Enzymes - Organic Catalysts (carbon & hydrogen) Flashcards
Structure of Enzymes
-cofactors
Enzymes are proteins
Enzymes that require additional non-protein parts are called:
COFACTORS- additional chemical components of an enzyme (not proteins)–(minerals & vitamins - help out enzymes)
(Eg. Iron, calcium, copper & zinc)
If the cofactor is an organic molecule its is called a COENZYME
Catalysts
- Molecules that speed up (catalyze) chemical reactions.
- Without catalysts reactions take place too slowly to sustain biological life.
- Enzymes are biological catalysts.
Enzymes and their Substrate
Enzymes act on a compound called a substrate
Highly specific-> each enzyme acts on a specific substrate only-> [called] specificity of enzymes (lock & key/induced fit)
Enzymes work by binding their substrate
Part of enzyme which binds to the substrate is called the ACTIVE SITE
What do Enzymes do?
Chemical reaction occurs if there is sufficient energy to begin the reaction
Enzymes reduce the amount of energy needed to begin a reaction- [important]
Enzymes reduce the Activation Energy
How do Enzymes work?
Two theories; - The lock & key - The induced-fit theory Enzymes are not 'used up' in a reaction-> available for reuse (recycled in a cell) pH & temperature can denature enzymes
The Lock-and-Key Theory
The substrate fits perfectly into the active site of the enzyme
- like a lock & key
{picture in PowerPoint}
The Induced-Fit Model
The shape of the active site varies slightly from the shape of the substrate and the substrate induces a change in shape of the active site so the two can fit together.
->Active sight varies to fit the substrate
{picture in PowerPoint}
Enzyme Theory
Why are there 2 theories/models to explain how enzymes work?
-Induced Fit = newer theory than the Lock & Key.
Which one do you think is the better theory/model that explains enzyme action?
-Induced Fit.
Factors Affecting Enzyme Activity
- TEMPERATURE
Denaturation- irreversible change in the protein structure resulting in permanent loss of protein function.
Enzymes have an OPTIMUM temperature range;
- temperatures between enzymes which activity is greatest
- most human enzymes have an optimal temperature of 37 degrees C
- heat-tolerant organisms (eg.bacteria) which live in hot springs have enzymes with higher optimal temperatures
Factors Affecting Enzyme Activity
- TEMPERATURE
(continued)
Critical temperature
-Temp at which denaturation of enzyme molecules begin to occur.
Lower temperatures
-Temporarily disrupt enzyme function but they do not denature the enzyme
Factors Affecting Enzyme Activity
- pH
Optimal pH = enzyme shows maximal activity.
Enzymes Optimal pH = NEUTRAL or SLIGHTLY ACIDIC
Optimal pH of human enzymes will vary with the site of enzyme function;
- Pepsin - stomach, pH 2
- Trypsin - small intestine, pH 8
- Carbonic anhydrase - human blood, pH 7.4
- Human Cell enzymes, pH 7.6
A change in pH can alter the 3-D structure of the enzyme - reducing enzyme function
Affect of Concentrations
Enzyme Concentration
- if the amount of enzyme is increased, the amount of product produced per unit time increases…. as long as….
Substrate Concentration
- if the amount of substrate is increased, the amount of product produced per unit time increases…as long as…
Enzyme Inhibitors
Chemical substances can inhibit enzyme function by;
- Binding to the Active Site of the enzyme thus preventing substrate from binding (competitive inhibitor)
- Combining with another part of the enzyme in a way that the shape of the binding site is altered (non-competitive inhibitor)
{pictures in PowerPoint}
Enzymes and Diseases
Several inherited diseases are caused by the inability to manufacture a particular enzyme.
- Galactosaemia -> error in the enzyme required to convert galactose.
- Lactose Intolerance -> low levels of the enzyme lactose.
- Phenylketonuria -> missing enzyme is phenylalanine hydroxlase.
Naming Enzymes
Normally an enzyme is named by attaching the suffix ‘-ase’ to the name of the substrate;
- (eg. CarbohydrASE, is an enzyme that acts on carbohydrates, lipASE acts on lipids, proteASE acts on proteins). - lactose (carbohydrate in dairy)-> lactASE, cellulose (plant cell walls)-> cellulASE
Naming rule NOT perfect*
- Trypsin & pepsin are both enzymes which act on proteins (they are proteASEs), but they were named before the rule came in.
- starch is digested by amylase?
