Biology free essay sample

The flow of genetic information from DNA to protein in eukaryotic cells is called the central dogma of biology. The role of RNA in protein synthesis is extremely important as protein synthesis could not occur without RNA. Three forms of RNA exist solely to create proteins. Through a process known as translation, RNA constructs the proteins necessary to sustain life. Spliceosomes Process pre-mRNA by splicing out intronic nucleic acids producing mRNA which is then translated to protein in ribosomes. Codons are three letter codes eg: AUG which codes for metheonine. Likewise there are many codons which code for different amino acids. Ribosomes bind to the mature mRNA at an AUG site and, for each codon (3 mRNA nucleic acids), a tRNA brings an amino acid for the translation, until the stop codon where the newly synthesized polypeptide is released in its primary structure. b) A eukaryotic cell has a nucleus that separates the processes of transcription and translation. This process is the closing f blood vessels to the skin surface and becoming more dilated. This allows the surface area to increase. By increasing the surface area, heat is lost to the external environment, cooling the body down back to normal temperature. However, shivering is the exact opposite of this response. When the body becomes too cold, the internal system works to bring it back up. This is also called Vasoconstriction. If the opposite occurs and body temperature drops, signals from the hypothalamus are sent to the cutaneous arteries (arteries supplying the skin) (2). When the body temperature of an rganism drops the blood vessels become constricted in order to decrease surface area. This allows for minimal heat loss. Warmer blood is seen to be immersed in the body so to keep heat from escaping at the surface (2). In human thermal regulation, the hairs on the body aid in insulation. The hairs stand on end and capture a layer of air between the skin and hair, serving as insulation. If the air held is warmer-with longer hairs- than the hairs will reduce heat loss and a thinner hair layer will allow for more heat to be loss, decreasing temperature. Due to these mechanisms, emperatures in the body rarely exceed . 5 degrees Celsius below or above its normal point. This negative feedback loop maintains body temperature and can also help regulate other process in the body. Plants are often subjected to periods of extreme water loss or gain. These fluctuations of water availability force vegetation to have responses in order to maintain homeostasis. These responses are complex and involve deleterious adjustments. This may be modified by the superimposition of other stresses, such as diseases or environmental disorders. All of these processes and practically all other he cellular level, water management coincides with cell damage or even adaptive processes. The molecular basis for responding to water deficits is not completely understood, however, it is known that it has much to do with a particular chemical called abscisic acid ABA (3). An increase of ABA in plant organs correlate with those plants living in areas undergoing a period of drought (3). Therefore, it is widely understood that ABA is involved in the adaptive mechanism in response to drought (3). There is also evidence that other signals may be involved in the process as well. Plants also exhibit secondary and tertiary controls when placed under water stress. In addition, they will also undergo primary effects if placed under longer periods of time. During water stress, like nutrient deficiencies, free amino acids and sugars accumulate. Though nutrient deficiencies may result in different metabolic functions, plants under water stress have been seen to go through similar changes in dealing with these environments(4). Because of this, it is hard to examine the mechanisms for dealing with water stress when observing such general patterns. Early responses sually are dependent on new metabolic abilities, while there is an alteration of gene expression.