Biochem Lab Proteins

Proteins

Proteins

are polymers of monomer amino acids.

Albumin

is a simple globular protein.

A typical protein

may be composed of two to hundreds of amino acids.

R-groups

of the amino acid may be nonpolar, polar, positively charged, or negatively charged.

PRIMARY STRUCTURE

the sequence of the amino acids in the chain and the disulfide links

SECONDARY STRUCTURE

structure formed by hydrogen bonding. examples: are alpha-helix and B-pleated sheets

Tertiary

complete 3-D conformation

Quaternary Structure

association of two or more peptide chains to form protein

PROTEIN DENATURATION

any process that change the protein conformation which results to loss of protein activity and function

PROTEIN DENATURATION

destruction of the quaternary, tertiary and secondary levels of structure of proteins

hydrolysis

destruction of the primary level of protein structure

DENATURATING AGENTS

heat, pH, organic solvents, and heavy metals

heat

causes the atoms to vibrate more rapidly by kinetic energy

HEAT

disruption of relatively weak forces such as H-bonds and hydrophobic interactions

pH

the R-groups in the amino acids are often charged and can form ionic bonds with a group of opposite charge

extremes of pH

can change these charges on the positive and negative groups, disrupting the ionic bonds

ORGANIC SOLVENTS

chemicals like ethanol can form H-bonds with protein molecules which disrupts the intramolecular H-bonds of the protein itself

70% ethanol

is used as a disinfectant because it denatures proteins of bacteria (can penetrate the bacterial cell wall)

95% ethanol

coagulates proteins at the cell wall surface, forming a crust that prevents the alcohol to penetrate bacterial cell

mercury (II), lead (II), and silver

can form strong bonds with disulfide groups of proteins

insoluble metal-protein salt

disrupted disulfide bridges and salt linkages cause the protein to precipitate out of the solution as

high-protein substances (egg whites, milk)

are used as antidotes for heavy metal poisoning

insoluble solids

their high-protein substances (egg whites, milk) combine with the heavy metals to form

emesis

these insoluble solids are removed by _ (to prevent gastric juices in destroying the protein)

Heated SAS

Formation of white solid particles

SAS + 1M HCl

Acidic solution

SAS + 10% NaOH

Alkali solution

SAS + Ethanol

More turbid solution

SAS + Lead Nitrate, and SAS + Silver Nitrate

formation of ppt

Control (SAS)

turbid solution