Proteins and Aminoacids

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

Peptide Bond: Joins amino acids

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.

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 2-aminocarboxylic 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 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 Isoleucine Glutaminc acid Methionine 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: Synthesize protein Provide energy if not enough carbohydrate and fat for this function Store as fat if too many amino acids present

Biological functions of proteins Enzyme Building blocks: Cell membrane structure and function Muscles Cytoplasm Storage Chromosome Protective Circulation and Transportation (Blood, 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) 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 Globulin and disease: 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)