Enzymes Flashcards
What is the benefit of enzymes to our body?
It speed up reactions in order to help biochemical reactions keep up with the pace of metabolisation
Define
Enzymes
An enzyme is a biological catalyst, protein in nature that alters the rate of a chemical reaction and itself not chemically altered at the end of the reaction
What protein structure do enzymes take?
Globular (tertiary or higher)
What are properties of enzymes?
- Enzymes are specific in their function; they will only catalyse one specific reaction, a specific chemical bond or functional group
- Enzymes are not altered in a catalysis; they alter the rate without being chemically altered; as they can be reused, enzymes are only required in minute amounts
- Enzymes catalyse by lowering the activation energy of a reaction
What are the two models of enzymatic action?
- Lock and key hypothesis
- Induced fit model
Explain how the lock and key hypothesis works
The model suggests that substrates with complementary shapes to the enzyme’s active site are engaged by the enzymes for catalysis to occur.
The stages are:
1. Substrate is the “key” and enzyme is the “lock”. The shape of the substrate must be complementary to the active site
2. The enzyme engages the substrate to form an enzyme-substrate complex. Catalysis occurs
3. Product(s) disengage. Enzyme can be used again
Explain how the induced fit model works
This model suggests that the active site in many enzymes are not exactly the same shape as the substrate, but instead moulds itself around the substrate during engagement
Stages:
1. The enzyme is in ‘relaxed’ state; substrate approaches enzyme.
2. When the substrate binds to enzyme, the enzyme goes through conformational change; active site moulds itself to form the correct shape for catalysis to happen
3. Product(s) disengage; enzyme is chemically unaltered and returns to ‘relaxed’ state
What are the factors that affect enzyme activity?
- pH
- Temperature
- Substrate concentration
- Enzyme concentration
- Presence of inhibitors
How does temperature affect the rate of enzyme activity?
The higher the temperature the faster the reaction, though only up to 40-45 degrees C.
As temperature increases, kinetic energy of molecules increase- increase in effective collisions- and hence higher rate of reactions
Beyond the optimal temperature, the enzyme activity drops sharply. The kinetic energy is so large the enzymes virate so violently that the delicate bonds -especially the ionic and hydrogen bonds that maintain the enzyme’s active site, break, causing the enzyme to lose its tertiary structure. This process is denaturisation and causes the enzyme to lose its function
At low temperatures, the enzyme is said to be inactive
How does pH affect the rate of enzyme activity?
pH measures the H+ ion concentration and does is a good indicator of OH- concentration
H+ and OH- ions are charged and therefore interfere with hydrogen and ionic bonds that hold parts of the enzyme together. This distorts the globular shape of the enzyme and hence its active site.
Small changes in pH do not permanently affect the enzyme as bonds can be reformed. Extreme changes can cause enzymes to denature and permanently lose their function
Note: Different enzymes in the body work within unique pH ranges
What is an enzyme that works best at pH 2?
Pepsin
What is the optimal pH for salivary amylase?
pH 7
How does substrate concentration affect rate of enzyme activity?
When the amount of enzymes is kept constant and the substrate concentration is gradually increased, the reaction velocity will increased until it reaches a maximum.
How does enzyme concentration affect rate of enzyme activity?
When there is an abundant supply of substrates, the rate of reaction is only limited by the number of enzymes. Thus when the enzyme concentration increases, the availability of active sites increase together with the rate of reaction
How do enzyme inhibitors affect the rate of enzyme activity?
Enzyme inhibitors lower the reaction rate of enzymes by preventing enzyme substrate complexes from forming
