Untitled Flashcards Set

Understanding DNA Structure

Nucleic Acids

• DNA: Deoxyribonucleic acid

• RNA: Ribonucleic acid

Composition of Nucleic Acids

• Comprised of nucleotides.

  • 5 Carbon Sugar:

    • Ribose for RNA

    • Deoxyribose for DNA

  • Phosphate Group: Forms the backbone of nucleic acids.

  • Nitrogenous Base: Located perpendicular to the backbone.

Classification of Nitrogenous Bases

• Purines: Adenine (A), Guanine (G)

• Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)

Base Pairing

• Complementary Base Pairs:

  • Purine paired with pyrimidine:

    • Thymine (T) bonds to Adenine (A)

    • Cytosine (C) bonds to Guanine (G)

• RNA Variation: RNA has Uracil (U) instead of Thymine (T); Uracil bonds with Adenine (A).

Sugar-Phosphate Backbone

• Leading Features:

  • Consists of a 5-carbon sugar (deoxyribose in DNA) and phosphate group.

  • Turns every 10 bases.

DNA Double Helix

• Structure:

  • DNA consists of two strands twisted into a double helix with uniform width.

• Orientation:

  • Strands run in opposite directions (antiparallel).

  • Each strand has a 5′ end and a 3′ end.

DNA Organization

• Two polynucleotide strands twisted in a double helix.

• Key Features:

  • Sugar-phosphate backbone on the outer part.

  • Nitrogenous bases located inward and perpendicular to the backbone.

  • DNA forms a double-stranded helix of uniform width.

  • Specific base pairing occurs (A pairs with T; G pairs with C).

Genetic Information

• The sequence of nitrogenous bases constitutes genetic information, e.g., AAGCTCGATACCGTG.

Key Figures in DNA Structure Discovery

• Erwin Chargaff (1950):

  • Discovered equal amounts of Adenine and Thymine (A=T) and Guanine and Cytosine (G=C).

  • Noted that relative amounts varied across species.

• Linus Pauling:

  • Proposed that some proteins have helical shapes, published a triplex model of DNA but was incorrect about phosphate being neutral.

• Rosalind Franklin:

  • Utilized X-ray crystallography to demonstrate DNA's helical structure.

  • Recognized as the unsung hero of DNA research despite limited recognition due to sexism in the field.

X-Ray Crystallography

• Purpose: A technique that reveals the shape of small biological structures, such as DNA.

Watson-Crick Model Features

• DNA consists of two polynucleotide strands.

• Key features include the DNA double helix turning every 10 bases.

• Example Sequence: CGCGGCGCT AATCGATTA CGCGGCATATTA.

Nobel Prize in Physiology and Medicine 1962

• Recipients: James D. Watson, Francis H. Crick, and Maurice H.F. Wilkins.

• Notable Publication: Watson and Crick's paper on nucleic acid structure published in Nature in 1953.