enzymes

substrate concentration

is proportional to rate of reaction until there are more substrates than enzymes present. Curve becomes constant.

Enzyme is not used up in the reaction (unlike substrates)

thus is reusable

pH

This graph shows the effect of ______ on the rate of enzyme action.

Catalyst

A chemical which speeds up the rate of a reaction

a pH of 9

At what pH does trypsin work best?

enzyme concentration

is proportional to rate of reaction, provided other conditions are constant. Straight line

In many cases, the final product of a Metabolic Pathway acts as a Non-competitive Inhibitor to one of the enzymes earlier along the chain. This means that the Metabolic Process controls itself, since the more product gets produced, the more it inhibits the pathway, and so the slower the process proceeds

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Following the course of an enzyme-catalysed reaction

Measurement of the rate of formation of the product or the rate of disappearance of the substrate.

Several different organisms produce lactase enzymes to hydrolyse lactose. The different enzymes have different molecular sizes. Which description of these different lactases is correct? A Their active sites have the same shape. B Their primary structure is the same. C They each contain the same number of amino acids. D They have exactly the same three-dimensional structure.

A Their active sites have the same shape

Lock-and-key model of enzyme action

A key fits a specific lock like an enzyme fits specific substrates. Enzymes catalyze the reaction of specific substrates.

Catalyst

A molecule that speeds up a chemical reaction but is not changed by the reaction.

Noncompetitive inhibitor

A non-substrate inhibitor binds to an allosteric site of an enzyme, causing a conformational change in the enzyme and altering the active site shape, which indirectly inhibits the substrate from accessing the active site

Competitive inhibitor

A non-substrate inhibitor that is a similar shape of the substrate becomes associated with the active site of the enzyme, directly blocking the substrate from accessing the active site.

Enzyme

A protein molecule that functions as an organic catalyst.

Enzyme

A protein which can either build up (catabolize) or break down (metabolize) a substrate, while the enzyme itself remains unchanged

Coenzyme

A substance (usually vitamins or minerals) which are needed to for an enzyme to function

Changes in pH

Affect attraction between substrate and enzyme and therefore efficiency of conversion process Ionic bonds can break and change shape / enzyme is denatured Charges on amino acids can change, ES complex cannot form Optimum pH pH 7 for intracellular enzymes Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin) Alkaline range (pH 8-14) in oral cavities (amylase) pH measures the conc. of H+ ions - higher conc. will give a lower pH

Which tests, carried out on samples taken at intervals during the course of the reaction below, would enable the progress of the reaction to be followed? 1 Benedict's test 2 biuret test 3 emulsion test 4 iodine in potassium iodide solution test A 1 or 2 B 1 or 4 C 2 or 3 D 3 or 4

B 1 or 4

These statements are about enzyme inhibitors. 1 binds reversibly to an enzyme 2 binds to a site on the enzyme different from the active site 3 has a structural similarity to the enzyme's normal substrate 4 can be displaced from the enzyme by a high concentration of the enzyme's normal substrate Which statements describe a competitive inhibitor? A 1, 2, 3 and 4 B 1, 3 and 4 only C 2 and 3 only D 3 and 4 only

B 1, 3 and 4 only

Which of the following describes the effects of temperature on an enzyme-controlled reaction? A At low temperatures, substrate molecules only rarely collide with an enzyme's active site. B At low temperatures, the enzyme loses its shape and activity. C At low temperatures, the enzyme becomes denatured. D As the temperature increases, the number of collisions between enzyme and substrate decrease.

At low temperatures, substrate molecules only rarely collide with an enzyme's active site.

a pH of 5.5

At what pH is there some enzyme activity for both pepsin and trypsin?

Fibrous protein from dead cells is difficult to remove from contact lenses. Some cleaning solutions contain an enzyme to digest this protein to soluble products. What describes the enzyme and its activity? A An active site on a fibrous protein binds to the enzyme and is hydrolysed. B An active site on a soluble product binds to the enzyme and is digested. C An active site on a globular protein binds to a soluble product and digests it. D An active site on a globular protein binds to a fibrous protein and hydrolyses it.

An active site on a globular protein binds to a fibrous protein and hydrolyses it.

