Chapter 14, Problem 3Q

Summary Introduction

To review:

The information that would be gathered after measuring the activities of the enzymes that catalyze the steps A, B, C, and D in the fused diploid and each haploid mutant strains.

Given:

Two mutant strains of Neurospora (Leu-1 and Leu-2), the wild-type and the fused type were supplied with different nutrient media and their growth was recorded in Table 1. The presence of growth is indicated by the positive sign (+) and the absence of growth is indicated by the negative sign (−).

Table 1: The results of the growth of different strains of Neurospora in different media.

Types of strains used in the experiment	The growth of different strains of Neurospora in different media
		Minimal medium	Minimal medium+2-isopropylmalate	Minimal medium+leucine	Minimal medium+3-isopropylmalate	Minimal medium+α-ketoisocaproate
Wild type (haploid)	+	+	+	+	+
Leu-1 (haploid)	-	-	+	-	+
Leu-2 (haploid)	-	-	+	+	+
Fused cells (diploid): Leu-1, Leu-2	-	+	+	+	+

The following metabolic reaction represents the steps, which are involved in the synthesis of leucine in Neurospora (Figure 1).

Figure 1:

Introduction:

Neurospora is a haploid organism and is able to grow in the minimal medium. The minimal medium is the medium that contains only the simple components that are required for the organism’s survival and lacks any additional amino acids. Neurospora is able to synthesize the amino acid leucine and hence, does not require the same in its medium, in order to grow.

However, the mutant strains lack one of the enzymes that are required in the leucine synthesis and therefore, are unable to grow on the minimal medium. Different types of media are used to differentiate between the wild-type and the mutant strains of the Neurospora.