Chapter 1 The Chemical Basis of Life

1. Essential Biochemistry Third Edition Charlotte W. Pratt | Kathleen Cornely Chapter 1 The Chemical Basis of Life

2. Biochemistry involves the study of 4 types of molecules. Nucleic Acids Proteins BiochemistryThe scientific discipline that seeks to explain life at the molecular level Carbohydrates Lipids

3. Central Questions in Biochemistry • What are living organisms made of? • How do organisms acquire and use energy? • How does an organism maintain its identity across generations?

4. KEY CONCEPTS: Section 1-2 • Biological molecules are composed of a subset of all possible elements and functional groups. • Cells contain four major types of biological molecules and three major types of polymers.

5. Elements Found in Biological Systems • Biological molecules are mainly composed of H, C, N, and O. • Other elements are also necessary for life. Abundant ModeratelyAbundant Trace

6. Cells contain four major types of biological molecules. • Amino acids • Carbohydrates (also called monosaccharides or sugars) • Nucleotides • Lipids

7. Amino Acids • Amino acids contain: • An amino group • A carboxylic acid group • A side chain

8. Carbohydrates • Carbohydrates are monosaccharides or sugars. • General chemical formula: (CH2O)nwhere n ≥ 3 Sugars can be drawn as a cyclicalHaworthrepresentation. Sugars can be drawn as a Fischer projection.

9. Nucleotides • Nucleotides are the building blocks of nucleic acids.

10. Lipids are a major type of biological molecule. • Lipids (fats) have a variety of structures. • An important lipid in human health is cholesterol.

11. Monomers link sequentially to form polymers.

12. There are three major kinds of biological polymers. • Polypeptides and proteins (amino acids) • DNA and RNA (nucleic acids) • Polysaccharides (carbohydrates)

13. Polypeptides and Proteins • Amino acid residues are connected via peptide bonds. • Polypeptide sequences are always read from the N terminus to the C terminus.

14. DNA & RNA

15. Polysaccharides Glycosidic Bond

16. KEY CONCEPTS: Section 1-3 • The free energy of a system is determined by its enthalpy and entropy. • Living organisms obey the laws of thermodynamics.

17. Thermodynamic Terms • Enthalpy, H • The heat content of a system • Units = J • mol-1 • Entropy, S • A measure of the system’s disorder or randomness • Units = J • K-1mol-1 • Gibbs free energy, G • A measure of the free energy of a system based on H and S • Units = J • mol-1

18. Basics of Thermodynamics • Many thermodynamic values cannot be measured directly. Therefore, we will look at changes (Δ). • ΔG = ΔH – TΔS • ΔG = Gibbs free energy change • ΔH = Enthalpy change • ΔS = Entropy change

19. The sign of ΔG is meaningful. • When ΔG <0, the reaction is spontaneous or exergonic. • When ΔG >0, the reaction is nonspontaneous or endergonic. • When ΔGº means standard conditions (general chemistry). • When ΔGº´ means standard conditions (biochemistry, at pH of 7).

20. Coupled Chemical Reaction ΔG is positive for the AB transition.Nonspontaneous reactionsdo not generally occur. ΔG is negative for the BC transition. Spontaneous reactionscan be coupled with nonspontaneous reactionsso that the net reactionoccurs spontaneously.

21. Energy from photosynthesis involves a coupled chemical reaction. Reduction = gain of electrons Oxidation = loss of electrons

22. Carbon has different oxidation states.