DNA Overview and Structure

DNA Overview

• DNA (deoxyribonucleic acid) is the primary carrier of genetic information.
• Miescher discovered DNA in 1869; Watson and Crick built the first model in 1953.

DNA Structure

• Nucleotide: The basic building block, composed of:
  • Nucleobase (Nitrogenous Base):
    • DNA bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
    • RNA bases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U)
  • Sugar (Pentose):
    • DNA: Deoxyribose
    • RNA: Ribose
  • Phosphate Group: Consists of H3PO4.

Polynucleotide Chain

• Composed of multiple nucleotides linked together.
• Hydrogen bonds hold nitrogenous bases in pairs.
• DNA strands adhere to complementary base pairing:
  • DNA pairs: Cytosine (C) with Guanine (G), Adenine (A) with Thymine (T)
  • RNA pairs: Cytosine (C) with Guanine (G), Adenine (A) with Uracil (U).

Functions of DNA and RNA

• DNA: Stores and transmits genetic information.
• RNA: Converts DNA information into proteins.

Transmission of Genetic Information

• Involves three key processes:
  • Replication: DNA copy-making in the cell nucleus before mitosis.
  • Transcription: Transcribing genetic information from DNA to messenger RNA (mRNA).
  • Translation: Protein synthesis from mRNA, occurring in ribosomes and the endoplasmic reticulum.

DNA Replication

• Takes place during the S phase of the cell cycle prior to mitosis.
• Human cells replicate 46 chromosomes to form 92 chromosomes for cell division.

Mechanism of DNA Replication

• The double helix structure "unzips" to separate strands before replication.
• Specialized enzymes break hydrogen bonds between base pairs to create a template for new strand synthesis.
• DNA polymerase enzyme assembles nucleotides to form a new strand guided by the old strand's sequence.
• Complementary base pairing directs the synthesis process, ultimately reforming the double helix.

Genetic Code Essentials

• The genetic code consists of nucleotide sequences that instruct protein synthesis.
• It provides rules for translating DNA or mRNA sequences into amino acid chains.

Properties of the Genetic Code

• Three-Letter (Triplet) Code:
  • Comprised of triplets of nucleotides known as codons (e.g., CCA, TGG).
  • Each codon specifies the insertion of a particular amino acid in a polypeptide chain during protein synthesis.