Question

determine the following: (25 pts)

1. the amino acid sequence using 3-letter code
2. the amino acid sequence using 1-letter code
3. the n-terminal amino acid
4. the c-terminal amino acid
5. the number of peptide bonds in the structure

Explanation:

1. Amino acid sequence (3 - letter code)

Step 1: Identify each amino acid by R - group

• First amino acid (N - terminal): Has \(H_3\stackrel{+}{N}-CH_2 - CO - \), R - group is \( - H\) (Glycine, Gly)
• Second amino acid: R - group is \( - CH_2 - OH\) (Serine, Ser)
• Third amino acid: R - group is \( - CH(CH_3)_2\) (Valine, Val)
• Fourth amino acid: R - group is \( - CH_3\) (Alanine, Ala)
• Fifth amino acid (C - terminal): R - group is \( - CH_2 - SH\) (Cysteine, Cys) (note the C - terminal has a \( - COO^-\) group)

So the 3 - letter sequence is Gly - Ser - Val - Ala - Cys

2. Amino acid sequence (1 - letter code)

Step 1: Recall 1 - letter codes

• Glycine (Gly) → G
• Serine (Ser) → S
• Valine (Val) → V
• Alanine (Ala) → A
• Cysteine (Cys) → C

So the 1 - letter sequence is G - S - V - A - C

3. N - Terminal amino acid

Step 1: Define N - Terminal

The N - terminal amino acid is the one with the free amino group (\(H_3\stackrel{+}{N}-\)) at the start of the peptide chain. From the structure, the first amino acid (with \(H_3\stackrel{+}{N}-\)) has R - group \( - H\), which is Glycine (Gly)

4. C - Terminal amino acid

Step 1: Define C - Terminal

The C - terminal amino acid is the one with the free carboxylate group (\( - COO^-\)) at the end of the peptide chain. From the structure, the last amino acid has R - group \( - CH_2 - SH\) and \( - COO^-\), which is Cysteine (Cys)

5. Number of peptide bonds

Step 1: Recall peptide bond formula

For a peptide with \(n\) amino acids, the number of peptide bonds is \(n - 1\). Here, we have 5 amino acids.

So number of peptide bonds \(=5 - 1 = 4\) (we can also count the \( - CO - NH -\) linkages: there are 4 such linkages between 5 amino acids)

1. Answer: Gly - Ser - Val - Ala - Cys

2. Answer: G - S - V - A - C

3. Answer: Glycine (Gly)

4. Answer: Cysteine (Cys)

5. Answer: 4

Answer:

1. Amino acid sequence (3 - letter code)

Step 1: Identify each amino acid by R - group

• First amino acid (N - terminal): Has \(H_3\stackrel{+}{N}-CH_2 - CO - \), R - group is \( - H\) (Glycine, Gly)
• Second amino acid: R - group is \( - CH_2 - OH\) (Serine, Ser)
• Third amino acid: R - group is \( - CH(CH_3)_2\) (Valine, Val)
• Fourth amino acid: R - group is \( - CH_3\) (Alanine, Ala)
• Fifth amino acid (C - terminal): R - group is \( - CH_2 - SH\) (Cysteine, Cys) (note the C - terminal has a \( - COO^-\) group)

So the 3 - letter sequence is Gly - Ser - Val - Ala - Cys

2. Amino acid sequence (1 - letter code)

Step 1: Recall 1 - letter codes

• Glycine (Gly) → G
• Serine (Ser) → S
• Valine (Val) → V
• Alanine (Ala) → A
• Cysteine (Cys) → C

So the 1 - letter sequence is G - S - V - A - C

3. N - Terminal amino acid

Step 1: Define N - Terminal

The N - terminal amino acid is the one with the free amino group (\(H_3\stackrel{+}{N}-\)) at the start of the peptide chain. From the structure, the first amino acid (with \(H_3\stackrel{+}{N}-\)) has R - group \( - H\), which is Glycine (Gly)

4. C - Terminal amino acid

Step 1: Define C - Terminal

The C - terminal amino acid is the one with the free carboxylate group (\( - COO^-\)) at the end of the peptide chain. From the structure, the last amino acid has R - group \( - CH_2 - SH\) and \( - COO^-\), which is Cysteine (Cys)

5. Number of peptide bonds

Step 1: Recall peptide bond formula

For a peptide with \(n\) amino acids, the number of peptide bonds is \(n - 1\). Here, we have 5 amino acids.

So number of peptide bonds \(=5 - 1 = 4\) (we can also count the \( - CO - NH -\) linkages: there are 4 such linkages between 5 amino acids)

1. Answer: Gly - Ser - Val - Ala - Cys

2. Answer: G - S - V - A - C

3. Answer: Glycine (Gly)

4. Answer: Cysteine (Cys)

5. Answer: 4