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 hydrogenAmino group (NH2)Carboxylic group (-COOH)R-group20 common amino acids (AA)Classified based on the properties of the R

groupsBody uses over 20 amino acids to make

proteins

~NHCHC- NHCHC~

R1

O O

R2

Peptide bond

NH2CH

COOH

RAmino Acid Structure

Protein Structure

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.

Proteins are classified based on number of amino acids (structure):

DipeptidesTripeptidesOligopeptidesPolypeptides 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 FunctionProteins 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 acids1- 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 diet8-10 essential amino acidsDepends on species and physiological state

Classification of amino acids2- 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 acidsNot necessary to consume these in the diet10-12 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: musclesTransport: hemoglobin, myoglobinStorage: milk, nuts, seedsHormonal: insulin, growth hormoneEnzyme: catalyzes reactions in cellsProtection: 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 protein2. Provide energy if not enough carbohydrate

and fat for this functionStore as fat if too many amino acids present

Biological functions of proteins1. Enzyme2. Building blocks:

Cell membrane structure and function

3. Muscles4. Cytoplasm5. Storage6. Chromosome7. Protective

8. Circulation and Transportation (Blood, P-proteins)

9. Hormones and other chemical messengers

10.Immunity: Immune factors (antibodies)

11.Fluid balance12.Acid-base balance13.Source of energy and

glucose.

Plasma Proteins

More than 200Most 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)pHelectrolyte balance

2-Transport of ions, fatty acids, steroids, hormones etc.Albumin (fatty acids), ceruloplasmin (Cu2+), transferrin

(Fe), lipoproteins (LDL, HDL)

3. Nutritional source of amino acids for tissues4. Hemostasis (coagulation proteins)5. Prevention of thrombosis (anticoagulant proteins)6. 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 000Single chain, 580 amino acids, sequence is

knownDimensions - Heart shaped molecule50% a helix Synthesis: Mainly liver cells then exported

Functions“Colloid” osmotic pressure of blood is 80% due

to albumin and thus regulates water distributionTransport 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 proteinsRepresents a group of proteins of variable

structureimmunoglobulins 5 classes of immunoglobulins: IgG, IgA, IgM, IgD, IgE

Main functional task is immunochemicalAntibodies - combine with specific antigens

FunctionsPrimary function is antigen binding (immune response)Secondary function is complement binding (after

antigen)

SynthesisIn 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:

FunctionBlood coagulation (clotting)