Enzymes Flashcards
Catalyst
Speeds up chemical reactions without being chemically changed.
Function (general)
Speeds up a metabolic reaction without being chemically changed.
Composition
Enzymes are composed of C, H, O and N. Sulphur (S) may also be present.
What are ENZYMES
are organic catalysts, typically proteins.
- The term catalyst refers to the ability of a compound to interact with reactants to allow them to form products at much lower energy (activation energy) levels then in its absence.
- The catalyst speeds up a reaction without being permanently changed.
- In biology, when we discuss catalysts, they are enzymes and the reactants are called substrates. Each enzyme is highly specific due to the shape of a region on the enzyme called the active site.
- So one enzyme one substrate. Enzymes are named after the substrate but include “ase”. Example: Starch, a complex sugar is known as “amyl” and therefore the starch enzyme is Amylase.
Exergonic/ catabolic
Reactions that break down substances
- Examples of these include cellular respiration, digestion or any lytic reactions.
Endergonic/ anabolic
Reactions that build up substances
- Examples of these include photosynthesis, protein synthesis
Biochemical pathway
- A series of enzyme-catalysed reactions that results in the conversion of a precursor molecule into a product molecule.
- Any sequence of chemical reactions leading from one compound to another; if taking place in living tissue, usually referred to as a biochemical pathway.
- Sometimes, the amount of energy (heat) in a reaction could be damaging if released all at once, therefore, a biochemical pathway does this in incremental steps that gives the body time to remove excess heat.
Enzyme regulation
Enzymes turn off, and on, depending on the needs of the cell or organism.
* On are the activators
* Off are the inhibitors
If inhibitors are irreversible a new enzyme will need to be made, if they are reversible, the enzyme can be active again.
Factors effecting enzyme activity:
- Temperature
- pH
- Enzyme concentration
- Substrate concentration
Enzyme concentration
As the concentration of an enzyme increases, the rate of reaction will also increase: provided that the substrate is also in excess.
Substrate Concentration
- Increasing Substrate Concentration increases the rate of reaction.
- This is because more substrate molecules will be colliding with enzyme molecules, so more product will be formed.
- However, after a certain concentration, any increase will have no effect on the rate of reaction, since Substrate Concentration will no longer be the limiting factor.
- The enzymes will effectively become saturated, and will be working at their maximum possible rate.
INHIBITORS:
these are substances that interact with enzymes to prevent them from catalysing reactions. They can be reversible (which means that they may not permanently disable an enzyme) which slow a reaction substantially. Orm inhibitors may be irreversible where they bind permanently to the enzyme, causing the reaction to get slower and slower as more enzymes are disabled the reaction eventually stops. There are two types of inhibitor:
Competitive inhibitors:
This will attach to the active site (not like a substrate) because is has some chemical components that will allow it to attach to part of the active site (i.e. chemically similar to the substrate) that is meant to be for the real substrate. The inhibitor may not fit the whole active site and it will not do anything, it will simply block the substrate from binding to the active site. This creates an inhibitor-enzyme complex, meaning that the enzyme is inactive.
Non - competitive inhibitors:
These attach at a site away from the active site called the ALLOSTERIC SITE. When they attach to this site, they alter the shape of the enzyme’s active site, preventing the substrate from entering.
ACTIVATOR:
An activator is a molecule or protein that increases the rate of a biological process by enhancing the function of an enzyme or a gene. In gene expression, activators are transcription factors that bind to enhancer regions of DNA, helping RNA polymerase initiate transcription. In enzymatic reactions, activators bind to enzymes to increase their catalytic activity, making biochemical processes more efficient.
Product inhibition:
Product inhibition is a regulatory mechanism in which the final product of a metabolic pathway inhibits an earlier enzyme in the same pathway, preventing overproduction. This form of negative feedback helps maintain homeostasis by conserving energy and resources.
pH - effecting rate of reaction.
(enzymes)
refers to the acidity and alkalinity of the conditions surrounding enzymes. Each enzymes has an optimal pH, most internal (cells and blood) enzymes work best in neutral conditions. Some exceptions are the digestive enzymes in the mouth (slightly acidic - pH6), stomach (highly acidic - pH2) or intestines (alkaline - pH8).
The ions in acidic or alkaline conditions can interact with the bonds holding the tertiary shape of the enzyme so if pH changes, it can cause enzymes to change shape - denature.
Apoenzyme
inactive enzyme without cofactor
Holoenzyme
whole enzyme with cofactor
TEMPERATURE - effecting rate of reaction:
As temperature increases, the rate of reaction will increase up until the Optimal Temperature of the enzymes catalysing the reaction. As the temperature rises above optimal temperature, enzymes begin to change shape (denature), due to the hydrogen bonds holding their tertiary shape breaking. This changing of shape is called DENATURING and stops enzymes working. In humans the optimal temperature is 37.
HOW SUBSTRATE CONCENTRATION EFFECTS THE RATE OF A REACTION:
The addition of more substrate will increase the rate of reaction as the substrate molecules will collide with the enzyme more frequently. However, a point will be reached where all the available active sites are being used, so no matter how much more substrate is added, the rate will not increase further.
HOW ENZYME CONCENTRATION EFFECTS RATE OF REACTION:
In a reaction where the substrate is in excess, the available enzymes can only work as fast as the substrate can move in and out of the available enzymes.
Cofactors & Coenzymes:
All enzymes are proteins, but some of these enzymes require some additional substances (that are not protein) to complete their active site to make the active site functional. These additional substances are generally referred to as cofactors. Cofactors can be minerals (inorganic) or organic compounds - to distinguish between inorganic and organic cofactors. Organic cofactors are called coenzymes (these are typically derived from vitamins).
How do enzymes catalyse reactions?
Stage 1: Specific (½) substrate molecule encounters active site of enzyme (½), causing
conformation change of active site (½).
Stage 2: Enzyme-substrate complex forms (½), holding substrate in position which reduces
the activation energy required to break chemical bonds (½) by changing the shape
of the substrate molecule, forming a temporary bond or changing the local
environment (Induced fit theory) (½).
Stage 3: Once the chemical bonds of the substrate are broken, products are released (½)
and active site changes back to original conformation (½).
