AddingД¬itrulline as a supplement complements the mutation and drives arginine synthesis to completion. Similarly, consider a genetic mutation in Mutant# 2 affecting the enzyme that makes the arginine precursor citrulline. If ornithine is added to the media, citrulline and then arginine would be made and Mutant# 1 could grow. So, the gene that makes the enzyme for ornithine synthesis must

Hypothetic examples using Figure 1 but no longer considering Table 1 so we can explore other possibilities and their consequences.ДЇor example, letвЂ™s say that Mutant# 1 couldn't make ornithine. Going Deeper: More about the 1 gene, 1 enzyme hypothesis and the importance within a metabolic pathway. This necessarily means that both P and Q have a functioning enzyme argininosuccinase (see Figure 1). The information in the table shows a (+) symbol in the last two columns indicating that both P and Q are able to convertДЄrgininosuccinate to arginine (see Table 1). X (the other interpretation is that they have no enzyme but that is not consistent with the data in the table provided).

Reinterpret the question: if neither P nor Q have a defective enzyme X, that suggests that both P and Q have a functioning enzyme So you can see that the figure provided indicates the 3 enzymes that are catalysts for the three reactions as shown. You should recognize that enzymes typically end with вЂ“ase and Neither mutant strain P nor Q have the defective enzyme: Question 2ДЄccording to the information provided, a conclusion that can be made with certainty is that Growth is indicated by (+), and no growth is indicated by (-). Table 1: Growth response of mutant strains in 'minimal' media with supplements as Each gene in italics in theДiagram produces one enzyme necessary for the synthesis of this essential amino acid required for growth. Other hand, if a 'complete' medium is provided, containing all required amino acids, then Neurospora wouldДЇigure 1: A synthesis pathway for the amino acid arginine. The mutant would only grow if the enzyme product were to be added as a supplement. Mutating any one of the genes that makes an enzyme can produce a Neurospora strain that cannot Grows normally in nature (wild type) has enzymes that convert these simple substances into the amino acids necessaryДЇor growth. Medium which is a fluid containing only a few simple sugars, inorganic salts, and vitamin. The red bread mold Neurospora crassa grows well on a cultural plate with 'minimal' MCAT Sample Question 2-3: Biology/Biochemistry High p53 concentrations: clearly we get the opposite of the above, meaning a decrease in CDK2. Which we already established means an eventual rise in CDK2. If PTEN goes up, then PIP3 must go down because of the negative feedback symbol), rise in AKT, rise in mdm2, decrease in p53 Thus we have a decrease in PTEN which will lead to a rise in PIP3 (if you are unsure, think of what happens

Low p53 means low p21 which we establishedДЄ mutation in the gene that produces PTEN: The great majority of mutations will result in an ineffective gene product Note that we used the mostДirect route to get to CDK2 as the question used the words вЂњmost reasonablyвЂќ. Mdm2 and low p53 (notice carefully, when we leave mdm2, there is only one place to go in the diagram becauseДЄll the other symbols are pointing to mdm2 and only one symbol is pointing away).

High cyclin G concentrations: From the bottom of Figure 1, we can see that high cyclin G leads to high Our instance, p21 is low (degraded) so this allows CDK2 to rise unchecked. In other words, when p21 is high, CDK2 goes low. Shows that p21 has a negative influence on CDK2. [Notice a key step inДegradation of p21 implies that the concentration of p21 in its active form goes down. Which means there will be some downregulation (amount/concentration goes down). Allow us to follow each arrow that stimulates the next protein and each symbol for negative feedback

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