Clin-Chem Lab AA Part 2

Structural Organization of Proteins

Primary Structure

Secondary Structure

Tertiary Structure

Quaternary Structure

Structural Organization of Protein wherein it has:

• Linear sequence of Amino Acids joined by peptide bonds.

• The order is determined by DNA sequence.

Primary Structure

In this type of protein structure the peptide bond is between the carboxyl group of amino acid “A” and amino group of amino acid “B”.

Primary Structure

Protein example of Primary Structure

Insulin

Structural Organization of Protein wherein it is:

Formed by hydrogen bonds between:

• Carbonyl (C=O) and Amino (N-H) groups of peptide backbones.

• Creates specific folding patterns.

Secondary Structure

A secondary structure of protein that is a right-handed spiral.

Alpha helix

A secondary structure of protein wherein polypeptide chains are arranged side by side (parallel/ antiparallel)

Beta Pleated Sheet

Protein example of Secondary Structure

Keratin (Alpha helix)

Silk Fibroin (Beta Pleated Sheet)

Structural Organization of Protein wherein it has:

• Overall 3D shape of a single polypeptide chain.

• Formed by interactions between R groups side chains of amino acids.

Tertiary Structure

What are the types of Bonds under Tertiary Structure

• Hydrogen Bonds

• Ionic Bonds (Salt Bridges)

• Disulfide Bonds

• Hydrophobic Interactions

• Van der Waals Forces

• Hydrogen Bonds →

• Ionic Bonds (Salt Bridges) →

• Disulfide Bonds →

• Hydrophobic Interactions →

• Van der Waals Forces →

• Hydrogen Bonds → polar side chains

• Ionic Bonds (Salt Bridges) → between + & - R group

• Disulfide Bonds → covalent bonds

• Hydrophobic Interactions → nonpolar side chains

• Van der Waals Forces → weak interactions of atoms

Protein example of Tertiary Structure

Lysozyme

Myoglobin

Structural Organization of Protein wherein it has:

Multiple polypeptide chains (subunits) that interact to form a functional protein complex.

Quaternary Structure

Types of Quaternary Structure

• Homodimer/ Heterodimer → 2 subunits (identical/ different)

• Tetramer → 4 subunits

Protein example of Quaternary Structure

Hemoglobin

Immunoglobin

Oxygen transport protein, carries oxygen from lungs and delivers to tissue sites. (Has Alpha and Beta Chains)

Hemoglobin

Antibody protein.

Immunoglobulin

Tests/ Procedures on protein. (Protein Methodologies)

Tests/ Procedure:

• Total protein

• Albumin

Sample of choice on protein tests?

Serum (Absence of fibrinogen)

Why is Serum preffered than Plasma?

Plasma contains coagulation factors (fibrinogen) that can interfere with the results.

Is fasting required, on protein tests?

No, because proteins don’t get metabolyzed that fast compared to lipids.

Interferences in specimen considerations?

Interferences:

• Lipemia (excess lipids in blood)

• Hemolysis (presence of hemoglobin)

Can slight hemolysis still be run as a sample?

Yes, but place a note on the request form.

Can Moderate and Gross hemolysis still be run as a sample?

No (big changes).

The Tests under Protein Methodologies

• Total protein

• Albumin

Methods under Total protein. (Protein Methodologies)

KJELDAHL

BIURET

DYE BINDING

REFRACTOMETRY

Methods under Albumin. (Protein Methodologies)

SALT PRECIPITATION

DYE BINDING