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It is ubiquitous, it is found in animal and in plant cells
Variation in stomatal resistance could be another factor associated with temperature effects on net assimilation of CO2. Adaptation to high temperature can be related to photosystem II electron transfer, the stability of chloroplast membrane-bound enzyme activities and the stability of the photosynthetic carbon metabolism enzymes that require light for activation. For example, enhanced assimilation of CO2 by rice at high temperature, in comparison with the more temperate C3 species, is associated with a greater response of ribulose-1,5-bisphosphate carboxylase in rice to increasing temperature.
For transpiration to occur, water contained in cells within a leaf must change into water vapour and escape through stomatal pores. For the water to move from a cell to the inter-cellular air space it must change from a liquid to a gas (water vapour). This phase change from liquid to gas consumes a large amount of energy and in doing so cools the leaf. This loss of energy is referred to as latent heat loss. The rate at which transpiration occurs is proportional to the difference in humidity and to the amount of resistance between the inside of the leaf and the surrounding air. As well as wind speed and boundary layer properties, transpiration is strongly influenced by stomatal resistance. When the stomata are closed, heat loss through transpiration is negligible. Although stomatal resistance has a large impact on leaf temperature, it is generally accepted that stomatal opening does not respond directly to changes in temperature. In hot, dry conditions stomata will typically remain closed even when a leaf is overheating (Lambers et al. 2008).
What is the role of RuBisCO in photosynthesis? - Quora
Cebic scientists have also begun to study recently discovered anaerobic alkane degraders. We have two model strains (a Desulfobacterium oleovorans from culture collection and a Desulfosarcina-like strain (AK01) isolated from sediment) that appear to possess distinct mechanisms of anoxic alkane degradation. This contrast provides us with a unique opportunity to determine the degradation pathway and the responsible genes, to establish structural and functional relationships between alkane oxidation enzyme groups, and to determine the role each group plays in the marine environment.
Denitrification is an important chemical transformation in the nitrogen cycle and the principal sink for fixed nitrogen in natural waters. Denitrification occurs as a result of the dissimilatory reduction of nitrogen oxides (nitrate and nitrite), in which nitrogen oxides are used as alternative electron acceptors during by anaerobic bacteria. Denitrification involves a suite of reductase enzymes, all of which require metal cofactors. We shall focus on the nitrate and nitrite reductases.
What is the role of RuBisCO in photosynthesis ..
Major proteins and protein complexes of the chloroplast photosynthetic apparatus of a higher plant exemplified by Arabidopsis thaliana.
The major objectives of this project are to establish the relationships between the availability of metals (molybdenum, iron, copper), the diversity and efficiency of enzymes (nitrate and nitrite reductases), and the structure and mechanisms of the enzymes' metal centers. In particular, we wish to understand how the relative availabilities of iron and copper influence the distribution of the different types of nitrite reductase in the environment, and the efficiency of denitrification.
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enzyme involved in photosynthesis?
When a plant is grown outside of its optimum thermal range, metabolic imbalances occur. Imbalances may result in a short-fall of essential metabolites or intermediaries, or in a build-up of substances that becomes toxic (e.g. aggregated proteins). Such imbalances cause further inhibition of processes such as photosynthesis and respiration. The imbalances can be due to differences in the thermal response of particular reactions. For instance, the enzymes used in photosynthesis are deactivated at a lower temperature than those used in respiration. This has the result that as temperatures increase, the rate of carbon fixation falls while the rate of carbon use may rise. The point at which the plant is using more carbon than it is assimilating is termed the ‘temperature compensation point’. Beyond the temperature compensation point, the plant begins to use up carbohydrate reserves, e.g. in many legumes the net uptake of CO2 by the green pod is low due to the high rate of pod and seed respiration, at high temperatures net uptake can become negative. As plants acclimate to high temperatures the rate of respiration falls lessening the impact on net photosynthesis.
Enzymes of chlorophyll biosynthesis | SpringerLink
For some reactions, the thermal response of a particular enzyme can be rate limiting. The inhibition of photosynthesis during moderate heat stress has been associated with a reduction in the catalytic activity of Rubisco (Ribulose 1:5 bisphosphate carboxylase/oxygenase), due in part to the thermal sensitivity of Rubisco activase. In some species, production of heat stable forms of Rubisco activase has been shown to play role in acclimation to high temperature (Yamori et al. 2013). There have been attempts to engineer less temperature sensitive forms of Rubisco activase in order to increase the thermal range of crop species, but it remains to be seen if altering a single component of the photosynthetic system will improve overall heat tolerance (Sharkey 2005; Allakhverdiev et al. 2008).
The enzymes responsible for chlorophyll biosynthesis in ..
For most metabolic reactions, the optimum and maximum temperatures are determined by the thermal response of key enzymes. Enzymes act to lower the activation energy and increase the rate of reactions at any given temperature. However, as temperature increases the catalytic properties of most enzymes are lost and they begin to denature (i.e. enzymes are thermolabile). The synthesis of replacement enzymes and other cell proteins is also impaired, resulting in an overall limitation due to reduced protein turnover. Under prolonged severe heat stress many enzymes will become denatured. This, combined with the loss of membrane function will result in cell death.
An enzyme involved in chlorophyll biosynthesis.
At high temperatures dry matter production is often more limited by photosynthesis than by cell expansion (while at low temperatures dry matter production is more limited by cell expansion than by photosynthesis). Generally, the inhibition of photosynthesis and other growth maintaining processes during moderate or short-term heat stress results in a comparatively small reduction in the rate of dry matter production (relative growth rate) (Chapter 6.2.2; ). As temperature increases within a plant’s thermal range, the duration of growth decreases but the rate of growth increases, as shown earlier in this chapter. As a consequence, organ size at maturity may change very little in response to temperature, despite variation in growth rate. As temperatures are raised further, an increased rate of growth is no longer able to compensate for a reduction in the duration of development, and the final mass of any given organ at maturity is reduced. This response can be seen in a range of tissues including leaves, stems and fruit. A smaller organ size at maturity due to high temperature is associated with smaller cells rather than a change in cell number. This implies that cell enlargement is more sensitive to temperature than is cell division. The reduced duration of development can also limit the number of organs that are produced, e.g. grain number in wheat is reduced when plants are grown at moderately high temperatures (Stone and Nicolas 1994). Under certain conditions plants grown under moderate heat stress accumulate sugars in their leaves, indicating that translocation can be more limiting than photosynthesis, but this is not thought to be a general limitation.
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