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Enzymes : (Structure of enzymes (The enzyme structure determines its…
Enzymes :
Structure of enzymes
The enzyme structure determines its function. For enzymes to catalyze reactions they need cofactors.
The instruction for making enzymes are encoded in genes
What are cofactors?
Some enzymes can only work if another small non protein molecule is attached to them. These small molecules are called cofactors. There are two types of cofactors coenzymes and co factors. Cofactors that are permanently bound by covalent bonds to an enzyme molecule prosthetic groups
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Coenzymes these are small organic non protein molecules that bind temporarily to the active site of the enzyme molecule
Indentation is Known as the active site . Consists of 6-10 amino acids and the tertiary structure of the active site is complementary to the substrate.
Effects on enzymes
Temperature
Kinetic energy of both enzyme molecules and substrate molecules increase when heated therefore there is an increased number of collisions between the enzyme and substrate meaning increased rate of reaction. The temperature that gives the maximum rate of reaction is called the enzymes optimum temperature. Heating also causes enzyme molecules to vibrate which can put a strain on the bonds that hold them together. Weaker bonds such as London bonds and ionic can break. This causes the structure of the enzyme to be held less in shape which results in the loss of shape for the active site. Therefore the tertiary structure is damaged so the enzyme is denatured
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pH
PH is a measure of the H plus ions concentration. A hydrogen ion which has a positive charge is attracted to the negatively charged ions. Excess hydrogen ions will interfere with the hydrogen bonds and ionic bonds holding the tertiary structure in place. Increasing or decreasing pH can cause changes to the shape of the active site. Increasing the concentration of hydrogen ions will alter the charges around the active site as more protons cluster around the negatively charged groups in the active site which will interfere with the binding of the substrate molecule to the active site. At the optimum pH the concentration of hydrogen ions in solution gives the active site of the enzyme the best overall shape.
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Enzyme action
Lock and key hypothesis
1.The substrate molecule fits into the enzymes active site
- Temporary hydrogen bonds hold the 2 together forming an ESC
- The substrate molecule is broken down or built up into the product molecules and these form an enzyme product complex whilst still in the active site
- The product molecule leaves the active site
- The enzyme molecule is now free to form another ESC
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Induced fit hypothesis
This theory states the enzyme is not a rigid fixed structure but the presence of the substrate molecule in it induces a change in shape good fit.
1.The active site still has a complementary shape of the substrate but subtle changes of the shape of the R groups gives a more precise conformation
- An ESC is formed and forces such as hydrogen bonds, ionic attractions and van Der waals forces and hydrophobic interaction bind the substrate to the active site
- Whilst still in the active site an EPC is formed
- the product now has a slightly different shape from the substrate molecule and detaches from the active site
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What are inhibitors?
Inhibitors are substances that reduce the activity of an enzyme. They combine with the enzyme molecule and this influences how the substrate binds to the enzyme or the turnover rate of the enzyme. There are 3 types of enzyme inhibition
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End product inhibition
This is when the catalyzed reaction has been completed but the product molecules stay tightly bound to the enzyme therefore the enzyme cannot form more of the product.
Competitive inhibition
A competitive inhibitor (CI) is a substance whose molecules have a similar shape to an enzymes substrate molecule. This reduces the number of free enzyme active sites available for then substrate molecule to bind to and form enzyme substrate complexes (ESC) and instead enzyme inhibitor complexes are formed. Most enzyme inhibition by CI is reversible- since collisions between enzyme and substrate are random a higher concentration of substrate increases the chances of ESC
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Functions
enzymes are biological catalysts. They speed up reactions without being used by themselves. Some of the essential reactions they catalyze include respiration, photosynthesis, protein synthesis, and digestion.