Activation Energy

An enzyme speeds up a chemical reaction by lowering the _______.

If it is the limiting factor, increasing concentration will increase the rate of reaction up to a point, after which any increase will not affect the rate of reaction. This is because it will no longer be the limiting factor and another factor will be limiting the maximum rate of reaction

As a reaction proceeds, the rate of reaction will decrease, since the Substrate will get used up. The highest rate of reaction, known as the Initial Reaction Rate is the maximum reaction rate for an enzyme in an experimental situation

However, increasing temperature also increases the Vibrational Energy that molecules have, specifically in this case enzyme molecules, which puts strain on the bonds that hold them together.

As temperature increases, more bonds, especially the weaker Hydrogen and Ionic bonds, will break as a result of this strain. Breaking bonds within the enzyme will cause the Active Site to change shape.

Which statement does not describe the effect on an enzyme's activity of changing the pH. A A pH that is very different from the enzyme's optimum pH can denature the enzyme. B At low pH there are fewer hydrogen ions to interact with the R groups of the amino acids that make up the enzyme. C Changing the pH alters the interactions of the amino acids that make up the enzyme. D Changing the pH alters the enzyme's three-dimensional shape.

At low pH there are fewer hydrogen ions to interact with the R groups of the amino acids that make up the enzyme.

Hydrolysis

Breaking apart a larger molecule into two smaller molecules. Requires a water molecule.

Active site

The portion of the enzyme in which the substrate is loosely associated

Induced fit theory

Enzyme's shape changes when substrate binds to active site Amino acids are moulded into a precise form to perform catalytic reaction effectively Enzyme wraps around substrate to distort it Forms an enzyme-substrate complex → fast reaction E + S → ES → P + E

Enzymes - active site, activation energy, enzyme specificity

Enzymes are globular proteins that serve as biological catalysts. They speed up or slow down metabolic reaction, but remain unchanged. They may facilitate the breaking of an existing bond or the formation of a new bond.

Changing the Enzyme and Substrate concentrations affect the rate of reaction of an enzyme-catalysed reaction. Controlling these factors in a cell is one way that an organism regulates its enzyme activity and so its Metabolism.

Changing the concentration of a substance only affects the rate of reaction if it is the limiting factor: that is, it the factor that is stopping a reaction from preceding at a higher rate.

Non-competitive Inhibitors

Chemical does not have to resemble the substrate Binds to enzyme other than at active site This changes the enzyme's active site and prevents access to it

Irreversible Inhibition

Chemical permanently binds to the enzyme or massively denatures the enzyme Nerve gas permanently blocks pathways involved in nerve message transmission, resulting in death Penicillin, the first of "wonder drug" antibiotics, permanently blocks pathways certain bacteria use to assemble their cell wall component (peptidoglycan)

Competitive Inhibitors

Compete with substrate for active site Shape similar to substrates / prevents access when bonded Can slow down a metabolic pathway

Enzyme Inhibitors reduce the rate of an enzyme catalysed reaction by interfering with the enzyme in some way. This effect may be permanent or temporary.

Competitive Enzyme Inhibitors work by preventing the formation of Enzyme-Substrate Complexes because they have a similar shape to the substrate molecule.

This means that they fit into the Active Site, but remain unreacted since they have a different structure to the substrate. Therefore less substrate molecules can bind to the enzymes so the reaction rate is decreased.

Competitive Inhibition is usually temporary, and the Inhibitor eventually leaves the enzyme. This means that the level of inhibition depends on the relative concentrations of substrate and Inhibitor, since they are competing for places in enzyme Active Sites

Decreased Temperature

Enzymes become less and less active, due to reductions in speed of molecular movement Below freezing point Inactivated, not denatured Regain their function when returning to normal temperature Thermophilic: heat-loving Hyperthermophilic: organisms are not able to grow below +70°C Psychrophiles: cold-loving

Many Non-competitive Inhibitors are irreversible and permanent, and effectively denature the enzymes which they inhibit. However, there are a lot of non-permanent and reversible Non-competitive Inhibitors which are vital in controlling Metabolic functions in organisms.

