Enzymes Part 2

Question 1

The increase in reaction rate with a 10 degrees Celsius rise in temperature.

Answer 1

Q10 (the temperature coefficient)

Question 2

For the chemical reactions, the Q10 is 2 to 3

Answer 2

(the rate of the reaction doubles or triples with every 10 degrees Celsius rise in temperature).

Question 3

Follow this rule as they are chemical reactions.

Answer 3

Enzyme-controlled reactions

Question 4

The optimum temperature for an enzyme-controlled reaction will be a balance _______.

Answer 4

between Q10 and denaturation (beyond the optimum temperature).

Question 5

For most enzymes (outside the human body), the optimum temperature is about ___________.

Answer 5

30 degrees Celsius.

Question 6

*Many are a lot lower, cold fish will die at ______________.

Answer 6

30 degrees Celsius because their enzymes denature

Question 7

A few bacteria have enzymes that can withstand _______________.

Answer 7

Very high temperatures up to 100 degrees Celsius.

Question 8

Most enzymes however are fully denatured at __________.

Answer 8

70 degrees Celsius.

Question 9

Each enzyme has an ________.

Answer 9

optimal pH or pH range (where the enzyme has maximal activity).

Question 10

Requirements for the catalytic groups in the active site in________________ is a common reason for this phenomenon.

Answer 10

appropriate ionization state

Question 11

The pH optimum varies for different enzymes, most enzymes are ____.

Answer 11

neutral pH (6- 8).

Question 12

Effects of pH to Enzyme

Answer 12

1. Variations in pH can affect a particular enzyme in many ways, especially if ionizable amino acid side chains are involved in binding of the substrate and/or catalysis.
2. Extremes of pH can also lead to denaturation of an enzyme if the ionization state of amino acids critical to correct folding are altered.
3. The effects of pH and temperature will vary for different enzymes and must be determined experimentally.

Question 13

Typically human enzymes (6-8) and depends on where in body, pepsin (stomach) is 3 and trypsin (small intestines) is 8

Answer 13

Changes in pH changes protein shape

Question 14

Enzymes are most active at _______.

Answer 14

Optimum pH

Question 15

With acidic or basic side chains have the proper charges when the pH is optimum.

Answer 15

Amino acids

Question 16

Activity is lost at low or high pH as tertiary structure is disrupted.

Answer 16

1.Extreme pH levels will produce denaturation
2. The structure of the enzyme is changed.
3. The active site is distorted and the substrate molecules will no longer fit in it.

Question 17

At pH values slightly different from the enzyme’s optimum value, ___________.

Answer 17

Small changes in the charges of the enzyme and its substrate molecules will occur.

Question 18

This ____________ will affect the binding of the substrate with the active site.

Answer 18

change in ionization

Question 19

Some enzymes of the body have an optimum pH of about 7.4.

Answer 19

However, in certain organs, enzymes operate at lower and higher optimum pH values.

Question 20

__________ are molecules that bind to enzymes and increase their activity.

Answer 20

Enzyme activators

Question 21

_______________ such as metal ions and anions, organic reducing agents, and proteins

Answer 21

Inorganic Ions

Question 22

Inhibition of Enzyme Activities:

Answer 22

• Inhibitor is any molecule which acts directly on an enzyme to lower its catalytic rate is called an inhibitor (not denaturation).
• Some enzyme inhibitors are normal body metabolites.
• Other may be foreign substances such as drugs or toxins.

Question 23

Other means to affect or regulate enzyme activity:

Answer 23

1. Allosteric Binding Sites
2. By covalent modification
3. Induction and repression of enzyme synthesis
4. Zymogen Cleavage
5. Location within the cell

Question 24

Allosteric enzymes are regulated by molecules called effectors (modifiers) that binds noncovalently at a site other than the active site

Answer 24

Allosteric Binding Sites

Question 25

Many enzymes are regulated by covalent modification, most frequently by the addition or removal of phosphate group to serine, threonine, or tyrosine residue of the enzyme by kinases (enzyme).

Answer 25

By covalent modification

Question 26

Cells can also regulate the number of enzymes present by altering the rate of enzyme synthesis.

Answer 26

Induction and repression of enzyme synthesis

Question 27

Some enzymes are synthesized as inactive precursor, called zymogens, that are activated by proteolysis (e.g., digestive enzyme, pepsinogen is inactive and cleaved to pepsin which is active chymotrypsin).

Answer 27

Zymogen Cleavage

Question 28

Many enzymes are localized in specific organelles within the cell. This, compartmentation helps in the regulation of the metabolic pathway.

Answer 28

Location within the cell

Question 29

Inhibitors:

Answer 29

• Inhibitors are chemicals that reduce the rate of enzymic reactions.
• They are usually specific and they work at low concentrations.
• They block the enzyme but they do not usually destroy it.
• Many drugs and poisons are inhibitors of enzymes in the nervous system.

Question 30

Are chemicals that reduce the rate of enzymic reactions.

