Question

Besides sugars and fats, organisms can use other molecules as fuel for cellular respiration. When protein molecules are used, _____ are produced as waste.

a) molecules of lactic acid
b) sugar molecules
c) fatty acids
c) amino groups

Answer 1

amino groups

Step-by-step explanation:

The cellular respiration pathways are central in the extraction of energy from all these different molecules. Amino acids, lipids and other carbohydrates can become different intermediates of glycolysis and the citric acid cycle; this allows them to enter the path of cellular respiration through other different doors. Once these molecules enter the pathway, there is no difference due to their origin: they simply continue through the remaining steps and produce NADH, FADH2 and ATP

When you eat proteins, your body has to break them down into amino acids before they can be used by your cells. Most of the time, amino acids are recycled and used to form new proteins, they do not oxidize as fuel.

However, if there are more amino acids than the body needs or if the cells are fasting, some amino acids are degraded for energy purposes by cellular respiration. In order to enter cellular respiration, amino acids must first get rid of their amino group. This step generates ammonia (NH 3) as a waste product, which - in humans and other mammals - is converted to urea and removed from the body through urine.