Molecular Basis
Approaches used in studying the molecular basis of human diseases:
Molecular Basis
- Hemoglobin (Hb) is composed of four polypeptide chains (two α-chains and two β-chains).
- The β-globin chain consists of 146 amino acids .
- In a normal hemoglobin (HbA) molecule, the 6th amino acid in the β-globin chain is glutamate (Glu).
- In sickle cell hemoglobin (HbS) , a point mutation occurs in the gene, leading to substitution of glutamate (Glu) with valine (Val) at position 6 .
Read this in Types of Mutations in ARBHN (Amino Acid Replacement Based on Hemoglobin to Produ
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Study material on Molecular Basis
- Clinical Genetics: Master Mendelian Disorders & Molecular Basis
- Hallmarks of Cancer: Molecular Basis, Cell Cycle & Oncogenes
- Molecular Basis of Cancer: Cell Cycle, Apoptosis & Angiogenesis
- GENETIC DISORDERS SAQs EXAMINATION
Practice questions on Molecular Basis
The molecular basis for the effect of cholera toxin on duodenal mucosa cells is
- Inactivation of G1 protein
- Increased generation of cAMP
- Activation of adenylate cyclase
- Increased ability of potassium pumps
- Ribosylation of guanosine triphosphate (GTP) binding protein Answer:
Answer: A. Cholera toxin ADP-ribosylates a G-protein, locking adenylate cyclase in an active state, which massively raises intracellular cAMP and drives chloride/water secretion into the gut lumen (option E describes the mechanism, but B describes the net physiological effect that's typically the marked answer in this exam's key). --- ---
What is the molecular basis for fragile X syndrome?
- Overexpression of FMRP
- Silencing of FMRP due to methylation
- Deletion of the FMR1 gene
- Point mutation in FMRP
- Usually mediated by non-specific mechanisms
Answer: B. When CGG repeats exceed 230, the DNA of the FMR1 gene becomes abnormally methylated, extending to the promoter region, resulting in transcriptional suppression and absence of FMRP. ---
Which application of genetics helps in understanding the molecular basis of human disease?
- Gene therapy only
- Functional and positional cloning approaches
- Production of biologics only
- None of the above
- Usually mediated by non-specific mechanisms
Answer: B. Both functional cloning and positional cloning approaches help understand the molecular basis of human disease by identifying genes and proteins involved in disease processes. ---
Which biochemical/molecular basis is NOT listed as a mechanism for Mendelian disorders?
- Enzyme defects
- Defects in receptors
- Prion protein misfolding
- Defects in transport systems
- Reduced by routine feedback control
Answer: A. The listed mechanisms include enzyme defects, receptor defects, transport defects, structural protein alterations, hemostasis defects, and growth regulation defects. Prion diseases are not typical Mendelian disorders. ---
The molecular basis for effect of cholera toxin on duodenal mucosa cells is
- Inactivation of G1 protein
- Increase generation of cyclic adenosine-monophosphate (cAMP)
- Activation of adenylate cyclase
- Increased ability of potassium pumps
- Ribosylation of guanosine triphosphate (GTP) binding protein
Answer: E. Cholera toxin's A subunit ADP-ribosylates the Gsα protein (GTP-binding protein), locking it in the active state. This permanently activates adenylate cyclase, causing continuous cAMP production, which drives massive chloride and water secretion into the intestinal lumen. ---
The molecular basis for cholera toxin's effect on duodenal cells is
- Inactivation of Gi protein
- Increased generation of cyclic AMP
- Activation of adenylyl cyclase
- Increased activity of potassium pumps
- Ribosylation of GTP-binding protein
Answer: E. Cholera toxin ADP-ribosylates the Gs protein, preventing GTPase activity and leading to continuous adenylyl cyclase activation and cAMP production. ---