Writing in Biology

Reactive oxygen species and physical damage cause endogenous damage to DNA. This makes DNA oxidized, have crosslinked bases, physical damage, and can lead to polymerase errors. Endogenous damage is repaired by homologous and non-homologous end joining. In homologous end joining, broken DNA uses the sister chromatid as a template to repair the broken strand. This allows for a complete repair without the loss of genetic material. In nonhomologous end joining, there is no sister chromatid available so the broken ends are cleaned up with an exonuclease and snapped back together with ligase.

The snow removal experiment in progress at Harvard Forest is addressing the effects of reduced snowfall in Massachusetts. They are using this experiment to predict how the vegetation would be affected if in the future, the snowfall keeps decreasing in the area. They have plots in which they don’t remove the soil and plots in which they do. So far, they have seen that removing the snow is causing the soil temperatures to drop because the snow is not there to insulate the soil. 

At Harvard Forest, a soil warming experiment is being done to address how the freezing soil is affecting tree growth. They plant young, new trees and artificially warm the soil in certain plots and leave the soil alone in other plots to see how warming the soil would affect tree growth. They also adjust the fertilizer levels in all plots, so certain plots have warmed soil and no fertilizer, others have warmed soil with fertilizer, not warmed soil with fertilizer and a control. This experiment is taking place over years to address long term effects of reduced snowfall in Massachusetts and the colder soil temperatures that result from it. So far, they have seen warming the soil is affecting growth positively.

The Conte Research Center is addressing how the sturgeons are being affected by waste in the area they live. This is an observational study where they take sturgeons from the area and run chemical tests on them. They have found that their endocrine systems have been affected negatively as it has affected sexual development. Males have been found to have more female qualities as a result. Endocrine disruptors could be affecting the newly born sturgeon. To address this, the gametes must be analyzed for any abnormalities and differences between sturgeon with these problems and sturgeons without from birth must be analyzed.

Prokaryotic DNA replication is THETA replication with one origin and five DNA polymerases. DNA Polymerase III is the main replicating enzyme with a high processivity and a fast 5'-3' polymerase and 3'-5' exonuclease. DNA Polymerase I has a low processivity and a slow 5'-3' polymerase and 3'-5' exonuclease. DNA Polymerase I, II, IV, and V are responsible for DNA repair in prokaryotes.

Nucleic Acid monomers are nucleotides (sugar, base and phosphate), or nucleoside (sugar and base). Ribose is a  5 carbon sugar where the 5^thcarbon is off of ring, and the base attaches to carbon 1. Carbon 2 only has H on DNA and has OH on RNA. RNA is more unstable than DNA because of the OH group. Nucleic acid polymerization removes two phosphates off of carbon 5, remaining phosphate forms phosphodiester bond. There is a 5’-3’ reading direction and synthesis.

As treatment with jasmonic acid was predicted to negatively growth, our results of root and shoot biomass supported this hypothesis. Our results of inhibited growth are consistent with previous studies show jasmonic acid as a growth inhibitor to plants (Dathe et al. 1981; Redman et al. 2001; Koussevitzky et al. 2004). Root weight for treated plants were significantly lower than root weight for control plants. Previous literature shows that root growth of plants treated with jasmonic acid should be significantly effected (Yu et al. 2000; Tung et al. 1996). However, it has been shown that jasmonic acid deters herbivores from consuming the roots of the plant (Lu et al.). Although root mass was significantly affected by treatment, the roots of these plants may be less preferable to herbivores. This is something that would require further experimentation.

The results of herbivore preference followed our hypothesis. Control low fertilized plants were significantly preferred over damage low fertilized plants, and preferred (not significantly, P 0.0844 > 0.05) control high fertilized plants over damage high fertilized plants. Although the result is not 0.05, it is close to significant. If the experiment was replicated, we may be able to determine a significant difference between high fertilized damage and control plants on herbivore preference. Preference between fertilizer groups was not tested for, but damage high fertilized plant leaves had a greater amount of leaf area consumed (0.7668286) over damage low fertilized plants (0.53268571). These results are what was hypothesized, as well fertilized plants have been shown to have less volatile organic compounds found in the leaves and therefore would be preferable to herbivores (Prudic et al. 2005). Our results show that our treatment of mechanical damage and jasmonic acid could be used to deter herbivores in plants receiving a similar amount of fertilizer as our low treatment group, but it is not known how the plants would be affected further in terms of fruit produced and plant success because we did not test for that.

The number of flowers decreased among damage and control groups across fertilizer treatments. As flowers are part of the reproductive system of tomato plants, plants with less flowers could be less successful at reproduction. This would mean our treatment had a negative effect on reproduction, which, if tested for, would be consistent with previous literature (Ziosi et al. 2008; Redman et al. 2001; Koussevitzky et al. 2004). The treatment, although successful on herbivore deterrence, may negatively affect the reproductive success of the plants. This would be another study, but it is important to assess the costs to plant success when considering the benefits of herbivore deterrence.