Friday, August 21, 2009

Super cells

Proteins are large complex molecules made up of amino acids that perform many diverse and essential functions within living cells; enzymes, for example, enable chemical reactions to take place. Their function is directly a consequence of the 3D arrangement of their amino acid chains in space. Physical and chemical stress factors interact with proteins to alter their structure and consequently, their function.
Whether cells can isolate themselves from their environment and protect themselves depends on the type of conditions they are exposed to as well as the properties of their cell membranes. Extreme environments that are mediated through chemicals (pH and salty environments) can be manipulated by cells so that their internal biochemistry need not be rewritten. For example, there is usually a difference of 2 pH units between the outside and inside of cells in an acid or alkali environment. Cells can achieve this by actively pumping ions out of the cell through specialised membrane protein channels.
Temperature and pressure cannot be restricted to the outside of the cell; consequently, organisms that live in extreme conditions must adapt their biochemistry. Some of the most common adaptations to extreme environments are made to membranes and enzymes to ensure their continued function.

Surviving extreme conditions

Every living organism has a range of conditions over which it is able to undergo normal activity, and when it is pushed to its limits, it struggles to survive. Some species that survive in extreme environments are true extremophiles and do not seem to find the conditions harsh at all. But in most cases, living things develop elegant tolerance mechanisms that help them adapt to their surroundings.
Animals seem to have developed three basic tolerance strategies. The first involves slowing down and sitting it out: animals often reduce their metabolism and sometimes enter into hibernation. Others may find a more favourable environment, like animals that migrate to avoid seasonal extremes. Living things sometimes also launch a counterattack, like wood frogs that produce antifreeze proteins to prevent ice crystals forming in their cells in the extreme cold.
However, these tactics usually only work for occasional exposure and to flourish, major adaptations are required at the biochemical level. For the most part, micro-organisms, like bacteria, archaea and fungi, have achieved these more complex adaptations.

Life at the Extremes

Life has flourished here on Earth. Typically, living things are found in warm, wet, sunlit zones, at pressures similar to those at sea level and in conditions that are neither acidic nor alkaline. But living cells have also been found in areas that seem inhospitable to life: in hot springs, lying dormant buried in ice, in acid-filled caves and in the depths of the ocean. By exploiting new environments, these pioneering organisms gain a competitive advantage that allows them to proliferate. How are they able to tolerate these conditions?