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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