# Chapter 1


## Primary classes of molecules in E. coli.

Compound % weight ave. MW #/cell # of kinds Comment
$$\mathrm{H_{2}O}$$ 70 18 $$4\times 10^{10}$$ 1
Ions (Na,K,$$\mathrm{S)_{4}}$$,etc.) 1 40 $$2.6\times 10^{8}$$ 20 major example-$$\mathrm{Na^{+}} \sim 0.05 \mathrm{M}$$
Carbohydrates 3 150 $$2\times 10^{8}$$ 250
Amino Acids 0.4 120 $$3\times 10^{7}$$ 20 main $$\sim 120$$ total
Nucleotides 0.4 300 $$1.2\times 10^{7}$$ 5 main $$\sim 100$$ total
Lipids 2 750 $$2.5\times 10^{7}$$ 50
Proteins 15 40,000 $$1\times 10^{6}$$ 4,288 35 -85,000 in humans!
RNA 6 $$10^{6}$$ $$2\times 10^{4}$$ $$\sim$$2,000 35 -85,000 in humans
DNA 1 $$2.5\times 10^{9}$$ 1 (4) 1 46 @ 5 X $$10^{10}$$ (human)

## Some Groupings of Amino Acids by Properties of Side Chains

This list is provided as a study guide to help remind you of the properties of the amino acids. You should not need to memorize the list, but should be able to predict the properties from your knowledge of the structures of the side chains and basic principles of organic chemistry.

1. $$\begin{matrix} \mathrm{Polar / hydrophilic - N, Q, S, T, K, R, H, D, E, (C, Y)*} \\ \mathrm{Non-polar / hydrophobic - (G), A, V, L, I, P, Y, F, W, M} \end{matrix}$$

2. H-bonding - C, W, N, Q, S, T, Y, K, R, H, D, E
3. Sulfur containing - C, M
4. Charged at Neutral pH $$\begin{matrix} \mathrm{Negative / acidic - D, E, (C)} \\ \mathrm{Positive / basic - K, R, (H)} \end{matrix}$$

5. Ionizable - D, E, H, C, Y, K, R
6. Aromatic - F, W, Y, (H, but no significant UV absorption)
7. Aliphatic - A, V, L, I, P
8. Forms covalent cross-link (disulfide bond) - C
9. Cyclic - P
10. Hard to remember one letter code - W, Y, K, N, Q, D, E

*Note: Amino acids in parentheses have the indicated character to a limited extent.

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