Chapter 4 - Enzymes Flashcards
What is the purpose of enzymes?
To provide a biological catalyst, and to speed up reactions within the body.
What are enzymes?
- Globular Proteins
- Biological Catalyst
What is the Vmax?
The maximum initial velocity of the rate of the enzyme-catalysed reaction, under constant temperature, pH, and pressure.
How do Enzymes catalyse reactions?
Enzymes help molecules collide successfully, therefore lowering the activation energy necessary for the reaction to occur.
What is Lock and Key Hypothesis?
The theory that the enzyme and the substrate are directly complimentary to one another, like a lock and a key.
What is formed when the enzyme and the substrate bond?
Enzyme-Substrate Complex.
True or False - The enzyme is included as one of the reactants in the reaction.
False - after catalysing the reaction, the products are released and the enzyme is left unchanged, therefore meaning it is not included as a reactant.
What is the Induced Fit Hypothesis?
The theory that the enzyme and the substrate are only partially complimentary, but the kinetic energy of the substrate colliding with the enzyme causes change in its tertiary structure.
How does the induced fit theory lower activation energy?
The weak interactions between the enzyme and the substrate change the tertiary structure of the enzyme, making the bonds stronger, which puts strain on the substrate, therefore reducing the activation energy for the reaction.
What is an Intracellular Enzyme?
An enzyme that acts within a cell.
What is an example of an intracellular enzyme?
Catalase - ensures breakdown of toxic Hydrogen Peroxide.
What is an Extracellular Enzyme?
An enzyme that works outside of the cell that created it.
What are examples of an extracellular enzyme?
Amylase + Trypsin - Used for digestion in the breakdown of big nutrient and vitamin molecules so that they can become useful to the body.
What is the first step of starch digestion?
Amylase (salivary gland) breaks down starch into maltose, a dissacharide.
What is the second step of starch digestion?
Maltase (small intestine) breaks down Maltose into Glucose, a monosaccharide; This is useful to the body, as glucose is small enough to be absorbed through small intestine lining.
How are proteins digested?
- Digested by Proteases, e.g. Trypsin, which catalyses the digestion of proteins into smaller peptides.
- Other proteases break these peptides down further into amino acids; These are small enough to be absorbed into the bloodstream.
What are some of the factors affecting enzyme activity?
- Temperature
- pH
- Concentration
How does temperature increase affect enzyme activity?
It accelerates the rate.
What is the Temperature Coefficient?
- Denoted by symbol Q10
- Shows how much the rate increases with a 10°C temperature increase.
What happens when the temperatures surpasses the optimum value?
The enzyme begins to denature, meaning that the vibrations caused by KE from the temp. increase changes the tertiary structure of the enzyme, meaning that it is no longer complimantary to the substrate.
What is the Optimum Temperature for most enzymes in the human body?
40°C
What is the Optimum Temperature for most enzymes in thermophilic bacteria?
70°C
What is the Optimum Temperature for most enzymes in psychrophilic bacteria?
> 5°C
What is the structure of enzymes in cold extremes?
Flexible structures, particularly at active site. This is good for cold temps, but means that any slight temperature change will be enough to denature the enzyme.
What is the structure of enzymes in hot extremes?
Rigid structures, due to an increased number of bonds, especially hydrogen bonds and disulphide bridges - this means that they are more stable and resistant to temperature change.
How does pH affect enzyme activity?
Enzymes need a specific concentration of H+ ions to be optimally functionally, usually around pH 7. However, any change in pH causes increase or decrease of H+ concentration, decreasing rate of reaction.
What happens when pH changes very significantly?
The enyzyme denatures.
Why does low pH affect tertiary structure?
Increase in H+ ions means that less R-Groups can interact with each other, leading to bonds breaking and tertiary strucure changing.
Why does high pH affect tertiary structure?
Decrease in H+ ions means that R-Groups interact too much, leading to bonds breaking and tertiary structure changing.
How does Concentration affect rate?
More enzymes means a higher collision rate, which leads to more enzyme-substrate complexes forming and a higher rate of reaction.
What is an inhibitor?
A molecule that can prevent enzymes from carrying out their normal process of catalysis
What are the two types of inhibition?
Competitive and Non-Competitive
What is competitive inhibition?
when the inhibitor has a similar shape to the substrate that can fit into an active site of an enzyme, it can fill the active site and block the substrate from entering the active site, preventing catalysis.
True or False: When most competitive inhibitors bind to an enzyme, the effect is reversible and temporary.
True - there are some exceptions, however, e.g. Aspirin, which permanently bonds to an enzyme.
What is an example of competitive inhibition?
Statins - competitive inhibitors for enzymes used in synthesis of cholesterol. Used to help people with high blood cholesterol concentration.
What is non-competitive inhibition?
when the inhibitor binds to a location other than the active site - the allosteric site. Binding to this site causes change in tertiary structure of enzyme, meaning that the active site is no longer complimentary to shape of substrate.
What happens when you increase concentration of enzyme inhibitor?
The rate of reaction decreases as more and more active sites become unavailable.
What is end-product inhibition?
Inhibition that occurs when the product of a reaction inhibits the enzyme that produces it - this acts as a negative-feedack control mechanism.
What is an advantage of end-product inhibition?
Excess products are not made and resources are not wasted.
What is an example of end-product inhibition?
Production of ATP - the enyme Phosphofructokinase (PFK) catalyses the reaction, but ATP inhibits use of PFK.
What is a Cofactor?
a ‘helper’ molecule to assist enymes in carrying out function as catalysts - Cofactors are NOT enzymes.
What is a Coenzyme?
an organic cofactor (a cofactor with carbon in it)
How are inorganic cofactors obtained?
Via minerals, e.g. Zinc, iron, calcium, and chloride ions. - for example, amylase has a chloride ion in it’s structure which is necessary for it to function.
How are organic coenzymes obtained?
via vitamins in the diet, e.g. vitamin B3 used to synthesize nicotinamide adenine dinucleotide (NAD)
What is a prosthetic group?
A type of cofactor that bonds tightly and permanently to enzymes, e.g. Zinc ions (Zn2+) to form carbonic anhydrase.
What is an inactive precursor enzyme?
a specific enzyme that needs to be activated only under certain conditions to not cause damage to the surrounding cell structures.
How do you activate a precursor enzyme?
You need to change it’s tertiary structure by adding a cofactor to activate it.
What is a precursor enzyme called before it is activated?
Apoenzyme
What is a precursor enzyme called after it is activated?
Holoenzyme
What is a precursor enzyme called after it has been activated by another enzyme, or when there is a sudden change in pH or temperature?
zymogens for enzyme activation
proenzymes for pH or temp. change
How is Pepsin activated?
When inactive pepsinogen is brought into contact with acidic pH, it is transformed into the active enzyme pepsin - this process is to protect the body tissues against the digestive actions of pepsin.
