What is the Central Dogma of molecular biology?

| Enzyme | Function | |--------|----------| | | Unwinds and separates the double helix by breaking hydrogen bonds. | | DNA Polymerase III | Synthesizes new DNA strands by adding nucleotides to the 3’ end; also has 3’→5’ proofreading ability. | | Primase | Synthesizes a short RNA primer to provide a 3’-OH group for DNA polymerase to begin adding nucleotides. | | Ligase | Seals nicks (joins Okazaki fragments) on the lagging strand by forming phosphodiester bonds. | | Topoisomerase | Relieves supercoiling ahead of the replication fork to prevent DNA breakage. |

| Feature | Leading Strand | Lagging Strand | |---------|----------------|----------------| | Direction of synthesis | Continuous 5’→3’ | Discontinuous 5’→3’ (Okazaki fragments) | | Requires multiple primers | No (one primer needed) | Yes (many primers needed) | | Template strand orientation | 3’→5’ (toward replication fork) | 5’→3’ (away from replication fork) |

If one strand of DNA has the sequence 5’-ATTCGAGC-3’, what is the complementary strand? Be sure to label the 5’ and 3’ ends.

| Purines (two rings) | Pyrimidines (one ring) | |---------------------|------------------------| | Adenine (A) | Cytosine (C) | | Guanine (G) | Thymine (T) | | (Also Uracil in RNA)| |

Let’s dive into the answers and explanations. Question 1: Draw and label a nucleotide. What are the three components?

The purine-to-pyrimidine ratio is always 1:1 in a double-stranded DNA molecule (Chargaff’s rule). Part 2: DNA Function (Replication & Central Dogma) Question 5: Explain the role of the following enzymes in DNA replication:

Semiconservative replication means that each new DNA double helix contains one original (parental) strand and one newly synthesized daughter strand . This was proven by the Meselson-Stahl experiment using isotopic nitrogen (¹⁵N and ¹⁴N).