Enzyme Inhibitors by organisms are used in controlling metabolic reactions. This allows product to be produced in very specific amounts.

Small changes in pH above or below the Optimum do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to Denature and permanently lose their function.

Enzymes in different locations have different Optimum pH values since their environmental conditions may be different. For example, the enzyme Pepsin functions best at around pH2 and is found in the stomach, which contains Hydrochloric Acid (pH2).

This change in shape means that the Active Site is less Complementary to the shape of the Substrate, so that it is less likely to catalyse the reaction.

Eventually, the enzyme will become Denatured and will no longer function.

Many poisons work by inhibiting the action of enzymes involved in Metabolic processes, which disturbs an organism.

For example, Potassium Cyanide is an irreversible Inhibitor of the enzyme Cytochrome C Oxidase, which takes part in respiration reactions in cells. If this enzyme is inhibited, ATP cannot be made since Oxygen use is decreased. This means that cells can only respire Anaerobically, leading to a build up of Lactic Acid in the blood. This is potentially fatal.The poison Malonate binds to the Active Site of the enzyme Succinate Dehydrogenase competing with Succinate, which is important in respiration.

Enzymes vastly increase the rate of a metabolic reaction, often by a factor of 10 million. This fact is essential to all life on earth, but it means that Enzyme activity must be very tightly controlled, since uncontrolled reactions can be fatal.

For example, in the disease 'multiple sclerosis', the immune system starts destroying nerves by allowing destructive Enzymes to attack nerve cells, often resulting in paralysis.

Some Enzyme Inhibitors can be used as Medicines in the treatment of conditions.

For example, infection by viruses can be treated by Inhibitors to the viral enzyme Protease, often competitive Inhibitors. This means that viruses cannot build new protein coats and therefore cannot replicate.Penicillin works by Inhibiting a bacterial enzyme that is responsible for forming cross-links in bacteria cell walls. This therefore halts reproduction.

Acid solutions have pH values below 7, and Basic solutions (alkalis are bases) have pH values above 7. Deionised water is pH7, which is termed 'neutral

H+ and OH- Ions are charged and therefore interfere with Hydrogen and Ionic bonds that hold together an enzyme, since they will be attracted or repelled by the charges created by the bonds. This interference causes a change in shape of the enzyme, and importantly, its Active Site.

Increasing Substrate Concentration increases the rate of reaction. This is because more substrate molecules will be colliding with enzyme molecules, so more product will be formed.

However, after a certain concentration, any increase will have no effect on the rate of reaction, since Substrate Concentration will no longer be the limiting factor. The enzymes will effectively become saturated, and will be working at their maximum possible rate.

Increasing Enzyme Concentration will increase the rate of reaction, as more enzymes will be colliding with substrate molecules

However, this too will only have an effect up to a certain concentration, where the Enzyme Concentration is no longer the limiting factor.

Activation energy B

In an enzyme controlled reaction which activation energy is needed to allow the reactants to be converted into products?

The activity of an Enzyme is affected by its environmental conditions. Changing these alter the rate of reaction caused by the enzyme.

In nature, organisms adjust the conditions of their enzymes to produce an Optimum rate of reaction, where necessary, or they may have enzymes which are adapted to function well in extreme conditions where they live.

As temperature increases, more enzymes' molecules' Active Sites' shapes will be less Complementary to the shape of their Substrate, and more enzymes will be Denatured. This will decrease the rate of reaction

In summary, as temperature increases, initially the rate of reaction will increase, because of increased Kinetic Energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.

Increased Temperature

Increases speed of molecular movement → chances of molecular collisions → more ES complexes At 0-42 °C rate of reaction is proportional to temp Enzymes have optimum temp. for their action (varies between different enzymes) Above ≈42°C, enzyme is denatured due to heavy vibration that break -H bonds Shape is changed / active site can't be used anymore

pH measures the Acidity and Basicity of a solution. It is a measure of the Hydrogen Ion (H+) concentration, and therefore a good indicator of the Hydroxide Ion (OH-) concentration. It ranges from pH1 to pH14

Lower pH values mean higher H+ concentrations and lower OH- concentrations.

