Which of the following is NOT a function of proteins?

a: act as a main fuel for cells
B: control chemical reactions in a cell

To determine which of the following options is NOT a function of proteins, we need to understand the general functions of proteins. Proteins are large biological molecules that are essential for the structure and function of cells in living organisms.

Option A suggests that proteins act as a main fuel for cells. This is not an accurate function of proteins. While proteins play a role in providing energy by breaking down into amino acids, they are not the primary source of fuel for cells. Carbohydrates and lipids are the main sources of energy for cells.

Option B states that proteins control chemical reactions in a cell. This is a valid function of proteins. Proteins called enzymes act as catalysts and regulate various chemical reactions that occur within cells. Enzymes help accelerate and control the rate of chemical reactions in biochemical pathways.

Therefore, based on the explanations above, option A ("act as a main fuel for cells") is NOT a function of proteins.