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1. The molecular logic of life (1) 2. Cells (2) 3. Biomolecules (2) 4. Water (2) 5. Amino acids…etc (2) 6. Protein structure (4); Protein action (2) 7. Protein function (4); Experimental techniques (2) 8. Enzymes: catalysis and regulation (6) midterm: review and Q&A (2); exam (2).
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1. The molecular logic of life (1) 2. Cells (2) 3. Biomolecules (2) 4. Water (2) 5. Amino acids…etc (2) 6. Protein structure (4); Protein action (2) 7. Protein function (4); Experimental techniques (2) 8. Enzymes: catalysis and regulation (6) midterm: review and Q&A (2); exam (2)
Chapter 2 Molecular Logic of Life Some Important Chemical Concepts and Principles for Studying Biochemistry
1. Living matter is composed mostly of the lighter elements 1.1 The composition of living matter is strikingly different from that of its physical environment (1810s) 1.2 The elements found in living organisms also exist in nature (especially in seawater and atmosphere). 1.2.1 99% of the mass of living organisms are made of H, O, N, and C. 1.2.2 H, O, N, and C are the lightest elements capable of forming one, two, three, and four bonds (in general, lightest elements form the strongest bonds). 1.2.3 The trace elements, although represent a miniscule fraction in living organisms, all are absolutely essential to life (Fe, Cu, Mn, Zn, I, Mg).
2. Carbon was selected as the key element for life due to its versatile bonding capacity 2.1 Carbon accounts for more than one-half the cell dry weight. 2.2 Each carbon atom can form very stable single bonds with one, two, three, or four other carbon atoms, and double or triple bonds can also be formed between two carbon atoms. 2.3 Covalently linked carbon atoms can form linear chains, branched chains, and cyclic and cagelike(笼形的)structures. 2.4 To these carbon skeletons are added functional groups conferring specific activities to the molecules.
2.4 Molecules containing covalently bonding carbon backbones are called organic compounds (including mainly alcohols, amines, aldehydes and ketones, carboxylic acids, sulfhydryls, … etc. Most biomolecules are organic compounds. 2.5 Carbon atoms have a characteristic tetrahedral arrangement of their four single bonds. Carbon-carbon single bonds have freedom of rotation, but not double nor triple bonds. 2.6 No other chemical element has the capacity to form molecules of such widely different sizes and shapes or with such a variety of functional groups.
Filled outer electron shells are more stable: covalent bonds by sharing unpaired electrons between two atoms.
Versatility of carbon in forming covalent bonds
3. Organic biomolecules have three dimensional structures 3.1 The central special feature of organic compounds is not their compositions but the way their atoms are combined, i.e., their structures (realized between 1820s-1860s). Corollary: two substances may show the same chemical formula but be physically and chemically different materials (different structures and functions).
Covalent bond length = sum of covalent radii
Space filling Ball-and-stick Fisher
Light absorbing pigment in rhodopsin an integral membrane protein