The Biochemical Basis of Life

It is imperative that we understand the concepts in chemistry that are relevant to the study of biology so that we can make sense of the processes that take place in living organisms

Basic Chemical Principles

  • · each atom has its own specific number that represents how many protons it, and only it, possesses
  • · this number is called the atomic number
  • · the number of neutrons in any atom is commonly the same as the number of protons
  • · the atomic mass of any atom is the sum of the number of protons plus the number of neutrons
  • · some atoms exist in more than one “variety” or “flavour”
  • · for example, hydrogen is found to exist in three main forms in the universe:
  • · normal hydrogen – 99.9% of all hydrogen
  • · deuterium – 0.2% of the rest
  • · tritium – exists in trace amounts
  • · notice that all three “varieties” of hydrogen possess 1 proton (i.e. they all have the same atomic number), yet they each possess a different atomic mass, which makes them all isotopes
  • · all isotopes possess similar chemical properties but different physical properties - namely mass
  • · for example, the element carbon, C, a major constituent of living organisms, consists of three isotopes:
  • · carbon-12 - accounts for 99% of the carbon atoms in nature
  • · cabon-13 – accounts for the rest
  • · carbon 14 - exists in trace amounts
  • · isotopes naturally break down (decay) thereby releasing subatomic particles and radiation – such isotopes are called radioisotopes
  • · of the three varieties of carbon, carbon-14 is radioactive
  • · Table 1, p. 8 summarizes the basic characteristics of the three isotopes of carbon and hydrogen
  • · all radioactive isotopes have a characteristic half-life – the time it takes for one half of the atoms in a sample to decay
  • · the half-life rate is constant for each isotope
  • · two useful applications of radioisotopes are:
1. radiometric dating
  • · radioactive carbon-14 becomes incorporated into living tissue
  • · when the tissue dies and becomes decomposed, the carbon-14 that it possesses begins to decay at a constant half-life rate
  • · when the ratio of carbon-12 to carbon-14 in a dead or fossilized organism is measured, scientists can predict the amount of time that has elapsed since the organism’s death
2. radioactive tracers
  • · when radioactive elements exist in living tissue, they emit radiation
  • · this radiation can be detected using various kinds of equipment – which means that any radioactive element can be followed or traced chemical reactions
  • · this is how scientists learn about reaction mechanisms and biochemical processes such as respiration and photosynthesis
  • · carbon-14 and hydrogen-3 (tritium) are commonly used tracers in biological research
  • · radioisotopes are also used in diagnoses and treatment
  • · for example, the thyroid gland, an important organ that regulates human metabolic activity and growth, actively absorbs iodine
  • · doctors are able to inject radioactive iodine into patients that possess abnormal thyroid activity to help diagnose their thyroid condition – normal, enlarged (over active), or cancerous
  • · the radioactivity is detected with a photographic device, creating an image of the thyroid gland