生物化学教学课件：Amino Acids,Peptides-2

1、Chapter 1 Amino Acids, Peptides and Proteins-2 -Polymers of amino acidsSummary一、肽键的结构二、氨基酸残基的顺序是蛋白质功能的基础三、蛋白质的一级结构四、蛋白质的二级结构Peptide bonds covalently join amino acid molecules, it is formed by the -carboxyl group and the -amino group.Hydroxyl group is not readily displacedPeptide一、肽键的结构residueresidue

2、residueThe peptide bonds are quite stable, and average half-life of about 7 years under most intracellular conditions.Peptide sequences and evolutionProtein sequences are a rich source of information about protein structure and function, as well as the evolution of life on this planet.肽链上氨基酸的顺序记录了蛋白

3、质的结构、功能和遗传信息二、肽链上氨基酸残基的顺序和性质是蛋白质功能的基础Alignment of homologous protein sequences Conformation: the spatial arragement of atoms in a protein.Native protein: proteins in any of their functional, folded conformations.A proteins conformation is stabilized largely by weak interactionsweak interactions:Disu

4、lfide bonds, hydrogen bonds, and hydrophobic and ionic interactions.1. Hydrophobic residues are largely buried in the protein interior, away from water;2. Hydrogen bonds and ionic interactions are optimized in the specific structures that are thermodynamically most stable.Proteins And Prosthetic gro

5、upsLevels of structure in proteinsPrimary structureThe peptide bond is rigid and planar!三、蛋白质的一级结构Peptide bondSecondary structure HelixHydrogen bond四、蛋白质的二级结构 Helix makes optimal use of internal hydrogen bonds.All residues must be of one stereoisomeric series.Naturally occurring L-amino acids can fo

6、rm either right- or left-handed helices, but only extended right-handed helices have been observed in proteins.Amino acid sequence affects helix stabilityA long block of Glu residues will not form an helix at pH7.0The charge of R group on Arg and LysBulk and shape of Asn, Ser, Thr, and Cys residuesT

7、he interactions between R groups spaced three or four residues apart.Proline and Glycine occure infrequently in helix.DipolePositive charged amino acids are often found near the carboxyl-terminal end of the helical segment.R group! SheetHydrogen bondHydrogen bondWhen two or more sheets are layered close together within a protein, the R groups of the amino acid residues on the touching surfaces must be relatively small, such as Gly or Ala in silk fibroin and the fibroin of spider webs. turnGly and Pro often occur. turns are often found near the surface