Question

Proteins are chains of amino acids. There are twenty different types of naturally occurring amino acids, and all organisms must have all twenty of them in order to survive. In this project we will be discussing the amino acid leucine. What are the two possible methods that a cell may employ to be certain that it has each of the 20 amino acids?

RNA is partly made of the base uracil. What are the two possible methods that a cell may employ to be certain that it has uracil?

Suppose that you have a particular S. cerevisiae mutant strain that cannot make the amino acid leucine. Will the strain grow on a YPD plate? What about a SD plate? How could you modify the SD plate to allow this strain to grow

Answer 1

1. There are various methods by which cell can ensure that it has all the 20 amino acids they are-

a. The amino acid (essential amino acids-eg- histidine, isoleucine, leucine, tryptophan, threonine, valine, lysine, phenlyalanine and methionine) can be obtained from food by digestion of the proteins present in the food.

b. The cells are capable of synthesizing some amino acids on its own.These aminoacds are also called non-essential amino acids

c. The cell can also utilize the mis-match repair mechanism along with the proof-reading activity of the DNA polymerase to ensure that there is no mistake in the DNA and eventually in the protein coded by the mRNA.

2. To ensure that the cell has uracil 2 methods can be employed

a. Release of enzyme Uracil DNA-glycosylae will remove the uracil if present .

b. The cell can promote cytosine deamination which leads to the formation of uracil.

3. Yes the strain will grow on YPD medium because it is a complete medium for the growth of yeast that has yeast extract, peptone, double-distilled water, and glucose. It also contains all the amino acids essential for the growth of the yeast. On the other hand SD medium is composed of yeast nitrogen base without amino acids and glucose.Therefore the strain will not be able to grow as it cannot make leucine on its own. For the growth of the auxotrophic strain in SD medium the amino acid leucine can be added which will support the growth.