Amino acids, peptides, and proteins
Key Principles In every living organism, proteins are constructed from a common set of 20 amino acids. In proteins, amino acids are joined in characteristic linear sequences through a common amide linkage, the peptide bond. For study, individual proteins can be separated from the thousands of other proteins present in a cell, based on differences in their chemical and functional properties arising from their distinct amino acid sequences. Shaped by evolution, amino acid sequences are a key resource for understanding the function of individual proteins and for tracing broader functional and evolutional relationships. [ˈæmaɪd] 酰胺
Proteins Elements •Carbon •Hydrogen •Oxygen •Nitrogen •sometimes Sulfur Components of life
Proteins Most structurally and functionally diverse group of bio-molecules Function (involved in almost everything ) enzymes (pepsin, polymerase, etc.)酶 structure (keratin, collagen)结构 carriers & transport (membrane channels)转运 receptors & binding (defence: antibodies) 受体 contraction (actin & myosin)收缩 signalling (hormones: insulin)信号 storage (bean seed proteins)储存 [ˈkerətɪn] [ˈkɒlədʒən]
Protein structure varies Most are globular Polypeptide DNA polymerase (E. coli Klenow fragment) Synthesizes a new DNA chain using an existing DNA strand as a template Polypeptides small Insulin (pig) Released from the pancreas to signal the availability of the metabolic fuel glucose Protein ≠ Polypeptides Maltoporin (E.coli) Protein ≠ Polypeptides Maltoporin (E.coli) Permits sugars to cross the bacterial cell membrane Complex of 3 peptides [ˈsɪnθɪˌsaɪz] maltose [ˈmɔːltəʊz]麦芽糖 maltoporin [‘mɔːltəpərɪn]麦芽糖孔蛋白
[ˈspeɪʃəl ]
Different side chain→
Mirror image of each other → interact with light differently
Amino acid chirality L = levorotatory; rotate polarized light to the left D = dextrorotatory; rotate polarized light to the right All amino acids found in proteins are L-enantiomers Stereochemistry in amino acids plays role in overall protein structure [ˌɡlɪsəˈrældəˌhaɪd]甘油醛 [ˌliːvəʊ'rəʊtətərɪ]