Enzyme Action

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  • Created by: Jacqui2
  • Created on: 03-05-17 10:46

Enzymes

Catabolic Reations - Breakdown of substances and release of energy

Anabolic Reactios - Use energy to build up complex molecules

Properties of Enzymes

  • Enzymes are not used up in the reactions that they catalyse
  • They form an enzyme / substrate complex when they combine with their substrates
  • Enzymes may need a cofactor to be present to work
  • An enzymes catalysed reaction can be stopped or slowed down  by inhibitors
  • They are highly specific
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Lock-and-Key Theory

Only the active site comes into contact with the substrate as the active sites shape is  complementary to the substrate

The substrate is the key that fits into the enzyme lock

Additional bonds will be broken, or made, to form the product(s) and they will then be repelled as they no longer fit the active site

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Induced Fit Theory

The active site has a more flexible shape and is able to mould itself around the substrate. It then distorts the substrate molecule, straining or twisting the bonds. The substrate becomes is less stable, has reduced potential energy and the activation energy is lowered

The enzyme returns to its original shape after products move away

(http://study.com/cimages/multimages/16/induced_fit_diagram.svg.png)

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Mark Scheme Answer

  • Enzyme and substrate molecules collide due to their kinetic energy
  • Enzymes, being globular, have a percise 3D structure
  • The substrate molecules fits comlemntary to trhe active site (lock-and-key theory)
  • The enzyme can induce a change in shape to its active site to allow the substrate to fit (induced-fit theory)
  • Activation energy, that's needed at the active site, is lowered
  • This can happen as correct alignment of substrate is ensured and bonding is facilitated during anabolic reactions
  • The products have differnet shapes from the substrate and so leave the active site, which is then free to accept another molecule
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Activation Energy

Heating molecules increases kinetic energy therefore leading to more collisions, increasing the rate of reactions.

The energy needed to start a chemical reaction is called the activation energy - this energy is needed to break existing bonds

Enzymes lower the activation energy needed to make chemical reactions start. The reaction scan take place at lower temperatures - high temperatures can denature the enzyme

By lowering the activation energy, enzymes reduce the input of energy needed to allow reactions to take place at lower temperatures.

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Temperature

Raising the trmperature, makes it more likely that the collisions will result in a reaction taking place.

  • The rate of an enzyme controlled reaction increases with temperature until a point- optimum temperature.
  • The change in rate of a reaction for each 10oC  rise in temp is called the temperature coefficient, Q10

At suboptimal temperatures the Q10 for enzyme catalysed reactions is approx 2 ( the rate doubles for each 10oC   rise in temperature

  • The prate continues to rise until it reaches its optimum temp
  • The rate will fall dramatically if the temperature rises above the optimum and causes hydrogen bonds to break - destroying secondary and tertiary structures
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pH

Most enzymes are only effective in only a narrow pH range

Devitations from the optimum pH causes bonds to be broken (particulary hydrogen and ionic) and cause the enzyme to become denatured

Free hydrogen ions or hydroxyl ions can effect the charges on the amino acid side-chains of the active site

(http://3.bp.blogspot.com/-YikqaMdlN2A/TdzzPh08o9I/AAAAAAAAAAk/Ao2R1N1NhMk/s1600/optimum_conditions.gif)

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Concentration

Enzyme Concentration

The number of substrate molecules one molecule of enzyme can turn into porducts in one minute is called the turnover number

The rate of reaction will be directly proportional to the enzyme concentration if conditions such as pH are suitable and there is excess substrate. If however the substrate is restricted, the it will limit the rate of reaction, even if you add more substrate. Therefore the substrate becomes the limiting factor.

Substrate Concentration

For a given amount of enzyme, the rate of reaction will increase in substrate concentration up to a point. At this stage all the active sites are filled and the enzyme becomes the limiting factor.

