 Protein: chain of amino acids joined by peptide
bonds
 Amino Acids: The Building Blocks of protein.
Consist of:
 Central carbon bonded to hydrogen
 Amino group (NH2)
 Carboxylic group (-COOH)
 R-group
 20 common amino acids (AA)
 Classified based on the properties of the R groups
 Body uses over 20 amino acids to make proteins
Amino Acid Structure
R
NH2CH
COOH
Protein Structure
O
O
~NHCHC-NHCHC~
R1
R2
Peptide bond
Peptide Bond: Joins amino acids
Peptide Chain
 Proteins are large organic compounds made of amino
acids arranged in a linear chain and joined together by
peptide bonds between the carboxyl and amino groups
of adjacent amino acid residues.
 They play key roles in constructing and maintaining
living cells.
 The word protein comes from the Greek ("prota");
meaning "of primary importance" and these molecules
were first described and named by the Swedish
chemist Jöns Jakob Berzelius in 1838. However,
proteins' central role in living organisms was not fully
appreciated until 1926, when James B. Sumner showed
that the enzyme urease was a protein.
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Proteins are classified based on number of amino
acids (structure):
Dipeptides
Tripeptides
Oligopeptides
Polypeptides
 Proteins in the Diet:
 9 of the 20 amino acids must be obtained from the
diet. These are referred to as the essential amino acids.
Protein Structure and Function
 Proteins are polymers of
Alpha-amino acids.
 The amino acids used to
make proteins are 2aminocarboxylic acids.
 The (alpha) carbon is the
carbon to which a
functional group is
attached.
Classification of amino acids
1- Essential amino acid:
 An amino acid that cannot be synthesized by the
organism (usually referring to humans), or can only
make in inadequate quantities and therefore must be
supplied in the diet.
 Need to be consumed from the diet
 8-10 essential amino acids
 Depends on species and physiological state
Classification of amino acids
2- Nonessential amino acid:
 Nonessential amino acids are that which is ``made by
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the body from the essential amino acids or normal
breakdown of proteins.
The body can make these Amino Acids in large enough
quantities
Made from essential amino acids
Not necessary to consume these in the diet
10-12 nonessential amino acids
Classification of amino acids
3- Conditionally essential amino acid.
 Meaning they are not normally required in the diet but
can become essential and must be supplied
exogenously in certain physiologic conditions in
populations that do not synthesize it in adequate
amounts.
 Example: Tyrosine becomes essential in people with
“Phenylketonuria (PKU)”
Classification of amino acids:
Essential (10):
Nonessential (10)
Conditionally essential
(3)
Phenylalanine
Alanine
Cysteine
Valine
Asparagine
Glutamine
Threonine
Aspartic acid
Tyrosine
Tryptophan
Cysteine
Isoleucine
Glutaminc acid
Methionine
Glutamine
Histidine
Glycine
Arginine
Proline
Leucine
Serine
Types of Proteins:
 Structural: tendons, cartilage, hair, nails
 Contractile: muscles
 Transport: hemoglobin, myoglobin
 Storage: milk, nuts, seeds
 Hormonal: insulin, growth hormone
 Enzyme: catalyzes reactions in cells
 Protection: immune response
Protein metabolism
 The liver uses amino acids for its own purposes or
sends them out into the blood for the other cells of the
body
 Cells use free amino acids for the functions of that cell.
These include:
1. Synthesize protein
2. Provide energy if not enough carbohydrate and fat
for this function
 Store as fat if too many amino acids present
Biological functions of proteins
1. Enzyme
8. Circulation and
Transportation (Blood,
2. Building blocks: Cell
3.
4.
5.
6.
7.
membrane structure
and function
Muscles
Cytoplasm
Storage
Chromosome
Protective
9.
10.
11.
12.
13.
P-proteins)
Hormones and other
chemical messengers
Immunity: Immune
factors (antibodies)
Fluid balance
Acid-base balance
Source of energy and
glucose.
Plasma Proteins
 More than 200
 Most abundant
 Albumin - 4-5 g/100 mL
 g-glubulins - ~1 g/100 mL
 fibrinogen - 0.2-0.4g/100 mL
 Original classification by zone electrophoresis at
pH 8.6
Functions of Plasma Proteins:
1-Maintenance of:
 Colloid osmotic pressure (p)
 pH
 electrolyte balance
2-Transport of ions, fatty acids, steroids, hormones etc.
 Albumin (fatty acids), ceruloplasmin (Cu2+), transferrin (Fe),
lipoproteins (LDL, HDL)
3.
4.
5.
6.
Nutritional source of amino acids for tissues
Hemostasis (coagulation proteins)
Prevention of thrombosis (anticoagulant proteins)
Defense against infection (antibodies, complement
proteins)
Proteins and disease
 Increase in serum total protein reflects increases
in albumin, globulin, or both.
 Generally significantly increased total protein is
seen in volume contraction, venous stasis, or in
hypergammaglobulinemia.
 Decrease in serum total protein reflects decreases
in albumin, globulin or both.
Albumin
 MW 66 000
 Single chain, 580 amino acids, sequence is known
 Dimensions - Heart shaped molecule
 50% a helix
Synthesis:
 Mainly liver cells then exported
Functions
 “Colloid” osmotic pressure of blood is 80% due to
albumin and thus regulates water distribution
 Transport of fatty acids from the Liver to tissues for
binding.
Albumin in disease:
Increased:
 Absolute serum albumin content is not seen as a
natural condition.
 Relative increase may occur in hemoconcentration.
 Absolute increase may occur artificially by infusion of
hyperoncotic albumin suspensions.
Albumin in disease:
Decreased:
 serum albumin is seen in states of decreased synthesis
(malnutrition, malabsorption, liver disease, and other
chronic diseases), increased loss (nephrotic syndrome,
many GI conditions, thermal burns, etc.), and
increased catabolism (thyrotoxicosis, cancer
chemotherapy, Cushing's disease, familial
hypoproteinemia).
2- Globulin, A/G ratio
 20% of plasma proteins
 Represents a group of proteins of variable structure
 immunoglobulins
 5 classes of immunoglobulins: IgG, IgA, IgM, IgD, IgE
 Main functional task is immunochemical
 Antibodies - combine with specific antigens
 Functions
 Primary function is antigen binding (immune response)
 Secondary function is complement binding (after antigen)
 Synthesis
 In lymphocytes (T and B)
 Made in response to presence of antigen (“foreign”
macromolecule, virus particle etc.)
Globulin and disease:
 Globulin is increased disproportionately to
albumin (decreasing the albumin/globulin ratio)
in states characterized by chronic inflammation
and in B-lymphocyte neoplasms, like myeloma
and Waldenström's macroglobulinemia. More
relevant information concerning increased
globulin may be obtained by serum protein
electrophoresis.
 Decreased globulin may be seen in congenital or acquired
hypogammaglobulinemic states. Serum and urine protein
electrophoresis may help to better define the clinical
problem.
Fibrinogen:
 Function
 Blood coagulation (clotting)