CHAPTER 2 Protein Section 2 Proteins: Their biological Functions and Primary structure
CHAPTER 2 Protein Section 2 Proteins: Their Biological Functions and Primary Structure
Outline 5.1 Proteins- Linear Polymers of Amino Acids 5.2 Architecture 5.3 Many biological Functions 5.4 May be conjugated with Other Groups 5.6 Purification 5.7 Primary Structure Determination 5.8 Consider the Nature of sequences
Outline 5.1 Proteins - Linear Polymers of Amino Acids 5.2 Architecture 5.3 Many Biological Functions 5.4 May be Conjugated with Other Groups 5.6 Purification 5.7 Primary Structure Determination 5.8 Consider the Nature of Sequences
5. 1 Proteins are Linear polymers ofamino Acids R RI O Ro HN—CH—C t Hgn-CH-c H3N-GH-C一N-GHC O H Amino acid I Amino acid 2 Dipeptide
5.1 Proteins are Linear Polymers of Amino Acids
The Peptide bond n partially positive, A pure double bond between C and O would permit free rotation o partially negative The other extreme would prohibit c-Nbond rotation but would place too great a charge on O and N (c) The true electron density is intermediate. The barrier to C-Nbond rotation of about 88 kI mol is enough to keep the amide group planar
•N partially positive; • O partially negative The Peptide Bond
1125nm R I21.1 12s.2 0.13m 14 1212 1156 118z° R 0.1m is usually found in the trans conformation .has partial ( 40%)double bond character .is about 0.133 nm long-shorter than a typical single bond but longer than a double bond
•is usually found in the trans conformation •has partial (40%) double bond character •is about 0.133 nm long - shorter than a typical single bond but longer than a double bond
The Coplanar Nature of the peptide bond Six atoms of the peptide group lie in a plane! R a-carbon N a-carbon R due to the double bond character. the six atoms of the peptide bond group are always planar
The Coplanar Nature of the Peptide Bond Six atoms of the peptide group lie in a plane! •Due to the double bond character, the six atoms of the peptide bond group are always planar!
Peptides classification Peptides--Short polymers of amino acids Each unit is called a residue 2 residues-dipeptide 3 residues-tripeptide 12-20 residues-oligopeptide many-polypeptide
Peptides Classification • Peptides --Short polymers of amino acids • Each unit is called a residue • 2 residues - dipeptide • 3 residues - tripeptide • 12-20 residues - oligopeptide • many - polypeptide
Proteins are composed of one or more polypeptide chains Protein---One or more polypeptide chains One polypeptide chain-a monomeric protein More than one- multimeric protein Homomultimer -one kind of chain Heteromultimer two or more different chains Hemoglobin, for example, is a heterotetramer It has two alpha chains and two beta chains
Proteins are composed of one or more polypeptide chains Protein---One or more polypeptide chains • One polypeptide chain - a monomeric protein • More than one - multimeric protein • Homomultimer - one kind of chain • Heteromultimer - two or more different chains • Hemoglobin, for example, is a heterotetramer • It has two alpha chains and two beta chains
Table 5.2 mino Acid Composition of Some Selected Proteins Values expressed are percent representation of each amino acid. mino Acid ADH Histone Hs 9,8 13.3 117 8.2 1.7 13.3 49 2.0 1.0 3.0 6.7 3.7 1.5 0 2.6 Glu 3.7 10.2 9.0 5.2 7.0 1.5 lle 5.2 17 2 13.0 3.6 1.5 0.7 4.6 3.0 1.2 25 4.4 225 12 3.9 3.7 3.8 Trp 0 3 0 0 LI Acidic 84 10 13.7 8. 75 15.0 13.1 21.8 72 5.2 17 Hydrophobic 30.7 6 2.0 "Proteins are as follows: RNase: Bowine ribonuclease A, an enzyme: 124 amino acid residues. Note that RNase lacks tryptophan. ADH: Horse liver alcohol dehydrogenase, an enzyme, dimer of identical 374 amino acid polypeptide chains. The amino acid composition of ADH is reasonably representative of th Mh b: Sperm whale myoglobin, an oxygen binding protein; 15 amino acid residues. Note that Mb lacks cysteine. Histone H3: Histones are DNA-binding proteins found in chromosomes: 135 amino acid residues. Note the very basic nature of this protein due to its abundance of Arg and Lys esidues. It abo lacks tryptophan Collagen Collagen is an extracellular structural protein; 1052 amino acid residues, Collagen s an unusual amino acid composition; it is about one third glycine and is rich in proline
Proteins- large and small Insulin -a chain of 2i residues b chain of 30 residues -total mol. wt of 5.733 Glutamine synthetase -12 subunits of 468 residues each -total mol wt. of 600.000 Connectin proteins(肌联蛋白)-apha-Mw 2. 8 million beta connectin -mw of 2.1 million with a length of 1000 nm -it can stretch to 3000 nm!
Proteins - Large and Small • Insulin - A chain of 21 residues, B chain of 30 residues -total mol. wt. of 5,733 • Glutamine synthetase - 12 subunits of 468 residues each - total mol. wt. of 600,000 • Connectin proteins(肌联蛋白）- alpha - MW 2.8 million! • beta connectin - MW of 2.1 million, with a length of 1000 nm -it can stretch to 3000 nm!
