DNA Structure and Replication

DNA Structure, Replication, and Scientists

• Genes: Blueprints of life, easily copied and replicated, carry heritable information for protein production. Found in chromosomes within the nucleus.

• DNA (Deoxyribonucleic Acid): A polymer made of nucleotides (phosphate, 5-carbon sugar deoxyribose, and a nitrogenous base). DNA structure resembles a twisted ladder (double helix).

• Nucleotide Components: The three components of DNA nucleotides are phosphate, a 5-carbon sugar (deoxyribose), and a nitrogenous base.

• DNA Structure: Looks like a twisted ladder (double helix). Base pairs (A-T, G-C) hold the two strands together via hydrogen bonds; A always pairs with T, and G always pairs with C.

• DNA Replication: A process that occurs when a cell divides; the DNA molecule unzips, and each strand serves as a template to create a new complementary strand. This is a semi-conservative process (one original strand remains in each new DNA molecule).

• Replication Enzymes: Helicase unzips the DNA, primase creates a primer to start replication, DNA polymerase builds new complementary strands, and ligase joins the gaps.

• DNA Scientists:

  • Watson and Crick: Discovered the double helix structure of DNA.
  • Erwin Chargaff: Stated that the percentages of nitrogen bases in DNA are complementary (A=T, G=C).
  • Rosalind Franklin: Used X-ray diffraction to confirm the structure and shape of DNA.

DNA Replication Steps

• Step 1: Unzipping: Helicase breaks hydrogen bonds between base pairs, creating a replication fork.

• Step 2: Creating Templates: Each strand of DNA becomes a template to build new strands.

• Step 3: Building Primers: Primase builds a short complementary DNA segment ("primer") to mark the start of replication.

• Step 4: Building Complementary Strands: DNA polymerase builds new complementary strands to the template strand, adding new nucleotides to the 3' end of the growing strand (5' to 3' direction).

• Step 5: Base Pairing: New nucleotides pair with their complementary base on the template strand (A-T, G-C).

• Step 6: Sealing the Strands: Ligase seals the gaps between the new segments of DNA.

• Step 7: Product: The result of replication is two identical DNA molecules, each with one original and one new strand (semi-conservative replication).