Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 438

Introductory Biochemistry

Spring 2010

Lecture Notes: 24 January

© R. Paselk 2006
 
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Cells and Organelles, cont.

Compartmentation in Eukaryotes

As mentioned earlier we will be focusing on eukaryotes in the rest of this course. Eukaryotes differ from prokaryotes in having a nucleus and cell organelles (their cells are physically compartmentalized). As a point of reference, an E. coli cell is about the size of a typical mammalian mitochondria.

Let's look at where different major metabolic pathways occur in a "typical" liver cell. [overhead-Animal cell]

eukaryote cell image

public domain image via Wikipedia Creative Commons

 

Not shown - Glycogen Granules: enzymes of glycogen synthesis and breakdown. including branching and debranching.

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:

plant cell structure diagram

Introduction to Vitamins and Cofactors

Terms:

Let's start with a brief overview of the names, structures and physiological functions of the common vitamins as shown on the overhead: Niacin, Riboflavin [B2], Thiamine, Pantothenic acid, Biotin, Pyridoxal [B6], Folic acid, Lipoic acid, Cobalamin [B12], L-Ascorbic acid [C], and the lipid soluble vitamins A, D, E, and K). Fun facts:

Note the relationships of the various cofactors to their vitamin precursors. Chapter 7 of your text has images of the various cofactors and vitamins, as well as example chemistries. You should keep it in mind to refer back too during our studies.

Nucleotide Functions: Most involve use of the nucleotide as a recognition molecule, e.g. ATP

structural diagram of ATP

Nicotinamide Adenine Dinucleotide (NAD+) uses ADP (bolded) as a recognition "handle." (Note the two nitrogenous bases each attached to a ribose and linked through a phosphoric acid anhydride linkage:

structural diagram of NAD

Similarly adenosine with a modified ribose (reduced to the alcohol - ribitol) is used in Flavin Adenine Dinucleotide = FAD (not truly a dinucleotide since ribitol instead of ribose!):

structural diagram of FAD

Coenzyme A has an ADP attached to an arm of pantothenic acid, which in turn is attached to beta-mercaptoethylamine. Acetyl groups can be carried on the sulfhydryl group:

structural diagram of Coenzyme A

Three vitamins give cofactors with long "arms" which enable the cofactors to shift an attached substrate between adjacent active sites on a single enzyme. (Note attachment of biotin and lipoate to lysine side-chain to give 10 atom arms.)

 

Pathway Diagrams

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Lecture Notes

Last modified 27 January 2010