Enzymes (3)

Question 1

What is an eznyme

Answer 1

Enzymes are globular proteins that catalyse
reactions inside cells (intracellular enzymes) or are secreted to
catalyse reactions outside cells (extracellular enzymes)

Biological catalyst that increases the rate of a reaction and remains unchanged when the reaction is complete

Question 2

What is metabolism

Answer 2

Metabolism is the sum of all chemical reactions that occur in living organisms

Question 3

What are the roles of enzymes in metabolsim

Answer 3

1. The conversion of food molecules to energy to run cellular processes
2. The conversion of food molecules to building blocks for proteins, lipids, nucleic acids and carbohydrates
3. The elimination of nitrogenous wastes

Question 4

What do metabolic reactions do

Answer 4

Allow organisms to grow and reproduce, maintain their structures and respond to their environments.

Question 5

What are anabolic reactions

Answer 5

A part of metabolism -anabolism
1. larger molecules are built up from smaller molecules (condensation)
2. Usually require energy

Question 6

What are catabolic reactions

Answer 6

A part of metabolism - catabolism
1. Larger molecules are broken down into their smaller subunits (hydrolysis)
2. Usually release energy

Question 7

What are chemical reactions of metabolism

Answer 7

Organized into linear metabolic chains or cyclic metabolic pathways.

Question 8

How do chemical reactions occur in nature

Answer 8

1. Do not occur spontaneously
2. If they occur, the rate of reaction is very low

Question 9

What do enzymes allow metabolic reactions to occur

Answer 9

1. Rapidly
2. At a constant rate
3. Under physiological conditions

• At very low concentrations of reacting molecules
• At normal body temperatures - 37
• In an almost neutral aqueous environment in the cells

Question 10

What are intracellular enzymes

Answer 10

Enzymes that catalyze reactions inside cells

Question 11

What are extracellular enzymes

Answer 11

Enzymes that are secreted from cells and catalyze reactions outside cells

Question 12

What is the specificity of enzymes and what is the cause of this

Answer 12

Enzymes have high specificity due to their active sites

The active site

1. Made up of specific amino acids
2. Consists of 2 parts

• Binding region which is made up of amino acids with R groups that form temporary bonds with the substrate and positions it correctly
• A catalytic region which is made up of amino acids with R groups that catalyze the reaction

Question 13

What does the Active Site do

Answer 13

1. Binds to the substrate with hydrogen bonds, hydrophobic interactions or ionic bonds depending on amino acid R groups
2. Has a precise 3D shape that is complementary to the substrate. This 3D shape refers to the chemical properties of the amino acids that make up the active site; they have R groups that can form bonds with the functional groups of one specific substrate only.
3. An enzyme with catalyze only one reaction

Question 14

What is activation energy and what do enzymes

Answer 14

Activation energy is the amount of kinetic energy that is needed to start a chemical reaction. Enzymes lower the activation energy.

Question 15

What is the mode of action for an enzyme

Answer 15

The function of an enzyme primarily depends on its 3D shape. The active site

1. Brings the substrates into physical closeness and the correct orientation for the reaction to take place
2. Depends on all the levels of protein structure, a change at any level due to denaturation will cause reduced or lose of function

Question 16

How are enzymes globular proteins

Answer 16

Non polar hydrophobic R groups point into the centre of the molecule - repelled by the watery surroundings

Polar hydrophillic R groups are located on the outside of the protein molecule - water molecules cluster around the hydrophillic R groups and make the protein soluble.

Question 17

How are each protein structure in the enzyme involved in specificity

Answer 17

1. Primary - Sequence of amino acids determines the amino acids of the active site
2. Secondary - Alpha and Beta pleated sheets place the R groups in the active site in the correct positions to form bonds with the substrate
3. Tertiary - Folding will further orient the R groups in the active site into the appropriate places for bonding to occur with the substrate
4. Quaternary - links between several polypeptide chains alter the overall electrical charge of the enzyme and hence its shape, binding properties and catalytic efficiency

Question 18

What does a chemical reaction need to proceed

Answer 18

The reactant molecules of the system need a kinetic energy equal to or greater than the activation energy and need an input of energy to proceed - increasing temp or pressure

Question 19

What do enzymes do to a chemical reaction

Answer 19

1. Lower the activation energy

• Causes improbable reactions to occur
• Increases the rate of plausible reactions
• Does not change the potential energy of the reactants and the potential energy of the products

Question 20

What happens to an enzyme after use

Answer 20

It is not consumed or altered by the reaction

Question 21

What energy is altered and not by an enzyme in a chemical reaction

Answer 21

Reactant (substrate) energy and the product energy remain the same

Only activation energy is lowered by the enzyme

Question 22

Why do we need enzymes

Answer 22

Chemical reactions in nature are normally too slow to maintain life

Temperatures, pressures or concentrations of reacting molecules cannot be increases inside living cells to levels high enough for metabolic reactions to happen without catalysts

