Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 438	Introductory Biochemistry	Spring 2007
Lecture Notes: 24 January	© R. Paselk 2006
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Cells and Organelles, cont.

Cool facts about E. coli :70% water, 15% protein, 7% nucleic acids, 3% polysaccharides, 3%, lipids, 1% inorganic ions, & 0.2% metabolites.

Complex, generalized organisms such as E. coli exhibit an amazing level of redundancy in enzymes etc. For example, of the approximately 4,000 genes in E. Coli less than 300 have been found to be "essential," where essential means the organism cannot grow on rich medium if the gene is deleted. Many genes also appear to be "silent: under more restrictive conditions as well - that is the organism often has more than one pathway to accomplish a given metabolic activity. (Cornish-Bowden & Cárdenas, Nature 14 Nov 2002, p 129)

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]

• Endoplasmic Reticulum: Lipid Synthesis; Steroid synthesis; Phase one detoxification reactions; Biosynthesis and modification of membrane and export proteins.
• Plasma Membrane: Active and passive transport systems; receptors and signal processing systems (synthesis of various second messengers etc.).
• Nucleus: DNA replication, synthesis and processing of messenger RNA's.
  • Nucleolus: localized region of the nucleus in which ribosomal RNA's are synthesized and processed.
• Cytosol: Glycolysis and most of gluconeogenesis; Pentose Phosphate shunt; Fatty acid biosynthesis.
• Mitochondria: Kreb's Citric Acid Cycle; Electron transport system and Oxidative Phosphorylation; Fatty acid oxidation; Amino acid catabolism; Interconversion of carbon skeletons.
• Golgi Complex: Further modification of membrane and export proteins.
• Lysosomes: Hydrolytic (digestive) enzyme localization.
• Peroxisomes: Amino acid oxidases, catalase-oxidative degradation reactions.
• 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: [overhead-Plant cell]

• Chloroplasts: Light capturing processes and electron transport & oxidative phosphorylation for photosynthesis; Calvin cycle (dark reactions of photosynthesis).
• Glyoxisomes: location of glyoxalate cycle.
• Cell wall: made up of cellulose glued together with lignin (a plastic like polymer) - maintains cell integrity against high osmotic pressure, gives cell rigidity.
• Vacuole: storage of dilute aqueous solutions, provides fluid for osmotic pressure.  

Chapter 2: Water

Water is a very unusual, even incredible substance whose amazing properties are often unappreciated because of its ubiquitousness. Water's special properties include extremely high mp and bp (0 °C & 100 °C K, compare to methane, -183 °C & -161 °C, with a MW of 16 vs. water's 18); a high heat capacity (18 cal/°C mol vs. 8 cal/°C mol for methane); it has a high viscosity; its solid form is less dense than the liquid form at the same temperature (ice floats on water - very rare), it has a large surface tension, and it has a high dielectric constant (78.5 vs. 1.9 for hexane).

Pathway Diagrams

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Last modified 24 January 2007