation of very simple living cells in four phases: 1. The abiotic synthesis of small organic molecules 2. The joining of these small molecules (monomers) into polymers 3. The packaging of these molecules into “protobionts”, small droplets with membranes that maintain an internal chemistry different from the environment 4. The origin of self-replicating molecules that would make inheritance possible

Stage 1 – A Testable Hypothesis The Oparin-Haldane Hypothesis  In the 1920’s, A.I. Oparin and J.B.S. Haldane independently hypothesized that the Earth’s early atmosphere had been an electron-adding (reducing) environment in which organic molecules could have formed from inorganic precursors.

Stage 1 – A Testable Hypothesis The Miller-Urey Experiment Figure 26.2 Inquiry: Can organic molecules form in reducing atmosphere? Experiment: Set up conditions in laboratory thought to have existed on Early Earth. A reducing atmosphere of H 2, CH 4, NH 3 and water vapour. A warmed flask as the primerval sea. Sparks as lightning. A condenser to cool the atmosphere and simulate rain. Results: A variety or organic compounds including amino acids. Conclusion: Organic molecules, the first step in the origin of life, can form in a reducing atmosphere.

The Early Earth – A Reducing Atmosphere?