DNA Structure, Replication, and Protein Synthesis
Structure of DNA
Components of DNA:
- Sugar
- Phosphate group
- Nitrogen-containing base
Nitrogen Bases:
- Four types: adenine (A), thymine (T), cytosine (C), guanine (G)
- Complementary base pairing:
- A pairs with T
- C pairs with G
Historical Context:
- Discoverers: James Watson and Francis Crick
- They described complementary base pairing.
Gene Theory
DNA Replication
Process Overview:
- Occurs during stage S of the cell cycle
- DNA strands separate due to hydrogen bonds breaking
- Enzymes involved:
- DNA Polymerase:
- Uses old strands as templates
- Lays down nucleotides one at a time based on complementary base pairing
Outcome:
- Two identical double-stranded DNA molecules
- Form sister chromatids that separate during anaphase of mitosis
Key Concept:
- Importance of complementary base pairing in DNA replication
From DNA to Protein
Translation
Process:
- Ribosomes read mRNA codons and assemble corresponding amino acids into proteins
- Start Codon:
- AUG (codes for methionine)
- Stop Codons:
- UAA, UGA, UAG
Mutations:
- Changes in the DNA base sequence that may affect protein synthesis
- Not all mutations result in changes to the amino acid sequence (silent mutations)
- Impact of mutations varies depending on the proteins affected
Recap & Next Steps
- Key Takeaways:
- Complementary base pairing is crucial in DNA replication and transcription
- The flow of genetic information: DNA ➜ mRNA ➜ Protein
- The complexity of gene expression and regulation will be discussed further in chapter 13
- Next Discussion:
- Further exploration of translation and protein synthesis
- Relationship between mutations and protein functionality