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Enzymes

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Hannah Walker

on 27 September 2013

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Transcript of Enzymes

What is an Enzyme?
An enzyme is a macromolecule that works as a catalyst*. They are proteins.
*Catalyst- A chemical agent that increases the rate of the reaction without being consumed by the reaction.

Enzymes only hasten reactions that occur naturally.
Enzymes are specific for the reactions they catalyze and determine which chemical process will occur.
The reactant an enzyme works on is called a substrate.
Enzyme+ Substrate= Substrate Complex
Enzymes have great molecular recognition because of 3D shape.
Location
Smooth E.R.- responsible for synthesis of lipids including oils, phospolipids, and steroids.
Rough E.R.- built into the membrane and are attached to proteins
Lysosomes- Used to break down other cellular materials including organelles.
=
Importance
Without enzymes, chemical traffic in the cell would be slow because chemical reactions would take such a long time
Function
Enzymes speed up chemical reactions that take place within the cell.
Example:
Sucrose+H2O>Sacrose> Glucose and Fructose
Enzymes and Regulations
Inhibitors
Inhibitors control the metabolism by acting as the "on" and "off" switches.

Inhibitors attach to the enzymes active site.
If it attaches with covalent bonds, inhibition is usually permanent.

If attached by weaker bonds, it's reversible
Competitive Inhibitors and Noncompetitive Inhibitors.
Two Types of Inhibitors
Toxins and poisons are also irreversible enzyme inhibitors
How enzymes are used to lower activation energy and increase the speed of the reaction.
An exergonic reaction is a spontaneous chemical reaction that can take a long time to occur.
An endergonic reaction is non spontaneous and involves absorbing free energy from from its surroundings
There are different types of enzymes that can help with both types of reactions.
Instead of heat, organisms use a "catalyst" to speed up reactions. It works by lowering the energy necesary for a reaction
These reactions occur when an Enzyme's ability to catalyze a reaction depends on molecules other than the substrate.
Allosteric Regulation in Enzymes
Cooperactivity.
This occurs when an Enzyme has several subunits. It is altered by the substrate of the enzyme where the substrate binds to the subunit to change the shape of the next subunit.
Interaction of Subunits
Activator or Inhibitor molecules bind to the Allosteric site on an enzyme.
Activators stabilize enzyme activity, inhibitors stabilize enzyme inactivity.
Once the Allosteric reaction occurs on one subunit, the reaction is communicated to the others, thus affecting them as well.
This process can occur in two ways: through the interaction of subunits (the polypeptide chains that make up enzymes) or through Cooperactivity.
These reactions occur as a regulatory molecule, either an activator or an inhibitor, bind to an enzyme to change it's function to regulate the enzyme's activity.
Positive cooperactivity occurs when the substrate bound to one subunit makes it easier for another substrate to bind to the next subunit.
Negative cooperactivity occurs when the substrate bound to one subunit makes it harder for another substrate to bind to the next subunit.
Feedback inhibition
Substrates control the activity of the enzyme. When concentration of the substrate increases, it causes the enzyme to stop synthesizing the substrate. Once the substrate has been used and the concentration lowers, the enzyme begins synthesizing the substrate again.
Specific Location of Enzymes Within the Cell
Multienzyme complex consists of a group of enzymes that are involved in many steps of a metabolic pathway.
This allows for a series of reactions to take place until a final product is released.
Enzymes in membranes, complexes, and organelles increase the metabolic process.
They have different roles in different areas of the cell.
Example: Enzymes for cellular respiration in eukaryotes are in the mitochondria.
Effects of Temperature
Up to a certain point, the rate of enzymatic reactions increases with the temperature, partly because subtrates collide more frequently when the molecules move rapidly.
Above that prime temperature the speed of enzymatic reactions drops sharply because the heat causes weak bonds to break and the molecules to denature
Effects of pH
Like temperature, enzymes have an optimal pH as well, for most it falls between 6-8 pH. However, some enzymes such as the enzymes in your stomach have adapted to handle very acidic environments.
Active Site- The restricted region of the enzyme molecule that binds to substrate.
Induced fit- The change in shape of active site so that it binds more snugly to the substrate.

A cellular control mechanism in which an enzyme that catalyzes the production of a particular substance in the cell is inhibited when that substance has accumulated to a certain level, thereby balancing the amount provided with the amount needed.

When feedback inhibition occurs, an enzyme is inhibited from catalyzing a reaction because of an overabundance of the reaction's products.

A feedback inhibitor is what you call that final substance if it is able to inhibit the first enzyme from working.

In feedback inhibition, the end product of a biochemical pathway reacts with the first enzyme that is unique to the pathway.
Fire can speed up these reactions but this is not a good solution because it denatures proteins kills cells and speeds up all reactions instead of just the necessary ones.
Enzymes enable reactants to absorb enough energy to reach the transition state even at moderate temperatures.
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