Summary AQA Biology: A Level - Unit 2 - Cells - Transport across cell membranes
Nucleic Acids: Chapter 2 A level AQA Biology
Biological Molecules: Chapter 1 AQA A level Biology
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The importance of nitrogen containing compounds
DNA is an important compound containing nitrogen through its nitrogenous
bases in the DNA nucleotide. These are in the form of the pyrimidines,
cytosine, thymine and uracil and the purines, adenine and guanine. Without
these bases, DNA replication would not occur. This is the process by which the
DNA replicates semi-conservatively to double the supply of DNA. The process
begins by DNA helicase breaking the hydrogen bonds between the
complementary nitrogenous bases to separate out the polynucleotide strands.
Both of these strands act as templates, allowing complementary free DNA
nucleotides to be attracted and align with the exposed DNA nucleotides. DNA
polymerase then catalyses the production of the sugar phosphate backbone,
via producing phosphodiester bonds. This produces the semi-conservative
product of the DNA helix; where one strand is from the original DNA and the
other has been newly synthesised. Without nitrogenous bases, this process
would not occur. This would limit the function of the s phase in interphase
which prepares the cell for the mitosis stage in the cell cycle. This would be
particularly important in the immune response as this would affect clonal
expansion of b lymphocytes and t lymphocytes so these cells wouldn’t be able
to neutralise and destroy a pathogen, which can cause harm to an organism.
Nitrates are a key source of growth for plants and are produced from nitrogen
gas in the air. Nitrogen fixation of this gas, by nitrogen fixing bacteria in the
root nodules in soil, must occur as otherwise there are no nitrates in the
plants. This is because plants lack the mechanism to take in and utilise nitrogen
gas to produce what they need. This nitrogen fixing bacteria enables plants to
produce nitrate which they can then utilise to produce the components, DNA
and ATP. DNA provides the genetic information to synthesise important
proteins that the plants need. ATP plays a vital role in the mass transport of
sucrose in the phloem from the source to the sink. If ATP was not used,
sucrose would not be able to reach the sink as this movement uses ATP to
move sucrose against its concentration gradient. This would mean respiration
of the plant would not occur as they wouldn’t have a supply of sugars. The lack
of nitrates in plants would not be beneficial to the mammals that eat and
digest plants as the 20 essential amino acids that a mammal requires need to
be provided for by diet. If they didn’t ingest these amino acids, when they die,
the proteins cannot undergo ammonification by saprobionts to produce
ammonia. This then means that nitrification to nitrites by nitrifying bacteria
cannot occur and then again to produce nitrates can’t occur. This prevents the
cycle of nitrogen from continuing which is important for the environment.
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