Molecular and Cellular Biology Flashcards
How is mRNA complementary to DNA
A strand of messenger RNA has a base sequence complementary to that of the DNA template strand, and the strand orientations are antiparallel. The only difference between DNA-DNA and DNA-RNA pairing is that uracil in RNA replaces thymine in DNA.
How is transcription initiated for a specific gene
In eukaryotic cells, an RNA polymerase cannot bind to a gene and initiate transcription until transcription factors have bound to the gene. Typically, cell-specific regulatory transcription factors bind to the enhancer sequences of a gene, which facilitates the binding of general basal transcription factors to the promoter sequence, and finally the binding of the RNA polymerase.
What is transpiration
Transpiration is the evaporation of water through stomata in plant leaves, which creates a negative pressure and causes water to be absorbed into the plant through the roots. In this setup, an increase in transpiration rate will be indicated by a decrease in water level in the pipet. Of the choices, only increasing the light intensity will increase the transpiration rate. Additional light will cause the stomata to open more fully so that additional CO2 can enter the leaves to allow an increase in photosynthesis. The increase in the size of the stomata will increase the rate of transpiration and will pull more water into the shoot to facilitate the light reactions of photosynthesis.
Which TWO of the following processes occur as part of DNA replication?
Because the two strands of a DNA molecule run antiparallel to each other, and because a single polymerase simultaneously adds nucleotides to the 3’ ends of each of the two new strands, one new strand of DNA is synthesized in a continuous fashion, and the other new strand is synthesized in a discontinuous fashion in a series of Okazaki fragments that are ligated together after synthesis. DNA polymerases can only add nucleotides to a preexisting 3’ end, but RNA polymerases do not have this requirement. Thus an RNA polymerase lays down an RNA primer with an available 3’ end to which the DNA polymerase can attach deoxynucleotides (dNTPs) for the start of both continuous synthesis and the synthesis of each Okazaki fragment. Another DNA polymerase later replaces the RNA primers with dNTPs.
