Enzymes ( Core concepts ) Flashcards
What is the difference between anabolic and catabolic reactions ?
Anabolic : larger molecules being made by the condensation of smaller molecules eg alpha glucose into starch.
Catabolic : involve the break down or hydrolysis of larger molecules to smaller ones eg polypeptide into amino acids
What is metabolism ?
It is a combination of anabolic and catablic reactions that are catalysed by enzymes. It is the sum of all the enzyme controlled chemical reactions taking place in a cell.
6 key traits of enzymes
Biological catalysts ( speed up chemical reactions without being used up during the reactions )
3D globular proteins with a specific tertiary structure ( held in place by ionic, hydrogen and disulphide bonds )
Specific ( can only catalyse one type of reaction and can only work on one specific type of substrate molecule )
Have an active site that is complementary shape to the shape of their specific substrate.
Require certain conditions to function
The active site lowers the activation energy required to start the reaction.
What does the substrate bind to ?
It binds to part of the protein called the active site.
What is the activation energy in a reaction ?
Activation energy is the minimum amount of energy required for a reaction to start.
Explain how the lock and key model works
Enzymes have a specific active site which is complementary to the shape of the substrate.
The substrate fits into the active site of an enzyme
An enzyme substrate complex forms
The reaction occurs - product is released whilst the active site does not change shape.
Explain the induced fit model ( eg lysozyme )
Substrate collides with active site
Active site shape changes to fit into the substrate
An enzyme substrate complex is formed
The change in the enzyme shape weakens the bonds in the substrate and places a strain on the substrate, lowering the activation energy.
Active site returns to original shape after reaction, product is released.
Where are enzymes made ?
Inside living cells
What are intracellular enzymes ?
Enzymes which remain inside the cell and function inside the cell eg respiratory enzymes such as glucose isomerase.
What are extracellular enzymes ?
Enzymes which are secreted from cells to function outside eg digestive enzymes such as amylase.
What is required for an enzyme reaction to take place ?
There must be successful collisions between enzyme active sites and substrate molecules leading to the formation of enzyme substrate complexes
What 5 factors effect enzyme catalysed reactions ?
Temperature
pH
Substrate concentration
Enzyme concentration
Presence of inhibitors / activators
Buffers can be important in investigations to maintain a constant pH and the requirement for adequate controls.
What happens to the rate of enzyme catalysed reactions with increasing temperature ?
Rate increases due to increased frequency of collisions between particles
Why does the rate of enzyme catalysed reactions vary with changes in pH ?
Each enzyme has an optimum pH. If the pH increases or decreases beyond this optimum point, the shape of groups at the active site and on the substrate may change, potentially slowing / preventing the formation of enzyme substrate complex.
Why does the rate of enzyme catalysed reactions vary with enzyme concentration ?
At low enzyme concentrations, there are more substrate molecules than there are available active sites. Increased concentration of enzyme leads to an increased number of active sites which increases ROR. There is no effect on ROR of increasing enzyme concentration when the number of substrate molecules becomes a limiting factor.
Why does the rate of enzyme catalysed reactions vary with substrate concentration ?
As substrate concentration increases, the ROR increases because there are more enzyme substrate complexes formed. There is no effect of increasing substrate concentration when all of the enzyme’s active sites are occupied by substrate molecules.
What is the importance of buffers in investigations ?
Buffers are used for maintaining a constant pH and the requirement for adequate controls.
How can environmental factors such as temperature and pH affect enzyme molecules ?
They can change the three dimensional structure of an enzyme molecule. Bonds are broken and hence the configuration of the active site is altered ( shape of active site changes so substrate can no longer fit in active site ).
What can small changes in pH cause ?
It can cause small reversible changes in enzyme structure, causing inactivation.
How can high temperatures and extreme changes in pH affect proteins ?
They can cause permanent change in protein structure, causing denaturation.
What is inhibition ?
When enzyme action is slowed down / stopped by another substance. It can be reversible and irreversible.
When is enzyme inhibition competitive ?
Competitive inhibitors are structurally similar to the normal substrate and compete with the normal substrate for the active sites. If the substrate concentration is increased then so will the rate of reaction.
When is enzyme inhibition not competitive ?
Non competitive inhibitors involve them combining away from the active site often altering the enzyme shape ( as illustrated by potassium cyanide ). The rate of reaction is not affected by substrate concentration.
What are immoblised enzymes ?
Enzymes that are fixed to an inert, insoluble substance over which the substrate passes and the reaction takes place.
