Enzymes
Reactions
• Most reactions take place in a number of
steps which need to be carefully controlled
if the cell is to function properly
• Enzymes are the most important
controllers of cellular reactions
Catalysts
• Catalysts speed up reactions without themselves
being involved in the reaction
• Enzymes are catalysts made of protein they
speed up a reaction without being used up
themselves in the reaction
• Because enzymes are made in living things they
are called biological (or organic catalysts)
• We learned in the chapter on food that
proteins are made when amino acids join
together
• The function of a protein is decided not
only by the sequence of amino acids but
also by the way the protein folds
• Most enzymes are globular proteins
Learning Check
• What is an Enzyme?
• What are catalysts?
• To what group of bio-molecules do
enzymes belong?
How enzymes work
• Enzymes are not flat they have a 3D
structure
• Each enzyme has its own
specific shape that will
only “fit” the molecule that
the enzyme is designed
to work on
• If the enzyme that breaks
starch into glucose meets
a fat molecule it will not fit
it and will not be able to
work on it
A movie on the action of Enzymes!
• http://www.bishopstopford.com/faculties/sc
ience/arthur/?sortby=3
• http://www.angelo.edu/faculty/nflynn/Bioch
emistry/
http://www.angelo.edu/faculty/nflynn/Biochemistry/
Learning Check
• Why is the shape of an enzyme important?
• Are enzymes flat, 3D or 2D in shape?
Enzyme Action
• The substance that an enzyme acts on is
its substrate
• The substance(s) that the enzyme forms is
called the product(s)
A Catabolic enzyme
• Amylase converts starch to maltose
• Catabolic as it breaks a big molecule into
a smaller one
• It is produced by saliva glands in mouth
and by the pancreas
An Anabolic Enzyme
• DNA Polymerase forms and repairs DNA
• Anabolic as it coverts simpler molecules
into more complex molecules
• Found in almost all living things
Consider This
• Amylase is an enzyme found in saliva. It breaks
starch molecules into smaller maltose molecules
• What is the substrate?
• What is the product?
• Will amylase break fats into fatty acids +
glycerol? Why?
• Is this an example of a catabolic or an anabolic
reaction? Why?
And This
• DNA Polymerase is an enzyme that builds
DNA using tiny molecules in our cells
• What is the substrate?
• What is the product?
• Will amylase build keratin out of peptides?
Why?
• Is this an example of a catabolic or an
anabolic reaction? Why?
• Enzymes work because they have the
correct shape to fit the substrate
• They have a complex 3 dimensional shape
to fit the substrate
• When enzymes and their substrates meet
and come together they form an
Enzyme/Substrate complex
Learning Check
• What is meant by a substrate?
• What is the unit formed when an enzyme
combines with its substrate called?
• Give an example of an anabolic reaction
• Give an example of a catabolic reaction
Reversible
• Enzyme Reactions are reversible
• Like a key can open or close a lock
enzymes can make reactions go in either
direction
Example
• In the following example the enzyme can
break molecule X into Y+Z but it can also
combine Y+Z to form X
X
Y+Z
Learning Check
• Can enzyme reactions be reversed?
Naming Enzymes
• Enzymes are named by adding the suffix
ase to the name of their substrate
Eg.
• Enzyme that acts on Amylose (starch) is
called amylase
• Enzymes that act on proteins are called
proteases
Learning Check
• Can you think of a name for enzymes that
act on Lipids?
• Amazingly enough they are called
Lipases!
Inhibitors
• Inhibitors attach to enzymes and destroy
their shape
• When this happens the enzymes are said
to be denatured
Nerve Gases
• The nerve gases we hear of terrorists
using are often inhibitors that attach to
enzymes involved in our nerve
transmissions
Poisoning people the old fashioned
way!
• Cyanide denatures an enzyme involved in
respiration
Beneficial Inhibitors
• Insecticides affect enzymes in insects
causing their death
• Drugs can affect enzymes involved in pain
causing the pain to stop
• Antibiotics can affect enzymes in bacteria
causing the bacteria to die
Learning Check
• What is an inhibitor?
