25/25 A Level biology essay written by a student who achieved A* in Biology at A Level. This essay is a great example of how to integrate beyond the specification content to get into the highest marking bracket.
The importance of proteins in the control of processes and responses in organisms
Proteins are extremely important biological molecules in a vast array of different metabolic
reactions and chemical processes in living organisms. In this essay I’ll be exploring how key
features of proteins, including their structure, allow enzymes like ATP hydrolase and rubisco for
example, to catalyse a wide variety of different important reactions.
Enzymes are proteins and so have a 3D structure. The unique bonding and folding in the
tertiary structure results in enzymes having a unique active site which can only bind to one
complementary substrate to form an enzyme-substrate complex. This specificity means
enzymes only catalyse specific reactions, and in this paragraph I’ll be looking particularly at the
importance of the role of DNA helicase and RNA polymerase in enabling transcription to occur.
Transcription starts with RNA polymerase attaching to the DNA double helix at the beginning of
the gene. DNA helicase acts to unwind the 2 antiparallel strands by breaking the hydrogen
bonds between the complementary bases and allowing 1 of the 2 strands to act as a template
strand for the synthesis of the mRNA copy. If the strands were not separated, the mRNA copy
could not be made because free RNA nucleotides would not be able to align opposite bases by
complementary base pairing. Alongside DNA helicase, DNA polymerase is also crucial. It
catalyses reactions enabling the joining together of the RNA nucleotides by phosphodiester
bonds thereby leading to the formation of single-stranded mRNA. This is extremely important
because mRNA is much shorter than DNA and can leave the nucleus through the nuclear pores
in the nuclear envelope. It can enter the cytoplasm and attach to a ribosome and a tRNA
molecule. Furthermore, it prevents the possibility of the genetic code being damaged or
destroyed by particular enzymes in the cytoplasm. The synthesis of this mRNA strand is
absolutely essential in enabling translation to take place and therefore, allow the development of
a wide variety of different proteins-E.g., melanin. Without protein synthesis we would not be able
to make components like hormones, new muscle or the other enzymes that I’ll write about
throughout the essay. Therefore, it’s of utmost importance that DNA helicase and RNA
polymerase are able to catalyse these reactions.
Transcription, as described above, is a key stage of protein synthesis. It is through protein
synthesis by which other key enzymes like ATP hydrolase can be made. ATP hydrolase is able
to catalyse the reaction involving the hydrolysis of ATP into ADP and Pi and this hydrolysis
reaction releases energy which can be harnessed in multiple different reactions such as muscle
contraction. It is the energy released from this hydrolysis reaction which enables the myosin
heads to bind to the binding sites on the actin filament, form cross-bridges and move the actin
filament. Therefore, it’s evident that ATP hydrolase is important in facilitating this sliding filament
mechanism and allowing muscle contraction to occur. Muscle contraction is vital in ensuring our
survival because it allows us to respond quickly to stimuli. Alongside muscle contraction the
energy released from ATP hydrolysis is also very important in glucose absorption into the blood.
This energy is used to actively transport sodium ions from the epithelial cell lining the ileum and
into the blood thus setting up a concentration gradient. Sodium ions can now move into the
epithelial cell from the ileum, down their concentration gradient, along with glucose via
co-transporter proteins. Without the active transport of sodium ions into the blood glucose
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