Biology, Eighth Edition (Raven)

Chapter 6: Energy and Metabolism

A Biochemical Pathway

How are substances brought into the body converted into molecules that make up the body? After the digestive system has broken down food into its component molecules, those molecules are used to make all the components of the organism. These components include a huge number of very specific molecules, including enzymes, structural proteins, hormones, nucleic acids, lipids, and so on. How are these substances made? Proteins are manufactured by ribosomes using information from RNA. Other biomolecules are synthesized by biochemical pathways.

The body’s metabolism consists of a large number of biochemical pathways that convert substrate molecules into specific products needed by the body. Biochemical pathways interact with one another so that cells have maximum flexibility in converting a wide array of substrates into specific molecules needed by body. There are two fundamental types of biochemical pathways. Anabolic pathways build complex products from less complex substrates while catabolic pathways break down complex molecules to make energy available for biological processes.

View the animation below, then complete the quiz to test your knowledge of the concept.


Which of the following statement(s) about biochemical pathways is(are) TRUE?
A)they are very well organized and structured
B)they convert an initial substrate via a series of steps into an end product
C)they can only function for a few runs
D)A and B
E)A, B and C

Consider the biochemical pathway: A – E1 –> B – E2 –> C
Enzyme 1 can utilize
A)only A as substrate.
B)only B as substrate.
C)both A and B as substrates.
D)neither A nor B as substrate.
E)either A or B as substrate, but not both.

Consider the biochemical pathway: A – E1 –> B – E2 –> C
If Enzyme 2 is inactive, which of the following compounds will accumulate?
A)A only
B)B only
C)C only
D)A and B
E)B and C

In a biochemical pathway, the product of the first reaction becomes the substrate in the second reaction.

All biochemical pathways have the same number of enzymatic reactions.
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