Proteins and Amino Acids Overview

Proteins and Amino Acids

• Proteins are polymers of amino acids linked by peptide bonds.
• Amino acids contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
• The presence of nitrogen distinguishes proteins from carbohydrates and lipids.
• Proteins are categorized based on the number of amino acids in their chain.
• Proteins have four structural levels: primary, secondary, tertiary, and quaternary.
• Protein properties include molecular size, solubility, electrical charge, adsorption to inert materials, and binding to other molecules (antibodies, coenzymes, hormones).
• Amino acids are the building blocks of proteins (approximately 20 unique types).
• Nine amino acids are essential (must be consumed in the diet) and eleven are non-essential (synthesized by the body).
• Some amino acids can be considered conditionally essential, depending on the individual's health state.
• Amino acids consist of a central carbon atom bonded to a hydrogen, carboxyl group, an amino group, and a unique side chain (R group).
• The R group varies among amino acids, leading to diverse properties.
• Different side chains determine protein folding and function.
• Peptide bonds form between the carboxyl group of one amino acid and the amino group of another.
• Condensation creates peptide bonds and releases water.
• Hydrolysis breaks the peptide bonds using water.
• Denaturing of proteins occurs through heat, acids, bases, salts, or mechanical agitation.
• Denaturing alters the protein's shape and thus its function.
• Protein digestion begins in the stomach with pepsin.
• Pepsin breaks down proteins into smaller peptides and amino acids.
• Proteolytic enzymes function in digestion by hydrolyzing peptide bonds.
• Trypsinogen and chymotrypsinogen (proenzymes) are secreted by the pancreas and activated in the small intestine.
• Endopeptidases cleave peptide bonds within the protein; exopeptidases cleave amino acids from the ends of peptide chains.
• Di- and tripeptides are actively transported into enterocytes using a specific transporter.
• Individual amino acids can be transported across the basolateral membrane independently or require cotransport carriers.
• Proteins in the digestive tract are hydrolyzed to individual amino acids for absorption.
• Diseases associated with protein absorption include Hartnup disease and cystinuria.
• Clinical significance of protein levels lies in identifying diseases (such as kidney disease, liver disease, malnutrition) or assessing hydration status and inflammatory processes.
• Examples of clinically important plasma proteins include albumin, alpha-1-acid glycoprotein, ceruloplasmin, C-reactive protein, complements, and immunoglobulins.

Methods of Protein Testing

• Biuret method involves the reaction between peptide bonds and copper ions to measure total protein.
• Direct photometric methods use UV light absorption at specific wavelengths to measure protein concentration, dependent on the aromatic amino acids, tyrosine and tryptophan.
• Dye-binding methods utilize dyes' binding capacity for protein measurement, mainly in CSF and urine samples.
• Turbidimetric and Nephelometric methods quantify protein via precipitation, measuring the turbidity (or light scattering) created.
• Techniques for serum albumin testing involve dye-binding, salt fractionation, electrophoresis, and immunochemical techniques.
• BCG (a dye) method is specific for albumin, determined at pH 4.2.
• Normal serum albumin range for adults is 3.5-5.0 g/dL.
• Methods for determining total globulins utilize colorimetric methods, difference measurement from total protein, electrophoresis, and immunochemical techniques.

Functions of Proteins

• Proteins are crucial in constructing body tissues and structures, catalyzing biochemical reactions, regulating metabolism, protecting against foreign substances, maintaining osmotic balance, transporting molecules, and promoting hemostasis.
• Proteins can be converted to carbohydrates, and some crucial hormones such as thyroid hormones, epinephrine, and norepinephrine are formed from proteins.

Clinical Significance of Protein Testing

• Elevated protein levels may arise from dehydration; decreased levels may indicate edema, inflammatory conditions, kidney disease, malnutrition, or other factors.
• Specific plasma proteins are used in diagnostics to assess conditions such as liver disease.

Diseases Associated with Protein Testing

• Some genetic disorders affect protein transport, causing specific health issues based on the specific proteins affected.

This quiz will test your knowledge on proteins and amino acids, including their structures, functions, and properties. You will learn about the different types of amino acids, their essential and non-essential categories, and the chemical elements they comprise. Get ready to delve into the fascinating world of these vital biomolecules!