In this lecture you will learn about:
|We are now at the midpoint of the semester.
We looked at how atoms combine into organic matter, and how cells are built
out of the organic molecules.
The vast majority of living things on Earth are not organized into anything more complex than a single cell. And everything more complex starts as a single cell anyway called an egg. Humans like order and like to classify things, like the periodic table for elements. We will look at how living cells are classified.
So the next step in classification is into procaryotes and eucaryotes except there is an older group of microbes, the Archae that were added. So instead of two basic "domains" there are three domains of life.
While two of the three domains are all single celled, the third, eucaryotes have both single celled and multiple celled members.
Multicellularity occurs under the direction of the "program" encoded in DNA so that a single cell/egg divides into many cells and rather than the cells parting ways and drifting off like bacteria the cells stay glued together and work cooperatively in ways more complex than a single cell. Only eucaryotes can do this.
In addition as complexity increases the groups of cells begin to specialize into "tissues" that perform specific functions. At a higher level of complexity the tissues group into organ systems within the body of the organism. Interestingly, organism is a rather generic term used to designate a single living thing and does not promise they have "organs".
It is the division of eucaryotes into single
and multiple cells that leads to a system of "kingdoms" where single cells
get one kingdom (Protista) and multiple celled critters are divided into
3 additional kingdoms mostly based on how they make a living.
"Living things are divided into three groups based on their genetic similarity. The three groups are:
* Archaea: very ancient prokaryotic microbes.
* Bacteria: More advanced prokaryotic microbes.
* Eukaryota: All life forms with eukaryotic cells including plants and animals
These three groups are called domains.
The figure at the left shows the three domains of life. The distance between
groups indicates how closely related they are. Groups that are close together,
like plants and animals, are much more closely related than groups that
are far apart, like plants and bacteria. Do you see how the two types of
microbes, Archaea and Bacteria, are about as similar to one another as
they are to animals? Recent studies have found that microbes are far more
diverse than anyone had suspected. "
This is the kingdom of the bacteria.
Notice that viruses dont make the list. They are not considered "living" in the same sense as celled organisms.
--the branch of science that classifies and names living things.
NOMENCLATURE --a system for naming things
In biology there is a two-word system that is used to name organisms. It is called BINOMIAL NOMENCLATURE (a two named--naming system).
Carolus Linnaeus devised this in the 1800's using these two subgroups for the name:
GENUS & SPECIES
|Taxonomy based on:
this is the "old" way of classifying things,
"if they look alike, they are alike". But it falls down when there are
birds that have color variation, for example.
|Taxonomy based on:
DNA Sequences - the new way of classifying things
With such information, one can reconstruct an evolutionary history of the molecule and thus of their respective owners. This requires
* using the genetic code to determine the minimum number of nucleotide substitutions in the DNA of the gene needed to derive one protein from another and
* a powerful computer
program to search for the shortest paths linking the molecules together.
- before 1980's and after