Question 23

What is the lock and key hypothesis

Answer 23

The lock and key hypothesis assumes that the active site is a perfect fit for a specific substance - Once the substrate binds to the active site, no further modifications occur

Question 24

What happens after enzyme and substrate bind in lock and key hypothesis

Answer 24

Form the enzyme-substrate complex, the substrate is rasied in energy to a transition state, equal to or higher than the activation energy of the reaction

• Substrate turns into the product
• Enzyme remains unchanged

Question 25

What is the induced fit hypothesis

Answer 25

The induced fit hypothesis assumes that the active site and substrate are not exactly complementary

Question 26

What is the process of the induced fit hypothesis

Answer 26

1. The arrangement of amino acids in the binding region of the active site matches certain parts of the substrate, allowing bonds and the enzyme - substrate complex to form 2. Active site is flexible and changes shape when the enzyme-substrate complex forms. The shape change in the active site raises the substrate to the transition state, enabling the reaction 3. Amino aids in the catalytic region of the active site place stresses (accepting or donating protons/electrostatic charges) onto the substrate, breaking or forming chemical bonds 4. After the products of the reaction move away from the enzyme, the active site returns to its initial shape

Question 27

How can the rate of an enzyme catalysed reaction be found

Answer 27

The rate can be studied by measuring the rate of substrate disappearance The rate can be studied by measuring the rate of product formation

Question 28

Why is it possible for us to measure rate of an enzyme catalyzed reaction

Answer 28

Enzyme catalysed reactions occur at very high rates so substrates can be converted to products by a given concentration of enzyme

Question 29

How is catalase used in enzyme catalyzed reactions

Answer 29

Catalase is found in tissues of living organisms - Catalyzes the breakdown of hydrogen peroxide into water and oxygen - Hydrogen peroxide is a highly toxic waste product formed in various metabolic reactions The oxygen formed can be collected and measured

Question 30

What is the process of catalase catalyzing hydrogen peroxide

Answer 30

Reaction begins very quickly 1. As soon as they come into contact, many O2 bubbles released - lots of substrate molecules and enzyme will be saturated, meaning that every enzyme molecule has a substrate molecule in the active site. At this point, the rate of reactions depends only on the number of enzyme molecules and their turnover speed - rate at which they convert substrate to product and bind with another As reaction continues, rate will slow down - Less O2 bubbles form and volume of product formed becomes smaller - More substrate is converted into product, there are fewer substrate molecules left - Enzyme is no longer saturated - some enzyme molecules will be waiting for substrate molecules to collide with active site Eventually reaction stops - No more O2 formed - All the substrate molecules have been converted into product and there are no more substrate molecules left

Question 31

What is the start of an enzyme catalyzed reaction called

Answer 31

The rate is called the initial rate of reaction

Question 32

How can a colorimeter be used to measure the progress of enzyme-catalyzed reactions involving color changes

Answer 32

1. Can be used to obtain a quantitative measurement of color intensity in a solution 2. Measures the amount of light that is absorbed by a tube (cuvette) containing a colored liquid. The deeper the color, the more light is absorbed. 3. Measures the concentration of an unknown solution, a colorimeter must be calibrated using standards of known concentration The absorbance readings for the standard solutions of known concentrations can be used to plot a standard curve. The absorbance reading of an unknown concentration can then be used to estimate the concentration of the solution

Question 33

Why use a colorimeter

Answer 33

Sensible suggestion if you are asked how you could improve the reliability of the results collected in an experiment involving color changes or comparisons

Question 34

How do enzyme catalyzed reactions vary with temperature

Answer 34

Low - Slow movement of molecules - Few collisions between substrate molecules and the active site of enzymes - Few enzyme-substrate complexes form since binding between substrate and enzyme are rare events. High - Molecules gain kinetic energy and start to move about with more speed - Enzyme and substrate molecules move faster and collisions happen more often - More enzyme-substrate complexes form as substrate molecules bind more frequently to the active sites - The collision also involves more energy which makes it easier for bonds to be formed or broken so that the reaction can occur Above certain temperature - The enzyme molecules vibrate so forcefully that bonds, especially hydrogen bonds, holding the enzymes in their precise 3D shapes begin to break - The active site loses its shape and the substrate can no longer bind (denaturation) - Since there are less enzyme-substrate complexes being formed, the activity decreases.

