Essential Biochemistry Third Edition Charlotte W. Pratt | Kathleen Cornely Chapter 1 The Chemical Basis of Life
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
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?
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.
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
Cells contain four major types of biological molecules. • Amino acids • Carbohydrates (also called monosaccharides or sugars) • Nucleotides • Lipids
Amino Acids • Amino acids contain: • An amino group • A carboxylic acid group • A side chain
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.
Nucleotides • Nucleotides are the building blocks of nucleic acids.
Lipids are a major type of biological molecule. • Lipids (fats) have a variety of structures. • An important lipid in human health is cholesterol.
There are three major kinds of biological polymers. • Polypeptides and proteins (amino acids) • DNA and RNA (nucleic acids) • Polysaccharides (carbohydrates)
Polypeptides and Proteins • Amino acid residues are connected via peptide bonds. • Polypeptide sequences are always read from the N terminus to the C terminus.
Polysaccharides Glycosidic Bond
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.
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
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
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).
Coupled Chemical Reaction ΔG is positive for the AB transition.Nonspontaneous reactionsdo not generally occur. ΔG is negative for the BC transition. Spontaneous reactionscan be coupled with nonspontaneous reactionsso that the net reactionoccurs spontaneously.
Energy from photosynthesis involves a coupled chemical reaction. Reduction = gain of electrons Oxidation = loss of electrons