Amino Acids Classification Quiz

Amino Acids

• 20 different amino acids are essential for human life.
• 12 amino acids can be synthesized by the human body.
• 8 essential amino acids must be obtained from food.
• Amino acids are classified based on their chemical structure and nutritional requirements.
• Chemical Classification:
  • Neutral Amino Acids: Contain an equal number of amino and carboxylic groups.
    • Aliphatic Amino Acids:
      • Glycine, Alanine, Valine, Isoleucine, Leucine
    • Hydroxy Amino Acids:
      • Serine, Threonine
    • Sulphur Amino Acids:
      • Cysteine, Cystine, Methionine
    • Aromatic Amino Acids:
      • Phenylalanine, Tyrosine, Tryptophan
  • Basic Amino Acids: Have more amino groups than carboxylic groups.
    • Histidine, Arginine, Lysine.
  • Acidic Amino Acids: Have more carboxylic groups than amino groups.
    • Glutamic acid, Aspartic acid.
  • Imino Acids: Contain an imino group (NH).
    • Proline, Hydroxyproline.
• Nutritional Classification:
  • Essential Amino Acids:
    • Cannot be synthesized by the body.
    • Must be obtained from diet.
    • Deficiency can lead to diseases.
    • Examples: Valine, Leucine, Isoleucine, Histidine, Phenylalanine, Tryptophan, Threonine, Methionine.
  • Nonessential Amino Acids:
    • Synthesized in the body.
    • Not essential for dietary intake.
    • Includes all other amino acids not classified as essential.
• Metabolic (Biological) Classification:
  • Based on the fate of amino acids in the body.
  • Glucogenic Amino Acids:
    • Converted into glucose.
    • All amino acids except leucine are glucogenic.
  • Ketogenic Amino Acids:
    • Converted into ketone bodies.
    • Examples: Leucine and lysine.
  • Both Glucogenic and Ketogenic:
    • Converted into both glucose and ketone bodies.
    • Examples: Tyrosine, Phenylalanine, Tryptophan, Isoleucine.

Proteins

• Definition: Polymers of amino acids linked by peptide bonds.
• Classification of Proteins:
  • According to Peptide Bond Structure:
    • Simple Proteins:
      • Only produce amino acids on hydrolysis.
      • Examples:
        • Albumin: Found in egg white, serum, and milk.
        • Globulin: Found in egg white, serum, and milk.
        • Histones: Associated with nucleic acids (chromatin) and in the globin part of hemoglobin.
        • Scleroproteins (Albuminoids):
          • Keratin: Found in hair, nails, and dermis.
          • Elastin: Found in elastic tissues.
    • Conjugated Proteins:
      • Have a non-protein component called a prosthetic group.
      • Examples:
        • Phosphoproteins: Contain phosphate groups.
        • Lipoproteins: Contain lipids.
        • Glycoproteins: Contain carbohydrates.
        • Chromoproteins: Contain pigments.
        • Nucleoproteins: Contain nucleic acids.
  • According to Function:
    • Catalytic Proteins (Enzymes): Act as biochemical catalysts.
      • Examples: Glucokinase, Dehydrogenase, Transaminase.
    • Defense Proteins: Bind to foreign substances (like bacteria and viruses) to combat invasion.
      • Examples: Immunoglobulins.
    • Transport Proteins: Bind to small biomolecules and transport them.
      • Examples:
        • Hemoglobin: Transports oxygen.
        • Transferrin: Transports iron.
    • Storage Proteins: Bind and store small molecules for future use.
      • Examples:
        • Ferritin: Stores iron in the liver.
        • Myoglobin: Stores oxygen in muscles.
    • Nutrient Proteins: Important in early life, from embryo to infant.
      • Example: Casein in milk.
    • Regulatory Proteins: Regulate cellular and physiological activities.
      • Example: Insulin.

Coenzymes in Group Transfer Reactions

• Coenzymes are non-protein organic molecules that assist enzymes in their function.
• They are often required for specific reactions.
• Examples of Coenzymes in Group Transfer Reactions:
  • Nicotine Adenine Dinucleotide: NAD and NADP
    • Functions: Electron (hydrogen atom) carriers in redox reactions.
  • Flavin Adenine Dinucleotide: FAD
    • Function: Electron (hydrogen atom) carrier in redox reactions.
  • Coenzyme A: CoA
    • Function: Carries acyl groups.
  • Coenzyme Q: CoQ
    • Function: Electron (hydrogen atom) carrier in redox reactions.
  • Thiamine Pyrophosphate: Vitamin B1
    • Function: Handles aldehydes.
  • Pyridoxal Phosphate: Vitamin B6
    • Function: Handles amino groups.
  • Biotin:
    • Function: Carries carbon dioxide.
  • Cobamide Coenzymes: Vitamin B12
    • Function: Carries alkyl groups.

