What are enzymes sometime known as?
Briefly describe the importance of enzymes..
They are a group of proteins that control the chemical reactions taking place in a cell. Cells contain hundreds of different enzymes, each catalysing a different reaction. Everything a cell does depends on which enzymes is can make, and this depends on which genes in the nucleus are working.
"The nucleus contains the genes, which control the production of enzymes, which catalyse reactions in the cytoplasm" What would the word equation for the above be?
Genes -> proteins (enzymes) -> catalyse reactions
What kind of reactions are the chemical reactions in a cell?
Chemical reactions in a cell are 'metabolic reactions'
What is the sum of all the metabolic reactions of a cell known as?
The 'metabolism' of the cell
What are enzymes required?
Enzymes are required as the temperature in organisms is generally too low for chemical reactions to take place fast enough on their own.
What is the average human body temperature?
37 deg C
What is the name of the molecule that an enzyme acts on?
It is called its 'substrate'
Describe the 'active site' on an enzyme..
Each enzyme has a small area on its surface called the 'active site'.
The substrate attaches itself to the active site, the reaction takes place and products are formed.
When the substrate joins with the active site, it lowers the energy needed for the reactions take place.
The substrate fits into the active site much like a key in a lock.
Once it has catalysed the reaction, the active site is free again and the enzyme moves on to act on more substrate molecules.
What is the terms for the commonly used model of enzyme action?
The 'lock and key' model
Taking the human body as an example, what do we mean when we refer to an enzyme's optimum temperature?
Enzymes in the human body have evolved to work best at 37 deg C, the average temperature of the human body.
In this case, 37 deg C is the enzyme's optimum temperature.
How does temperature affect enzymes?
As an enzyme is heated up towards its optimum temperature, the increasing temperature speeds up the rate of reaction.
This is because higher temperatures give the molecules of the enzyme and substrate energy so they collide more often - more collisions means more chemical reactions.
However, enzymes are made of proteins and proteins are broken down by heat, so too far above the optimum temperature and the heat destroys the enzyme.
We would say the enzyme has been 'denatured'.
Eg: when you cook an egg, the egg white is made of protein and turns white as the heat denatures the protein.
Describe how pH can affect enzymes..
The pH inside cells is around neutral and most enzymes have evolved to work best at this pH. At extremes of pH either side of neutral, the enzyme activity decreases and the structure of the enzyme molecule is affected, changing the shape of its active site so the substrate doesn't fit so well.
The pH at which an enzyme works best at is called its...
Give an example where enzymes have an optimum pH below or above pH7...
The stomach produces hydrochloric acid which gives the area a very low pH. The stomach makes an enzyme called 'pepsin' which has an optimum pH of around 2.
Describe an experiment to demonstrate the effect of temperature on an enzyme...
Amylase breaks down starch into the sugar maltose.
By recording the speed at which the starch disappears we can measure the activity of the amylase.
1) spots of iodine are put into the depressions on a spotting tile
2) 5cm 3 of starch suspension is placed in one boiling tube and 5cm 3 of amylase solution is placed in another (separate syringes must be used to transport each solution)
3) a beaker is filled with water at room temperature and both boiling tubes are placed in the water for 5 minutes, recording the temperature
4) the amylase solution is poured into the starch suspension, leaving the tube with the mixture in the water bath
5) immediately, a small sample of the mixture is removed from the tube using a pipette and added to the first drop of iodine
6) the colour of the iodine is recorded
7) a sample of the mixture is then taken every 30 seconds for 10 minutes and tested for starch as above, until the iodine remains yellow, showing that all the starch is used up
8) the experiment is repeated, maintaining the water bath at different temperatures between 20 deg C and 60 deg C
- the results can be plotted on a table with temperature along the top, time down the side, and the relative colours written within the table itself
- the rate of the reaction can be calculated by dividing the volume of the starch - in this case, 5cm 3 by the time
Eg: rate = 5 cm 3 / 3.5 minutes = 1.4 cm 3 / minute