• How do inhibitors work?
• Can you give an example of a harmful
inhibitor?
• Can you give an example of a beneficial
inhibitor?
Enzymes at work!
Enzymes work best in certain conditions
Factors that affect enzymes include
• Temperature
• pH
• Substrate concentration
• Enzyme concentration
We will be examining these in experiments
Temperature
• At very low temperatures ice forms, liquids
become solids and enzymes can’t work
• As temperature increases molecules start
to move and bump into each other causing
the rate of reaction to increase
Optimum Temperature
• Human enzymes work best at body temperature
(37°C)
• Plant Enzymes work best at 20-30 °C
• Above certain temperatures enzymes start to
lose their shape the rate of reaction falls
• When the shape is fully lost the enzyme is said
to be denatured this is usually a permanent
condition
pH
• pH scale goes from 0 -14
• 0-7 is acidic
• 7-14 is basic (or alkaline)
Optimum pH
• Enzymes work over a very narrow pH
• Most enzymes work at pH 6-8
• Outside this they lose shape and get
denatured
• The optimum or best ph is usually pH 7
An Exception!
• Is our stomach acid or basic?
• Do you think there are enzymes in our
stomach?
• Pepsin is an enzyme in the stomach that
works best at pH 2!
Learning Check
• What factors affect enzyme action?
• What is the best temperature for (a)
human enzymes and (b) plant enzymes
• What is meant by pH?
• Do enzymes work over a narrow or wide
pH range?
Immobilised Enzymes
• Bio-processing is the use of enzyme
controlled reactions to produce a product
• Bio-processing can be used to produce a
vast range of products such as cheeses,
beer, antibiotics, vaccines, methane gas,
food flavours, vitamins and perfumes
Bioprocessing
• Traditionally micro-organisms such as
bacteria and yeast were used but since
the 1900’s and especially since the 1950’s
enzymes are being used
Immobilized Enzymes
• If enzymes are used freely dissolved in a vessel
it can be very wasteful as they are lost at the
end of the process
• To prevent this problem enzymes are often
immobilised or fixed
• This means they are attached to each other or
an inert substance and can be used repeatedly
Learning Check
• What is bio-processing?
• What type of organisms are uasually used
in bio-processing?
• Why is bio-processing advantageous?
How to immobilise enzymes
• Physical methods
• Adsorption where enzymes are physically
attached to inactive supports such as
glass beads or ceramics
• Enclosed by a membrane when
enzymes are kept within a membrane
• Trapped in a gel, sodium alginate is
commonly used this allows substrates in
and products out
• Chemical Methods
• Bonded to a support enzymes
chemically bonded to a support such as
glass beads or ceramics
• Bonded to each other Enzymes are
chemically bonded to each other
Learning Check
• Describe 2 physical methods of
immobilising enzymes
• Describe 2 chemical methods of
immobilising enzymes
Advantages of Immobilised
Enzymes
• Efficiency of enzyme is not affected
• Immobilised enzymes can be easily recovered
from the product so you can get a pure sample
of product easily
• Immobilised enzymes can be reused this cuts
costs
• Enzymes frequently become more stable when
immobilised
Uses of Immobilised Enzymes
• Immobilised glucose isomerase converts
glucose to fructose which is used to
sweeten drinks
Antibiotics
• Penicillin acylase changes the structure of
penicillin to make more antibiotics that will
fight a wider range of bacteria
Lactose
• Lactase converts lactose to sweeter
sugars glucose and galactose which are
then used by food manufacturers
Learning check
• What are the advantages of immobilising
enzymes?
• Can you name 3 things immobilised
enzymes are used for?
Syllabus Can you.......
• Define the term: enzymes
• State the nature, folded shape & functions of
enzymes.
• Explain the role of enzymes in plants and
animals including role in metabolism
• Explain the effects of pH & temperature on
enzyme activity.
• State the procedure and advantages of Bioprocessing.
• State the use of Bio-processing.