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Water-borne diseases

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       Water-borne diseases are infections transmitted through the ingestion of contaminated water , often containing pathogenic microorganisms, chemicals, or toxic substances. Main transmission route: Fecal-oral Contaminants include: Bacteria, viruses, protozoa, helminths , and toxic chemicals . Historical Perspective 1854 London Cholera Outbreak : John Snow linked cholera to contaminated water, founding modern epidemiology. 19th-20th Century : Water filtration and chlorination drastically reduced waterborne diseases in developed nations. 21st Century Challenges : Climate change, urbanization, and antibiotic resistance exacerbate risks. Classification of Water-Borne Diseases Bacteria - Cholera, Typhoid, Paratyphoid, Shigellosis Viruses -  Hepatitis A, Hepatitis E, Polio, Norovirus Protozoa -  Amoebiasis, Giardiasis, Cryptosporidiosis Helminths -  Dracunculiasis (Guinea worm), Schistosomiasis Chemical -  Fluorosis, Arsenicosis, Nitrate poisoning ...
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DNA Helix

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  Definition & Overview DNA (Deoxyribonucleic Acid) is the genetic material that carries hereditary information in living organisms. The  double helix  is the three-dimensional structure of DNA, first proposed by  James Watson and Francis Crick  in 1953, based on Rosalind Franklin’s X-ray diffraction  Chargaff’s base-pairing rules . The  DNA helix  is the twisted, ladder-like structure of  deoxyribonucleic acid (DNA) , the molecule that carries genetic instructions. It consists of  two antiparallel strands  coiled into a  right-handed double helix  (B-DNA form). Discovery & Nobel Prize 1953 : Watson and Crick proposed the model using Franklin’s X-ray data. 1962 : Watson, Crick, and Wilkins received the Nobel Prize in Physiology or Medicine (Franklin had passed away by then). Key Components a) Sugar-Phosphate Backbone Made of alternating  deoxyribose sugar  and  phosphate group...
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Forms of DNA

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     DNA (Deoxyribonucleic Acid) is the genetic material found in almost all living organisms. While its most familiar structure is the double helix , DNA can exist in multiple structural forms , depending on conditions like hydration, ionic strength, and sequence. Primary Forms of DNA A. B-DNA (Standard Watson-Crick Form) Structure : Right-handed double helix . 10.5 base pairs per turn . Helix diameter : ~20 Å. Major and minor grooves  (important for protein binding). Conditions : Most common in  physiological conditions  (92% relative humidity, low salt). Features : Anti-parallel strands . Base pairs perpendicular to the helix axis . B. A-DNA (Dehydrated or Compact Form) Structure : Right-handed but shorter and wider  than B-DNA. 11 base pairs per turn . Helix diameter : ~23 Å. Conditions : Forms under  low humidity  (75%) or  high salt concentrations . Biological Role : Found in  DNA-RNA hybrids  (e...
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History of DNA

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  Pre-Mendelian Theories of Heredity Pangenesis (Hippocrates, 400 BCE) Proposed that "gemmules" from all body parts travel to reproductive cells. Flaw : No experimental evidence; purely speculative. Preformationism (17th–18th Century) Suggested sperm or eggs contained a miniature human ("homunculus"). Disproven  by microscopy showing embryonic development. Blending Inheritance (Darwin’s Era) Hypothesized that parental traits "blend" irreversibly in offspring. Contradicted by : Mendel’s discrete inheritance patterns. Gregor Mendel’s Foundation (1865) Experiments : Crossed pea plants ( Pisum sativum ) tracking 7 traits (e.g., seed shape, flower color). Key Laws : Law of Segregation : Alleles separate during gamete formation. Law of Independent Assortment : Traits are inherited independently (later modified for linked genes). Limitations : Ignored  chromosomes  (discovered later by Waldeyer in 1888). Work was ignored until  190...
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