Chapter 15 Part 2 Factors and Cofactors

8/17/2019 Chapter 15 Part 2 Factors and Cofactors

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Chapter 15

Biocatalysis (Part 2)


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Chapter review…

biocatalysisbiocatalysis

roperties and

mechanisms of

actions

roperties

of enzymes

Mechanism

of enzyme

action

Activation

energy

Models

Lock

and key

2 hypotheses

Induced

fit

Cofactors

Types &

f(x) of

cofactors

Inhibition

reversible irreversible

Competitive Non

competitive

Factors

affecting

enzymatic

reaction

Classification


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LEARNING OUTCOMES

• Explain factors that affect the enzymatic

reaction.


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Factors affecting the rate of enzymereactions

Enzyme Concentration

Substrate Concentration

Temperature

pH

Cofactors


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Rate of reaction is proportional to the enzymeconcentration (pH and temperature kept

constant)

The rate of reaction .... by increasing theenzyme concentration

Enzyme Concentration


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[Enzyme]

• At low concentration of enzymedecreases , rate of reaction increases.

• As enzyme concentration increases,

more active sites available forsubstrate to bind.• Rate of reaction keeps increasing if the

substrate is in excess•

If amount of substrate is limited, rateof reaction reaches its max


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Substrate Concentration

The rate of enzyme reaction …… with increasingsubstrate concentration

Any further increase in substrate concentration

- no significant change in rate of reaction.

At high substrate concentration, all the activesites are fully occupied by substrate molecules.

Any extra substrate molecules will have to wait

for the ES complex to release the product andbecome available again.

What is the rate of reaction now?


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•• At low [substrate], the rate of enzyme reactionAt low [substrate], the rate of enzyme reaction

increase as [substrateincrease as [substrate]] ……....

•• There areThere are moremore enzyme molecules comparedenzyme molecules compared

substrates, not all active sites aresubstrates, not all active sites are occupied.occupied.


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Figure : Effect of

temperature on therate of enzyme

–controlled reaction.

TemperatureTemperature

Optimum temperature -temperature that promotesmax. rate of reaction

At low temp, rate ofreaction is very lowmolecules move slowly,decreasing chances of

substrate molecules tocollide with enzymemolecules at active sites.


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Figure : Effect of

temperature on the rate

of and enzyme –controlledreaction.

as temperature increases,the kinetic Energy ofenzyme & substrateincreases, molecules movefaster, more effective

collision occur betweensubstrate & active site ofenzyme

More ES complexesform.

Rate of reactionincreases


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For every 100C rise in temperature, the

rate of reaction is doubled

until it reaches optimum temperature

at which the rate of reaction reaches itsmaximum

beyond the optimum temperature, therate of reaction decrease drastically

due to denaturation of enzyme


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• High temperature causes the weak bonds such as ionic/

H/ van der Waals/ hydrophobic interaction to break.

• Change the conformation of active sites

• Substrates can no longer bind to the active sites of the

enzyme


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Figure : Effect of temperature on the rate of and

enzyme –controlled reaction.


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pH

Every enzyme functions most effective/efficient over a NARROW pH range.

Optimum pH – max. rate of reaction

Changes in pH above/ below optimum pH change H+ concentration alter ionic charges of functional/ sidechain/ acidic & basic groups of amino acids in the enzyme

Ionic & Hydrogen bonds that hold specific 3D shape ofenzyme disrupted change conformation of active sites substrate cannot fit into active site to form ES Complex

different enzymes have different optimum pH values


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• The rate of reaction decreases quickly

• If the changes in pH is too high or too low, active

sites are distorted causing enzyme to denature

• Rate of reaction decreases drastically


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Optimum pH values for someenzymes

Enzyme Optimum pH

Pepsin 2.00

Sucrase 4.50

Enterokinase 5.50

Salivary Amylase 4.80

Catalase 7.60

Trypsin 8.00


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COFACTORS

LEARNING OUTCOME:

Define the meaning of cofactors

Explain the types and functions ofthree cofactors: metal ions,coenzymes, and prosthetic groups.


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Chapter review…

biocatalysisbiocatalysis

roperties and

mechanisms of

actions

roperties

of enzymes

Mechanism

of enzyme

action

Activation

energy

Models

Lock

and key

2 hypotheses

Induced

fit

Cofactors

Types &

f(x) of

cofactors

Inhibition

reversible irreversible

Competitive Non-

competitive

Factors

affecting

enzymatic

reaction

Classification


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Cofactors Non-protein substance (organic/inorganic

ions) essential for some enzymes tofunction efficiently.

may be bound tightly to the active site as permanent

residents.

loosely & reversibly along with the substrate.


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Three types of cofactors

Metal ions(activators)

Coenzymes

Prosthetic group

Cofactors


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BASIC TERMS

• Apoenzyme – the enzyme alone• Holoenzyme – enzyme + cofactor


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Metal ions

Inorganic substances, mostly trace elements(micronutrients) - required in very smallamounts

Bound tightly & temporarily to the enzyme/substrate & change its active site/ shape

Easier for substrate molecules to fit intoactive site/ assist in the formation ESC

Increase the rate of reaction May also bind the enzyme & substrate

together


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Examples of metal ion/ mineral

cofactors

Salivary amylase requires the presence of(Cl-) ions before efficiently convert starch

maltose.

The enzyme thrombokinase, which convertsprothrombin into thrombin during bloodclotting, is activated by calcium (Ca2+) ions.


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Action of metal cofactors. In this cartoon an enzyme is unable

to become functionally formed unless a metal ion is available.

Once the metal is bound the active site forms and the enzyme

is ready to carry out its function.


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Coenzymes

organic non-protein molecule bind loosely & temporarily to the enzyme.

many coenzymes are derived from vitaminsespecially vitamin B.

Vitamin K is found in alfalfa,

fish livers, leafy/green

vegetables, egg yolks, andsoybean oil. It is a

coenzyme that helps in

blood clotting.


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NAD+ acts as a coenzyme todehydrogenases by acting as an

electron & hydrogen acceptor.

Glyceraldehyde-3-phosphate

1,3-diphosphoglycerate

dehydrogenase

NAD+NADH + H+


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Coenzymes

Vitamin Vitamin CoenzymesCoenzymes

Niacin (Vit B3)Niacin (Vit B3) NADNAD++

Panthothenic acidPanthothenic acid

(Vit B5)(Vit B5)Coenzyme A (coA)Coenzyme A (coA)

Coenzymes, consists of small organic molecules, many of

which are derived from vitamins. Hence, vitamins are often

precursors to coenzymes.


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Structure of FADnitrogens 1 & 5 carry hydrogen atoms in FADH2


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Prosthetic groups

organic non-protein molecules

Binds tightly and permanently to theenzyme a part of the enzyme.

As carriers & transfer grps of atoms/electrons from 1 molecule to another

Example:Example: haemhaem.. a ring- shaped organic molecule with

iron at its center


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cofactorcofactor

Summary

3 types3 types

(metal ions)(metal ions)

ProstheticProsthetic

groupgroup

coenzymescoenzymes

Chapter 15 Part 2 Factors and Cofactors

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Transcript of Chapter 15 Part 2 Factors and Cofactors