Lecture 6 BGYA01 September 27, 2007
All right so far we have talked about the macromolecules that make up the cell, and we
have lloked at the process by which cells make their DNA, RNA and proteins.
The carbohydrates and lipids are made in biochemical pathways that are controlled by the
Now I would like to look at how the proteins , carbohydrates and lipids are organized into
cells and cellular structures, and where the DNA and RNA are found and organized.
THE MAJOR GROUPS OF ORGANISMS
Scientists have studied organisms, living and extinct, and have placed them into groups of
related organisms. The kinds of properties they consider when classifying organisms are:
- the structure of the cells
- the organization of cells into an organism
- the methods of acquiring their building materials and energy
- the method of reproduction.
Current classification schemes group the living and extinct species into three domains.
The three domains are Bacteria, Archaea, and Eukarya. Figure 1.11 page 12.
The tree diagram of figure 1.11 illustrates the idea that the first type of organism diverged into
two types of organisms. One type gave rise to the domain known as Bacteria, and the second
type was the ancestor of both the Archaea and the Eukarya.
Available evidence suggests that the Archaea and Eukarya share a common ancestor, not shared
with the Bacteria. At a later point in time this second type of organism diverged into the separate
domains of Archaea and Eukarya.
It is estimated that organisms within a domain have been evolving separately from organisms in
the other domains for at least a billion years.
Let’s look at some key characteristics of the three domains. (We’ll discuss these characteristics
in more detail later).
(1) Have cells that lack double membrane bound organelles
(2) Are single celled organisms
(3) Have either no cell walls OR a cell wall containing peptidoglycan
(4) Most have a single circular double stranded DNA as its hereditary material