Flashcards in Enzyme Action And Inhibtion Deck (18):
What is an activation energy?
An enzyme binds to a substrate and stresses some of its chemical bonds, or binds to two substrates and forces them close together. These effects lower the activation energy needed to make a reaction happen. This means that the reaction is catalysed- it is much more likely to happen, so it speeds up.
What are metabolic enzymes?
Enzymes that regulate all the metabolic reactions in a cell. Some enzymes are involved in synthesis or anabolic reactions - these join molecules together, usually by a condensation reaction where a water molecule is removed. Other enzymes perform degradation or catabolic reactions which break molecules apart, often by hydrolysis where a water molecule is added.
Which reactions are endogonic and which are exergonic?
Endogonic= anabolic require energy
Exergonic= catabolic don't require energy
How are enzymes specific?
Most enzymes are made of protein. The amino acid sequence determines the shape of the protein molecule and, as a result, also affects:
-the shape of the active site where the substrate binds
-which amino acids are present in the active site
The picture of the primary structure of lysozyme shows that the amino acids of the active site are found far apart in the chain; the other amino acids provide the exact folding needed to hold the active site in position. why?
Because if their highly defined structured , enzymes are specific to one substrate, or to a group of very similar of substrates. For example, the enzyme glucokinase is specific to glucose, while hexokinase works on glucose and some other 6-carbon sugars.
What is the induced fit model?
The shape of the active site still complements the shape of the substrate, but the active site also has amino acids with an affinity for areas on the substrate molecule. This means that the active site and the substrate bind by forming hydrogen bonds and ionic bonds.
What does the arrival of the substrate bring about?
A change in shape - a conformational change - in the enzyme due to the bonding between the active site and the substrate, which pulls the enzyme towards the substrate. The enzyme is showing an induced fit to the substrate. This makes the reaction more likely as the substrate is under tension - activation energy of the catalysed reaction is lowered by stressing the bonds in the substrate.
What are enzyme cofactors used for?
To help some enzymes to be active. Cofactors may be permanently attached in which they are called prosynthetic groups or they can be temporarily added.
What are proteases?
The action of the enzyme is hydrolysis of peptide bonds to break down proteins examples of these are pepsin and trypsin from digestive system and bromelain from pineapples.
What are nucleases?
The action of the enzyme is hydrolysis of phosphodiester bonds to break down nucleic acids. Eg EcoRl used in genetic engineering to cut DNA.
What are ATPases?
The action of this enzyme is hydrolysis of the Phosphoester bond in ATP to form ADP and phosphate. Eg the sodium-potassium pump in the membrane of cells.
What are kinases?
The action of this enzyme is condensation reaction to add a phosphate group to another molecule. Eg a kinase adds a phosphate to inactive glycogen synthase.
What is the role of inhibiitors?
Can reduce reaction rates in one of two ways; they can resemble the substrate, or they can alter the enzymes shape so that it becomes inactive.
Explain how the activity of an enzyme is found?
By using a constant concentration of enzyme and then measuring the initial rate of reaction at different substrate concentrations. As substrates concentration is increased, the initial rate of reaction increases until a maximum rate is reached (Vmax).
What is competitive inhibitor?
It is similar to the substrate in size, shape and charge pattern. If a fixed concentration if a competitive inhibitor is used when measuring enzyme activity, the increasing substrate concentration will eventually dilute the competitive inhibitor so much that all enzyme molecules bind to the genuine substrate and Vmax is reached, albeit at a higher substrate concentration.
What is a non-competitive inhibitor?
It binds to another part of the enzyme, away from the active site. Heavy metals (such as mercury and lead) bind to the - SH groups of cysteines in the protein, and so change the enzyme shape. If the active site no longer fits the substrate. If a fixed concentration of a non-competitive inhibitor is used when measuring enzyme activity, a proportion of the enzyme molecules are inactive, so Vmax is reduced.
How do non-competitive inhibitors work?
They bind to the allosteric site of an enzyme and change the shape of the active site.