0000000000033933
AUTHOR
Kensal E. Van Holde
Oxygen and the Exploration of the Universe
Humankind has begun, in a tentative way, the immense project of exploring, and perhaps colonizing, other worlds. The grand enterprise has hardly begun and will certainly suffer many defeats and reversals, but it seems destined to go forward. In the course of this, both in seeking life in extraterrestrial environments and voyaging into them, we shall encounter a number of problems concerning the existence or provision of oxygen. The basis for this has been described in previous chapters. First, we would like to summarize arguments as to why life could have evolved on other planets. We need to know what to expect.
Global Warming: Human Intervention in World Climate
In the preceding chapter, we described climate changes that have occurred over very long geological periods. We concluded that Earth is currently in an interglacial interval within a rather long period of glaciations. Indeed, average carbon dioxide concentrations in the atmosphere have been slowly decreasing over the past 600,000 years, with accompanying cooling (Fig. 6.3). There have been, of course, many periodic changes in the CO2 concentrations and average temperature over this period (see Fig. 7.1). However, very recently, something quite unique and startling has occurred. As Fig. 7.1 shows, there has been a remarkable increase in CO2 levels, actually during the past 200 years, from 28…
Oxygen in Medicine
The implications of oxygen for medicine are basically of two kinds. First, there is the continued need by human tissues for an adequate supply of dioxygen; if that is not met, a condition called hypoxia may arise, with serious medical consequences. There are a wide number of causes for hypoxia, and a variety of medical responses.
Oxygen, Its Nature and Chemistry: What Is so Special About This Element?
It would seem that an introduction to oxygen is unnecessary, for we deal with it and depend upon it every moment of our lives. Oxygen is to us the essential stuff of the air we breathe. We are aerobic animals who obtain energy by oxidizing foodstuffs. As such, we are wholly dependent on oxygen for life – go without it for a couple of minutes and we panic and may even suffer irreversible brain damage. In a few more minutes, we perish. Animal metabolism depends upon oxygen for almost all of its energy-generating processes. Yet this was not always so. Early in the history of the Earth, there was essentially no free oxygen anywhere, although oxygen has always been one of the most abundant eleme…
Structures of two molluscan hemocyanin genes: significance for gene evolution.
We present here the description of genes coding for molluscan hemocyanins. Two distantly related mollusks, Haliotis tuberculata and Octopus dofleini , were studied. The typical architecture of a molluscan hemocyanin subunit, which is a string of seven or eight globular functional units (FUs, designated a to h, about 50 kDa each), is reflected by the gene organization: a series of eight structurally related coding regions in Haliotis , corresponding to FU-a to FU-h, with seven highly variable linker introns of 174 to 3,198 bp length (all in phase 1). In Octopus seven coding regions (FU-a to FU-g) are found, separated by phase 1 introns varying in length from 100 bp to 910 bp. Both genes exh…
Coping with Oxygen
Sometime before 2.7 BYA, a new and biologically toxic substance began to appear in the environment. Biologically produced dioxygen, O2, probably first began to accumulate in small pools or layers above cyanobacterial mats. These photosynthesizers must have already developed ways to at least partially deal with dioxygen and, with greater difficulty, the reactive oxygen species (ROS) derived from it (see Chap. 1 and below). But for primitive anaerobes in the vicinity, these new substances must have been especially toxic. Nevertheless, it is clear that they evolved ways to cope with the new threats. One way was to simply avoid dioxygen altogether.
A Brief History of Oxygen
Where did oxygen come from? Remarkably, that atom of oxygen you have just breathed had its origin in the heart of an ancient star. To understand this, one has to make an imaginary journey back to the creation of the universe, the “big bang,” more than 12 BYA. We shall avoid details of physics, and simply describe a reasonable scenario that is accepted by most physicists today.
Facilitated Oxygen Transport
The amount of dioxygen an organism needs for aerobic metabolism depends on many factors, size and activity being the most important. However, as an approximate figure, we may say that a typical higher eukaryote will utilize about 3.5 ml dioxygen kg−1 body weight per minute. This must reach the tissues where active metabolism is occurring and be maintained there at a steady-state pressure of approximately 2 Torr. This will assure a sufficient rate of delivery to mitochondria and allow continued utilization therein for oxidative reactions (see Chap. 4). The problem faced by the organism is how to assure sufficient delivery to all the tissues, even those buried deep in the body, sometimes whil…
Aerobic Metabolism: Benefits from an Oxygenated World
In the preceding chapter, we have emphasized the dangers that the advent of dioxygen presented to the existing anaerobic organisms, and the ways they evolved to deal with the problems. However, this is only part of the story and were it to have ended here, we and the world we know would not exist. What happened instead was quite remarkable; for life seized upon an opportunity presented by the presence of free dioxygen to become many-fold more efficient in extracting energy from foodstuffs. As we shall see, this aerobic, oxidative metabolism opened in turn a multitude of new opportunities for growth and diversification.
Climate Over the Ages; Is the Environment Stable?
As described in Chaps. 3 and 4, the advent of oxygenic photosynthesis triggered worldwide environmental changes. A world that had been reductive passed over into a state in which free dioxygen was available in the oceans and the atmosphere. We have already described the likely catastrophic effects on an anaerobic biota, but the changes were much broader than that. Dioxygen in the seas led to major changes in seawater chemistry. Iron, which had previously been soluble as ferrous salts, was precipitated in the ferric form. Copper, which had been insoluble in the anaerobic ocean as cuprous sulphide (Cu+-state), now became moderately soluble in the cupric form (Cu++-state).