河南农业大学：《生物化学》课程PPT教学课件（本科双语教学）第二章 蛋白质 Amino Acids

Chapter 2 Amino Acids

Chapter 2 Amino Acids

Proteins are the indispensable agents of biological function, and amino acids are the building blocks of proteins.The stunning diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids

Proteins are the indispensable agents of biological function, and amino acids are the building blocks of proteins. The stunning diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids

These features include (1)the capacity to polymerize, (2)novel acid-base properties, ·(③)varied structure and chemical functionality in the amino acid side chains,and 。(4)chirality

• These features include : • (1) the capacity to polymerize, • (2) novel acid-base properties, • (3) varied structure and chemical functionality in the amino acid side chains, and • (4) chirality

2.1.Amino Acids:Building Blocks of Proteins Central to this structure is the tetrahedral alpha (a) carbon(C),which is HaN-C-H covalently linked to both the amino group and the carboxyl group.Also bonded to this a-carbon is a R hydrogen and a variable side chain.It is the side chain,the so-called R group,that gives minoAcid each amino acid its identity

2.1 · Amino Acids: Building Blocks of Proteins Structure of a Typical Amino Acid • Central to this structure is the tetrahedral alpha (a) carbon (Ca ), which is covalently linked to both the amino group and the carboxyl group. Also bonded to this a-carbon is a hydrogen and a variable side chain. It is the side chain, the so-called R group, that gives each amino acid its identity

5 2 1 CH2-CH2-CH2-CH2-CH-COO +NH3 +NH3 Lysine

coo C00 H H NHa C00 COO C00 C00 HaN- C-H H-GNH, HN-C-H H-C-NH CH CHa CHa CHa CH CHa L-Alanine D-Alanine L-Alanine D-Alanine L-Alanine DAlanine (a) (b) (c) Because the resulting amino acid contains one positive and one negative charge,it is a neutral molecule called a zwitterion.Amino acids are also chiral molecules.With four different groups attached to it,the a-carbon is said to be asymmetric.The two possible configurations for the a- carbon constitute nonidentical mirror image isomers or enantiomers(对映体)

• Because the resulting amino acid contains one positive and one negative charge, it is a neutral molecule called a zwitterion. Amino acids are also chiral molecules. With four different groups attached to it, the a-carbon is said to be asymmetric. The two possible configurations for the a￾carbon constitute nonidentical mirror image isomers or enantiomers(对映体)

C00 C00 H H NH3 CH3 CH3 L-Alanine D-Alanine (a) All objects have mirror images.Like many biomolecules, amino acids exist in mirror-image forms (stereoisomers) Only the L-isomers of amino acids commonly occur in nature

All objects have mirror images. Like many biomolecules, amino acids exist in mirror-image forms (stereoisomers). Only the L-isomers of amino acids commonly occur in nature

The a-amino carboxylic acids (amino acids can be of two stereoisomers R H NH3" C00 c00 Lisomer D isomer

The a-amino carboxylic acids (amino acids) can be of two stereoisomers

C00 C00 HN-C-H H- NH3 三。 CH3 CH3 L-Alanine D-Alanine (b)

C00 C00 HN-C-H H-C-NH3 CH3 CH3 L-Alanine D-Alanine (c)