Answer
**Defining Characteristics of Amino Acids:**
Amino acids are the building blocks of proteins and share certain defining characteristics:
1. **Amino Group (-NH2):** All amino acids have an amino group (-NH2) as one of their functional groups. This group consists of a nitrogen atom bonded to two hydrogen atoms.
2. **Carboxyl Group (-COOH):** Amino acids also contain a carboxyl group (-COOH) as another functional group. This group consists of a carbon atom double-bonded to an oxygen atom and single-bonded to an oxygen atom and a hydroxyl group (-OH).
3. **Alpha Carbon (α-Carbon):** A central carbon atom, known as the alpha carbon (α-carbon), is bonded to the amino group, carboxyl group, a hydrogen atom, and an R-group (side chain).
4. **R-Group (Side Chain):** The R-group varies among different amino acids and distinguishes one amino acid from another. The R-group can be a hydrogen atom (in glycine), a simple methyl group (in alanine), or a complex arrangement of atoms in other amino acids. The specific properties of the R-group determine the amino acid's characteristics and role in protein structure and function.
**Differences Among the 20 Amino Acids Involved in Protein Structure:**
There are 20 commonly occurring amino acids that are involved in protein structure, and they differ from each other based on the structure and properties of their R-groups. Here's a brief overview of these amino acids:
1. **Alanine (Ala, A):** Simple methyl (-CH3) R-group.
2. **Arginine (Arg, R):** Contains a guanidinium group; positively charged at physiological pH.
3. **Asparagine (Asn, N):** Contains an amide (-CONH2) group.
4. **Aspartic Acid (Asp, D):** Contains a carboxylate (-COO-) group; negatively charged at physiological pH.
5. **Cysteine (Cys, C):** Contains a thiol (-SH) group, forming disulfide bonds.
6. **Glutamine (Gln, Q):** Contains an amide (-CONH2) group.
7. **Glutamic Acid (Glu, E):** Contains a carboxylate (-COO-) group; negatively charged at physiological pH.
8. **Glycine (Gly, G):** The simplest amino acid with a hydrogen atom as the R-group.
9. **Histidine (His, H):** Contains an imidazole group; can be positively charged depending on pH.
10. **Isoleucine (Ile, I):** Branched aliphatic R-group.
11. **Leucine (Leu, L):** Branched aliphatic R-group.
12. **Lysine (Lys, K):** Contains an amino group; positively charged at physiological pH.
13. **Methionine (Met, M):** Contains a thioether group.
14. **Phenylalanine (Phe, F):** Aromatic R-group.
15. **Proline (Pro, P):** Contains a cyclic structure; can disrupt protein secondary structure.
16. **Serine (Ser, S):** Contains a hydroxyl (-OH) group.
17. **Threonine (Thr, T):** Contains a hydroxyl (-OH) group.
18. **Tryptophan (Trp, W):** Contains a bulky aromatic ring.
19. **Tyrosine (Tyr, Y):** Contains a hydroxyl (-OH) group attached to an aromatic ring.
20. **Valine (Val, V):** Branched aliphatic R-group.
The unique properties of the R-groups, including their size, charge, polarity, and chemical reactivity, influence the amino acids' interactions within proteins and their roles in protein structure, function, and specificity. These differences are critical for the diverse functions of proteins in biological systems.
Work Step by Step
**Defining Characteristics of Amino Acids:**
Amino acids are the building blocks of proteins and share certain defining characteristics:
1. **Amino Group (-NH2):** All amino acids have an amino group (-NH2) as one of their functional groups. This group consists of a nitrogen atom bonded to two hydrogen atoms.
2. **Carboxyl Group (-COOH):** Amino acids also contain a carboxyl group (-COOH) as another functional group. This group consists of a carbon atom double-bonded to an oxygen atom and single-bonded to an oxygen atom and a hydroxyl group (-OH).
3. **Alpha Carbon (α-Carbon):** A central carbon atom, known as the alpha carbon (α-carbon), is bonded to the amino group, carboxyl group, a hydrogen atom, and an R-group (side chain).
4. **R-Group (Side Chain):** The R-group varies among different amino acids and distinguishes one amino acid from another. The R-group can be a hydrogen atom (in glycine), a simple methyl group (in alanine), or a complex arrangement of atoms in other amino acids. The specific properties of the R-group determine the amino acid's characteristics and role in protein structure and function.
**Differences Among the 20 Amino Acids Involved in Protein Structure:**
There are 20 commonly occurring amino acids that are involved in protein structure, and they differ from each other based on the structure and properties of their R-groups. Here's a brief overview of these amino acids:
1. **Alanine (Ala, A):** Simple methyl (-CH3) R-group.
2. **Arginine (Arg, R):** Contains a guanidinium group; positively charged at physiological pH.
3. **Asparagine (Asn, N):** Contains an amide (-CONH2) group.
4. **Aspartic Acid (Asp, D):** Contains a carboxylate (-COO-) group; negatively charged at physiological pH.
5. **Cysteine (Cys, C):** Contains a thiol (-SH) group, forming disulfide bonds.
6. **Glutamine (Gln, Q):** Contains an amide (-CONH2) group.
7. **Glutamic Acid (Glu, E):** Contains a carboxylate (-COO-) group; negatively charged at physiological pH.
8. **Glycine (Gly, G):** The simplest amino acid with a hydrogen atom as the R-group.
9. **Histidine (His, H):** Contains an imidazole group; can be positively charged depending on pH.
10. **Isoleucine (Ile, I):** Branched aliphatic R-group.
11. **Leucine (Leu, L):** Branched aliphatic R-group.
12. **Lysine (Lys, K):** Contains an amino group; positively charged at physiological pH.
13. **Methionine (Met, M):** Contains a thioether group.
14. **Phenylalanine (Phe, F):** Aromatic R-group.
15. **Proline (Pro, P):** Contains a cyclic structure; can disrupt protein secondary structure.
16. **Serine (Ser, S):** Contains a hydroxyl (-OH) group.
17. **Threonine (Thr, T):** Contains a hydroxyl (-OH) group.
18. **Tryptophan (Trp, W):** Contains a bulky aromatic ring.
19. **Tyrosine (Tyr, Y):** Contains a hydroxyl (-OH) group attached to an aromatic ring.
20. **Valine (Val, V):** Branched aliphatic R-group.
The unique properties of the R-groups, including their size, charge, polarity, and chemical reactivity, influence the amino acids' interactions within proteins and their roles in protein structure, function, and specificity. These differences are critical for the diverse functions of proteins in biological systems.