Question 35

What are the stages of denaturation of an enzyme due to high temps

Answer 35

Partial denaturation - At first, substrate molecules fit less well into the active sites and the rate of the reaction begins to slow down Complete denaturation - Eventually, the active sites become so distorted that the substrates no longer fit at all

Question 36

What is pre-incubation

Answer 36

Using a pre-heated water bath, the solutions of enzyme and substrate are brought to the same temperature before being mixed together

Question 37

What is the pH and what is the concentration when low

Answer 37

The measure of the concentration of H+ ions in solution The lower the pH, the higher the H+ concentration

Question 38

How does pH affect enzyme catalyzed reactions

Answer 38

Hydrogen ions can interact with the R groups of amino acids and affect their ionisation - the + or - charges of the R groups This will disrupt ionic bonds and cause changes in the 3D tertiary and quaternary structures of the enzymes - the shape of the active site may b altered, decreasing likelihood of substrate binding.

Question 39

Can denaturation by pH be reversed

Answer 39

Denaturation of active site by changes in pH is normally reversible if the change in acidity or alkalinity is not too extreme - if the optimum pH is brought back, the active site might be reformed

Question 40

What does amylase do

Answer 40

Breaks down start into maltose Found in the saliva with a pH of 7

Question 41

What does trypsin do

Answer 41

Trypsin is a protease. Found in the small intestine where the optimum pH is 7.5-8

Question 42

What are buffer solutions

Answer 42

Buffer solutions are used when investigating the effect of pH on enzyme activity - A buffer solutions maintains a particular pH, even if the reaction that takes place produces an acidic or alkaline substance that would otherwise cause pH to change - A measured volume of the buffer solution is added to the reacting mixture

Question 43

What is competitive inhibitor and what does it do

Answer 43

They are molecules that resemble the shape of the substrate The inhibitor is complementary to the active site, reversibly binds to it and blocks it and prevents the substance from entering. The number of available enzymes does not change since not destroyed or altered (the active is site is temporarily blocked) so the maximum rate of reaction will be achieved if the concentration of substrate increases.

Question 44

What are non-competitive inhibitors and what does it do

Answer 44

The inhibitor binds to an allosteric (other) site, causing a conformational change in the active site so the substrate can no longer bind to the active site Non-competitive inhibition can be irreversible or reversible

Question 45

Why are enzymes inhibited

Answer 45

It is essential to cells 1. Control chemical reactions 2. Keep metabolic pathways balanced 3. Keep product formation in equilibrium

Question 46

What is end-product inhibition

Answer 46

The final product of a complex metabolic pathway is used as a competitive or non-competitive inhibitor It will temporarily or permanently slow down the rate of the reaction and decrease the concentration of the product

Question 47

Can denaturation by temperature be reveresed

Answer 47

Denaturation by temperature is irreversible

Question 48

What is the temperature coefficient Q10 of a reaction

Answer 48

The rate of reaction approximately doubles for evert 10 degrees increase in temperature - temperature coefficient of a chemical reaction

Question 49

What is the optimum temperature?

Answer 49

The temperature at which an enzyme catalyzes a reaction at the maximum rate.

Question 50

How does substrate concentration and enzyme activity work

Answer 50

Initially, rates of reaction low as concentration of substrate low Increasing substrate concentration increases rate of reaction as more enzyme-substrate complex formed At the optimum concentration of substrate molecules, all active sites are full and working at maximum efficiency. Any increase in concentration beyond this point will have no extra effect as no free active sites

Question 51

How does enzyme concentration and enzyme activity work

Answer 51

The reaction rate increases with increased enzyme concentrations - more available active sites that can react with the substrate molecules Scenario requires a large excess of substrate where an enzyme is present in low concentrations and substrate in high concentrations

Question 52

What is Vmax

Answer 52

The theoretical maximum rate of the reaction All active sites are occupied by a substrate molecule, the enzyme is saturated with substrate

Question 53

What is the Michaelis-Menten constant Km

Answer 53

Km is the substrate concentration at which the enzyme works at half its maximum rate 50% of the enzyme's active sites are occupied by substrate and the enzyme is said to be at 50% saturation It is a measure of the affinity of an enzyme for its substrate - Low Km means high affinity since the reaction will quickly proceed to Vmax. High Km values mean low affinity, the reaction needs more time to reach Vmax

Question 54

How do Vm and Km compare the efficiency of different enzymes

Answer 54

Vmax gives information about the maximum rate of reaction that is possible Km gives information about the affinity of the enzyme for the substrate, the higher the affinity, the more easily a substrate molecule binds to the active site and the product forms

Question 55

What are immobilized enzymes

Answer 55

Enzymes fixed to alginate beads

Question 56

Benefits of using immobilized enzymes to produce lactose free milk

Answer 56

Enzymes can be re-used More resistant to denaturation from pH changes and high temperatures since the enzymes are held firmly in shape and the fixation in the alginate beads also minimizes exposure of the enzymes to changes in pH and temperature No enzymes in the milk produced - No contamination