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The importance of nitrogen containing substances in biological systems.
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Hi, This is a model essay for A-level Biology on the importance of nitrogen containing compounds in biological systems.
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The importance of nitrogen-containing substances in biological systems.One of the most important nitrogen-containing substances in biological systems is DNA.
DNA contains nitrogenous organic bases which bind to adjacent bases by complementary
pairing. This process occurs during semi-conservative replication and allows us to produce a
new strand of DNA in the interphase stage of mitosis. DNA is also involved in protein
synthesis where it is transcribed into mRNA then translated to produce a sequence of amino
acids which make up a polypeptide chain. These polypeptide chains can join together in a
quaternary structure to produce functional proteins such as enzymes. DNA is essential for
the growth of biological organisms as it is involved in both mitosis (repairing tissues) and
meiosis (production of gametes that fuse together to form an embryo). Additionally, DNA is
used in recombinant DNA technologies such as in vitro and in vivo cloning to produce a copy
of an organism’s target DNA and proteins. This has applications both in medicine and
science.
Haemoglobin is an essential protein in some biological systems. It is a protein with a
quaternary structure of 2 alpha and 2 beta chains, each with a haem group that contains an
Fe2+ ion. As a result, each haemoglobin molecule can carry up to 4 oxygen molecules around
the body. Haemoglobin molecules have different affinities for oxygen which makes it very
useful. For example, at respiring tissues there is a low pO 2 and a high pCO2. This means that
haemoglobin has a low affinity for oxygen, so oxyhaemoglobin dissociates to unload the
oxygen to the respiring cells. This is important as oxygen is involved in respiration and is
used as the terminal electron acceptor in oxidative phosphorylation when protons,
electrons and oxygen combine to form water. Finally, unloading oxygen helps to counteract
the effects of CO2 on the blood as it would lower the pH of the blood which may denature
enzymes, leading them to become dysfunctional.
In respiration, organisms use glucose to produce ATP which is yet another important
nitrogen-containing compound. Glycolysis produces 2 molecules of ATP when glucose is
converted into pyruvate. This is then converted into acetate, combines with co-enzyme A
and enters the Krebs cycle to generate more ATP as well as NADH and FADH 2. Both of these
substances have important roles in oxidative phosphorylation as they release electrons
which can be passed down the electron transport chain to produce ATP. ATP is used is most
metabolic processes, including co-transport of glucose and muscle contraction. For example,
without ATP, glucose may not be able to be absorbed from the ileum into the bloodstream
to be used as a respiratory substrate. In muscle contraction, the myosin and actin filaments
wouldn’t be able to slide across each other without ATP.
Photosynthesis also relies on the use of ATP in the chemiosmotic theory and later in the
Calvin cycle. Protons are pumped from the thylakoid membranes into the granum to create
an electrochemical gradient for H+ ions to diffuse into the thylakoid membranes where they
combine with electrons and NADP to form NADPH. As well as ATP, these products from the
light-dependent reaction are required in the Calvin cycle. NADPH loses hydrogen ions to
reduce glycerate-3-phosphate into triose phosphate and ATP provides the energy to drive
this reaction. By producing triose-phosphate, macromolecules such as starch and cellulose
can be produced. Starch is used as a storage molecule as it is insoluble and compact which is
particularly useful for plants that store seeds in the winter. Cellulose provides rigidity for a
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