Ακολουθίες και Μουσικοί Όροι

Proteins

• Derived from the Greek word proteios, meaning "of first rank of importance"
• Large molecules called macromolecules
• Fundamental building block: amino acids
• Protein soluble in water: albumin
• Element distinguishing protein from carbohydrates and lipids: nitrogen

Amino Acids

• Simple organic compounds, building blocks of proteins
• Used to synthesize nitrogen-containing non-protein compounds (purines, pyrimidines, porphyrins, creatine, histamine, thyroxine, epinephrine, coenzyme NAD)

Amino Acids: Basic Structure

• Amphoteric, classified as zwitterions
• Peptide bond: formed when the carboxyl group (-COOH) of one amino acid links to the amino (-NH2) group of another, releasing a water molecule.
• N-terminal: end of a protein structure with a free amino group
• C-terminal: end of a protein structure with a free carboxyl group

Amino Acids: Metabolism

• Food is mechanically digested in the mouth then stomach.
• Gastrin stimulates HCl and proteolytic enzymes secretion in the stomach for protein denaturation and hydrolysis into polypeptides.
• HCl neutralization by sodium bicarbonate from the pancreas under the direction of secretin.
• Secretin and cholecystokinin stimulate pancreas and bile release.
• Pancreatic enzymes hydrolyze polypeptides into tripeptides, dipeptides, and the constituent amino acids.
• Dipeptides, tripeptides, and amino acids are absorbed via cotransporters and then, peptidases cleave any remaining peptide bonds into free amino acids.
• Free amino acids are transported into the bloodstream and then to the liver.
• Liver synthesizes proteins, NPN compounds, or energy through gluconeogenesis or ketogenesis.

Essential Amino Acids

• Nine essential amino acids: histidine, isoleucine, leucine, lysine, phenylalanine, threonine, tryptophan, and valine.
• Histidine: growth and repair of body tissues, myelin sheath protection, precursor for hormones.
• Isoleucine, leucine, and valine: branched-chain amino acids, concentrated in muscle tissues; essential for healing, immune function, glucose regulation, and hemoglobin formation. Promotes mental and muscle coordination.
• Lysine: antibody production, healthy tissues, calcium absorption.
• Methionine: initiates messenger RNA translation, cellular antioxidant, sulfur source for metabolism and growth, breakdown of fats and detoxifies lead and other heavy metals.
• Phenylalanine: precursor for tyrosine, dopamine, norepinephrine, epinephrine production.
• Threonine: formation of collagen, elastin, tooth enamel, neurotransmitters, proper protein balance, and porphyrins metabolism.
• Tryptophan: precursor for serotonin and melatonin; natural relaxant alleviating insomnia and depression; essential for niacin production.
• Valine: promotes mental and muscle health, crucial for coordination.

Nonessential Amino Acids

• Alanine: pivotal in carbohydrate metabolism (glycolysis), nitrogen transfer from peripheral tissues to the liver, energy source, immune function, toxic substance reduction.
• Asparagine: crucial for the synthesis of ammonia, via amination and transamination.
• Aspartate: precursor for several amino acids, including asparagine, arginine, lysine, methionine, threonine, and isoleucine.
• Glutamate: key role in neurotransmission, carbohydrate and lipid metabolism.
• Glutathione: important for lipid and fatty acid metabolism, crucial for the synthesis of pyrimidines, purines, creatine, and porphyrins, forming protective myelin sheaths around nerve fibers, and antibody production.
• Serine: necessary for proper lipid metabolism, essential for synthetic pathways of pyrimidines, purines, creatine, porphyrins, and myelination. Helps with antibody production
• Selenocysteine: not directly coded; has selenium as a constituent, crucial for metabolic pathways.

Conditionally Essential Amino Acids

• Arginine: role in cell division, wound healing, hormone release, immune function and ammonia conversion to urea.
• Cysteine: component of proteins and plays a role in detoxification.
• Glutamine: crucial for acid-base balance, fuel for digestive tract health, critical for RNA and DNA synthesis.
• Glycine: crucial for nucleic acids, bile acids, proteins, peptides, purines, ATP, porphyrins, hemoglobin, glutathione, creatine, bile salts, glucose, glycogen, muscle function, healing, and detoxification.
• Proline: precursor for hydroxyproline, formation of collagen, tendons, ligaments, cardiac tissues, and wound healing.
• Tyrosine: precursor for adrenal and thyroid hormones, metabolism, and nerve function.

Amino Acidopathies

• Inborn errors of metabolism impairing amino acid breakdown, potentially leading to severe medical complications like brain damage.
• Newborn screening tests are frequently performed for early detection.

