Figure 1 NH₂ H-C-COOH R Figure 2 NH₂ H-C- coo 1. R The general (un-ionized) structure for an amino acid is shown in Figu

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Figure 1 Nh H C Cooh R Figure 2 Nh H C Coo 1 R The General Un Ionized Structure For An Amino Acid Is Shown In Figu 1 (203.73 KiB) Viewed 40 times

Figure 1 NH₂ H-C-COOH R Figure 2 NH₂ H-C- coo 1. R The general (un-ionized) structure for an amino acid is shown in Figure 1 on the right. 'R' refers to that part of an amino acid that varies with the particular type of amino acid. For example, the 'R' group of the amino acid glycine is simply a hydrogen atom (-H) whereas the 'R' group of the amino acid, glutamic acid contains two CH₂ groups along with a carboxyl group (-CH₂-CH₂-COOH). These 'R' groups can vary considerably and contain acidic as well as basic groups. Individual amino acids in water have an ionized form shown in Figure 2 at right. 250 mL of a 0.10 M aqueous solution of an amino acid is titrated with 0.40 M NaOH. It requires 127.0 mL of NaOH to reach the equivalence point. a. Does the 'R' of this amino acid contain a carboxyl (-COO") or an amide (-NH3*) group? Explain your reasoning. b. Predict the number carboxyl or amide groups that are contained in the 'R' group. Justify your prediction with a calculation. c. Would the resulting solution at the equivalence point be acidic, neutral, or basic? Explain your reasoning. d. The simplest amino acid is glycine. In glycine, the 'R' group is a single hydrogen atom. Would the un-ionized form of glycine be soluble in n-hexane (C6H₁4)? Justify your answer. e. Originally scientists thought that proteins, and not DNA, must be the coding molecules for life since there are 20 different amino acids that can be used to make proteins, but there are only 4 different nucleotides that make DNA. When it was discovered that a specific sequence of 3 nucleotides coded for one amino acid, they realized that DNA could contain the code for all life. i. Why did they originally think that DNA could not be the code for all life? ii. How was the new information able to change their views on the ability of DNA to be able to function as the code for all life?