DNA and Its Role as the Molecular Basis of Heredity
Structure of DNA
- DNA is structured as a double helix, often described as a twisted ladder.
- The molecule can be tens of millions of base pairs long, though often depicted in smaller fragments for illustration.
DNA Replication
- Purpose: Essential for heredity; replicating genetic material during cell division.
- Process:
- DNA strands split, each strand serves as a template for a new complementary strand.
- Base pairing rules: Adenine (A) pairs with Thymine (T), Guanine (G) pairs with Cytosine (C).
- Results in two identical DNA molecules.
Expression of Genes
- DNA vs. Chromosome vs. Gene:
- DNA: Molecule itself, with a sugar-phosphate backbone and base pairs.
- Chromosome: Structured DNA packaged with proteins.
- Gene: Section of DNA coding for proteins or traits.
- Gene expression: From DNA to protein involves two major processes: Transcription and Translation.
Transcription
- Role of RNA: Messenger between DNA and the cellular machinery outside the nucleus.
- Process:
- Converts DNA sequence into mRNA (messenger RNA).
- Base pairing in RNA: Adenine pairs with Uracil (U) instead of Thymine.
Translation
- From mRNA to Protein:
- mRNA leaves the nucleus and attaches to a ribosome.
- Codons: Sets of three bases on the mRNA that code for specific amino acids.
- 64 possible codons exist, coding for 20 amino acids, allowing for redundancy.
- tRNA's Role: Transfers amino acids to the ribosome by matching codons with anticodons.
- Sequence of amino acids forms proteins.
Importance of Proteins
- Proteins are critical for life functions, acting as enzymes, structural components, and more.
- Proteins are constructed as long sequences of amino acids that fold into complex shapes to perform various functions.
These notes cover the conceptual understanding of how DNA serves as the molecular basis of heredity by being replicable and allowing for the expression of genetic information through processes such as replication, transcription, and translation.