A "pinch" is about 1/16 teaspoon, and that amount of sugar is about 0.2 grams. Your 284 grams of flour alone will have about 3.7 grams of sugars, in the form of mono-and disaccharides. The effects of the pinch of sugar and the natural sugars in the flour on bake performance will be about zero.
Yeast can only consume simple sugars, called monosaccharides. Sucrose, or ordinary table sugar, is a disaccharide. Before it can be used as food by the yeast, it has to be cleaved into the two monosaccharides fructose and glucose. This happens when the water (the yeast hydrating liquid) to which the sugar is added is warm. Otherwise, you would have to use an acid or an enzyme. So, adding a pinch of sugar to yeast in cold water may not help, or you might have to let the mixture sit until it warms up.
To atom's point, sugar added to the hydrating liquid will have a positive effect insofar as giving the yeast a jump start. To prove this, this afternoon I put 1/2 teaspoon of SAF Red IDY into each of two identical containers, along with 1/4 cup of warm water at a temperature of 95 degrees F. I added a pinch (1/16 teaspoon) of sugar to one of the containers but not to the other. I stirred both containers to dissolve the yeast, and let the containers sit at room temperature for 10 minutes. At the end of that time, the liquid in the container with the sugar was frothy with a profusion of very small bubbles. The liquid in the other container was as flat and lifeless as when I stirred it.