Enzymes. Enzymes, substrates and active sites. Enzymes are globular proteins that work as catalysts Substrates are the substances that enzymes convert into products during metabolic reactions.
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Enzymes are globular proteins that work as catalysts
Substrates are the substances that enzymes convert into products during metabolic reactions.
Active site is the region on the surface of an enzyme to which substrates bind and which catalyzes the reaction.
Once a substrate has been locked into the active site, the reaction is catalyzed
The products are released and the enzyme is used again.
Animation: How Enzymes Work
The German scientist Emil Fisher introduced the lock and key model in 1890. Daniel Koshland suggested the induced-fit model in 1959 in the US. The conformational changes predicted by Koshland’s model were subsequently observed using high-resolution X-rays analysis of enzymes and other newly developed techniques. Although much experimental evidence has accumulated confirming predictions based on the induced-fit model, it is still just viewed as a model of enzyme activity.
Why has the lock and key model been superseded by the induced-fit model?
Could there ever be a situation in which two models are both retained?
Why is the induced-fit model not now called the Law of Induced Fit?
Activation energy is the amount of energy that must be put into a reaction to make it occur.
An enzyme stresses the bonds in the substrate(s), reducing the activation energy required for the reaction to occur.
Enzymes are globular proteins with a tridimentional structure
Their structure can be altered by several factors
When the shape of their active site is changed considerabily they will not function.
Denaturation is changing the structure of a protein (enzyme) so that it can not carry out its function.
Effect of pH on enzyme activity
Effect of temperature on enzyme activity
Lactose, the sugar found in milk causes allergies in some people because they are unable to produce enough of the enzyme lactase.
lactose - lactase-- glucose + galactose
Global estimates of lactose intolerance
Chains or cycles of enzyme catalyzed reactions
The Krebs cycle (cell respiration) and the Calvin cycle (photosynthesis) are examples of metabolic pathways that form cycles
Protein synthesis is a metabolic pathway that occurs in a chain.
Metabolic pathways can be switched off completely in cells where there is an excess of product.
The end product inhibition prevents a build up of intermediate products.
Feedback Inhibiton of Metabolic Pathways