Basic Basis of Inheritance
Key Points
Importance of DNA
- DNA: Source of genetic information and present in chromosomes
- Two types of nucleic acids: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)
Structure of Nucleotides
- Basic Units: Nucleotides
- Each nucleotide contains:
- Pentose sugar
- Phosphate group
- Nitrogenous bases (Aromatic compounds)
- Combination of nucleotides: Form polymeric polynucleotide chain
Structure of DNA
- Double Helix Model: Proposed by Watson and Crick
- Formed by sugar-phosphate backbone and nitrogenous bases
- Based on hydrogen bonding:
- Adenine (A) binds with Thymine (T)
- Guanine (G) binds with Cytosine (C)
- Antiparallel strands with uniform spacing
DNA Packaging
- Read and compressed by positive charge proteins (Histones)
- Nucleosomes: DNA bound with histones
- Chromatin: Two types
- Euchromatin: Fit for transcription
- Heterochromatin: Unfit for transcription
Transforming Principle
- Griffith's Experiment: With killed and living bacteria
- Avery's Experiment: Testing the transforming principle: DNA is it, not proteins or carbohydrates
DNA Replication
- Semi-Conservative Model: Two new strands form using old strands as templates
- Meselson and Stahl Experiment:
- Use of light and heavy nitrogen
- Result: Semi-conservative replication confirmed
Polymerization and Enzymes
- DNA Polymerase: Adds nucleotides to form DNA
- Proofreading: Corrects errors in the newly formed DNA strand
Transcription
- Template Strand: To form complementary RNA
- RNA Polymerase: Forms RNA using DNA template
- Three major stages:
- Initiation: Binding of polymerase at the promoter region
- Elongation: Adding nucleotides
- Termination: End of transcription
Translation and Function of RNA
- mRNA (Messenger RNA): Template for proteins
- tRNA (Transfer RNA): Brings amino acids
- rRNA (Ribosomal RNA): Main component of ribosomes
Conclusion
Both DNA and RNA can function as genetic material. Due to its stability and lower mutation rate, DNA is considered the primary genetic material.