Enzymes Flashcards
Enzymes
Enzymes
Enzymes increase the speed of reactions. They are often called biological catalysts. The active site of an enzyme is very important:
Active site activity
To catalyse (speed up) a reaction, the reacting chemical (substrate) must bind to the enzyme’s active site.
The active site will only fit specific substrates.
Lock and key
Lock and key
The active site is like a lock and the substrate is like a key.
In the same way, there is usually only one enzyme for every substrate (or one key for each lock).
Enzyme activity
The substrate binds to the active site of an enzyme, which has a matching shape. Here, it’s reaction is sped up. In this case, the molecule is broken down.
Why are enzymes called biological catalysts
Enzymes increase the speed of reactions, so are often called biological catalysts.
Substrate Concentration
Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases.
But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.
What happens to an enzyme’s pH is very high?
Denature
Enzyme Activity and pH
Enzymes have an optimum pH (measure of acidity). If the pH changes away from the optimum, then the enzyme activity decreases. If the pH is too low or too high, then the enzyme is denatured and will not function.
Calculating Rate of Reaction
The rate of reaction is equal to the gradient of the graph, which shows mass of the product plotted against the reaction time.
The gradient is calculated by picking two points on the graph, then dividing the change in the value on the y axis (mass) by the change in the x axis value (time), between those two points.
In the example above, the rate of reaction = 10g ÷ 60s = 0.17 g/s.
In a reaction involving enzymes, the change in mass is 10g and the change in time is 60 seconds. What is the rate of reaction?
0.17 g/s
Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: Temperature
Increasing the temperature of a working enzyme initially increases the reacting activity.
Enzymes have an optimum temperature. Once this temperature is reached, the activity decreases.
Past a certain temperature, the active site changes shape, and the enzyme is denatured (loses its catalytic activity).
Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: pH
pH (measure of acidity)
Enzymes have an optimum pH (measure of acidity).
If the pH changes away from the optimum pH, then the enzyme activity decreases.
If the pH is too low or too high, then the enzyme is denatured and will not function.
Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: Substrate concentration
Substrate concentration
Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases. But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.
Calculating Rate of Reaction
The rate of reaction is equal to the gradient of the graph, which shows mass of the product plotted against the reaction time.
The gradient is calculated by picking two points on the graph, then dividing the change in the value on the y axis (mass) by the change in the x axis value (time), between those two points. In the example above, the rate of reaction = 10g ÷ 60s = 0.17 g/s.
Investigating the Effect of pH on Amylase: What do amylase break down?
Amylase breaks down starch, which can be detected using iodine solution.
Measuring reaction time
-Add amylase to starch solution.
-Every 30 seconds, take a drop of the mixture and add a drop of iodine solution.
-Record the total time taken for the iodine solution to stop turning blue when added (which indicates that all the starch has been broken down).
Finding amylase’s optimal pH
Repeat this experiment using starch solutions with different pHs.
The shorter the time taken for the iodine to stop changing colour, the faster the amylase has broken down the starch and the closer this pH is to amylase’s optimal pH.
What are the dependent and independent variables in the experiment investigating the effect of pH on amylase?
The independent variable is pH. the dependent variable is the time taken for the starch to be broken down.
Iodine
Iodine is a test for starch; when iodine is added to a solution that contains starch, it turns blue.
A graph, with enzyme activity on the y axis, has a steep curve. This reflects:
Fast rate of reaction
Equation for reaction rate
reaction rate= change in mass/change in time
reaction rate is equal to the change in mass divided by the change in time.
Enzymes in Digestion
Digestive enzymes are produced by specialised cells (perform a specific function) in the glands and the lining of the gut. They are then secreted (released) out of the body cells and into the cavity of the digestive system.
Digestive enzymes are used to: Breakdown large food molecules
The digestive enzymes catalyse (speed up) the breakdown of large, insoluble food molecules into smaller, soluble (can be dissolved) molecules that are then small enough to be absorbed into the bloodstream.
Digested molecules can be used to construct new carbohydrates, proteins and lipids in the body.
Some glucose produced by digestion is used for respiration.