Proteins: Synthesis

• Central dogma: DNA to RNA to Protein.
• DNA: replication
• RNA: transcription
• Protein: translation

Protein Structures

• Primary structure: linear sequence of amino acids, determines protein identity, and recognition capacity.
• Secondary structure: polypeptide chain folding into alpha-helix, beta-pleated sheets, and beta forms. Uses H+ bonds.
• Tertiary structure: three-dimensional configuration of a polypeptide chain; electrovalent linkages, hydrogen bonds, disulfide bridges, and hydrophobic interactions contribute to its structure.
• Quaternary structure: association of two or more polypeptide chains to form a functional protein.

Proteins: Denaturation

• Loss of native or naturally occurring protein structure.
• Results from changes in temperature, pH, or chemical activities disrupting hydrogen bonds..
• Types include heat, chemical, and mechanical.

Proteins: Nitrogen Balance

• Equality between proteins synthesis and breakdown
• Positive nitrogen balance: incorporation exceeds excretion; typical of growth and recovery stages.
• Negative nitrogen balance: excretion exceeds incorporation; occurs during starvation, severe illness, and injury.
• Lysosomal pathway: degrades extracellular proteins.
• Cytosolic pathway: degrades intracellular proteins.
• Transamination: crucial in removing amino acid nitrogen to the body

Proteins: Electrophoresis

• Zwitterion: form of amino acid with two different charges and a net charge of zero.
• Isoelectric point (pI): pH where the sum of a molecule’s charges equals zero.
• Rate of migration depends on size, shape, and charge. Different dyes are used in electrophoresis .

Proteins: Digestion of Proteins

• Dietary protein digestion begins in the stomach (100 g).
• Endogenous proteins are also digested (~100 g).
• Stomach: HCl denaturation, protease activation (pepsin).
• Pancreas: trypsin, chymotrypsin, elastase, carboxypeptidase, aminopeptidase.
• Small intestine: protein hydrolysis into amino acids for absorption.

Proteins: Classification of Proteins

• Simple proteins: composed only of amino acids (fibrous- collagen, fibrinogen- globulins, plasma proteins, enzymes, hormones).
• Conjugated proteins: composed of amino acids and non-protein parts (prosthetic groups). Example: metalloproteins (metal ions attached to protein), lipoproteins (lipids), mucoproteins (carbohydrates), glycoproteins (carbohydrates), and nucleoproteins (nucleic acids).

Proteins: Plasma Proteins

• Prealbumin/Transthyretin: migrates ahead of albumin, diagnostic of CSF. Increased: alcohol use, chronic renal failure, steroid treatments. Decreased: poor nutrition, inflammation, malignancy. Measured by nephelometry; 18–45 mg/dl range.
• Albumin: most abundant, transports proteins, buffers pH, negative acute-phase reactant, osmotic pressure. Marker for nutritional status, drug half-life; 3.5–5.0 g/dl range.
• Globulin: group of proteins including α1, α2, β, and γ fractions; measured indirectly (total protein – albumin); reference range: 2.3–3.5 g/dl.

Proteins: Alpha 1-Globulins

• Alpha-1-antitrypsin (AAT): acute phase reactant, protease inhibitor; inactivates trypsin; 145–270 mg/dl range. Increase in inflammation, pregnancy, and estrogen use. Decrease in AAT deficiency that may lead to emphysema and liver disease.
• Alpha-1-fetoprotein (AFP): glycoprotein; used to evaluate chromosomal abnormalities, fetal serum peaks at 13 weeks; 5 ng/ml range. Increase in neural tube defects, twins, hepatitis, and certain cancers, and decrease in certain diseases.
• Alpha-1-acid glycoprotein (orosomucoid): major plasma glycoprotein; negative charge; acute phase reactant; useful in identifying neonatal infections; 55–140 mg/dl range. Increase seen with pregnancy, inflammations, and cancers. Decrease is seen in patients with nephrotic syndrome.
• Alpha-1-lipoprotein: transports lipids (HDL); positive risk factor for atherosclerosis and carbohydrates.
• Alpha-1 Antichymotrypsin: serine protease inhibitor that inactivates chymotrypsin, elastase, and pancreatic elastase; component of Alzheimer's amyloid deposits; 30–60 mg/dl range. Increase is indicated in malignancies, infections, and burns; decrease in liver disease.
• Inter-a-trypsin inhibitor: inhibits serine proteases; increased in inflammation.

Proteins: Alpha 2-Globulins

• Haptoglobin: acute-phase reactant, synthesizes by hepatocytes, evaluate hemolytic anemia, binds free hemoglobin to prevent urine loss; marker for hemolysis and hemoglobinuria; 26–185 mg/dl range. Increase is seen with steroid therapy and acute inflammatory response. Decrease in severe infections, injuries, and blood loss.
• Ceruloplasmin: acute-phase reactant; copper-carrying protein (90% bound), marker for Wilson's disease; 18–45 mg/dl range. Increased in inflammatory diseases, and decreased in Wilson's disease
• Alpha 2-macroglobulin: protease inhibitor, important component of α2-globulin; 18–45 mg/dl range. Increase in nephrotic conditions; decreased in peptic ulcers and other diseases.

