3.6, 7.6 Enzymes

Many chemical changes within a cell are a result of metabolic reactions. Metabolic reactions begin with a specific reactant/substrate and a product. Most of these reactions require the help of enzymes to help speed up the reaction process. All reactions require activation energy to start the reaction process, which with the help of enzymes will lower the energy needed to start the process.

Enzyme: A globular protein that lowers the energy needed for a biochemical reaction to occur.
Active Site: On an enzyme's surface, there is a location where the substrate molecule can bind

• Each active site has a specific shape and chemical properties that is meant for a specific substrate molecule
• The binding of the substrate to the active site creates an enzyme-substrate complex
• The substrate is converted into an enzyme-product complex that is catalyzed by the enzyme
• Enzymes are not  consumed when combined with the substrate, but the substrate can break into simpler products. Enzymes are present in low concentrations because it is reusable 

Induced Fit Model: 

• Proposed by Daniel Koshland regarding the fit of a substrate to the active site of an enzyme
• Suggested that enzymes are quite flexible allowing the active site to change shape as it interacts with the substrate. The amino acid side chains of the active site will mold around the substrate

Coenzymes:

• Cofactors (also called organic coenzymes) are ions or non-proteins that are sometimes required by enzymes in order to work 
• These will bind to the enzymes with chemical groups or electrons
• Created in the body using vitamins. If the body is lacking vitamins then certain enzymes will not work
• Participate in the reaction

Effects of Various factors on Enzyme Activity 

Temperature:

• Low temperatures: leads to less thermal/kinetic energy and more difficulty for the reaction to reach it's activation energy
• Increasing the temperature will provide more kinetic energy for the enzyme and substrate resulting in more collisions between the two.There will be more enzyme activity. 
• At the optimal temperature for the enzyme the enzyme activity will reach it's maximum efficiency
• Further increasing the temperature beyond this point will denature the enzyme. The increased amount of thermal energy will disturbed the hydrogen bonds that the enzyme/protein together. The enzyme and the active site will lose it's shape

pH:

• Altering the pH will affect the charge of the enzyme, directly changing the solubility of the enzyme and the possible alteration of its shape. The active site will lose it's ability to bind to a substrate and harm the enzyme activity. 
• There is an optimum pH for enzymes and any divergence from this range will affect the enzyme activity 

Substrate Concentration:

• More substrates will increase enzyme activity. More substrates increases the chance of the enzyme forming into an enzyme-product complex and more reactions
• As all the enzymes are reacting with substrates, any increase in substrate concentration will not affect the enzyme activity as it has reached its peak

Denaturation alters the shape of a protein because of weakened bonds within the protein. This is usually a permanent effect caused by factors such as increased heat or altered ph. 

Lactase usage in making Lactose Free milk

• Lactose can be broken down via the enzyme lactase to form the monosaccharides glucose and galactose
• Lactose-free milk is made by purifying lactase and then binding it to a substance. Milk can be poured over the substance, that is binded with the enzyme lactase, to become lactose free.
• Lactose-free milk can be given to lactose intolerant people, to increase sweetness or to shorten the time needed to ferment yogurts and cheeses.

Inhibitors

Competitive inhibitors:

• A molecule acts as an inhibitors when it binds to the active site of an enzyme
• It is structurally and chemically similar to the substrate which is suppose to bind to the active site
• Blocks the active site from the substrate from binding
• Increased substrate concentration will lower the effects of a competitive inhibitor since there is more competition against the inhibitor

Non-Competitive inhibitor

• It's structure is not similar to the substrate and binds to the allosteric site of the enzyme. This is not the active site, but binding to it will cause a physical change to the active site. 
• Since it is not competing against the substrate, increased substrate concentration will not reduce the effects

End-Product Inhibition:

• Negative feedback: increased products leads to decreased production
• A metabolic pathway (usually chains or cycles) can limits it's own production by limiting it's enzymes
• Products will bind to the allosteric site to cause a change in the active site