NEET MDS Lessons
Biochemistry
Function of Calcium
The major functions of calcium are
(a) Excitation and contraction of muscle fibres needs calcium. The active transport system utilizing calcium binding protein is called Calsequestrin. Calcium decreases neuromuscular irritability.
(b) Calcium is necessary for transmission of nerve impulse from presynaptic to postsynaptic region.
(c) Calcium is used as second messenger in system involving protein and inositol triphosphate.
(d) Secretion of insulin, parathyroid hormone, calcium etc, from the cells requires calcium.
(e) Calcium decrease the passage of serum through capillaries thus, calcium is clinically used to reduce allergic exudates.
(f) Calcium is also required for coagulation factors such as prothrombin.
(g) Calcium prolongs systole.
(h) Bone and teeth contains bulk quantity of calcium.
The amino acids buffer system
Amino acids contain in their molecule both an acidic (− COOH) and a basic (− NH2) group. They can be visualized as existing in the form of a neutral zwitterion in which a hydrogen atom can pass between the carboxyl and amino groups.
By the addition or subtraction of a hydrogen ion to or from the zwitterion, either the cation or anion form will be produced
Thus, when OH− ions are added to the solution of amino acid, they take up H+ from it to form water, and the anion is produced. If H+ ions are added, they are taken up by the zwitterion to produce the cation form. In practice, if NaOH is added, the salt H2N - CH2 - COONa would be formed. and the addition of HCl would result in the formation of amino acid hydrochloride.
ZINC
The enzyme RNA polymerase, which is required for transcription, contains zinc and it is essential for protein bio synthesis.
Deficiency in Zinc leads to poor wound healing, lesions of skin impaired spermatogenesis, hyperkeratosis, dermatitis and alopecia
Protein electrophoresis is a laboratory technique used to separate proteins based on their size, charge, or other physical properties. It plays a vital role in diagnosing and monitoring various diseases, especially those involving abnormal protein production or structure.
Types of Protein Electrophoresis
1. SPE (Serum Protein Electrophoresis)
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Principle: Separation of serum proteins based on their charge.
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Major Fractions:
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Albumin
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Alpha-1 globulin
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Alpha-2 globulin
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Beta globulin
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Gamma globulin
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Clinical Applications:
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Multiple Myeloma: Detects monoclonal spike (M-protein) in gamma region.
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Chronic Infections: Polyclonal increase in gamma globulins.
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Nephrotic Syndrome: Decreased albumin, increased alpha-2 globulin.
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Liver Disease: Altered albumin and beta-gamma bridging.
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2. Hemoglobin Electrophoresis
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Principle: Separation of hemoglobin variants based on charge differences.
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Common Hemoglobins:
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HbA, HbA₂, HbF, HbS, HbC, HbE
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Clinical Applications:
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Thalassemia: Elevated HbA₂ or HbF levels.
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Sickle Cell Disease: Presence of HbS.
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Hemoglobinopathies: Differentiates variants like HbC, HbE, etc.
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3. SDS-PAGE (Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis)
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Principle: Proteins are denatured and separated by molecular weight.
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SDS: Imparts uniform negative charge, eliminating charge-based separation.
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Clinical Applications:
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Protein Purification: Identifies specific proteins in research and diagnostics.
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Genetic Disorders: Detects abnormal or truncated proteins.
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Muscular Dystrophies: Analyzes dystrophin protein expression.
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Cancer Research: Studies tumor markers and oncogenic proteins.
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The Protein Buffer Systems
The protein buffers are very important in the plasma and the intracellular fluids but their concentration is very low in cerebrospinal fluid, lymph and interstitial fluids.
The proteins exist as anions serving as conjugate bases (Pr − ) at the blood pH 7.4 and form conjugate acids (HPr) accepting H+ . They have the capacity to buffer some H2CO3 in the blood.
| Enzyme | Clinical Use | Timing |
|---|---|---|
| Troponin I/T | Gold standard for myocardial infarction | Rises in 3–6 hrs, peaks at 12–24 hrs |
| CK-MB | Specific to cardiac muscle damage | Rises in 4–6 hrs, peaks at 24 hrs |
| LDH (Isoenzyme 1) | Used historically for MI diagnosis | Peaks at 48–72 hrs |
Troponins remain elevated for up to 10 days—ideal for late diagnosis.
Pepsin
- Primary enzyme for protein degradation in stomach
- Optimal pH: 1.5-2.0 (acidic)
- Secreted as inactive pepsinogen
- Cleaves proteins into smaller peptides
Histone
- Protein rich in basic amino acids (lysine and arginine)
- Packages DNA in chromosomes
- Forms nucleosomes with DNA
- Types: H1, H2A, H2B, H3, H4
Casein
- Example of phosphoprotein
- Major protein in milk
- Contains phosphate groups attached to serine residues
- Forms micelles in milk
Antibodies (Immunoglobulins)
- Structure composed of 2 long (heavy) & 2 short (light) peptide chains
- Y-shaped structure
- Connected by disulfide bonds
- Variable regions bind to antigens
- Constant regions determine antibody class
Insulin Receptors
- Tetrameric glycoprotein
- Consists of 2 α and 2 β subunits
- α subunits: Extracellular, insulin-binding
- β subunits: Transmembrane, tyrosine kinase activity
- Essential for glucose homeostasis
Collagen
- Contains triple helix structure
- Most abundant protein in mammals
- Composed of three polypeptide chains (tropocollagen)
- Amino acid sequence: Gly-X-Y (where X is often proline, Y is often hydroxyproline)
- Provides structural support to tissues