Chapter 4- Enzymes + Factors Flashcards
What are enzymes
Enzymes speed up reactions by acting as biological catalysts. They catalyse metabolic reactions both at cellular level and for the organism as a whole. They can either be intraceullar (work inside the cell) or extracellular (work outside the cell).
Example of intracellular enzyme
Catalase is an enzyme that catalyses the breakdown of hydrogen peroxide to oxygen and water. Hydrogen peroxide is the toxic by product of many cellular reactions and if it is left to build up, it can kill cells.
Examples of extracellular enzymes
1) amylase is found in saliva. It is secreted by the mouth by cells in the salivary glands. The catalyses the hydrolysis of starch into maltose. (Maltose is broken down into glucose by Maltase after)
2) Trypsin catalyses the hydrolysis of peptide bonds, turning big polypeptides into smaller ones. (These get broken down into amino acids bu other enzymes after). Trypsin is produced by cells in the pancreas and secreted inti the small intestine.
Enzyme structure
Enzymes are globular proteins that have an active site. This is where they bind to a substrate to catalyse a reaction. The active site has a specific shape which is determined by the enzyme’s tertiary structure. The enzyme’s active site and substrate have to be of complementary shape. When a substrate binds to an enzyme’s active site, an enzyme substrate complex is formed.
How do enzymes speed up reactions
Enzymes reduce the amount of activation energy needed, making the reactions happen at a lower temperature . This speeds up the rate of reaction.
How do enzymes lower activation energy
1) when an enzyme breaks down substances, fitting into the active site puts strain on the bonds in the substrate, so the bond can be broken more easily.
2) when an enzyme holds two substrate molecules close together, it reduces the repulsion between the molecules so they can bond together more easily.
What is the lock and key model
1) the active site of the enzyme has a complementary shape to the substrate so the enzyme and substrate fit into each other like a lock and key.
2) when the substrate is bound to the enzyme active site, an enzyme substrate complex is formed.
What is the induced-fit model
1) the initial interactions between the enzyme and substrate are relatively weak, but these weak interactions induce changes in the enzyme’s tertiary structure.
2) this puts strain on the substrate molecule, helping to weaken particular bonds in the substrate.
3) this lowers the activation energy, the enzyme can exploit this and catalyse the reaction.
What are the four factors that affect enzyme activity
1) temperature
2) pH
3) enzyme concentration
4) substrate concentration
How does temperature affect enzyme activity
1) as temperature increases, the kinetic energy of the molecules increases, so the molecules move faster. This makes it more likely for a substrate to collide with the enzyme’s active site. This increases reaction rate.
2) this is the case until an optimum temperature is reached. If temperature goes above this level, the vibrations in the enzyme molecule breaks some of the bonds that hold the enzyme in shape. This changes the enzyme’s tertiary structure and it is no longer complementary to the substrate. It is denatured.
What is temperature coefficient (Q10)
The temperature coefficient or Q10 shows how much the rate of reaction changes when the temperature is raised by 10 degrees Celsius. Most enzyme-controlled reactions have a Q10 value if 2, meaning reaction rate doubles, with an increase of 10 degrees.
How does pH affect enzyme activity
All enzymes have an optimum pH value, where enzyme-controlled reactions happen the fastest. Most human enzymes work Best at pH 7. However Pepsin works best at pH 2 which is useful since it is found in the stomach.
Above and below the optimum pH, the H+ and OH- ions found in acids and alkalis can break the ionic bonds and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes the enzyme’s active site change shape, so the enzyme is denatured.
How does enzyme concentration affect enzyme activity
The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme substrate complex. So an increase in enzyme concentration, increases reaction rate.
However, if there is a limited number of substrates, the substrates will be used up so enzyme activity drops as the enzymes no longer have anything to catalyse.
How does substrate concentration affect enzyme activity
The higher the substrate concentration, the higher the rate of reaction. More substrate molecules means a collision between a substrate and enzyme is more likely, so more enzyme substrate molecules are formed.
This is true up to a saturation point, as there becomes a point where all the enzymes, are occupied with substrates and adding more substrates makes no difference. So enzyme concentration becomes a limiting factor.