Answer 30

Inhibitors

Question 31

They are usually specific and they work at low concentrations.

Answer 31

Inhibitors

Question 32

They block the enzyme but they do not usually destroy it.

Answer 32

Inhibitors

Question 33

Many drugs and poisons are inhibitors of enzymes in the nervous system.

Answer 33

Inhibitors

Question 34

Enzyme activity can be assayed in many ways:

For example, you could measure appearance of colored product made from an uncolored substrate, appearance of a UV absorbent product made from a non-UV absorbent substrate, and the appearance of radioactive produce made from radioactive substrate.

Answer 34

1. Disappearance of substrate
2. Appearance of product
3. Continuous assay
4. End point assay

Question 35

The ________ of an enzyme-catalyzed reaction is dependent upon the substrate concentration.

Answer 35

velocity V

Question 36

______ are often just above the substrate concentration in a cell. Rates of reaction are sensitive to small changes in cellular substrate concentrations.

Answer 36

𝐾m values

Question 37

_____________________ are often referred to as Michaelis Menten Kinetics or Saturation Kinetics.

Answer 37

Kinetics of simple enzyme-catalyzed reactions

Question 38

These models like __________________ are based on data from batch reactors with constant liquid volume with initial substrate, [𝑆0 ], and enzyme, [𝐸0 ], concentrations are known.

Answer 38

Langmuir-Hinshelwood Kinetics

Question 39

Most complicated enzyme-substrate interactions such as ______________ can take place in biological systems.

Answer 39

multisubstrate-multienzyme reactions

Question 40

An ____________ has a fixed number of active sites to which substrates can bind. At high substrate concentrations, all these sites may be occupied by substrates or the enzyme is saturated.

Answer 40

enzyme solution

Question 41

_____________ can be obtained from simple reaction scheme that involves a reversible step for enzyme-substrate complex formation and a dissociation step from the ES complex.

Answer 41

Saturation kinetics

Question 42

Two major approaches used in developing a rate expression for the enzyme catalyzed reactions are;

Answer 42

(1.) rapid-equilibrium approach and
(2.) quasi-steady state approach.

Question 43

In______________, the maximum forward velocity of the reaction changes if more enzyme is added, but the addition of more substrate has no influence on it.

Answer 43

rapid equilibrium assumption

Question 44

A low value of ___________________ suggests that the enzyme has a high affinity for the substrate. Also, this constant corresponds to the substrate concentration, giving the half maximal reaction velocity

Answer 44

Michaelis-Menten constant

Question 45

Only enzymes that remains _____________will be measured. The enzyme may be denatured if it unfolds or has its three-dimensional shape altered by pH extremes or temperature during purification. The denatured enzyme will have no activity.

Answer 45

catalytically active

Question 46

Models for more complex enzyme kinetic:

Answer 46

Allosteric Enzymes
Inhibited enzyme kinetics

Question 47

Some enzymes have more than one substrate binding site. The binding of one substrate to the enzyme facilitates binding of other substrate molecules. This behavior is known as allostery or cooperative binding and regulatory enzymes show this behavior.

Answer 47

Allosteric Enzymes

Question 48

Certain compounds may bind to enzymes and reduce their activity. These compounds are known to be enzyme inhibitors. Enzyme inhibitions may be irreversible or reversible. Irreversible inhibitors such as heavy metals (lead, cadmium, mercury, and others) form a stable complex with enzyme and reduce enzyme activity. Such enzyme inhibition may be reversed only by using chelating agents such as EDTA and citrate. Reversible inhibitors may dissociate more easily from the enzyme after binding.

Answer 48

Inhibited enzyme kinetics

Question 49

The three major classes of reversible enzyme inhibitions are ____,______,_______.

Answer 49

competitive, noncompetitive, and uncompetitive.

Question 50

Are usually substrate analogs and compete with substrate for the active site of the enzyme. (Direct Competition)

Answer 50

(a) Competitive inhibitors

Question 51

The net effect of competitive inhibition is an _____________of the denominator without substrate concentration, therefore reduced reaction rate. Competitive inhibition can be overcome by high concentrations of substrate.

Answer 51

increased value

Question 52

Are not substrate analogs. Inhibitors bind on sites other than the active site and reduce enzyme affinity to substrate. (Both inhibitors can attach to Enzyme and ES)

Answer 52

(b) Noncompetitive inhibitors

Question 53

Bind to the ES complex only and have no affinity for the enzyme itself. (To produce ESI)

Answer 53

(c) Uncompetitive inhibitors

Question 54

High substrate concentrations may cause inhibition in some enzymatic reactions.

Answer 54

(d) Substrate inhibition

Question 55

Stomach = _______ = ________

Answer 55

Pepsin, 3

Question 56

Small Intestine = ______ = ______

Answer 56

Trypsin ,8

Question 57

_______ which hydrolyzes the cell wall of gram-positive bacteria, is used as an antibacterial agent.

Answer 57

lysozyme