Chapter 8.1 Metabolism Flashcards Preview

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Flashcards in Chapter 8.1 Metabolism Deck (16):

Metabolic pathway

consists of chains and cycles of enzyme-catalyzed reactions. They can be controlled by end-product inhibition


Enzymes in metabolic pathways

Enzymes in metabolic pathways



Effects of pH, temperature, and substrate concentration on the action of enzymes. There are 2 types of inhibitors: Competitive and Non-Competitive


Application 1: End product inhibition of the pathway of threonine

The bacterium Escherichia coli uses a metabolic pathway to produce the amino acid isoleucine from threonine. It is a 5 step process. If isoleucine is added to the growth medium of E.coli, it inhibits the 1st enzyme in the pathway and isoleucine will not be synthesized. The situation will exist until the isoleucine is used up. The inhibition of the 1st enzyme in the pathway prevents the build-up of intermediates in the cell. This is a form of negative feedback.


Application 2: Use of databases to identify potential new anti-malarial drugs

Development in bioinformatics have enhanced research into metabolic pathways, using computer science and mathematics using data stored in databases. In 2011, a team discovered a new group of compounds that may lead to a new generation of anti-malarial drugs capable of both preventing the disease and of alleviating symptoms when the disease is already present in an individual. This discovery came after research in related compounds in the liver.



sum of all the chemical reactions that occur within you as a living organism



type of reaction that uses energy to build complex organic molecules from simpler ones. Endergonic reactions meaning they require energy. Is biosynthetic.
ex: Photosynthesis



type of reaction that breaks down complex organic molecules with the release of energy. Exergonic reactions meaning they release energy. Is degradative.
ex: Cellular Respiration


Induced fit-model

- Enzyme-substrate specificity is made possible by enzyme structure. Enzymes undergo significant changes in their conformation when substrates combine with their active site. This is the new model, with as an example the hand any glove, the hand being the substrate and the glove being the enzyme. The glove looks a bit like the hand, however when the hand is placed in the glove, there is an interaction that results in a conformational change of the glove.
- conformational changes and induced fit are the result of changes in the R-groups of the amino acids at the active site of the enzyme, as the enzyme interacts with the substrate(s).


Activation Energy

Energy necessary to destabilize the existing chemical bonds in the substrate of an enzyme-substrate catalyzed reaction. Enzymes work by lowering the AE required, causing chemical reactions to occur faster because they reduce the amount of energy needed to bring about the chemical reaction


Enzyme Action (6 points)

- surface of the substrate contacts the active site of the enzyme
- enzyme changes shape to accommodate the substrate
- temporary complex called the enzyme-substrate complex forms
- activation energy is lowered and the substrate is altered by the rearrangement of the existing atoms
- the transformed substrate, the product, is released from the active site
- unchanged enzyme is then free to combine with other substrate molecules


Competitive inhibitors

- molecule competing directly with the usual substrate for the active site of an enzyme. The result is that the substrate will have fewer encounters with the active site and rate of the chemical reaction will be decreased.
- must have similar structure to the substrate
- can be reversible or irreversible: reversible competitive inhibition may be overcome by increasing the substrate concentration --> more substrate molecules to bind with the active sites as they become available --> chemical reactions may proceed more rapidly


Example of Competitive inhibitors

Use of sulfanilamide (salfa drug) to kill bacteria during an infection. Folic acid is essential to bacteria as a coenzyme. It is produced in bacterial cells by enzyme action on paraminobenzoic acid (PABA). The sulfanilamide competes with the PABA and blocks the enzyme, preventing the production of folic acid resulting in death of the bacteria.


Non-Competitive Inhibition

interacts with another site on the enzyme, also called allosteric inhibition. Binding at the allosteric site causes a change in the shape of the enzyme's active site, making it non-functional.
- reversible or irreversible


Example of Non-Competitive Inhibition

Metallic ions (mercury) binding to the sulfur groups of the component amino acids of many enzymes, resulting in shape changes of the protein, which causes inhibition of the enzyme


End-product inhibition

- prevents the cell from wasting chemical resources and energy by making more of a substance than it needs.
- assembly-line type of process so that a specific end product can be achieved, each step catalyzed by a specific enzyme
- When the end product is present in a sufficient quantity, the assembly line is shut down --> by inhibiting the action of the enzyme in the 1st step of the pathway, reactivating it
-the enzyme that is reactivated is an allosteric enzyme, when present in higher concentrations, the end products binds with the allosteric site of the 1st site --> inhibition
- lower concentrations of the end product result in fewer binding with the allosteric site of the 1st enzyme --> activation of enzyme