Enzymes
Lesson objectives
•
•
•
•
•
By the end of this lesson you should be able to:
Define and discuss metabolism
Discuss sources of energy with reference to
solar and cellular energy
Define enzymes
Discuss enzymes with respect to their protein
nature, folded shape, roles in plants and animals
and their role in metabolism
Discuss the effect of temperature and pH on
enzyme activity
Metabolism
• All the reactions
taking place in an
organism are referred
to as it metabolism
• Metabolic reactions
can be divided up into
anabolic reactions
and catabolic
reactions
Sources of energy
What are enzymes?
• A catalyst is a substance
that speeds up a reaction
• Enzymes are catalysts made
of protein
• Enzymes are proteins but
not all proteins are enzymes
“Enzymes are proteins that
speed up a chemical
reaction without being
used up in the reaction”
What are enzymes?
• Enzymes are made from
amino acids together to
form a long chain
• Enzyme function is
determined by amino
acid sequence and 3D
shape of protein
• An enzyme acts as a very
efficient catalyst for a
specific chemical
reaction.
• The enzyme speeds that
reaction up tremendously
• Anything that changes
the shape of the enzyme
will reduce the
efficiency of the enzyme
Features of enzymes
• An enzyme binds to a substrate in a region
called the active site
• Only certain substrates can fit the active site
• An Enzyme-substrate complex forms
• Substrate reacts to form product
• A Product is released
• Enzyme reactions are reversible
X
Y+Z
• Enzymes are named by adding the ending ase
to the name of their substrate e.g. lipase lipids and amylase – amylose (starch)
The Role of Enzymes Necessary in plants and animals
to control metabolic reactions
Catabolic enzymes
•
•
•
Amylase (diastase)
converts starch into
maltose
Produced in salivary
glands and pancreas &
converts starch to
maltose
Seeds contain starch:
when seeds germinate
the enzyme amylase
converts starch to
maltose
Anabolic enzymes
• DNA polymerase is an
enzyme that forms and
repairs DNA – found in
plants and animals
• The enzymes that control
photosynthesis are also
examples of anabolic
enzymes – CO2 and H2O
are converted into C6H12O6
• DNA ligase is used in
genetic engineering to join
2 pieces of DNA together
Factors affecting enzyme activity
• Enzymes work best
under ideal conditions
• Any change in these
will slow down the
rate of reaction
• These conditions
include temperature
and pH values
Temperature
• At very low temps (0oC
for pure water), ice forms
•• Above
a certain
This
means
that
cellbe
Enzymes
may
also
temperature
contents
solid
denaturedbecome
byenzymes
other
begin
tosuch
loose
heir 3D
and
enzymes
factors
ascannot
shape
and pH,
the rate
of
work
unsuitable
inhibitors
fallsincreases
• reaction
As
temp
andthe
radiation
• When
the
of anhas
the
rate
of shape
molecular
“A denatured
enzyme
enzyme
is fully
lostcan no
movement
increases
lost its shape
and
oC) the
(usually
above
50
• This
causes
substrate
longer
carry out
its
enzyme
is
said
to
be
molecules
function” and enzymes
denatured
to bump into each other
• In
thisoften
condition the
more
hasthe
lost
its of
ability
• enzyme
As a result
rate
to
function
and thiswith
is
reaction
increases
often
permanent
increasing
temp Human
enzymes work best at
37oC (body temperature)
while most plant enzymes
prefer 20 - 30oC
Temperature Affects Enzyme
Action
Optimum temperature
Reaction
Rate
Low
High
Temperature
pH
• Enzymes work over a
very narrow pH range
• For most enzymes this is
pH 6-8
• Outside this range the
activity of the enzyme
falls as the enzyme
shape changes –
denatured
• The optimum for most is
pH 7
• Enzyme activity is also
affected by enzyme and
substrate concentration
Factors Affecting Enzyme Action
Reaction
Rate
Optimum pH
3
5
7
pH
9
11
What have you learned?
•
•
•
•
•
Can you. .
Define and discuss metabolism?
Discuss sources of energy with reference to
solar and cellular energy?
Define enzymes?
Discuss enzymes with respect to their protein
nature, folded shape, roles in plants and animals
and their role in metabolism?
Discuss the effect of temperature and pH on
enzyme activity?
• Bioprocessing is the use
Immobilised
of enzyme controlled
reactions to produce a
product
• Traditional examples
involved the use of micro –
organisms such as yeast
and bacteria
• In recent times it has had
been used to produce a
vast range of other products
• Since the 1950’s the cells
used in many of these
bioprocesses have been
replaced by purified
enzymes
• The use of free enzymes is
wasteful
• To prevent this problem
enzymes are immobilised –
attached or fixed to each
other or an inert material
enzymes
Methods of immobilising
enzymes
Syllabus links
• H.2.2.7 Enzymes (Extended Study)
The Active Site Theory to explain enzyme
function and "specificity". Explanation of
the term "optimum activity“ under specific
conditions as applied to pH range. Heat
denaturation of protein.
• PA: Investigate the effect of heat
denaturation on the activity of one
enzyme.
Induced Fit Model
• Enzyme structure flexible, not rigid
• Enzyme and active site adjust shape to bind
substrate
• Increases range of substrate specificity
• Shape changes also improve catalysis
during reaction
Enzyme Action:
Induced Fit Model
P
S
S
P
E
+
S
ES complex
The induced fit model of enzyme action
E
+
P
Denaturation
• Heat proteins above
40oC (or treat with
certain chemicals or
radiation) they will
gradually loose their
3D shape
• Ability to react with
substrate is lost
• This change in shape
and loss of biological
activity is called
DENATURATION
• Normally permanent
process
The substrate no
longer fits the active
site, so that is not
converted into
product
Learning Check
A. The active site is
(1) the enzyme
(2) a section of the enzyme
(3) the substrate
B. In the induced fit model, the shape of the
enzyme when substrate binds
(1) Stays the same
(2) adapts to the shape of the substrate
Lesson Objectives
By the end of this lesson you will know:
• The nature and role of ATP in the
processes of photosynthesis and
repiration, production of ATP from ADP +
P + Energy
• Nature and role of NADP+ and NAD+in
trapping and transferring electrons and
hydrogen ions in cell activities.
Energy carriers
ATP
+
NADP
+
NAD
Structure of ADP – low energy
molecule
Structure of ATP – high energy
molecule
Phosphorylation of ADP to form
ATP
ADP + energy + P→ ATP + Water
(Condensation reaction)
Hydrolysis of ATP to form ADP
ATP + Water → ADP + Phosphate + energy
(Hydrolysis reaction)
+
NADP
and NADPH
Only involved with photosynthesis
NADP+ + 2 electrons + H+ → NADPH
(low energy)
(high energy)
(high energy)
NADPH → NADP+ + 2 electrons + H+
(high energy)
(low energy)
(high energy)
+
NAD
and NADH
Only involved with respiration
NAD+ + 2 e- + H+ → NADH
NADH → NAD+ + 2 e- + H+
Energy carriers in summary
Energy carriers
Process
Low
energy
Photosynthesis ADP,
NADP+
High
energy
ATP,
NADPH
Respiration
ATP, NADH
ADP,
NAD+
What have you learned?
Do you know….
• The nature and role of ATP in the
processes of photosynthesis and
repiration, production of ATP from ADP +
P + Energy?
• Nature and role of NADP+ and NAD+in
trapping and transferring electrons and
hydrogen ions in cell activities?