Enzyme models, environmental effect, velocity, substrate level, Michaelis Menten and its derivatives Flashcards
Enzyme definition and function
Organic catalyst that speeds up chemical reactions in the cell, without themselves being changed.
Enzyme catalyzed reactions are 10^3 to 10^17 times faster than uncatalyzed reactions. Without enzymes, reactions in the cell would be extremely slow.
3 characteristics of enzyme function
Enzymes are specific
Enzymes remains unchanged after they are used as catalyst
Enzymes work in either directions in reversible, direction depends on the amount of substrate/product present and the reaction continues until equilibrium is reached
Holoenzymes and Apoenzymes
Holoenzymes are the active form of enzymes, they represent the apoenzyme bound to its necessary cofactors or prosthetics groups.
Apoenzymes are enzymes that require a cofactor but are not bound by one.
Enzyme cofactors function
The 3 types of enzyme cofactors
Present at the active site of the enzyme
Non-protein
1. Activators can be metal ions or other inorganic ions
Examples Zn in metalloproteases
2. Coenzymes Organic non-protein compounds Many which are derived from vitamins Not covalently bound Examples is Co-enzyme A used to form acetyl-COA in kreb cycle
3.Prosthetics groups
Metal ion or an organic compound that is covalently bound to an enzyme
Example is Heme in hemoglobin
Enzyme active site
Groove in the enzyme that binds to specific substrates, a small part of the enzyme
Specific shape
Only specific substrate molecules will fit into the active site to form an enzyme-substrate complex
Catalytically active amino acids within the active site of the enzyme site of the enzyme act on the substrate t convert it to product
How does an enzyme work
An enzyme works by catalyzing reactions that convert the substrates to products via a temporary enzyme-substrate complex
What are the 3 ways which enzymes work
- Activation energy
- Lock and Key model
- Induced fit model
Activation energy and the 2 ways which enzymes lower activation energy
Activation energy is the initial energy needed to start a reaction between substrate molecules
Enzymes lower the activation energy by bringing the substrates closer together, which increase the chance of successful reactions
They distort and weakens bonds between the substrates?? (ask)
What is a lock and key model
- Describe that the shapes of the substrate and the active site of enzymes are fixed
- Only a specific substrate can fit into the active site
What is a induced fit model
- Describes that the shape of the substrate and active site are not fixed
- Binding of substrate induce a conformational change in the active site of enzyme
List 4 factors that affect the rate of reaction
Enzymes and Substrate concentration
Heat and pH
Presence of Cofactors - Metal ions, organic and organometallic species
Presence of Inhibitors
Describe how enzymes concentration affects the rate of reaction
At low enzyme concentration, there is great competition for the active sites and the rate of reaction is low.
As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate.
Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor.
Describe how substrate concentration affects the rate of reaction
At a low substrate concentration there are many active sites that are not occupied. This means that the reaction rate is low.
When more substrate molecules are added, more enzyme-substrate complexes can be formed. As there are more active sites, and the rate of reaction increases.
Eventually, increasing the substrate concentration yet further will have no effect.
The active sites will be saturated so no more enzyme-substrate complexes can be formed.
Describe the enzyme reaction graph
Initial velocity - The reaction rate of an enzymatic reaction is always fastest at the beginning of the reaction when there is the greatest concentration of substrate.
The graph represents the amount of product formed. At first, the amount of product formed increases, then the rate slows down as the concentration of substrate decreases. The fastest rate of product formation is at the beginning and is called the initial velocity. It is more likely to get an effective collision between enzyme and substrate molecules if there are more substrate molecules present; as in the beginning of the reaction. If the enzyme is kept constant and there is an increase in the amount of substrate, there will be an increase in the initial velocity until a saturation point is reached.
Rates increase until a saturated point, max velocity also known as Vmax
Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied.
If you alter the concentration of the enzyme then Vmax will change too
Saturation point is the point when there are enough substrate molecules to completely saturate the enzyme’s active sites, Vmax is the rate under these conditions.
