2.5 Enzymes Flashcards
What is an enzyme?
An enzyme is a globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction - by lowering the activation energy of the reaction.
- Enzymes are not changed or consumed by the reactions they catalyse and thus can be reused
Active site
The active site is the region on the surface of the enzyme which binds to the substrate molecule.
It has a specific shape so that only certain substrates can bind.
Substrate
The chemical that is broken down the a reaction
Lock and key theory
The lock and key theory explains enzymes work.
- The substrate (key) fits into the enzyme’s active site (lock), this results in an enzyme-substrate complex.
- The substrate is then broken down into products.
Induced fit theory
The lock and key theory has been modified slightly as it did not fully explain how enzymes worked. The modified theory is known as the induced fit theory.
- This theory states that the enzyme’s active site can change shape slightly, which is why some enzymes can act on more than one type of substrate molecule.
Enzyme-substrate complex
When a substrate binds to the enzyme’s active site.
Collision frequency
- For the substrate to fit into the active site it has to collide with the enzyme in the right orientation
- The substrate will undergo many random collisions until it possibly connects with an active site of the proper enzyme
Catabolic enzymes
Enzymes that break down chemicals
Anabolic enzymes
Enzymes that build products from smaller substrate molecules
How to improve the frequency of collusions - which will in turn increase the rate of enzyme catalysis
- Increasing the molecular motion of the particles (thermal energy can be introduced to increase kinetic energy)
- Increasing the concentration of particles (either substrate or enzyme concentrations)
Denaturation of enzymes
Caused by: high temperatures and extreme pH
These factors disrupt the chemical bonds which are necessary to maintain the tertiary structure of the enzyme.
Any change to the structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate
Factors affecting enzyme activity
- Temperature: increasing curve until peak (optimum temperature), sharp decrease
- pH: symmetrical bell curve (enzymes work effectively within a specific pH range)
- Concentration of enzyme: plateau
- Concentration of substrate: plateau
Imobilised enzymes
Imobolised enzymes are widely used in the industry.
- The idea is to stick enzymes in a place where they can not move and then run substrates through them to help carry out the desired chemical reaction and then collect the products
Imobilised enzymes example in the industry - lactose free milk
- Imobilised lactase enzymes in beads placed in a specially designed container
- Milk containing lactose (made of galactose and glucose) is passed through this
- As the lactose passes through the lactase enzymes the enzymes lower the activation energy for the sugars (glucose and galactose) resulting in the breaking of the chemical bond
- Out of the other end of the container will then be milk with separate monosaccharides of glucose and galactose, meaning that lactose is no longer present
Ways to measure enzyme activity
Skill: design experiments to test the factors affecting enzyme activity
- Gas production: counting bubble formation, displacement of syringe cap with increasing colume of gas
- Digestion of a solid: calculating % weight change, change in diameter, volume of liquid produced
- Digestion of a liquid: diffusion out of dialysis tube
- Colour change: starch reacts with iodine, peptide bonds are stained via the Biuret test, reducing sugars Benedict’s test
