Lecture Outline for Wednesday September 13, 2000
Cellular Basis of Life
Reading reference: BCC Chapter 2, 3,4
On-line resources:
Textbook
Companion Web Site
The Biology Place (login required)
Biologist of the Day: Microbiologist and Evolutionary Theorist Lynn Margulis
In biological circles, the endosymbiotic theory of Lynn Margulis is as well known as Charles Darwin's theory of natural selection. Now generally accepted and supported by experimental evidence, the endosymbiotic theory was once extraordinarily controversial. Her current work, the Gaia theory-the Earth as a "superorganismic system" (Margulis) is even more so. Read about Dr. Margulis's work.
Read more about some, and only some, female scientists at 4000 Years of Women in Science
Today's lecture
Chemical properties are the starting point for biological function.
The majority of atoms used to build bio-molecules are Carbon, Hydrogen,
Oxygen, Nitrogen, Phosphorus and Sulfur.
These atoms are extremely good at combining with themselves and with
other atoms.
Carbon hydrogen skeletons form the backbones of all bio-molecules.
The combining properties of atoms are largely a function of the number
and position of electrons.
Bonding refers to the equal (non-polar bonds) or unequal sharing
(polar bonds) of outer shell electrons.
Molecules that have lots of polar bonds mix well with the water, which
is a polar molecule. Non-polar molecules exclude water (oil and water don't
mix!)
Water is essential for life on earth, it is liquid over a wide temperature
range, is an excellent solvent and has cohesive properties.
Chemical reactions change matter. Biochemical reactions nearly always
take place in water. Organisms are mostly water
Macromolecules are made when smaller units are joined together, such
as when amino acids are used by a cell to construct proteins.
Important macromolecules are proteins, carbohydrates, lipids (or fats)
and nucleic acids.
All macromolecules have structures (shapes) and function, the structure
fits or dictates the function.
DNA is an information molecule, the cell's DNA, or genes, provides
the coded instructions for nearly the all the cell's structures and functions.
All organisms are composed of cells.
Cells have a simple basic form, a two layer (lipid bilayer) membrane,
that isolates the cell from the outside, and a watery cytoplasm.
Prokaryotic cells have their DNA free in the cytoplasm, eukaryotic
cells sequester their DNA in a nucleus.
Eukaryotic cells have many internal features called organelles.
Organelles have specialized functions.
Organelles are likely to have arisen by endosymbiosis (living inside)
from free living bacteria or photosynthetic algae.
Mitochondria (energy suppliers) and chloroplasts (photosynthetic organelles
of plants) have their own DNA, but most of the cell's functions are under
control of the nuclear DNA or genome.
Mitochondria are maternally inherited (mostly??) due to the larger
contribution of egg cytoplasm to the fertilized egg in vertebrates.
This has lead to the use of information from samples of mt DNA to trace
the evolution of humans and other species. Extraordinary mathematical models,
with numerous hotly debated assumptions have been used to suggest that
a single, African
Eve
was
ancestor to all human populations. Mitochondrial DNA information is not
the only DNA information used in evolutionary studies. This article
report the use of the Y
chromosome to track migrations of our ancestors.