Chapter 16 - - - - Proteins and Enzymes Proteins are probably the most important of the Biological Compounds because even though they carry out different functions in the body, they all have one important function in common: THEY PROMOTE GROWTH. Any living thing that cannot grow will die.

Proteins are classified according to their function in the body: See Page 558 The 4 most important classes of proteins are: Examples: Structural - - - They provide structure to the body Collagen, Keratin Transport - - - They carry substances throughout the body Hemoglobin Hormonal - - - They regulate body metabolism Insulin Enzymes - - - They make chemical reactions happen in the body Sucrase Collagen is the most abundant and most important protein in the human body

Functions of Proteins [See Page 558]

Like all biological compounds, Proteins are long chain molecules. The basic unit (or building block) that forms long chains of proteins is an “Amino acid”

A base An acid

Amino Acids Amino acids 1 - are the molecular building blocks of proteins 2 - contain a carboxylic acid group and an amino group on the alpha () carbon 3 - each contain a different side group (R) (or side chain) side chain R │ H2N—C —COOH H

Examples of Amino Acids H + │ H3N—C—COO− │ H Glycine CH3 + │ H Alanine

by Pearson Education, Inc. Nonpolar Amino Acids See page 561 – Table 16.2 The essential non-polar amino acids Copyright © 2009 by Pearson Education, Inc.

Copyright © 2009 by Pearson Education, Inc. Amino Acids Some polar amino acids Copyright © 2009 by Pearson Education, Inc.

Acidic and Basic Amino Acids An amino acid is acidic when the R group is a carboxylic acid. basic when the R group is an amine.

Amino acids will link together to form chains called “Peptides” The linkage occurs by the bonding of the N-terminal of one amino acid with the C-terminal of another. This forms a train-like chain, and the chain can be any number of units in lenghth Two amino acids linked together is called a DIPEPTIDE. Three amino acids linked together is called a TRIPEPTIDE. More than 3 amino acids linked together is a POLYPEPTIDE. A protein is defined as a polypeptide containing 50 or more amino acids linked together.

The Peptide Bond A peptide bond is an amide bond. forms between the carboxyl group of one amino acid and the amino group of the next amino acid. O CH3 O + || + | || H3N—CH2—C—O– + H3N—CH—C—O– O H CH3 O + || | | || H3N—CH2—C—N—CH—C—O– peptide bond

The primary structure of a protein can be shown as: An example of a polypeptide containing 4 amino acids linked. The blue boxes surround individual amino acids. The red text shows the position of the peptide bonds (peptide or amide linkages) joining the amino acids together.

Write the dipeptide Ser-Thr. OH CH3 | | CH2 O HCOH O + | ║ + | ║ | | CH2 O HCOH O + | ║ + | ║ H3N─CH─C─O– + H3N─CH─C─O– OH CH3 | | CH2O H HCOH O + | ║ | | ║ NH3─CH─C─N ─CH─ C─O– + H2O Ser-Thr The PEPTIDE bond

See Pages 566 - 568 A typical tripeptide N Terminal C Terminal

A peptide chain will always contain a “C-terminal” at one end and an “N-terminal” at the other end. Both ends are open to extend the chain by adding more amino-acids