Graded A level biology essay 'The importance of nitrogen containing compounds in organisms'. Graded A* by tutor and teacher. Structured and written to meet the mark scheme criteria.
6 in depth paragraphs with 1381 words, written this year so marked accurately.
One example of how nitrogen containing compounds are important is in the
nitrogen cycle, where nitrogen is recycled in ecosystems. The first stage of the
nitrogen cycle is nitrogen fixation, nitrogen gas in the atmosphere is turned into
nitrogen containing compounds such as DNA. Biological fixation is carried out by
nitrogen fixing bacteria e.g. Rhizobium found in the root nodules of leguminous
plants these form a mutualistic relationship with the plants. They catalyse the
reaction of nitrogen into ammonia, which then forms ammonium ions in solution
which is used in plants. The second stage of the nitrogen cycle is ammonification.
This is where organic nitrogen compounds in dead remains, excretory and
egested material are broken down and inorganic compounds released. Urea is
converted by saprobiants into ammonia while amino acids are also deaminated
to produce ammonia, ammonium ions are also released.
Saprobionts e.g fungi and bacteria use extracellular digestion to break this
material down by realeasing enzymes. This process is important as broken down
material is stored or used in respiration by the saprobiants. The third stage in
the nitrogen cycle is nitrification, ammounium ions are converted to nitrate ions
via nitrite ions by nitrifying bacteria and then by other species to nitrate.
This only occurs under aerobic conditions (which is why soil is ploughed, to
aerate it) this process is important as it makes nitrogen available to primary
producers to be used in functions such as producing amino acids which form the
primary structure of proteins, or for making DNA from nucleoides containing
nitrogenous bases. The final stage of the nitrogen cycle is denitrification. Under
anaerobic conditions ammonium ions are converted back to nitrogen gas in the
atmosphere this process is important as it prevents the build up of ammonium
ions in the ecosystem, denitrifying bacteria are needed for this process to occur.
Nitrates are also converted to nitrogen gas. This process is also important as
nitrates are used by the bacteria for respiration.
As mentioned above nitrogen is a component of amino acids, which contain an
amino group and a carboxyl group. Amino acids are joined by condensation
reactions, with peptide bonds holding them together which are strong bonds.
Amino acids are important nitrogen containing compounds as they form the
primary structure of proteins-the sequence of amino acids in a polypeptide
chain. For example the specific primary structure of antibodies gives rise to their
tertiary structure, variable regions which form antigen binding sites that are
complementary to one specific antigen. An antibody has two binding sites that
can bind to two pathogens at once. This process is important as pathogens can be
clumped together – agglutination. Hence phagocytes can bind to the antibodies
and phagocytose many pathogens at once. It’s the specificity of the antibodies
derived from the sequence of amino acids in the polypeptide chain of the protein
that gives antibodies this unique property. This process leads to the destruction
of pathogens carrying this antigen in the body.
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