IB biology HL A2.1.7— Evidence for a last universal common ancestor; A2.1.8— Approaches used to estimate dates of the first living cells and the last universal common ancestor; A2.1.9— Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents.

LUCA stands for…

Last Universal Common Ancestor

LUCA

All cells on Earth share characteristics, including a genetic code that were inherited from a common ancestror.

Describe what LUCA would’ve looked like.

It would have been a small, single-celled prokaryotic cell

What were the 2 earliest domains?

Bacteria and Archea

Madeline Weiss et al. study the genomes of living bacteria and archaea to find out more about LUCA and concluded:

• Bacteria and archaea have been diverging for a very long time.

• Any genes shared between bacteria and archaea were probably inherited from their common ancestor LUCA (as opposed to independently appearing).

The 355 genes (referring to the Madeline Weiss et al. experiment) indicate that LUCA:

• was an obligate anaerobe (did not use oxygen, B4.2.2)

• was a chemoautotroph, obtaining energy from hydrogen and converting carbon dioxide and nitrogen into essential organic compounds (C4.2.7)

• was able to live in extreme heat

Definition of Hydrothermal vents

the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centers or subduction zones

Deductive reasoning

using a general premise to form a specific conclusion.

Exaple for chemical evidence:

The earliest evidence of life is found in rocks containing fossil-like structures with isotopes suggesting may be the remains of living organisms.

Biomarkers

the molecular fossils of lipids and other organic compounds

Example for fossil evidence

Stromatolites

Define stromatolites

structures created by photosynthetic bacteria that live in shallow water

Stromatolites are made up of:

Photosynthetic bacteria

The earliest habitable environment on the planet and are the proposed location of LUCA:

Hydrothermal vents (as a living environment)

Molecular clock

uses differences in the genomes of species to tell how much time has passed since they shared a common ancestor

The idea of a molecular clock:

the number of differences in the genomes of two species is proportional to the time since they diverged from a common ancestor