(http://www.rsc.org/Education/Teachers/Resources/cfb/images/07D.jpg)

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Cofactors

  • Some enzymes need the presence of another molecule to work
  • Cofactors are non-protein molecules
  • They modify the chemical structure

1. Prosthetic Group

  • Are organic molecules that permanently attach to the enzyme
    • Heam enables a heamoglobin molecule to carry oxygen

2. Coenzyme

  • Are not permanently attached; - help substrates to bond with eachother
  • The enzyme can only function if the coenzyme is present

3. Activators

  • Inorganic metal ions (Mg, Fe, Ca, Zn)
  • Form a temporary attachment to the enzyme and change its active site so that the reaction is more likely to take place
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Reversible Inhibitors

An inhibitros is a substrate that can stop or slow down a reaction

  • The effects of reversible inhibitors are temporary and when it's removed, the enzyme gains its full activity

1. Competitive Inhibitor

  • Have a structure similar to the substrate and therefore competes with the substrate
  • Rate of reaction will decrease as the competitive inhibitors take up the active site

Increasing the concentration of the substrate will reduce the chances for a competitive inhibitor

2. Non - competitive Inhibitors

  • Do not bind to the active site. Attaches to another part of the enzyme
  • This alters the overall shape including the active site

Increasing the amount of substrate will NOT reduce the inhibition

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Enzymes as Biomarkers of Disease - Reversible Inhi

Some enzymes are only present or active during the process of diesase and their presence can be used to diagnose. They are therefore called Biomarkers

1). Elastase (type of protease enzyme)

  • Produced by white blood cells a called Neutrophils, when a respiratory infection is present
  • As a result the elastase hydrolyses elastin, within the lung tissue, reducing lung function and inflammation of the airways
    • Elastase inhibitor, e.g alpha-1 antitrypsin

2). Phosphokinase-2(cpk-2)

  • Produced by injured heart muscle as a result of a heart attack
  • Leaks into the blood from damaged cardiac tissue

3). Esterase

  • White blood cells become trapped in ducts during a urinary track infection and relase enzyme
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Enzymes as Biomarkers of Disease - Reversible Inhi

4). ACE 

  • Converts angiotensin I to angiotensin II
  • Increases blood pressure - Heart Disease
    • ACE inhibiotr

5). Cyclooxygenase

  • Produce prostaglandins which bring about inflammation - Headache/Toothache
    • Paracetamol 
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Non-Reversible Inhibitors

Non-reversible inhibitors alter the enzyme permanently

  • Alter tertiary structure as heavy metal ions such as silver cause the disulphide bonds to break

Uses of enzymes in industrial proceses

1. Batch reactor - the enzyme and substrate are dissloved and mix together in solution. Solution would have to be purified to get enzyme and product

2. Column reactor - substrate, dissolved in solutin, flow past immobilised enzyme using inert support material. This allows continous flow - continous flow column reactor

(http://www.saburchill.com/IBbiology/chapters01/images/040207032.jpg)

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Immobilisation

Advantages:

  • Can be used continously - cost effective
  • No costly, time consuming purificaion is needed
  • Active site is not as easliy distrupted by high temp or pH - prevents distruption in teh tertiary structure

Disadvantages:

  • Slower overall reaction times due to:
    • Active sites may be slightly altered during immobilisation
    • Supporting material may reduce opportunity for substrate molecules to bind with enzymes
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Immobilisation

(http://www.easybiologyclass.com/wp-content/uploads/2015/04/Enzyme-whole-cell-immobilization-methods-easybiologyclass.jpg)

Properties of  material used:

  • Must be inert
  • Must be peremable if entrapment is being used
  • Insouble so that the enzyme can be recovered
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Diagnostic Reagent Strips as Biosensors

Biosensors are immobilised enzymes that work to produce a a colour change or an electrical signal.

  • Clinistix
    • Works using glucose oxidase and an enzyme peroxidase. It cataliseshydrogen peroxide to form glucose + oxygen. The oxygen reacts with the colour dye to change the colour of the *****. The intensity of the colour indicates the intensity of glucose present.
  • Glucose metre
    • Measure the level of glucose in a blood droplet. The amount of gluconic acid produced by glucose oxidase is converted into an electrical signal which is converetd into a digital read out.
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Diagnostic Reagent Strips as Biosensors

Biosensors are immobilised enzymes that work to produce a a colour change or an electrical signal.

  • Clinistix
    • Works using glucose oxidase and an enzyme peroxidase. It cataliseshydrogen peroxide to form glucose + oxygen. The oxygen reacts with the colour dye to change the colour of the *****. The intensity of the colour indicates the intensity of glucose present.
  • Glucose metre
    • Measure the level of glucose in a blood droplet. The amount of gluconic acid produced by glucose oxidase is converted into an electrical signal which is converetd into a digital read out.
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