DNA Replication Overview

DNA Replication

• Purpose: DNA replication is the process of creating an identical copy of a DNA molecule. This is crucial for cell division and passing on genetic information.
• Site: DNA replication occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.
• Semi-Conservative Replication: DNA replication is semi-conservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.
• Steps:
  • Unzipping (DNA Helicase): Specific enzymes, DNA helicases, unwind the DNA double helix, separating the two strands.
  • Complementary Base Pairing (DNA Polymerase): Free-floating nucleotides pair with their complementary bases on each exposed strand. DNA polymerase catalyzes the formation of phosphodiester bonds between the nucleotides, forming a new strand.
  • Joining of Adjacent Nucleotides (DNA Ligase): DNA ligase joins the Okazaki fragments produced on the lagging strand, creating a continuous new strand.

Recombinant DNA

• Definition: Recombinant DNA is DNA that has been artificially manipulated to combine DNA sequences from different sources.
• Enzymes Involved: Specific enzymes, like restriction enzymes, cut DNA at specific sequences & DNA ligase joins the segments together.
• Uses: Recombinant DNA technology has various applications, including producing pharmaceuticals, genetically modified organisms, and treating genetic disorders. At least three examples are needed for the required depth of knowledge.

Protein Synthesis

• Process: Protein synthesis involves two main stages: Transcription and Translation.
• Transcription: DNA sequence dictates mRNA sequence, a process that occurs inside the nucleus. Enzymes like RNA polymerase play a significant role.
• Translation: mRNA moves out of the nucleus and into a ribosome. tRNA carries specific amino acids to the ribosome based on the mRNA codons; this arrangement is crucial. The order of amino acids is dictated by the mRNA sequence.
• Components:
  • DNA: The original code holds the instructions for creating proteins
  • mRNA: Carries the copy of the DNA instructions (code) into the cytoplasm.
  • tRNA: Brings the specific amino acids to the ribosome based on the code in the mRNA.
  • Ribosomes: The site of protein assembly, where tRNA reads the mRNA code and joins amino acids together.

Mutations and Protein Synthesis

• Mutations: Changes to the DNA sequence can alter the resulting protein.
• Environmental Mutagens: Certain environmental factors can cause DNA mutations. Examples include radiation and some chemicals.
• Genetic Disorders: Mutations can cause changes in the sequence of amino acids in the polypeptide chain, potentially leading to genetic disorders. Sickle cell anemia is a well-known example.
• Importance of Degeneracy and Universality: The genetic code is degenerate meaning multiple codons can code for the same amino acid. The genetic code is also universal. meaning the same codons code for the same amino acids in most organisms.
• Initiation, Elongation, Termination: These are the stages of translating a mRNA sequence into amino acid sequence. Initiation starts, elongation continues the creation of the polypeptide chain, and termination stops it.