2.4 Enzymes Flashcards
What are enzymes?
They are biological catalysts because they speed up chemical reactions without being used up in living systems.
What can enzymes be used to control?
They can be used to control metabolic pathways as almost all metabolic reactions are controlled by them.
What is the structure of proteins?
They are globular proteins with a complex tertiary structure. Some are formed of one polypeptide and others two or more (these therefore have a quaternary structure).
What are intracellular and extracellular organisms?
Intracellular enzymes are produced and function inside the cell. (E.g. Catalase)
Extracellular enzymes are secreted by cells and catalyse reactions outside of cells. (E.g. Amylase)
What is an enzyme’s active site?
A unique place within the enzyme where temporary bonds form between it and the substrate.
It is complementary to a specific type of substrate molecule.
It can be denatured by extremes of temperature or pH.
What determines an enzyme’s active site?
It is determined by it’s tertiary structure:
- Proteins are formed of chains of amino acids held together by peptide bonds.
- Order of the amino acids determines the shape.
- If order is altered, the 3D shape changes.
What is the lock-and-key hypothesis?
Suggested that enzymes and substrates were rigid structures that locked into each other precisely, like a key going into a lock.
When and who suggested the lock-and-key hypothesis?
It was suggested in the 1890’s by Emil Fischer.
What is the induced-fit hypothesis?
It suggests that the enzyme’s active site can change shape slightly so the molecule can fit exactly into the enzyme.
These are known as conformational changes and ensure an ideal binding arrangement is achieved.
What is activation energy?
The minimum amount of energy required for a reaction to take place. In this case, it is the minimum amount of energy needed by the substrate to become just unstable enough for it to be broken down into products.
How do enzymes speed up reactions?
They speed up chemical reactions by reducing the stability of bonds in the reactants. The destabilisation of bonds in the substrate make it more reactive.
How do enzymes lower the activation energy?
They provide an alternative pathway with a lower activation energy.
How are enzymes denatured by extremes of pH?
Solutions with an excess of H+ or OH- ions can cause the hydrogen and ionic bonds to break. This alters the tertiary structure, changing the shape of the active site.
How do you investigate the effect of pH on enzyme reaction rates?
- Add iodine to spotting tile.
- Add amylase and buffer solution to a test tube, mix then add starch solution.
- Start the stopwatch.
- After 10s, add a drop of solution to iodine in spotting tile.
- Repeat every 10s until the iodine doesn’t change colour.
- Repeat steps 1-5 using buffer solutions of different pH.
What are the limitations of the investigation of pH on enzyme activity?
There may be differences in what is interpreted as no colour change. Using a colorimeter may give more accurate results.
How does a low temperature affect enzyme controlled reactions?
Will prevent or slow down reactions because:
- Molecules move slowlydue to less kinetic energy.
- Therefore, a lower frequency of successful collisions leading to less frequent formations of enzyme-substrate complexes.
- Also, they collide with less energy so less likely for the molecules to have the required energy for new bonds to be made and older ones to be broken.
