Common Ancestry (College Board AP® Biology): Study Guide

Shared features of all organisms

• Ancestry between organisms can be studied by tracing the lines of descent of heritable traits and identifying conserved mechanisms

  • Many key metabolic pathways are shown to be conserved across all domains, including:

    • carbohydrate metabolism

    • energy metabolism

    • amino acids and nucleotide processing

• These conserved features indicate that all currently recognized domains originated from a common ancestor

• Major features of the genetic code are shared by all modern living systems

• Heritable molecules that are inherited from one organism to the next through reproduction allow continuity of life

  • The heritable molecules include DNA and RNA which carry the genetic information required to produce new cells and organisms

DNA and RNA

DNA

• DNA carries the genetic code in all organisms

• This is the reason why the genetic code is said to be universal

• DNA is mainly found in the nucleus of all eukaryotic organisms but it is also found in chloroplasts and mitochondria of eukaryotic cells

RNA

• RNA is another type of nucleic acid which is the main component of ribosomes, which play an important role in protein synthesis 

  • Ribosomes are found in all forms of life

  • Some RNA is also found in the nucleus and cytoplasm

• Certain viruses (such as SARS-CoV-2) contain RNA as their genetic material (instead of DNA)

• Although viruses are not considered to be living organisms the inclusion of RNA in their genetic material highlights a shared feature common to all

Ribosomes

• Ribosomes are found freely in the cytoplasm of cells or as part of the rough endoplasmic reticulum in all life forms

• Each ribosome is a complex of ribosomal RNA (rRNA) and proteins

• Ribosomes are the site of translation in protein synthesis

  • A biochemical process important in all living organisms