Video Transcript
A student reads about metabolism in
humans. They conclude that the cells of
humans require larger amounts of energy to break down complex molecules into smaller
ones than they require to synthesize complex molecules from small ones. Are they correct? (A) No, it is the synthesis of
complex molecules that requires a relatively larger amount of energy. Or (B) yes, it is the breaking down
of complex molecules that requires a relatively larger input of energy.
Metabolism refers to all of the
chemical reactions that take place within the body to support and maintain life. There are two types of metabolic
reactions, anabolic reactions and catabolic reactions. Let’s take a look at each of these
types of reaction. In anabolic reactions, small
molecules are linked together through chemical bonds to form larger, more complex
molecules. The formation of these chemical
bonds requires energy which cells obtain from a molecule called ATP. In catabolic reactions, on the
other hand, large and complex molecules are broken down into smaller units. This process involves breaking
chemical bonds, and so it releases energy in the form of ATP.
Let’s take another look at the
conclusion that the student in our question has made. They’ve stated that larger amounts
of energy is required to break down large complex molecules into smaller ones than
is needed to synthesize large molecules from small ones. This is in fact the opposite of
what we’ve learned about anabolic and catabolic reactions. While catabolic reactions that
break down large complex molecules into multiple smaller ones release energy in the
form of ATP, anabolic reactions that synthesize large complex molecules from
multiple smaller ones require an input of ATP. So the correct answer is therefore
“No, it is the synthesis of complex molecules that requires a relatively larger
amount of energy.”
