Unit 11 - Study Notes on Proteins and Amino Acids

Proteins and Amino Acids

Introduction to Proteins

  • Proteins are formed by different arrangements of amino acids.
  • A short chain of amino acids is referred to as a peptide, whereas a longer chain is classified as a protein.
  • There are only 20 different amino acids that make up all the proteins in a mammal's body.

Structural Hierarchy of Proteins

  • The arrangement of amino acids determines the type of protein formed.
    • Primary Structure: The linear sequence of amino acids in the protein chain.
    • Secondary Structure: The folding or coiling of the amino acid chain into shapes such as alpha helices and beta sheets.
    • Tertiary Structure: The overall three-dimensional shape of a polypeptide, determined by interactions among the various side chains.
    • Quaternary Structure: The complex formed by the combination of two or more polypeptides.

Modifications of Proteins

  • Proteins can be modified by the addition of carbohydrates or lipids:
    • Glycoprotein: A compound formed when a protein is bound to a carbohydrate.
    • Lipoprotein: A compound formed when a protein is bound to a lipid.
  • These modifications are particularly relevant in the context of cell membranes.
  • The body cannot directly digest proteins; instead, it breaks them down into smaller components, primarily amino acids.

Types of Protein Structures

  • Proteins can be classified as either:
    • Globular Proteins: Often functional, playing roles in chemical reactions, signaling, and immune response.
    • Fibrous Proteins: Generally structural, providing support and strength to tissues.
    • Examples:
    • Fibrous Proteins: Elastin and collagen, which contribute to the structural integrity of tissues.
    • Globular Proteins: They often have a role in processes such as transport and catalysis.

Functions of Proteins

A) Functions of Globular Proteins

  • Hormones: Serve as chemical messengers (e.g., insulin).
  • Enzymes: Catalysts that accelerate chemical reactions (e.g., lipase involved in digestion).
  • Receptors: Proteins that receive and transmit signals within the body.
  • Antibodies: Immunoglobulins that play a crucial role in immune defense (e.g., responding to vaccinations).

B) Functions of Fibrous Proteins

  • Bind together cells and tissues providing support.
  • Examples:
    • Keratin: Found in hair, nails, and skin.
    • Collagen: Key component of connective tissues in bones and cartilage.
    • Contractile Proteins: Present in muscle tissues facilitating movement.

Amino Acids

  • Non-essential Amino Acids: Produced by the mammalian body (the body can synthesize them).
  • Essential Amino Acids: Must be obtained from the diet as the body cannot synthesize them. Examples include leucine, taurine, and arginine.
  • Deficiencies:
    • Taurine Deficiency: Notable in cats.
    • Methionine Deficiency: Known to occur in dogs.

Protein Analysis

Total Protein Content Measurement

  • Analyzed using large machine analyzers or simple refractometry methods.
  • Evaluation of total protein (TP) includes two main types:
    1. Albumin: Represents 50-60% of the protein content in plasma.
    2. Globulins: Proteins primarily involved in immune defense.

Blood Chemistry Screen Analyzer

  • Measurements include:
    • Total Protein: The aggregate measure of albumin and globulins.
    • Results are often shown in g/L, with a typical range for total protein being 52-82 g/L.

Specific Blood Chemistry Results

Example Analysis (Results taken from a specific test)

  • Glucose: 6.18 mmol/L
  • Creatinine: 90 μmol/L (reference range 53-141 μmol/L)
  • Blood Urea Nitrogen (BUN): 7.4 mmol/L (reference range 5.7-11.8 mmol/L)
  • Sodium: 162 mmol/L, Potassium: 3.5 mmol/L
  • Total Protein: 67 g/L (reference range 52-82 g/L)
  • Albumin: 25 g/L, Globulin: 42 g/L
  • Albumin: Globulin Ratio: 0.6

Plasma Proteins and Variations

Albumin Functions and Variations

  • Albumin produced in the liver plays a major role in maintaining osmotic pressure and carries various substances in the blood.
  • Hyperalbuminemia: Increase in albumin levels can indicate physiological hemoconcentration due to dehydration or actual overproduction (rare).
  • Hypoalbuminemia: Common causes include;
    1. Hemodilution: Resulting from fluid overload.
    2. Decreased Production: Often due to liver disease (>80% impairment).
    3. Increased Loss: Protein-losing conditions through kidneys or GIT (e.g., nephropathy, enteropathies).
    4. Catabolism due to malnutrition.

Increased Loss and Catabolism of Albumin

  1. Protein-losing Nephropathy (PLN): Damage to kidney's glomerulus results in leaking of albumin into the urine.
  2. Protein-losing Enteropathy (PLE): Loss of albumin through the intestines due to diseases like inflammatory bowel disease.
  3. Catabolism: Severe chronic malnutrition leads to decreased availability of amino acids for protein synthesis, impacting albumin levels.

Globulins Overview

  • Globulins are key components involved in immune defense.
  • Gamma Globulins: A subclass of globulins that includes immunoglobulins (IgM, IgA, IgG, IgD, IgE) which function as antibodies.

Variations of Globulins

  1. Hypoglobulinemia: Can occur in conditions like failure of passive transfer where newborns do not get colostrum from mothers, leading to insufficient maternal antibodies.
  2. Hyperglobulinemia: Typically due to increased antibody production in response to diseases, such as chronic skin conditions.

Enzymatic Activity Assessment in Biochemistry

  • Enzymes: Classification such as “-ases” refers to their function in accelerating chemical reactions.
  • Notable enzyme examples:
    • Lipase: Indicates gastrointestinal function and may suggest damage to digestive organs.
    • Creatine Kinase: Elevated level can indicate muscle damage or heart disease.
    • Key Liver Enzymes: ALT, AST, GGT, which reveal liver function or damage.

Specific Enzymatic Insights

  • Measurement of specific enzymes assists in determining underlying diseases:
    • Amylase and Lipase: Both pancreatic enzymes that may indicate GI or renal disease.
    • Pancreas-Specific Lipase: A specialized measurement indicating pancreatitis specifically, and typically added on tests if pancreatitis is suspected.

Summary of Enzyme Measurement Protocols

  • Serum rather than plasma should be used for the collection of enzyme-related tests.
  • Lab protocols vary; specific tests may require unique sample handling protocols (e.g., freezing samples on ice). Adjustment to methods might be necessary based on individual laboratory instructions.