DNA Composition and Structure

DNA Composition

• Deoxyribose is the sugar found in DNA, while Ribose is found in RNA.

Nitrogenous Bases

• Adenine, Guanine, Cytosine, and Thymine are the nitrogenous bases found in DNA.
• Uracil is found in RNA, replacing Thymine.
• Purines are nitrogen bases containing two rings, including Adenine and Guanine.
• Pyrimidines are nitrogen bases containing one ring, including Cytosine, Thymine, and Uracil.

Phosphate

• The phosphate group is represented by O-P-O- OH.

Nucleosides vs. Nucleotides

• A Nucleoside or Deoxynucleoside is a nitrogenous base bound to a sugar.
• A Nucleotide or Deoxynucleotide is a nitrogenous base bound to a sugar and a phosphate group.
• A Nucleic Acid is a polymer (chain) of nucleotides.

Facts

• Nucleic acids are polymers, and their monomers are called nucleotides.
• Nucleotides consist of a base, sugar, and phosphate group.
• Sugar can be deoxyribose or ribose.
• Phosphate groups link sugar molecules together through phosphodiester bonds.

Famous Experiments

Chargaff's Rules

• The amounts of Adenine (A) and Thymine (T) are equal, and the amounts of Guanine (G) and Cytosine (C) are equal.
• The amounts of A&T and G&C differ between species.

The Hershey-Chase Experiment

• The experiment showed that DNA, not protein, carries genetic information.
• Radioactive phosphorus, which labels DNA, was found in bacteria, while radioactive sulfur, which labels protein, was not.

DNA Composition - Double Helix

• The double helix structure of DNA consists of anti-parallel strands.
• Adenine (A) pairs with Thymine (T) through two hydrogen bonds.
• Cytosine (C) pairs with Guanine (G) through three hydrogen bonds.
• The major and minor grooves are formed due to the alignment of sugar-phosphate backbones.

DNA Conformations

• A-DNA is a short, wide, right-handed helix.
• B-DNA is the most common DNA form in solution, a right-handed helix.
• Z-DNA is a long, slender, left-handed helix.

The Meselson-Stahl Experiment

• The experiment showed that DNA replication is semi-conservative, not conservative or dispersive.
• Each new strand contains one original and one new strand.

DNA Replication

• DNA replication is semi-conservative and depends on complementary base pairing.
• Each new strand contains one original and one new strand, making it a semi-conservative process.

Learn about the components of DNA, including sugars, nitrogenous bases, and phosphate groups, and how they come together to form nucleosides and nucleotides.