DNA and RNA Composition and Structure

DNA and RNA Composition and Structure

• Nucleic acids are biopolymers, large biomolecules made of monomers called nucleotides.
• Two types of nucleic acids:
  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)

History of DNA

• Genetic research began with Gregor Mendel, the "Father of Genetics," who experimented with plants in 1857.
• DNA was first observed by Friedrich Miescher in 1869.

DNA Structure

• DNA is a double-stranded helix.
• James Watson and Francis Crick determined the 3-dimensional structure of DNA in 1953, based on Rosalind Franklin's work.

DNA Composition

• DNA is a long polymer made of repeating nucleotides.
• Nucleotides consist of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
• Nitrogenous bases in DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
• Base pairs:
  • Adenine pairs with Thymine (A-T)
  • Guanine pairs with Cytosine (G-C)
• The base pairs form a spiral staircase in the interior of the double helix.
• Hydrogen bonds connect the base pairs. Millions of weak hydrogen bonds hold the two strands together in the DNA double helix.

Forms of DNA

• B-form: Right-handed helix with 10 base pairs per turn (described by Watson and Crick).
• A-form: More compact than B-form.
• Z-form: Left-handed helix and bases are positioned more toward the periphery.

DNA Orientation

• Strands run from 5' to 3' and are antiparallel. This arrangement is necessary for DNA replication.

Chemical Bonds in DNA

• Covalent bonds: Between sugar and phosphate groups of two nucleotides (phosphodiester bonds).
• Hydrogen Bonds: Between complementary nitrogenous bases.

DNA in Prokaryotes and Eukaryotes

• Prokaryotic DNA: Smaller, circular, located in the cytoplasm.
• Eukaryotic DNA: Larger, arranged on chromosomes, located in the nucleus.

DNA vs RNA

• DNA:
  • Site: Nucleus
  • Sugar: Deoxyribose
  • Nucleotides: A, T, G, C
  • Arrangement: Double helix
  • Types: One
  • Synthesis: By replication
  • Function: Storage and transfer of genetic and hereditary characters
• RNA:
  • Site: Cytoplasm
  • Sugar: Ribose
  • Nucleotides: A, U, G, C (Uracil replaces Thymine)
  • Arrangement: Single helix
  • Types: mRNA, tRNA, rRNA
  • Synthesis: By transcription
  • Function: Protein synthesis by translation

DNA Denaturation and Renaturation

• Denaturation: Alkali or heat causes the DNA strands to separate.
• Renaturation: If DNA strands are separated (by heat), and the temperature decreases, base pairs reform, and the complementary strands come back together.
• Hybridization: A single strand of DNA or RNA pairs with complementary bases on another strand.

Mitochondrial DNA

• Mitochondrial DNA (mtDNA) is a double-stranded circular DNA molecule in the mitochondrial matrix.
• mtDNA has a different genetic code than genomic DNA.
• mtDNA codes for 13 protein subunits of the electron transport chain, a large and small ribosomal RNA (rRNA), and 22 transfer RNAs (tRNAs).
• mtDNA is maternally inherited.
• mtDNA has a higher mutation rate than nuclear DNA. (about 5-10 times higher).