SCIENCE Q3 CENTRAL DOGMA

• The central dogma is a term that Francis Crick first coined in 1958. It is a theory stating that the genetic information in cell flows from DNA to RNA to proteins.
• from existing DNA to make new DNA in a process called replication (DNA synthesis). This process happens during S phase of the cell cycle before cell division (mitosis and meiosis) and allows to pass the genetic information from the parent cell to the daughter cell.
• from DNA to make RNA in a process called transcription (RNA synthesis). It is the first stage of the gene expression, process by which information encoded in a gene is turned on to make RNA and proteins. Messenger RNA molecules are responsible for the transfer of information from the nucleus to the cytoplasm.
• from RNA to make protein in a process called translation (Protein synthesis). The final stage of the gene expression process. The ribosomes translate the messages carried in the RNA code into a final product, usually protein.
• Replication is a process by which DNA produces at exact copy of itself. DNA replicates to generate a copy of the genetic material to be transferred during mitosis to new cells, or during meiosis to new gametes. It happens inside the nucleus of a eukaryotic cell and various enzymes, proteins that speed up chemical reactions, are involved in the process.
• (Replication) Initiation: Helicase unzips the DNA by breaking the hydrogen bonds (Replication)between base pairs, separating the two strands, creating a replication fork. A replication fork serves as template for replication to begin. Unzipping opens up the DNA nucleotides so that they can be read, and complementary strand can be formed.

  A) Helicase

  B) Replication fork

  
• Elongation: DNA polymerases attach themselves to the DNA and elongate the new strand   by adding nucleotide bases. The nucleotide complementary to the template nucleotide is added in each position along the new chain. Complementary base pairing follow Chargaff’s rule: Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G). Replication proceeds in the 5’ to 3’ direction. Therefore, in one strand (the template 3’ to 5’) replication is continuous. On the other hand, in one strand (the template 5’ to 3’) replication is discontinuous, forming Okazaki fragments.
• (Replication) Termination: Replication ends when the two replication forks meet. DNA ligase joins the Okazaki fragments. Once completed, the parent strand and its complementary DNA strands coils to form the double helix. In the end, replication produces two identical DNA molecules. DNA replication is semi-conservative, each with one parent strand and one new strand.