28 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”boxylic acid (TCA) cycle taking place inside the mitochondria, and the
third stage is the electron transport chain (also in mitochondria) where
electrons and protons (hydrogen) are separately carried along the mito-
chondrial membrane. The final stage is called oxidative phosphorylation,
in which hydrogen meets oxygen (taken in from the air) to form water,
providing energy to generate ATP. The general chemical equation for
the oxidation of glucose is C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O. Overall,
38 molecules of ATP are generated from one molecule of glucose.
Figure 3.7 is a simplified diagram of energy utilization starting from
glucose. Figure 3.8 shows the complex network of overall metabolism
including energy utilization and the biosynthetic pathways.
Other organelles are lysosomes, which are the “garbage disposal” of
the cell where waste molecules are chewed up with hydrolytic enzymes;
and peroxisomes, which contain enzymes capable of degrading reactive
oxygen species (toxic byproducts of oxidative phosphorylation). The
endoplasmic reticulum (ER) is a series of membranous channels within
the cytoplasm on which the ribosomes (see Figs. 3.1, 3.3, and 3.4C) are
anchored. After proteins are synthesized on the ribosomes, they are
transported through the endoplasmic reticulum to different parts of a
Table 3.4. Types of Proteins
(1) Structural proteins
Building materials for cellular components in an aqueous environment, including
plasma membrane and intracellular membranes (e.g., nuclear membrane, endoplasmic
reticulum, Golgi apparatus) and organelles (e.g., mitochondria, lysosomes); usually in
combination with lipids and carbohydrates.
(2) Functional proteins
(a) Catalytic proteins– Also known as enzymes. Expedite the making and breaking
of chemical bonds; synthesize and degrade biomolecules such as proteins, DNA,
RNA, lipids, and carbohydrates; help in harnessing energy.
(b) Regulatory proteins– Monitor the process of cell division; involved in myriads
of functions including gene regulation, signal transduction, transcription,
translation, protein folding, protein translocation, protein disposal, intracellular
homeostasis, intercellular communication, and interaction with environment;
movement at all levels; defense against invaders (immunity) and noxious
chemicals; transport of oxygen, nutrients, and minerals.