Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 431

Biochemistry

Fall 2008

Lecture Notes: 29 August

© R. Paselk 2008
 
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Cells and Organelles

Let's look at a "typical" plant cell for a moment. All of the organelles we saw in animals are here as well, but with a few additions: (text Figure 1-7b)

Eukaryotes also have dynamic cytoskeletons. (text Figure 1-9)

In summary then, we can look at an overview of the hierarchy of eukaryote cell organization. (text Figure 1-11), and compare the prokaryote and eukaryote levels of cellular organization. (text Table 1-3)

The Elements of Life

First, we will start with the basic requirements of an idealized, simplest life form and ask why life should use the particular atoms and molecules we see dominating in living organisms. (see also text Figure 1-12)

Periodic Table of Biologically Important Elements
 

 H
 

 He

 Li

Be
 

 B

C

N

O

F

Ne

Na

Mg

 Al

Si

P

S

Cl

Ar

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr
         

Mo
               Sn    

I
 

The following observations may be made regarding the elements of life:

Life is largely a phenomena of hydrogen and the second period of the Periodic Table. That is, the major component elements (red) in all known organisms are from these periods. Why these four elements?

The next important elements to life occur in Period 3: P and S (orange). These are the smallest elements capable of multiple covalent bonds to C, O and N, and which also have available d-shells. The d-shells allow additional transition states and reaction mechanisms. P and S are particularly important in the capture, storage, and distribution of chemical energy.

Conveniently, all of these elements are among the most abundant in the Universe. None-the-less, we hypothesize that they were chosen for their special properties, specifically strong covalent bond formation (to enable the formation of stable biomolecules), the ability of carbon to form large branched molecules, and for C, N, and O the formation of multiple bonds which provides chemical flexibility (step-wise oxidations, different hybridization geometries etc.).

(Aside: So why not have Si based life instead of C based?)

Elemental Ions:

 


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Last modified 29 August 2008