1.3 Enzymes - Biochemical Reactions

All information on the biochemical catalysts; enzymes!

What is an Enzyme?

* acts on a molecule called a substrate
* activity depends on the enzyme’s shape and its active site (binding site for the substrate)
* enzymes are affected by the temperature and pH, and usually have an optimum range for each

What is a substrate?

molecules that are the specific reactants of the reaction

What are the functions of an Enzyme?

1. proteins that speed up the chemical reactions of a cell
2. do not cause reactions to happen. They speed up reactions that will already occur
3. without them, reactions in the cell would proceed so slowly, the cell would die
4. enzymes are very specific. they can only carry out one job, but they do that job very well
5. they are never used up in a reaction, they are used over again

How do enzymes work?

* reactions with enzymes depend on physical fit between the enzyme and its specific substrate

What is the general equation for an enzyme reaction?

Enzyme + substrate → Enzyme-substrate Complex → Enzyme + Product

What are products?

new substances formed as a result of the reaction

What is the active site?

a fold or groove on the surface of the enzyme into which substrate molecules “fit” and bind to the enzyme.

* the fit is so precise, it is compared to a lock and key

Key Ideas:

* the shape of the enzyme is so specific that only one shaped substrate can fit
* and enzyme can only catalyze one specific reaction
* a specific enzyme is required for each reaction in the cell
* there are over 2000 known enzymes
* enzymes are unchanged during the reaction. they are available to carry out the reaction over and over

What are the Effects of pH on Enzymes?

* enzymes are denatured (made by non-functional extremes) of pH
* within these extremes, most enzymes are still influenced by pH
* there is a particular pH for the optimum activity of each enzyme.
* active site can be disabled by wrong pH

What are the affects of temperature change and enzyme activity?

* reactions occur faster at higher temperatures, but the rate of denaturation of enzymes also increases at higher temperatures
* high temperatures break disulfide bonds important for the tertiary structure of the enzyme
* disrupts the active sites and makes the enzyme unable to function

What affects enzyme concentration and enzyme activity?

* assume the amount of substrate is not limiting, an increase in enzyme concentration causes an increase in reactant concentration
* cells may increase the amount of enzyme present by increasing the rate of its synthesis to meet demand

\
linear

How does the substrate concentration affect the enzyme activity?

* assume the amount of enzyme is constant and non-limiting, an increase in substrate concentration causes a lesser rate of increase in the reaction rate
* the maximum rate is obtained at a certain substrate concentration where all the enzymes are occupied by substrate
* the reaction cannot increase further

\
linear, curved

How do cells regulate cellular activities?

* they control their enzymatic pathways to coordinate cell activities
* limit the production of specific enzymes
* inhibit the action of an enzyme that has already been produced

What is a competitive Inhibition?

* inhibitor is so similar to the regular substrate, it is able to enter the enzyme’s active site
* can stop a substrate from entering the enzyme’s active site
* is normally reversible by increasing substrate concentration

What is an example of Competitive Inhibition?

**Neuraminidase** - a viral protein that cuts the haemagglutinin anchor and allows the virus to be released, infecting other cells

**Relenza** - a drug that competitively binds with neuraminidase and prevents it from ‘cutting’ the anchor (virus won’t spread)

What is a Non-Competitive Inhibition?

* inhibitor does not compete for the enzymes active site
* binds to enzyme’s allosteric site
* can be reversible or irreversible
* irreversible modify key amino acid residues needed for enzymatic activity
* reversible bind non-covalently and different types of inhibition are produced depending on whether these inhibitors bind to the enzyme, they enzyme-substrate complex, or both

What is an example of Non-Competitive Inhibition?

**Strychnine** - binds to an allosteric site on glycine receptors and prevents glycine (an inhibitory neurotransmitter) from binding, causes muscles to fire uncontrollably (convulsions and asphyxia) - used in animal traps and bait

What are Allosteric Regulators

* molecules that promote the action of enzymes can bind to the allosteric site
* known as activators

What is a Precursor Activation?

* accumulation of a substance within a cell may specifically activate an enzyme by binding to its allosteric site and setting in motion a new sequence of reactions for which the activated substance is the initial substrate

What are Allosteric Regulators- Inhibitors?

* prevent the action of specific enzymes
* occur naturally and are involved in the regulation of metabolism
* many drug molecules are enzyme inhibitors
* medicinal enzyme inhibitor is often judged by its specificity, or its lack of binding to other proteins, and its potency
* high specificity and potency ensure that a drug will have few side effects, and thus, low toxicity

What is Feedback Inhibition?

* enzymes in a metabolic pathway can be inhibited by a product produced further along the pathway
* slows the pathway so a specific product does not build up in system
* type of non-competitive inhibition in which the end product of s series of enzymatic reactions binds at an allosteric site on the first enzyme pathway
* how the cell keeps homeostasis
* natural enzyme inhibitors can be poisons and are used as defense mechanisms against predators or as a way of killing prey (venom)

What are Cofactors?

* some enzymes require a non-protein assistant to help them carry out functions
* are inorganic ions, like magnesium and calcium

What are Coenzymes?

* organic molecules that bind to enzymes and serve as carriers for chemical groups or electrons
* many are dependent on vitamin intake

What do most Enzymes end in

* -Ase

What do most Disaccharides end in?

* -Ose