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8/7/2019 BIOLOGY F4 C4 4.2 Enzyme
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Scientists aregreat people straightens
the ? to become !-- Anonymous
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4.5 Enzymes
Lesson Review
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Role of Enzyme in Organisms
Enzymes are biological catalysts that regulate
almost all the cellular reaction they speed
up biochemical reactions in the cells
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General Characteristics of Enzymes
Enzymes are proteins synthesised by living
organisms
In enzymatic reactions, enzymes bind to theirsubstrates and convert them to product
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enzyme
Substrate products
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General Characteristics of Enzymes
Enzymes speed up the rates of chemical
reactions, but remain unchanged at the end
of the reactions.
They are not destroyed by the reactions they
catalyse.
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General Characteristics of Enzymes
Enzymes have
specific sites called
active sites tobind to specificsubstrates thats
why enzymes are
highly specific
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General Characteristics of Enzymes
Each enzyme can
only catalyse one
kind of substrate Amylase starch
molecule can fit in
Sucrase starchmolecule cannot fit
in
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General Characteristics of Enzymes
Enzymes are needed in small quantities
Reason: they are not used up but released at
the end of reaction
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General Characteristics of Enzymes
Most enzyme-catalysed reactions are reversible
or
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Naming of Enzymes
Most enzymes have a name derived by adding
the suffix ase at the end of the name of their
substrates
Eg: Enzyme for hydrolisis of lactose is lactase
Eg: Sucrose: sucrase
Eg: Lipid: lipase
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Naming of Enzymes
Then pepsin? Trypsin? Rennin?
They were named before this systematic way
naming enzymes was formed
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Naming of Enzymes
Then pepsin? Trypsin? Rennin?
They were named before this systematic way
naming enzymes was formed
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Sites of Enzyme Synthesis
Enzymes are proteins
So RIBOSOMES are
also the sites ofenzyme synthesis
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2Types of Enzyme
INTRACELLULARENZYMES Enzymes synthesised and
retained in the cell for the
use of the cell itself
They are found in: Cytoplasm
Nuclues
Mitochondria
Chloroplast
EXTRACELLULARENZYMES Enzymes synthesised in the
cell, but secreted from the
cell to work externally
Example: Digestive enzymes produced
by the pancreas, transported
to duodenum
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Production of Extracellular Enzyme
Protein produced in ribosomes
Spaces between Endoplasmic Reticulum(ER)
Wrapped in vesicles. Bud off
Fuse withG
olgi apparatus.
Maybemodified here. Bud off
Fuse with plasma membrane, releasingout as Enzymes
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The Mechanism of Enzyme Action: TheThe Mechanism of Enzyme Action: The
LOCK AND KEY HypothesisLOCK AND KEY Hypothesis
Enzyme + Substrate Enzyme-substrate
Complex
Enzyme + Product
ACTIVESITEACTIVESITE
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The Mechanism of Enzyme Action: TheThe Mechanism of Enzyme Action: The
LOCK AND KEY HypothesisLOCK AND KEY Hypothesis
Enzyme + Substrate
Substrate: KEY
Enzyme: LOCK
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Review
Enzymes have
specific sites called
active sites tobind to specificsubstrates thats
why enzymes are
highly specific
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CAN WESTOP ENZYMES???
Question:
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YES!
Answer:
Thats why we have activators &
inhibitors. Factors taking place also
includes:(i) Temperature
(ii) pH
(iii) Substrate concentration(iv) Enzyme concentration
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CONT
ROLLING
ENZ
YMES
Yes!! We can do it~
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Faster!! Faster!!!
Helper molecules
called COFACTORS
Inorganic, eg:
Ferum
Copper
Organic cofactor, eg:
B vitamins
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Slowing it down.../STOP!!
INHIBITORS
They often bondto the protein,changing the
overall shape ofthe enzyme
Remember, whenthe shapechanges, the
enzyme will notwork the sameway
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Slowing it down./STOP!!
INHIBITORS
Example: heavy metals such as lead (Pb) and
mercury (Hg)
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TEMPERATURE
Factor 1
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Factor 1: Temperature
Low Temperature
Enzyme-catalysed reaction takes place slowly
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Factor 1: Temperature
As the temperature increases
The movement of substrate molecules increases
The rapid movements of the substrate molecules
increase their chance of colliding with one
another and with the active sites of the enzyme
molecule
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Factor 1: Temperature
This is only true up to OPTIMUM TEMPERATURE
O.T.: Temperature at which an enzyme catalyses a
reaction at the maximum rate
Most human enzyme ~37oC, plant ~ 25oC
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Factor 1: Temperature
High temperature
No increase in rate of reaction
Reason: Bonds that hold enzyme molecules
together begin to break at high T, changing the 3D
shape of enzyme, eventually destroying their
active sites.
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Factor 1: Temperature
High temperature
The enzyme lose their activities and are said to be
DENATURED!!
Denaturation is IRREVERSIBLE!
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Factor 1: Temperature
Optimal functioning of enzyme: 37oC
Most organisms cannot survive at
temperature above40o
C
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Graph: The effects of temperature on theGraph: The effects of temperature on the
rate of an enzymerate of an enzyme--catalysedcatalysed reactionreaction
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pH
Factor 2
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Factor 2: pH
Enzymes are sensitive to thechanges of pH in theirsurroundings.
A change in pH can alter thecharges on the active sites ofthe E and the S surfaces
This can reduce the ability ofboth molecules to bind each
other.
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Graph: The Optimum pH of Some EnzymesGraph: The Optimum pH of Some Enzymes
Pepsin stomach (acidic condition, pH2)
Trypsin duodenum (alkaline condition, pH8.5)
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Factor: pH
Effects of pH on enzymes
are normally reversible
pH in environment back
to optimum level, ionic
charges on the active
sites are restored
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Factor 3: Substrate Concentration
[substrate] , the more substrate molecules
are available to bind the active sites of the
enzymes => more products will be produced
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Factor 3: Substrate Concentration
Reason: More chances of collisions between
substrate molecules and the enzyme molecules
for a catalytic reaction to take place.
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Factor 3: Substrate Concentration
Limiting factor: [ENZYME].
Must have enough enzyme molecules to
catalyse the additional substrate molecules
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Factor 3: Substrate Concentration
Thus, the rate of
reaction is directly
proportional to the
[substrate] until thereaction reaches the
maximum rate
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Factor 3: Substrate Concentration
After maximum rate: all active sites of theenzymes molecules are filled and engaged incatalysis.The enzyme is said to be satured.
So what to do? [enzyme]
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ENZYMECONCENTRATION
Factor 4
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Factor 4: Enzyme Concentration
[Enzyme] , more enzyme molecules available.
So, more active sites are made available for
the catalytic reaction.
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Factor 4: Enzyme Concentration
Limiting factor: [substrate molecule]
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Graph: The Relationship between theGraph: The Relationship between the
rate of reaction and enzyme concentrationrate of reaction and enzyme concentration
Reaction rateReaction rate direct proportionaldirect proportional to [enzyme],to [enzyme],
until a maximum rate is achieveduntil a maximum rate is achieved
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Homework
Worksheet. Draw out all 4 graphs for Factors
Effecting Enzyme Activity
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Next class
Quiz
The uses of enzyme very important!!
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Science-Technology-Society
Raw fruits with enzymes
http://www.healingdaily.com/detoxification-
diet/enzymes.htm
Garbage enzymes
Making your own enzyme juice? Eg:
dragonfruit enzyme, papaya enzyme?
Enzyme found in your washing powder
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References
http://www.chem4kids.com/files/bio_enzyme
s.html