1. Building Blocks:
* Nucleotides: All DNA is composed of the same four nucleotides: adenine (A), guanine (G), cytosine (C), and thymine (T). These nucleotides form the "letters" of the genetic code.
* Double Helix Structure: The DNA molecule is a double helix in all organisms, with two strands of nucleotides winding around each other like a twisted ladder. The two strands are held together by hydrogen bonds between complementary bases (A with T, and G with C).
2. Genetic Code:
* Codons: The sequence of nucleotides within a gene is read in groups of three, called codons. Each codon codes for a specific amino acid, the building blocks of proteins.
* Universality: The genetic code is almost universal, meaning that the same codons specify the same amino acids in almost all organisms. This suggests a common ancestor for all life.
3. Replication and Transcription:
* Replication: The process of DNA copying itself is remarkably similar across all organisms. It involves unwinding the double helix, separating the strands, and using each strand as a template to build a new complementary strand.
* Transcription: The process of converting DNA information into RNA is also very similar across organisms. RNA polymerase binds to DNA and creates a complementary RNA copy of a gene.
4. Function:
* Carrying Genetic Information: DNA stores the instructions for building and maintaining an organism. These instructions are passed down from generation to generation.
* Protein Synthesis: DNA provides the blueprint for protein synthesis, which is essential for all biological processes.
Differences in DNA:
While the fundamental structure and function of DNA are the same, there are also significant differences between organisms:
* Genome Size: The amount of DNA in an organism's genome varies greatly. Humans have a much larger genome than bacteria, for example.
* Gene Content: Different organisms have different genes, reflecting their unique adaptations and evolutionary history.
* Sequence Variation: Even within the same species, individuals have unique DNA sequences. This is the basis of genetic diversity.
In Summary:
DNA is remarkably similar across all living organisms in its building blocks, structure, genetic code, and fundamental functions. These similarities point to a common ancestor for all life on Earth. However, variations in genome size, gene content, and specific DNA sequences contribute to the diversity of life we see today.
