Essay 1 Flashcards
Enzymes are important in the process of semi-conservative DNA replication,
the mechanism of which was elucidated by Watson and Crick. In DNA replication, the enzyme DNA helicase breaks hydrogen bonds between complementary base pairs (adenine to thymine, cytosine to guanine). This allows free, activated, DNA nucleotides to be attracted to both template strands by hydrogen bonding.
Another enzyme, DNA polymerase
catalyses a condensation reaction (producing a molecule of water each time), which causes the formation of phosphodiester bonds between DNA nucleotides on the leading strand (continuously) and lagging stand (discontinuously), joining them together. DNA ligase is another important enzyme that joins together the Okazaki fragments created through the discontinuous catalysis of DNA polymerase on the lagging strand.
This is important to organism for the process of mitosis,
which is essential for the growth, repair and replacement of cells. DNA replication is necessary to facilitate mitosis because it occurs in the S phase of interphase, doubling the genetic information in the cell so that it can divide to produce two genetically identical diploid daughter cells. Hence, mitosis depends upon this important enzyme.
DNA helicase is also involved in
the transcription stage of protein synthesis. It once again completes its function of breaking the hydrogen bonds between the complementary DNA base-pairs. This allows free, activated RNA nucleotides to be attracted to the single template strand by hydrogen bonding in new complementary base pairs (DNA to RNA: adenine to uracil, cytosine to guanine, guanine to cytosine, thymine to adenine). This allows another enzyme RNA polymerase, to complete the similar function of the condensation catalysis of phosphodiester bond formation to join the RNA nucleotides together.
Translation is
an important process in organisms because it leads to translation and therefore polypeptide chain production. Proteins are made of polypeptide chains folded into a specific tertiary structure through hydrogen, ionic and covalent bonding. An example of important proteins the enzymes that need active sites complementary to their substrates. Hence, enzyme production and therefore all biochemical reactions that require enzyme catalysis, relies on DNA helicase.
A class of enzymes produced through translation
are the digestive enzymes. The enzyme amylase catalyses the hydrolysis of the glycosidic bonds in starch (an alpha-glucose polysaccharide) into maltose (an alpha glucose disaccharide), using a molecule of water each time. Maltose is then hydrolysed into alpha-glucose monomers by maltase. Other disaccharide hydrolysis reactions involving enzyme are catalysis are: sucrose to alpha-glucose and alpha-fructose by sucrase and lactose to alpha-glucose and beta-galactose by lactase.
These hydrolysis reactions are important
because they produce glucose, which is necessary as the initial reactant for the glycolysis stage of respiration in the cytoplasm, and therefore the production of ATP that drives all active reactions, such as active transport.
Other enzymes involved in the glycolysis stage
of respirations are phosphofructokinase and isomerase. Initially, glucose is phosphorylated into glucose-6-phosphate, using a molecule of ATP. Then, the important enzyme isomerase catalyses the isomerisation of glucose-6-phosphate into fructose-6-phosphate. Then, phosphofructokinase catalyses the phosphorylation of fructose-6-phospjhate into fructose-1,6-diphosphate, using another molecule of ATP. This can then split into two molecules of triose phosphate, which are oxidised via a series of intermediates into pyruvate, alongside the substrate-level phosphorylation of 2 ADP molecules with Pi to produce ATP.
This is important because mitochondria only have
channels for pyruvate, not glucose – the conversion of glucose into pyruvate allows it to enter the mitochondria to continue with the stages of aerobic respiration: the link reaction, the Krebs cycle and oxidative phosphorylation. This is important because it allows the production of ATP in oxidative phosphorylation. This proton motive force results in the by the chemiosmosis of protons down a proton gradient through the ATP synthase enzymes, inducing conformational changes in the ADP substrate that allow it to bind to Pi. ATP is necessary to drive all active reactions such as active transport.
Plants do not derive their glucose necessary for respiration from digestive enzyme hydrolysis
, but from the process of photosynthesis. Enzymes are also crucial to photosynthesis; specifically, the light-dependent stage. Initially carbon dioxide reacts with ribulose bisphospahte to create two molecules of glycerate-3-phosphate. This is catalysed by the enzyme RUBISCO. RUBISCO’s activity then allows the glycerate-3-phopshate produced to react with NADPH to produce triose phosphate and NADP, using a molecule of ATP. The NADP must be regenerated so that it can return to the light-dependent stage, in order to keep the process of photosynthesis continuous. 1/6 of the TP produced is converted into organic substances such as glucose, to be used for respiration. However, 5/6 are used to regenerate RuBP using ATP, so that the light-independent reactions can continue, creating the Calvin Cycle.
Another enzyme important to the Calvin Cycle
is rubsico activase, which promotes the release of a competitive inhibitor of RUBISCO, known as CA1P from RUBISCO’s active site, in order to maximise RUBISCO’s catalytic efficiency. As well as maintaining the plants ability to respire, the uptake of carbon dioxide by this important rubisco enzyme, and conversion into organic matter is important, because it creates a carbon sink that reduced the amount of carbon dioxide in the atmosphere, slowing the rate of global warming by infra-red radiation absorption.
