identifying and investigating the role of enzymes n.
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Identifying and investigating the role of enzymes. Investigating Enzymes. Enzymes speed up metabolic reactions by lowering energy barriers Enzymes are substrate specific The active site is an enzyme’s catalytic center A cell’s physical and chemical environment affects enzyme activity.

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Enzymes speed up metabolic reactions by lowering energy barriers

Enzymes are substrate specific

The active site is an enzyme’s catalytic center

A cell’s physical and chemical environment affects enzyme activity


A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction

An enzyme is a catalytic protein

the activation energy barrier

Enzymes speed up metabolic reactions by lowering energy barriers

Initial investment of energy for starting a reaction is known as activation energy

Activation energy is energy required to break bonds

The activation energy barrier
enzymes and activation energy

Some chemical reactions that make life possible have activation energies that are too high

Catalysts speed up the rate of chemical reactions

Catalysts work by lowering a reaction’s activation energy

Enzymes are proteins that act as biological catalysts

Enzymes and activation energy
enzymes are substrate specific1


Substrate(s) ---------> Product(s)

For example,


Sucrose + H2O ---------> Glucose + Fructose

Enzymes are substrate specific
enzymes are substrate specific2

An enzyme can distinguish its substrate from even closely related properties

Each type of enzyme catalyzes a particular reaction

For example, sucrase will act only on sucrose and will reject other disaccharides, such as maltose

Enzymes are substrate specific
enzymes are substrate specific3

Active sites are restricted regions of the enzyme molecule that bind to the substrate

The active site is typically a pocket or a groove on the surface of the protein

Enzymes are substrate specific
enzymes are substrate specific4
Enzymes are substrate specific
  • Specificity of an enzyme is due to a compatible fit between the shape of its active site and the shape of the substrate
  • The substrate binds to the active site to form an enzyme-substrate complex
the catalytic cycle of an enzyme

Side chains (R groups) of amino acids make up the active site

Side chains catalyze the conversion of substrate to product

The catalytic cycle of an enzyme
the catalytic cycle of an enzyme1

After the conversion from substrate to product, the product departs from the active site

After the cycle, the enzyme is then free to take another substrate molecule into its active site

Enzymes emerge from the reaction in their original form

The catalytic cycle of an enzyme
the catalytic cycle of an enzyme2

The rate at which a given amount of enzyme converts substrate to product is partly a function of the initial concentration of the substrate

The more substrate molecules available, the more frequently they access the active sites of the enzyme molecules

The catalytic cycle of an enzyme

Denaturing is the process of changing an enzyme’s shape because of high temperatures or extreme pH values

Denaturing makes the enzyme less effective of even completely useless

effects of temperature

The velocity of enzymatic activity reaction increases with increasing temperature

With increasing temperatures, substrates collide with active sites more frequently

Beyond that temperature, bonds that stabilize active conformation become disrupted

When this occurs, the protein molecule denatures

Effects of temperature
effects of temperature1

Each enzyme has an optimal temperature at which its reaction rate is fastest

This temperature allows the greatest number of molecular collisions without denaturing the enzyme

Effects of temperature
enzyme inhibitors

Inhibitors slow down or stop the activity of an enzyme

Inhibitors usually bond to the protein and change the shape of the enzyme, causing it to become ineffective

Enzyme inhibitors
enzyme inhibitors1

Competitive inhibitors mimic the substrate and competes for the active site

Competitive inhibitors reduce the productivity of enzymes by blocking substrates from entering active sites

Enzyme inhibitors
enzyme inhibitors2

Non-competitive inhibitors do not directly compete with the substrate at the active site

Noncompetitive inhibitors slow enzymatic reactions by binding to another part of the enzyme

This alters the conformation of the enzyme so that the active site is no longer fully functional

Enzyme inhibitors
salivary amylase

Enzyme that catalyzes the hydrolysis of starch into simpler compounds

Present in human saliva

If salivary amylase were not present, we would not be able to break down complex sugars into simpler compound sugars in our mouths, which would make digestion of sugars difficult

Salivary amylase
pepsin protease

Pepsin helps breakdown proteins like those in dairy, meat, nuts, and eggs

Without pepsin, the body would be unable to breakdown proteins into their peptide amino acid parts

Pepsin (protease)

Found in the small intestine, liver, and kidney

Breaks down the milk sugar and lactose into simpler sugars (glucose and galactose)

Without lactase, the body is unable to breakdown milk products

People without lactase are said to be lactose intolerant


Found throughout the body, usually in cell organelles called peroxisomes

Breaks down hydrogen peroxide into water and oxygen

Hydrogen peroxide is a waste product of cells, but is toxic to the body

Without catalase, hydrogen peroxide would build up and cause cell and tissue damage