Essay
The Importance of Nitrogen essay
An essay on the importance of nitrogen for AQA A-level biology
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The importance of Nitrogen-containing compounds in Biological systemsAll organisms rely upon nitrogen-containing compounds for their structure, their energy transfer,
their information storage and their metabolic processes. For energy transfer within cells and
organisms, ATP is a vital chemical. It is made up of a nitrogenous nucleotide derivative (adenosine),
joined to three phosphate groups. When ATP is hydrolysed, a small quantity of energy is released in
a single stage reaction and made available to the cell for a variety of processes. One of these is active
transport, where ATP binds to a membrane protein on the inside of the cell or organelle, causing the
protein carrier to change shape so that the molecule to be transported can cross to the inside
through the carrier. Without the energy from the ATP molecule, the important molecule could not
move against its concentration gradient. ATP can be regenerated from ADP and inorganic phosphate
using the ATP synthase channel in the thylakoid membrane when protons move by facilitated
diffusion from the thylakoid space into stroma. This process is called chemiosmosis, and it happens
during the light-dependent reaction of photosynthesis.
As aforementioned, ATP contains the nucleotide derivative adenosine which is a nitrogenous base
combined with a pentose sugar. This derivative also forms part of a DNA nucleotide, containing a
deoxyribose pentose sugar, a phosphate molecule and the base adenine. In DNA, there are four
different iterations of a nucleotide, all containing the phosphate group and the pentose sugar.
However, they differ by the nitrogenous base which can take the form of adenine, thymine, cytosine
and guanine. Each nucleotide is linked by a phosphodiester bond from the phosphate of one
molecule a carbon atom on the pentose sugar of another molecule. DNA has a double-helix
structure, meaning it is formed from two strands of nucleotides that run in opposite directions –
described as anti-parallel. One runs from the 3’ to 5’ and the other from 5’ to 3’. These strands are
then combined by hydrogens bonds that form between complementary base pairs. Adenine always
binds to thymine and forms two hydrogen bonds between the nitrogenous bases, and guanine
always binds with cytosine, forming three hydrogen bonds. It is these hydrogen bonds which allow
DNA to be replicated by semi-conservative replication. DNA replication is a necessity in order for
organisms to grow and reproduce. In order for the replication to occur, the DNA double-helix must
be separated, which can only be done by the splitting of the hydrogen bonds formed between the
nitrogenous bases. This is completed by the enzyme DNA helicase. These single strands then act as
template strand to which complimentary free base nucleotides can bind by complementary base
pairing. DNA polymerase then forms phosphodiester bonds to form a new sugar-phosphate
backbone. Thus, DNA replication is known to be semi-conservative as it is formed from one ‘old’
strand and one ‘new’ strand, a discovery made by the Meselson-Stahl experiment. Before a nucleus
divides via mitosis, the DNA must be copied to ensure each new daughter cell contains the correct
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