Cofactors

• Inorganic substances that are required for, or increase the rate of, catalysis.
• Often metal ions.
• Examples of Enzymes with Metal Ion Cofactors:
  • Carbonic Anhydrase: Zn++
  • Alcohol Dehydrogenase: Zn++
  • Cytochromes, Hemoglobin: Fe+++ or Fe++
  • Ferredoxin: Fe+++ or Fe++
  • Cytochrome Oxidase: Cu++ or Cu+
    • Pyruvate Phosphokinase: K+ and Mg++

Enzyme Specificity

• Enzymes are highly specific:
  • Absolute Specificity: Enzyme acts on only one substrate.
    • Examples: Uricase and uric acid, Urease and urea.
  • Relative Specificity: Enzyme acts on a group of similar compounds.
    • Often targets a specific bond or functional group.
  • Stereochemical Specificity: Enzyme distinguishes between stereoisomers.

Hormonal Action:

• Hormones are chemical messengers that regulate various bodily processes.

• They differ from enzymes in their site of production and mode of action.

• Classification of Hormones:

  • According to Chemical Nature:

    • Amino Acid Derivatives:
      • Thyroid hormones (T3 and T4)
      • Catecholamines (Epinephrine and norepinephrine)
      • Melatonin
    • Polypeptide or Protein Hormones:
      • Hypothalamic, pituitary, parathyroid, and pancreatic hormones.
    • Steroid Hormones:
      • Adrenocortical hormones
      • Calcitriol hormone

  • According to Location of Receptors:

    • Intracellular Receptors (Group I):
      • Intracytoplasmic Receptors: Steroid hormones.
      • Intranuclear Receptors: Thyroid hormones.
    • Extracellular Receptors (Group II):
      • Catecholamines, Glucagons, Calcitonin, Pituitary hormones.

• Mechanisms of Hormone Action:

  • Group I: Hormones with Intracellular Receptors:

    • Lipophilic (fat-soluble) hormones diffuse through the plasma membrane.
    • Bind to high-affinity receptors in the target cell.
    • The hormone-receptor complex binds to specific regions of DNA called hormone response elements (HRE).
    • This activates gene transcription and mRNA production.
    • The mRNA translates to a specific protein (enzyme).
    • The new enzyme then activates the metabolic process.

  • Group II: Hormones with Extracellular Receptors:

    • Water-soluble hormones interact with plasma membrane receptors.
    • This interaction can activate or inactivate adenylate cyclase.
    • Activation of adenylate cyclase leads to cAMP (cyclic adenosine monophosphate) production from ATP.
    • cAMP is considered a second messenger.
    • cAMP activates protein kinase, which phosphorylates proteins and elicits physiological effects.

• Examples of Hormones That Activate Adenylate Cyclase:

  • Epinephrine, Norepinephrine, Glucagon, Parathyroid Hormone, FSH, LH, ACTH, MSH.

• Effects of cAMP Activation:

  • Stimulates glycogenolysis via phosphorylase activation.
  • Stimulates lipolysis via lipase activation.
  • Inhibits glycogenesis by inhibiting glycogen synthetase.

• G-Proteins and Hormonal Action:

  • Hormones bind to the external face of the G-protein coupled receptor.
  • The receptor undergoes a conformational change, which is propagated to the G-protein binding site.
  • The G-protein binding site binds to the trimeric G-protein (αβγ), causing it to exchange bound GDP for GTP.
  • Exchange of GDP to GTP causes the G-protein to dissociate into α-GTP and βγ subunits.
  • The α-GTP subunit diffuses across the inner face of the plasma membrane and interacts with adenylate cyclase.
  • Adenylate cyclase becomes activated and converts ATP to cAMP as long as α-GTP is bound to it.
  • The α-subunit has GTPase activity and eventually hydrolyzes its bound GTP to GDP + Pi.
  • The α-subunit then dissociates from adenylate cyclase and diffuses back to re-associate with βγ to form an inactive molecule.

Pituitary Hormones:

• The pituitary gland is often referred to as the "master gland" of the endocrine system because it controls the functions of other endocrine glands.

• It is located at the base of the brain and is connected to the hypothalamus by nerve fibers.

• The pituitary gland has three sections:

  • Anterior Lobe (Adenohypophysis)
  • Intermediate Lobe (Pars Intermedia)
  • Posterior Lobe (Neurohypophysis)

• **Hormones of the Anterior Lobe: **

  • Growth Hormone (GH)
  • Adrenocorticotropic Hormone (ACTH)
  • Thyroid Stimulating Hormone (TSH)
  • Follicle-Stimulating Hormone (FSH)
  • Luteinizing Hormone (LH)
  • Prolactin