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What are enzymes

Enzymes are protein molecules that catalyze chemical reactions – (biological catalysts)
Catalysts – increase the rate of chemical reactions, without changing itself
Can be used over and over again
Without enzymes, most biochemical reactions are too slow to be useful


What kind of shapes do enzymes have and what do they do?

Enzymes have a three dimensional shape that recognize and bind reacting molecule called substrate
Enzymes convert / increase the rate of reaction of a substrate into end products
Enzymes are specific (active sites) for a particular substrate / reactant
Lactase acts on lactose
Maltase catalyze the hydrolysis of maltose
Pepsin acts on proteins


How do enzymes function?

Enzyme functions range from digestion of food to aiding with the elimination of toxins
They work by lowering the activation energy for a reaction
Activation energy is the energy that must be overcome in order for a chemical reaction to occur
Enzymes are present throughout the human body


How are enzymes named?

Most enzymes have names ending in ase
Amylase, Lipase, Protease, Lactase, Cellulase
Sugars usually end in – ose
Lactose, sucrose and maltose
Lactase acts upon the sugar lactose
Sucrase is an enzyme which acts on sucrose
Maltase catalyze maltose
Variation of naming system –
Type of reaction followed by ase
Reaction catalyzed by Hydrolase, Oxidase
Examples are Carbohydrates, lipids and proteins
Carbohydrates are catalyzed by carbohydrases
Lipids are broken down by lipase
Proteins are broken down by protease
DNA broken down by DNase
After the substrate followed by ase
Sucrose is broken down by sucrase
Lactose is catalyzed by lactase
Lactase catalyzes the reaction that hydrolyzes lactose into two simpler sugars


What is the lock and key hypothesis?

The substrate simply fits into the active site to form a reaction – complementary shapes
Two elements attach to an enzyme, react and form a compound – or –
One compound forming two or more products
Enzymes capable of reacting again
Theory does not allow for the flexibility of the tertiary shape


What is induced fit theory?

Substrate binds at active site and changes the shape of the enzyme when reaction takes place
The active site is flexible…adapts to shape of the substrate
Shape of the substrate can be modified to fit the shape of the active site
Fit of both active site and substrate = best catalytic reaction


What are protein part and a nonprotein parts of an enzyme?

Some enzymes also have a protein part and a nonprotein part
Both are needed for enzyme functions
The protein part is referred to as apoenzyme
The nonprotein is called coenzyme / cofactor

Many vitamins as well as several metals act as cofactors


What is a co enzyme?

Coenzymes are organic molecules that are required by certain enzymes to carry out catalysis
They bind to the active site of the enzyme
Coenzymes undergo chemical changes during the reaction
Regenerated in a subsequent reaction
They are not considered substrates of the reaction


What are some properties of enzymes?

Enzymes operate near physiological temperature and pH
Optimum temperature: 37°C for most enzymes
Optimum pH: 7.3 for most enzymes
Acid pH for gastric enzymes (pH 1 – 2.5)
Alkaline pH for duodenal enzymes


What is an enzyme inhibitor and name two types?

Molecules that bind to an enzyme and stop or reduce the rate of catalysis of the enzyme
Affect a variety of enzyme functions
Two main types of inhibitors
Competitive & Noncompetitive inhibitors


What is a competitive inhibitor?

A substance that competes for a position at the active site of an enzyme
Have a shape similar to the substrate
Binds to the same active site as the normal enzyme substrate, without undergoing a reaction
Prevent an enzyme from catalyzing it’s reaction
Blocks the substrate
Competitive inhibition is usually temporary

Example of inhibitors are poisons and some pharmaceuticals


What is a Noncompetitive inhibitor?

Bind to the enzyme at a different location, other than the active site
Result in changes to the shape of the active site
This change in shape means the enzyme is no longer able to bind to the substrate
The enzyme can no longer catalyze a reaction
The enzyme is denatured and is sometimes irreversible


What factors affect enzyme activity?

Enzyme concentration
Substrate concentration
Temperature effects
Effects of pH


What is transferase?

Involve in the transfer of a specific group from one compound to another compound
Transfer of one amino group to another – aminotransferase
Methyltransferase – involved in the transfer of a methyl group
Methyl groups are not functional groups – they can impart specific biological properties to some substances


What is a standard graph?

Plotting a standard curve in order to obtain accurate patient and control values
One method of obtaining concentration from % transmittance or absorbance is through the use of a standard curve
Measuring the colour of a series of known concentrations, plotting a graph and reading the concentration of the unknown directly from the graph


How to prepare a standard graph?

A single standard can be used to make a set of standards
By using increasing amounts of this standard in a series of dilutions
The concentration of each of the dilutions can be calculated
The blank which contains only diluent corresponds to a concentration of zero
Colour is measured by spectrophotometric readings of Absorbance or %Transmittance
The blank is used to set %T or zero Absorbance
The blank is always shown on the graph as the point (0, 100%) when Transmittance is used and (0,0) when Absorbance is used
Absorption or %T plotted on the Y axis, and increasing concentrations of standard along the X axis
A standard curve is constructed after obtaining the %T / Abs readings from a number of solutions of known concentration (standards)
If Beer’s Law is followed, the resulting line representing absorbance vs concentration will be straight


How can the concentration of controls be determined?

The concentration of controls and patient samples can be determined by locating their %T / Abs reading on the line, then dropping an imaginary line down from that point to intersect the concentration axis


When you do construct a new graph?

When there is a change in:
reagent lot numbers
an instrument parameter (change bulb, optics cleaned, etc.)
New instrumentation


When is a standard graph acceptable?

When the majority of the curve’s points are on or close to the line. (best fit)

Errors – or – problems
Accuracy of the dilutions
Calculations of the dilutions
Spectrophotometer errors


How is the graph labeled?

Preparing a standard graph
Use the X axis for concentration
The Y axis is labeled either %T (semi-log paper) or Absorbance (linear paper)
Draw curve – best line fit