Proteins and Amino Acids Overview

Proteins

• A group of complex organic macromolecules containing carbon, hydrogen, oxygen, nitrogen, and usually sulfur.
• Linear polymers of amino acids connected by peptide bonds.
• Most important of all biological compounds.
• Constitutes about 50% of the dry weight of cells.
• Must be consumed daily because they are not stored.
• Dietary protein usually comes from meat and dairy products.
• Recommended daily intake for adults: 0.8 grams of protein per kg of body weight.

Amino Acids

• Organic compounds containing an amino group (NH2) and a carboxylic acid group (COOH).
• Building blocks of protein.
• Most are chiral molecules.
• Chiral carbon centers are carbon atoms attached to four different substituents.
• Most common amino acids are α-amino acids.
• All amino acids in the body are L-isomers.
• Glycine is the simplest amino acid.
• Peptides and proteins are formed when amino acids are joined together by amide bonds.

Types of Proteins

• Actin: Spherical protein, thin filament, two long chains, each has a myosin-binding site.
• Serum Albumin: Largest protein component of human blood (50-60%), regulates plasma volume and tissue fluid balance.
• Tropomyosin: Blocks myosin binding sites on actin molecules, preventing contraction in a muscle without nervous input.
• Troponin: Globular protein, protein complex that binds to tropomyosin, helps position tropomyosin on the actin molecule.
• Erythropoietin: Glycoprotein hormone, naturally produced by the peritubular cells of the kidney, acts on red blood cells to protect them against destruction, stimulates stem cells of the bone marrow to increase RBC production.
• Growth Hormone: Secreted by the anterior lobe of the pituitary gland, stimulates the growth of essentially all tissues of the body, keeps blood glucose levels within set levels, decreases the rate of glucose uptake and metabolism.
• Vasopressin: Antidiuretic hormone, produced in the hypothalamus, helps control blood pressure by acting on the kidneys and blood vessels, conserves body water by reducing the loss of water in urine.
• Immunoglobulin: Antibodies.
• Fibrinogen: Involved in blood clotting.
• Thrombin: Involved in blood clotting.
• Ovalbumin: Major egg white protein, responsible for egg white formation.
• Casein: Storage protein found in milk.
• Ferritin: Protein complex that stores iron in a soluble, non-toxic form.
• Myoglobin: Monomeric protein found mainly in muscle tissue, serves as an intracellular storage site for oxygen.

Levels of Protein Structure

• Primary Structure: Linear sequence of amino acids connected by peptide bonds.
• Secondary Structure: Local folding patterns of the polypeptide chain.
• Tertiary Structure: Complete 3D arrangement of the atoms in a protein, held together by peptide bonds, hydrogen bonds, disulfide bonds, and salt bridges.
• Quaternary Structure: The spatial relationship and interactions between subunits in a protein that has more than one polypeptide chain, held together by peptide bonds, hydrogen bonds, disulfide bonds, and salt bridges.

Protein Digestion

• Begins in the stomach with the help of pepsin, which cuts proteins into smaller polypeptides.
• Continues in the small intestine where chyme is neutralized and trypsin, chymotrypsin, and elastase are activated.

Enzymes Involved in Protein Digestion

• Carboxypeptidase: Released from the pancreas as procarboxypeptidase, breaks down aromatic and branched amino acids.
• Aminopeptidase: Released from the small intestine as proaminopeptidase, breaks down peptides from the amino end.

Diseases Associated with Proteins

• Protein Deficiency: State of relative or absolute deficiency of body proteins or one or more of the essential amino acids.
• Hypoproteinemia: A state of relative or absolute deficiency of body proteins or one or more of the essential amino acids.
• Marasmus: Severe form of malnutrition, visible wasting of fat and muscle under the skin.
• Kwashiorkor: Severe form of protein malnutrition, characterized by bilateral extremity swelling, abdominal distension, round face, subcutaneous fat retention, thin, dry, peeling skin, growth retardation, psychic changes, skin lesions/dermatitis.
• Phenylketonuria: Rare inherited disorder, causes an amino acid called phenylalanine to build up in the body, caused by a change in the phenylalanine hydroxylase (PAH) gene.

Explore the fundamental concepts of proteins and amino acids in this quiz. Learn about their structures, importance, and daily intake recommendations. Discover the types of proteins and the key role amino acids play in building these essential macromolecules.