Proteins: Beta Globulins

• Transferrin (Siderophilin): synthesized by the liver; binds iron; 215–365 (male) and 250–380 mg/dl (female) range; negative acute-phase reactant. Increase in hemochromatosis and iron anemia; decrease in infections, liver diseases, and malnutrition.
• Complement: natural defense through cell lysis; synthesized by the liver. Most abundant- C3. C3 and C4 are essential components; useful in evaluating inflammatory conditions and some immune processes
• Fibrinogen: precursor of a fibrin clot; one of the largest plasma proteins; classified as glycoprotein and is often located in the beta-gamma region in electrophoresis; 200-400 mg/dl range Increase can indicate inflammation and pregnancy. Decrease during extensive coagulations.
• Hemopexin: synthesized by liver, binds free heme (protoporphyrin IX); used in diagnosing hemolytic uremic syndrome (HUS); increase in inflammation; decrease in hemolytic anemia diagnosis.
• Pre-B-lipoprotein (VLDL): transports lipids, increased in hyperlipoproteinemia and atherosclerosis, decreased due to starvation.
• B-lipoprotein (LDL): transports lipids, increased in hyperlipoproteinemia and atherosclerosis; increased in cardiovascular diseases.
• B-2-microglobulin: single polypeptide chain, component of HLA class I proteins. Increase seen associated with diseases like multiple myeloma, acute inflammatory diseases, and rheumatoid arthritis. Decreased in various conditions

Proteins: Gamma Globulins

• Immunoglobulins: glycoproteins produced by plasma B-cells; important for immune responses; IgG is the most abundant antibody in plasma. Increase in immunodeficiency diseases; decrease in hypogammaglobulinemia.

Proteins: Multiple Myeloma

• Cancer of plasma cells in the bone marrow; increased plasma cells, total protein, serum creatinine, and ionized calcium. Urine analysis shows the presence of Bence Jones protein; electrophoretic pattern shows a peaked gamma globulin region.

Proteins: Multiple Sclerosis

• Autoimmune disorder attacking the myelin sheath in the central nervous system; presence of oligoclonal bands in CSF and increased myelin basic protein.

Proteins: Minor Plasma Proteins

• Fibronectin: increased risk of premature birth, cell adhesion, tissue differentiation, wound healing, nutritional marker.
• Cross-Linked C-Telopeptides (CTX): biochemical marker of bone resorption; useful for monitoring antiresorptive therapy response and to identify diseases like osteoporosis.
• Amyloid: insoluble fibrous protein aggregates forming secondary structure (beta-pleated sheets) due to alteration; indicative of Alzheimer's disease, and dementia. High Tau protein is a strong indicator.
• Cystatin C: cysteine protease inhibitor, marker for glomerular filtration rate (GFR) changes, use in kidney dysfunction screening and monitoring.
• Adiponectin: inverse correlation with body mass index; low levels correlate with risk of heart disease, type 2 diabetes and metabolic syndrome.
• -Trace protein:* marker for CSF leakage, impaired renal function.

Cardiac Proteins

• Brain Natriuretic Peptide (BNP): marker for congestive heart failure, left ventricular myocardium, and right ventricle myocardium; elevated in heart failure; used to test for heart failure.
• Myoglobin: heme protein in skeletal and cardiac muscles; higher affinity for oxygen than hemoglobin; elevated in myocardial infarction; marker for occult blood related to pseudoperoxidase activity
• Troponin: gold standard for diagnosing acute coronary syndrome (ACS); TnI and TnT are more specific to cardiac injury than creatine kinase MB (CK-MB). Elevated in myocardial infarction and unstable angina; 3-4 hours after onset of cardiac events.
• Troponins (cTn): proteins that regulate actin and myosin in muscles; cTnT and cTnI are cardiac markers specific for cardiac injury.

Myocardial Infarction (MI)

• Reduced or stopped blood flow to the heart muscle (myocardium)
• Clinical criteria include symptoms, abnormal cardiac biomarkers, and myocardial ischemia.
• Detected by ECG, history, and possible coronary angiography results.
• Types 1, 2, 3, 4a, 4b, 4c, 5, are classified according to the cause of myocardial injury.

Laboratory Procedures

• Various laboratory tests (qualitative or quantitative) are performed using different methods (e.g. spectrophotometry, refractometry, turbidimetry, immunoassay, dipstick tests, and electrophoresis) to measure the concentrations of various proteins (e.g., total protein, albumin, globulins) in body fluids like serum, urine, CSF, and bodily fluids.

Proteins: Specimen Considerations

• Freezing and thawing specimens may damage protein structure.
• Hemolysis increased by hemoglobin will falsely elevate total protein levels.

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