Enzymes in digestion
The 3 main digestive enzymes are:
Amylase
Protease
Lipase
Digestive enzymes
Digestive enzymes are produced by specialised cells in the glands and the lining of the gut.
Enzymes in Digestion
Digestive enzymes are produced by specialised cells in the glands and the lining of the gut. They are then secreted (released) out of the body cells and into the cavity of the digestive system.
Breakdown large food molecules
Catalyse the breakdown of large, insoluble food molecules into smaller, soluble molecules.
Why is it necessary to breakdown large, insoluble food molecules into smaller, soluble molecules?
Large, insoluble food molecules can’t be absorbed into the bloodstream.
Small, soluble molecules can be absorbed into the bloodstream and used to construct new carbohydrates, proteins and lipids in the body.
Some glucose produced by digestion is used for respiration.
Digestive enzymes catalyse
Digestive enzymes catalyse (speed up) the breakdown of large, insoluble food molecules into smaller, soluble molecules.
Amylase
Carbohydrases break carbohydrates down into sugars. Amylase is a type of carbohydrase that breaks down starch in our bodies.
Action sites
The sites of action of amylase are:
The small intestine
The mouth
Purpose
Amylase breaks down starch into its constituent simple sugars (predominantly maltose).
Starch → Maltose (+ other sugars).
Proteases
Proteases are digestive enzymes that break down proteins into amino acids.
Action sites
The sites of action of proteases are the:
small intestine
stomach
Production Proteases are produced in the:
Proteases are produced in the:
small intestine
pancreas
stomach
Purpose
Proteases break down proteins into amino acids.
Protein → Amino acids.
Digestive enzymes break proteins into
Amino acids
Lipase
Lipase is a type of digestive enzyme that breaks down lipids into glycerol and fatty acids.
Production
Lipase is produced in the:
Small intestine
Pancreas
Purpose
Lipase breaks down lipids into a molecule called glycerol and fatty acids.
Lipid → Glycerol + Fatty Acids.
Write the correct digestive enzyme next to its function:
Lipase
Breaks down lipids into a molecule called glycerol and fatty acids.
Proteases
Break down proteins into their constituent amino acids.
Amylase
Breaks down starch into its constituent simple sugars (predominantly maltose).
Lipase catalyses the break down of lipids:
Lipid → Glycerol + Fatty acids.
Testing For Carbohydrates, Lipids & Proteins
Reagents can be used to test for the presence of various food substances. first step is to grind up the food and add distilled water to dissolve some of the food. You can then test for the food substances
Proteins
To test for proteins, add Biuret solution.
It will turn mauve or purple if proteins are present.
Lipids
To test for lipids, add ethanol and water and shake.
If lipids are present, a white emulsion (cloudy liquid) will form.
Calorimetry
We can also test the calorie content of foods:
Burn a known mass of the food under a boiling tube filled with a known volume of water.
Calculate the change in temperature of the water.
Sugar
To test for sugar, add Benedict’s reagent and heat for about two minutes.
It will turn any of green, yellow or red if sugar is present.
The colour depends on the concentration.
Starch
To test for starch, add iodine solution.
It will turn blue-black if starch is present.
Tests for various food substances:
Proteins
Add Biuret solution. It will turn mauve or purple if present.
Starch
Add iodine solution. It will turn blue-black if present.
Sugar
Add Benedict’s reagent and heat for about two minutes. It will turn any of green, yellow or red if this food substance is present.
Lipids
Add ethanol and water and shake. A white emulsion (cloudy liquid) will form if present.
Calorie
content
Burn a known mass of a food under a boiling tube of water. Calculate change in water temperature.
If we add iodine to starch then it will turn.
Blue-black
What are proteins broken down into during digestion?
Amino acids
What does the small intestine do?
Absorbs soluble food molecules, digests foods
Where is amylase produced?
Smaller intestines, pancreas
Name one different digestive enzyme
Pepsin
The ‘lock and key theory’ is a model used to explain enzyme action
The key is the substrate.
The lock is the active site of an enzyme.
The substrate fits into the active site.
There is usually only one enzyme for every substrate.
