A1.2.1 DNA as the genetic material of all living organisms Notes

DNA As The Defining Molecule of Life

1. In eukaryotes, DNA is packed inside the nucleus as chromosomes.
2. Smaller, separate DNA molecules also exist in mitochondria (mtDNA) and, in plants and algae, in chloroplasts (cpDNA).

RNA As The Working Copy of Genetic Information

1. RNA is found in both the nucleus and cytoplasm, acting as the link between genetic information and protein synthesis.
2. Its key forms and functions are:
   1. mRNA: carries genetic code from DNA to ribosomes.
   2. tRNA: delivers amino acids to the ribosome.
   3. rRNA: forms part of ribosomes and catalyses peptide bond formation.

RNA as Genetic Material in Viruses

1. Some viruses contain RNA instead of DNA as their genetic material.
2. Their RNA carries the information needed to make viral proteins, but replication only occurs inside a host cell.

RNA and Its Role in Cells

1. RNA (ribonucleic acid) is another nucleic acid, chemically different from DNA because it contains ribose sugar and uracil instead of thymine.
2. Functions of RNA:
   1. Messenger RNA (mRNA): carries genetic code from DNA to ribosomes.
   2. Transfer RNA (tRNA): brings amino acids during protein synthesis.
   3. Ribosomal RNA (rRNA): structural and catalytic component of ribosomes.
3. RNA can be found in the nucleus and the cytoplasm.

Why Viruses Are Not Classified as Living

1. Although viruses contain genetic material and can evolve, they fail the key criteria for life:
   1. No Cellular Structure: They lack membranes, cytoplasm, and organelles.
   2. No Independent Reproduction: They must infect a host to replicate.
   3. No Metabolism: They cannot produce or use energy.