Enzymes

What are the advantages of using immobilised enzymes?

Can be recovered for reuse. As the enzyme is fixed it does not get mixed up with the products and is therefore cheaper to separate. Enzymes can tolerate a wider range of conditions. Several enzymes with different pH or temperature optima can be used together. Enzymes can be easily added or removed giving greater control over the reaction.

What are the 2 types of enzyme reactions?

.Reactions where larger molecules are broken down into smaller molecules .Reactions where small molecules build up to form larger more complex molecules.

What happens to enzymes above the optimum?

Above this temperature the increasing vibration of the molecules cause the hydrogen bonds to break and cause a change in the tertiary structure of the enzyme ,This ALTERS THE SHAPE OF THE ACTIVE SITE and the substrate molecule will no longer fit. The enzyme is then said to be denatured. This is a permanent change in the structure.

How does temperature affect affect the rate of reaction?

As temperature increases, there is greater kinetic energy and they move around more quickly, increasing the chance of molecules colliding. Increasing the temperature of an enzyme controlled reaction results in an increase in the rate of reaction. If enzymes are subjected to low temperatures such as freezing the enzyme will be inactivated as the molecule has no kinetic energy . However the change is not permanent and the enzyme can still work if the temperature is raised.

How do environmental conditions such as pH and temperature affect enzymes? (short answer)

Change the 3D structure of enzyme molecules-bonds are broken and and the configuration of the active site is changed?

What is competitive inhibition?

Competitive -where the inhibitor is STRUCTURALLY SIMILAR TO THE SUBSTRATE and competes with the active site of the enzyme I,e the inhibitor has a shape that lets it fit into the active site of the enzyme in place of the substrate. If substrate concentration is increased it will reduce the effect of the inhibitor . This is because the more substrate molecules present the greater the chance of finding active sites, leaving fewer to be occupied by the inhibitor.

Why aren't free enzymes more widly used?

Enzyme instability is one of the key factors that prevent the wider use of 'free' enzymes. Chemicals such as organic solvents ,raised temperatures and pH values outside the norm can denature the enzyme with a consequent loss of activity. Immobilising enzymes with a polymer matrix creates a micro-environment. By allowing processes to occur at higher temperatures than normal means that activity is increased and so production is increased.

What does enzyme + substrate equal?

Enzyme+substrate= enzyme-substrate complex = enzyme + product

What are enzymes and what is their main job?

Enzymes are biological catalysts that speed up the rate of metabolic reactions.

What are some properties of enzymes?

Enzymes are specific -each enzyme will catalyse only one particular reaction (sucrase acts on sugar sucrose) Enzymes are very efficient and have a high turnover number -meaning that they can convert many molecules of substrate per unit time. (e.g. catalase which breaks down waste products hydrogen peroxide in the body and has a turnover number of several million) Chemical reactions need energy to start them off and this is called activation energy. Enzymes lower the activation energy and allow reactions to take place at lower temperatures.

What do enzymes react with?

Enzymes react with another molecule called a substrate .Each enzyme has its own special shape with an area called the active site (specific), onto which the substrate molecules bind . This creates an enzyme-substrate complex.

Order and control are essential if reactions are to not interfere with each other.what are hese features of metabolism made possible by?

Enzymes.

What structure of protein are enzymes?

Held together in tertiary form by hydrogen bonds, disulphide bridges and ionic bonds. This complex 3-D shape gives the enzyme many of its properties.

What are immobilised enzymes?

Immobilised enzymes are enzyme molecules that are fixed ,bound or trapped on an inert matrix such a a gel capsule (alginate beads) .These beads can be packed into glass columns ,substrate can be added to the top of the column and it reacts with the enzyme as it slowly flows down the column. Once set up the column can be used again and again.

Whats a use of immobilised enzyme?

In biosensores.

What does intracellular mean?

Inside the cell.

What does modern interpretation of the lock and key theory suggest?

It suggests that the active site may change in order to select the substrate's shape. This is called the induce fit hypothesis.

What is the job of buffers?

Maintain a constant pH- by "absorbing H+ ions".

How is a biosensor used in blood-sugar detection?

One particular use of a biosensor is the detection of blood sugar in diabetics. Here the biosensor uses an enzyme together with a transducer ,which produces an electrical signal in response to substrate transformation. The strength of the electrical signal may be measured with a suitable meter.

What does extracellular mean?

Outside of the cell.

What is the principle of using biosensors?

That enzymes are specific and are able to select one type of molecule from a mixture even in very low concentrations. A biosensor can be used in the rapid and accurate detection of minute traces of biologically important molecules.

Describe how the chrges in the amino side-chains of the enzyme's active sites are affected by free hydrogen ions ?

The charges on the amino acid side-chains of the enzyme's active sites are affected by free hydrogen ions or hydroxyl ions. In the formation of an enzyme substrate complex the charge on the active site must match those on the substrate .If the active site has too many H+ ions (e.g) the active site and the substrate may both have the same charge and the enzyme will repel the substrate .

Explain in detail how a biosensor is used to detect blood-sugar levels in a diabetic?

The electrode probe which has a specific enzyme immobilised in a membrane ,is placed in the blood sample. If glucose is present it diffuses through the membrane ,produces an enzyme-substrate complex. The reaction produces a small electrical current which is picked up by the electrode(transducer). The current is read by the meter which produces a reading of blood glucose. Steps using a biosensor: blood contains a mixture of different molecules enzyme electrode is placed in blood sample glucose diffuses into immobilised enzyme layer oxygen is taken up the rate of oxygen uptake is proportional to the glucose concentration

What is the relationship as temperature doubles and the rate of the reaction and what is the optimum temperature for enzyme controlled reactions?

The general rule is : the rate of reaction doubles for each 10' C rise in temperature until the optimum is reached. For most enzymes this is 40'C.

What's incompetitive inhibition?

The inhibitor binds to the enzyme at a site away from the active site . This alters the overall shape of the enzyme molecule including the active site,in such a way that the active site can no longer accommodate the substrate. As the substrate and inhibitor molecules attach to different parts of the enzyme, they are not competing for the same sites. The rate of reaction is therefore unaffected by substrate concentration.

How does increasing the amount of enzyme concentration affect the rate of reaction?

The rate of an enzyme catalysed reaction will vary with changes in enzyme concentration . Increasing enzyme concentration will increase the rate of reaction.

How does increasing the substrate concentration affect rate of reaction if amount of enzyme is constant?

The rate of an enzyme catalysed reaction will vary with changes in substrate concentration . If the amount of enzyme is constant the rate of reaction will increase as the substrate increases. But there must come a point when all the enzyme's active sites are working to full capacity I.e all the active sites are filled.

How does pH affect the rate of enzyme controlled reactions?

The rate of an enzyme controlled reaction depends on the pH. Enzymes have a narrow optimum range and small changes in pH affect the rate of reaction without affecting the structure of the enzyme. Small changes outside the optimum can cause reversible changes in enzyme structure and results in inactivation .Extremes of pH can cause denaturing. At extremes of pH the hydrogen bonding is affected and the 3D shape of the enzyme is altered and so is the shape of the active site.

What is enzyme inhibition?

When enzyme action is slowed down or stopped by another substance. The inhibitor combines with the enzyme and stops it forming an enzyme-substrate complex.