All living things require a constant source of energy. Cells do not produce their own energy, they must somehow extract it from their environment. Cells are tiny chemical reaction vats that are continually synthesizing and breaking down various molecules using chemical processes that require an input of energy. The sum of all chemical reactions in a cell is referred to as metabolism. The reactions that synthesize molecules for the cell (biosynthetic reactions) are termed anabolic reactions, and those which break down molecules are called catabolic. Enzymes, a type of protein, are biological catalysts that aid most chemical reactions in the cell. The exercise today will explore the basic aspects of energy use and transfer in biological systems.
Using the diagrams above, your textbook, and your note set, answer the following questions.
In model 1, what type of biological molecule are glutamate and glutamine?
The designation R is being used in a different way than it was during the discussion of amino acids. Draw the chemical structure of the two R groups on those two molecules.
In model 1, ATP is a reactant that is broken down into what?
In model 1, where does the energy come from?
In model 1, which is the endergonic and which is the exergonic reaction?
What are the reactants and products of the reactions shown in model 1?
Write the chemical reactions shown in model 1 as a single chemical reaction.
Model 2 illustrates the concept of activation energy. What is meant by the term ‘free energy’ on the Y axis of the graph?
In model 2, the reactants are converted into what?
Are the products in model 2 in a state with more or less free energy than the reactants?
The energy barrier that many reactions must overcome is referred to as what?
If activation energy is not provided, what will happen to the reactants?
Enzymes can help overcome the activation energy barrier. How do they do this?
Where do the substrate/s bind an enzyme?
What happens to the active site once the product has been formed?
What do we call non-substrate molecules that bind to the active site and prevent binding of substrate?
Using a series of reactions called ‘Glycolysis’ most cells can break down glucose, extracting energy to produce ATP. In one reaction an intermediate breakdown product of glucose, 1,3-bisphosphoglycerate, is converted into 3-phosphoglcerate. The enzyme that catalyzes this reactions simultaneously converts ADP + inorganic phosphate into ATP.
The chemical equation can be written as follows:
1,3 bisphosphoglycerate + ADP 3-phosphoglycerate + ATP + H2O
a) Is this reaction endergonic, exergonic, or neither? b) The reaction is catalyzed by the enzyme phosphoglycerate kinase.
Would you expect the free energy of the reactants to be more or less than that of the products? Explain your answer in terms of an activation energy graph.