Enzymes Flashcards
(21 cards)
What are enzymes?
- Enzymes are a type of protein
- that act as biological catalysts
- and control all the chemical reactions that take place within cells,
- meaning they are involved in all metabolic reactions.
What is a catalyst?
A catalyst is:
1. a chemical that speeds up a reaction
2. without being used up itself
3. that does take part in the reaction
4. but afterwards is unchanged
5. and free to catalyse more reactions.
What kinds of reactions can enzymes catalyze?
- break things apart — break the bonds between the units in polymers to break them back down into monomers
- build things up — connect monomer units together to build them up into polymers
What are the two main types of enzymes?
-
extracellular
- secreted (released from the cell)
- therefore function outside the cell
-
intracellular
- stay inside cells
- carry out their functions inside the cytoplasm, organelles, membranes, etc.
Is it possible to have more than 2 types of enzymes?
- It is possible for there to be thousands of different sorts of enzymes
- because they are proteins,
- and protein molecules have an enormous range of structures and shapes
- this means that it is possible to have a specific enzyme for each reaction.
Why do we need enzymes?
We need enzymes because:
1. the temperatures inside organisms are low (human body temperature is about 37 °C),
2. so without catalysts, most of the reactions that happen in cells would take place far too slowly to allow life to go on,
3. and therefore the reactions can only take place quickly enough for life to survive when enzymes are present to speed up (catalyse) the reactions.
What is a substrate?
The molecule that an enzyme acts on is called its substrate.
What is an active site?
Each enzyme has a small area on its surface into which substrate fits called the active site.
Why does an enzyme catalyze only one type of reaction?
- Just as a key will only fit one lock, a substrate will only fit into the active site of a particular enzyme.
- This is known as the lock and key model of enzyme action.
- Since only one substrate can fit into the active site of an enzyme, the enzyme is specific, i.e. it will catalyse only one reaction.
How do enzymes work?
- The substrate attaches to the active site of the enzyme.
- The substrate and the enzyme together are called the substrate-enzyme complex.
- When the substrate joins up with the active site it lowers the energy needed for the reaction to start, allowing the products to be formed more easily.
- The reaction then takes place and products are formed.
- The products and the enzyme are now bound together in the enzyme-product complex.
- After an enzyme molecule has catalysed a reaction, the product is released from the active site.
- The enzyme is now free to act on more substrate molecules.
What factors can affect the activity of an enzyme?
The rate of an enzymatically-catalyzed reaction may be increased or decreased by raising or lowering:
1. the concentration of the enzyme, the substrate or the cofactors/coenzymes,
2. the temperature, or
3. the pH.
Which effect does temperature have on enzyme activity?
- Every enzyme has its own optimum tempature conditions.
- As the enzyme is heated up to its optimum temperature, the rise in temperature increases the rate of reaction.
- Above the optimum temperature, a further increase in temperature starts to have a detrimental effect on the rate of reaction.
- Denaturing is permanent meaning the enzyme will no longer catalyse the reaction.
Why does temperature affect enzyme activity the way it does?
- Enzyme activity increases as temperature goes towards its optimum temperature because:
- higher temperatures give the molecules of the enzyme and the substrate more kinetic energy,
- so they collide more often,
- and more collisions means that the reaction will take place more frequently.
- Enzyme activity decreases as temperature goes over the optimum temperature because:
- high temperatures denature the enzyme, and
- denaturing changes the shape of the active site,
- which means the substrate will no longer fit into it.
What is meant by the optimum temperature of an enzyme?
The optimum temperature is the best temperature meaning the temperature at which the reaction takes place most rapidly. Above and below the optimum temperature, the enzyme catalyzes the reaction more slowly.
Which is the optimum temperature of enzymes?
- Enzymes have evolved to work best at the normal body temperature of the organism they are from.
- Enzymes of animals such as mammals and birds, which all have body temperatures close to 37 °C, have optimum temperatures near this value.
- Not all enzymes have an optimum temperature near 37 °C. Bacteria that always live at an average temperature of 10 °C will probably have enzymes with an optimum temperature near 10 °C.
How can pH affect enzyme activity?
Similar to temperature, the pH around the enzyme is important. At extremes of pH either side of neutral, the enzyme activity decreases.
What does optimum pH mean?
The pH at which the enzyme works best is called its optimum pH. At pHs either side of optimal, the enzyme activity decreases.
What is the optimum pH for enzymes?
The pH inside cells is neutral (pH 7) and most enzymes have evolved to work best at this pH.
Why does pH change affect enzyme activity the way that it does?
- Either side of the optimum pH value,
- the pH affects the structure of the enzyme and changes the shape of its active site.
- These changes in the shape of the active site mean that the substrate will not fit well.
- This results in a loss of efficiency for the enzyme.
What is denaturing, when does it happen, and which effect does it have on enzyme activity?
- Enzymes are made of protein.
- Proteins are broken down (denatured) by extremes of heat and pH.
- For example, from 40 °C upwards, the heat destroys the enzyme.
- This can cause either slowing down the reaction, or stopping it completely.
What is metabolism?
The chemical reactions taking place in a cell are known as metabolic reactions and the sum of all the metabolic reactions is known as the metabolism of the cell.
