Chapter 16.1Functions of Proteins

SWBAT: Classify proteins by their functions in the cells

Proteins•Proteins are polymers of amino acids chemically bonded to each other•All proteins in humans are made up from 20 different amino acids•Protein Subclasses are:

• structural, contractile, transport, hormones, enzymes, immunoprotein, AA storage

•Identification: many end with –in, -en, -ase

Table 16.1 – page 534

Chapter 16.2Amino Acids

SWBAT: know the structure of an amino acid and be familiar with the classification of amino acids

AA are all the same with regard to• Central carbon• Amino group• Carboxyl group• Hydrogen Differ with regard to the R-side chain

Anatomy of an Amino Acid

Amino AcidsAt normal body pH (~7.4) the functional groups are

COO-

Remember that carboxylic acids are acids and can lose a proton

NH3+

Remember that amines are bases and can accept a proton

This form of the amino acid is called a zwitterion…which has no net charge (one positive and one negative).

Side Chain (R) Group can be:• Alkyl• Hydroxyl• Thiol• Amino• Carboxyl• Aromatic • Cyclical• Amide

Amino Acid (R) Group

Classification of Amino Acids

Non-polar

Polar

Neutral (not

charged)Positively charged(Basic)

Negatively charged(Acidic)

Charged

Amino Acid

Nonpolar Amino AcidsR can be:• Alkyl side chain• Aromatic side chain

All are nonpolar

amino acids

Polar Amino AcidsR can be: • Hydroxyl (-OH)• Thiol (-SH)• Amide (-CONH2)

All can H-bond with water

Acidic Amino AcidsR will be: Carboxylic acid (-COOH)

Can ionize as a weak

acid

Basic Amino AcidsR group will contain:an amino group that ionizes as a weak base

All are polar amino acids…

All of the alpha amino acids (except glycine) are chiral – can exist as D or L enantiomers

Fisher projections with –COOH at the top and (R) group at bottomL isomer – NH2 group on leftD isomer – NH2 group on right

Amino Acid Stereoisomers

L-serine

D-serine

In biological systems, only L amino acids are in proteins

Homework:

pg 534 16.1 – 16.2

pg 537 16.3 – 16.12