MLAB 2401: Clinical Chemistry
Keri Brophy-Martinez
Overview:
Amino Acids & Proteins
Amino Acids
Building blocks of proteins
 Chemical properties determine biological
activity
 Origin

◦ Majority made in the human
 Generated from amino acid pool
 Generated from breakdown of proteins
◦ Essential Amino acids
 Ingested in diet
 “MILL PATH TV”
Amino Acids

Linked together by peptide bonds to form
the building blocks of proteins
Peptide
bond
Aminoacidopathies
Rare inherited disorders
• Enzyme defect that inhibits the body’s ability
to metabolize certain amino acids
• Abnormality due to problem with enzyme
activity or the membrane transport system
for amino acids
• Cause severe medical problems due to the
buildup of toxic amino acids and/or
byproducts of amino acid metabolism in
blood
•
Aminoacidopathies: Disorders
– Phenylketonuria
• Absence of phenylalanine hydrolase
• Mousy odor of the urine
• Causes significant brain damage
– Tyrosinemia
• Three types
• Type I most severe
• Causes liver and kidney damage, affects CNS
– Alkaptonuria
• Absence of homogentisate oxidase
• Urine turns brownish-black upon exposure to air
Aminoacidopathies: Disorders
–
–
Maple syrup urine disease
• Absence or reduction of alpha-ketoacid
decarboxylase
• Hallmark feature is the odor of maple syrup or burnt
sugar in the urine, breath and skin
Isovaleric Acidemia
• Absence of isovaleryl-CoA dehydrogenase
• Distinctive odor of sweaty feet due to build up of
isovaleric acid
Aminoacidopathies: Disorders
–
Homocystinuria
• Absence of cystathionine-beta-synthetase
–
Cystinuria
• Defect in amino acid transport system
• Results in the formation of stones
Proteins
•
Built from one or more chains of amino acids
•
Specific
•
Contain carbon, hydrogen, oxygen, sulfur and
nitrogen
•
Nucleotide sequence in the genes dictates the
amino acid sequence of the protein
Proteins

Synthesis
◦ Plasma proteins made in liver then secreted
by hepatocyte into circulation
◦ Immunoglobulins made in plasma cells
◦ Insufficient dietary quantities of amino acids
will limit synthesis and lower body levels of
proteins
Proteins

Catabolism (Breakdown)
◦ Goal is to remove nitrogen from the system
◦ Occurs in the digestive tract, kidneys, and liver
◦ Produces ammonia, then urea
 Urea excreted via urine
◦ Produces ketoacids
 Ketoacids converted to glucose or fat
Structure of Proteins
Denaturation
Disruption of structure
 Results in loss of function and protein
chemical properties
 Caused by:

◦
◦
◦
◦
◦
Heat
pH changes
Mechanical forces
Exposure to UV light
Exposure to chemicals
Classification of Proteins


Simple proteins
◦ Proteins made of only amino acids
◦ Further classified as globular or fibrous
Conjugated proteins
◦ Proteins with nonprotein groups attached
◦ Metalloproteins
◦ Lipoproteins
◦ Glycoproteins
◦ Mucoproteins
◦ Nucleoproteins
◦ Phosphoproteins
Functions of Proteins
Protein
Function
Examples
Enzymes
Catalyse chemical reactions
Transminases, phosphatases,
dehydrogenases
Hormones
Chemical messengers that
control the actions of
specific cells or organs
Insulin, growth hormone,
cortisol
Transport Proteins
Transport ions, small
molecules or
macromolecules across
biological membranes
Hemoglobin, albumin,
transferrin
Immunoglobulins
Mediate humoral immune
response to id and
neutralize foreign objects
IgG, IgM, IgA
Structural
Structures of cells and
tissues
Collagen, elastin, keratin
Functions of Proteins
Protein
Function
Examples
Storage
Serve as reserves of metal
ions and amino acids
ferritin
Energy
Reserve source of energy
Osmotic Force
Maintain water distribution
between cells and tissue,
interstitial compartments
and the vasculature
albumin
References



Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry:
Techniques, principles, Correlations. Baltimore: Wolters
Kluwer Lippincott Williams & Wilkins.
http://www.stanford.edu/group/pandegroup/folding/educ
ation/prstruc.html
Sunheimer, R., & Graves, L. (2010). Clinical Laboratory
Chemistry. Upper Saddle River: Pearson .