BIOCHEM LAB EXPT. 3 - PROTEINS

protein

greek word: proteios “of first importance”

protein

most abundant macromolecule in the body, 15% of total cell’s mass

protein structure

long chain of a-amino acid, containing 50 amino acid residues

peptide

long chain of a-amino acid, containing NO amino acid residues

R-group

the side chain of proteins giving it its “identity”

20 common amino acids in human proteins

Standard Amino Acids

how to classify standard amino acids?

according to polarity of side chains

polarity of side chains

• non-polar amino acids

• polar neutral amino acids

• polar acidic amino acids

• polar basic amino acids

amino acids in peptides & proteins are connected via _____

peptide bond

native conformation

protein’s three dimensional structure

based on native conformation proteins can be:

• globular (spherical) ex. albumin

• fibrous (elongated) ex. gelatin

denaturation

a change in native conformation of proteins impacting function

Denaturation

disruption and unfolding of protein

common manifestation: protein losing solubility in water

irreversible denaturation

result:

• precipitation

• coagulation

precipitation

sticking of molecules together forming a solid coming out of solution

coagulation

clumping of particles in a solution

results in coagulum

precipitation of proteins 3 ways

A. by heavy metal salts

B. by strong mineral acids

• heller’s test

• robert’s test

C. by alkaloidal reagents

color reaction of proteins

used to transform colorless chemical compounds => colored

is characteristic of the present functional groups in amino acids

color reaction tests

A. biuret test for peptide bonds

B. ninhydrin test for free alpha-amino group

C. xanthoproteic test for phenyl-containing amino acids

D. adamkiewicz reaction for tryptophan

E. reduced sulfur test for cysteine

Molisch’s Test

for presence of carbohydrate moiety

glycoproteins

protein with carbohydrate prosthetic group

Modified Neuman’s Test

for presence of phosphate