End-product inhibition

Metabolic reactions are multi-stepped, each controlled by a single enzyme End-products accumulate within the cell and stop the reaction when sufficient product is made This is achieved by non-competitive inhibition by the end-product The enzyme early in the reaction pathway is inhibited by the end-product The metabolic pathway contains a series of individual chemical reactions that combine to perform one or more important functions. The product of one reaction in a pathway serves as the substrate for the following reaction.

Michaelis - Menten Equation and Immobilising an enzyme

Michaelis-Menten equation describes the velocity of enzymatic reactions (v) by relating it to [S] - concentration of a substrate S.

The temperature at which the maximum rate of reaction occurs is called the enzyme's

Optimum Temperature. This is different for different enzymes. Most enzymes in the human body have an Optimum Temperature of around 37.0 °C.

Dehydration Synthesis

Putting together smaller molecules to make a larger molecule by removing a water molecule.

Enzymes are catalysts→ speed up chemical reactions

Reduce activation energy required to start a reaction between molecules Substrates (reactants) are converted into products Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action) Enzymes catalyse a reaction at max. rate at an optimum state

Increasing temperature increases the Kinetic Energy that molecules possess. In a fluid, this means that there are more random collisions between molecules per unit time

Since enzymes catalyse reactions by randomly colliding with Substrate molecules, increasing temperature increases the rate of reaction, forming more product.

Inhibitors

Slow down rate of reaction of enzyme when necessary (e.g. when temp is too high) Molecule present in highest conc. is most likely to form an ES-complex

Activation Energy

The amount of energy required to start a reaction

Enzyme-Substrate Complex

The complex created when the enzyme and substrate are loosely associated in an induced fit

enzyme concentration, substrate concentration, temperature and pH

The four factors that affect enzyme action.

enzyme concentration

The graph shows the effect of ______ on the rate of enzyme action.

substrate concentration

The graph shows the effect of ______ on the rate of enzyme action.

Substrates

The molecules that interact with a specific enzyme at the active site and are converted into products.

Active Site

The part of an enzyme that has a specific shape that fits a specific substrate. The part of an enzyme where the substrate binds to the enzyme forming the enzyme-substrate complex.

Allosteric site

The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active

Substrate

The substance, which fits into the active site of an enzyme, and is acted upon by the enzyme

Factors affecting the rate of enzyme-catalysed reactions

These factors are: - Temperature - pH - Enzyme concentration - Substrate concentration - Inhibitor concentration

Temperature

This graph shows the effect of ______ on enzymes.

Different enzymes have different Optimum pH values.

This is the pH value at which the bonds within them are influenced by H+ and OH- Ions in such a way that the shape of their Active Site is the most Complementary to the shape of their Substrate. At the Optimum pH, the rate of reaction is at an optimum.

Denature

Treating an enzyme with chemical or physical means that alters the shape of the enzyme to the point where it cannot function, such as by altering the pH or temperature

Non-competitive Enzyme Inhibitors work not by preventing the formation of Enzyme-Substrate Complexes, but by preventing the formation of Enzyme-Product Complexes. So they prevent the substrate from reacting to form product.

Usually, Non-competitive Inhibitors bind to a site other than the Active Site, called an Allosteric Site. Doing so distorts the 3D Tertiary structure of the enzyme, such that it can no longer catalyse a reaction

The shape

What determines the function of an enzyme?

a pH of 2.5

What is the optimum pH for pepsin?

36 degrees celsius

What is the optimum temperature in this graph?

As enzyme concentration increases the rate of reaction increases and then levels off.

What is the relationship show in this graph?

As substrate concentration increases the rate of reaction increases and then levels off.

What is the relationship show in this graph?

Proteins

What type of organic molecule are enzymes?

Denatured

When an enzyme loses its shape it is said to have become _____________.

Enzyme-substrate complex

When the substrate is interacting with the enzyme at the active site and is in the process of being converted into products.

1 Which of the following describes an enzyme? A) a catalyst with an active site which binds to the product of a reaction B) a fibrous protein with an active site which binds to a substrate C) a globular protein with hydrophilic groups on its surface D) an insoluble biological catalyst

c) a globular protein with hydrophilic groups on its surface