During transcription, the DNA of a gene serves as a template for , and an called II catalyzes the formation of a pre-mRNA molecule, which is then processed to form mature mRNA (Figure 1). The resulting mRNA is a single-stranded copy of the gene, which next must be translated into a protein molecule. Figure 1: A gene is expressed through the processes of transcription and translation. During transcription, the enzyme RNA polymerase (green) uses DNA as a template to produce a pre-mRNA transcript (pink).
Viscosity (a fluid's resistance to flow) is rated at 0Â° F (represented by the number preceding the W [for Winter]) and at 212Â° F (represented by the second number in the viscosity designation). So 10W-30 oil has less viscosity when cold and hot than does 20W-50. Motor oil thins as it heats and thickens as it cools.So, with the right additives to help it resist thinning too much, an oil can be rated for one viscosity when cold, another when hot.or example, oil tends to lose viscosity from shear, the sliding motion between close-fitted metal surfaces of moving parts such as bearings. So resistance to viscosity loss (shear stability) is necessary to enable the oil to maintain the lubricating film between those parts.
The advantage to the multi-weight is that when starting the engine, the multi-viscosity oil (with its thickness of an SAE 5W when cold), allows the engine to spin over more easily. The most common diesel use oil is 15W/40.traight Weight vs. Multi-Grade Engine oil can be either a straight weight or a multi-grade viscosity. Originally, all oil was straight weight. Relatively few straight weights are manufactured today since most gas-or diesel-engine manufacturers recommend multi-grades.