Chapter 20 Enzymes and Vitamins

What is the name and classification of the enzyme that catalyzes the hydrolysis of lipids?

An enzyme that hydrolyzes a lipid is a lipase, which is classified as a hydrolase.

What is the difference between a kinase and a phosphatase if they both transfer phosphates?

a kinase adds a phosphate to activate the enzyme. phosphatase removes a phosphate to activate the enzyme.

20.26 What is the difference between a negative regulator and a positive regulator?

Positive regulators are molecules that bind the allosteric enzyme at the allosteric site, able to induce a change in the shape of the enzymes active site, to favor catalyzation of a particular substrate. Negative regulators are molecules that bind at the same site, but induce the enzymes active site to change to a shape that inhibits formation of an enzyme-substrate complex, thus inhibiting catalyzation of the substrate.

What is covalent modification?

Regulation of an enzyme by addition or removal of a group to the enzyme through a covalent bond.

what are different factors that affect enzyme activity?

Temperature, pH, concentration of enzyme, and concentration of substrate all affect enzyme activity.

Using Table 20.2, identify the chemical reaction each of the following enzymes catalyzes and classify the enzyme: a. aminotransferase b. lactate dehydrogenase

a. An aminotransferase catalyzes the transfer of an amino group between two substrates, which is classified as a transferase. b. Lactate dehydrogenase catalyzes the removal of two H atoms from lactate, which is classified as an oxidoreductase.

How is the composition of a catalyst changed after a reaction?

catalyst remains unchanged, substrate only thing broken down

How do lyase work?

catalyze addition or removal of a group without hydrolysis

How do hydrolase work?

catalyze hydrolysis reactions by adding water, which splits compound into two products.

How do oxidoreductases work?

catalyze oxidation reduction reactions oxidases catalyze oxidation dehydrogenase catalyze loss or gain of 2 H atoms.(utilize co enzyme)

How do isomerase work?

catalyze rearrangement of atoms within a substrate, also called isomerization.

How do transferase work?

catalyze the transfer of two functional groups between two compounds

What are isoenzymes?

different molecular forms of the same enzyme, think of how isomers are different compounds with same molecular formula. they catalyze the same reaction, however in different cells or tissues.

Which part of an enzyme plays an important role on how a substrate is catalyzed?

enzymes are globular proteins, the tertiary structure plays most important role on how efficient a substrate is catalyzed

Which is a larger molecule, glucose or hexokinase?

hexokinase. Enzymes are larger than substrates.

why are enzymes more active in higher temperatures?

high temps cause reacting molecules to move faster, causing collisions with enzymes.

20.32 The zymogen trypsinogen produced in the pancreas is activated in the small intestine, where it catalyzes the digestion of proteins. Explain how the activation of the zymogen in the pancreas can lead to an inflammation of the pancreas called pancreatitis.

if activated in pancreas, it would digest the proteins of the pancreas, causing inflammation.

How do the different forms of an enzyme allow a medical diagnosis?

in healthy tissues, enzymes function in cells, when an organ is damaged, cells die, which releases these enzymes and isoenzymes in blood. When found in irregular location, and elevated levels in blood, can help identify disease and location in body.

Why do enzymes show little activity during at low temperatures?

low temps provide insufficient energy levels to catalyze reactions.

How do enzymes act as a catalyst?

lower activation energy for a chemical reaction, thus less energy needed to convert reactant into product. This contributes to the reason why catalyzed reactions are faster than uncatalyzed.

the addition or removal of a phosphate group is known as?

phosphorylation, induces structural change of enzyme and changing it catalytic activity.

What are some examples of zymogens and proenzymes?

zymogens include digestive enzymes such as pepsinogen for digestion, fibrinogen for blood clotting. Proenzymes include prothrombin, the inactive form of thrombin, coagulation. Proinsulin, inactive form of insulin, aids in digestion

what are the two forms of covalent modification?

zymogens, proenzymes, and phosphorylation

What are zymogens and proenzymes?

inactive forms of enzymes stored for later use when needed.

what is the optimum temperature of enzymes in our body?

37C, (body temp)

Compare and contrast the affects of small changes vs large changes in pH with regards to enzyme activity.

small changes in pH are reversible, however large changes are irreversible due to permanent damage done to tertiary structure or quaternary structure.

What happens when an enzyme is present at a level lower or higher than its optimal pH level?

tertiary structure and active site destroyed, due to r groups of amino acid residues being disrupted.

What does high heat, 50C or higher do to enzymes?

tertiary structure and shapes of proteins denatured

The enzyme-product complex is a result of?

the amino acid residues of the R group of the enzyme catalyzing the substrate at the active site.

How does the induced-fit model explain the binding of the substrate at the active site?

the shapes of the substrate and the active site adjust so that the substrate is in the optimum position needed for the enzyme to carry out reaction catalysis.

What is an enzyme?

A globular protein, sometimes with a cofactor, that catalyzes a biological reaction. in short, a biological catalyst.

How do ligases work?

Catalyze the joining of two substrates using ATP energy

The combination of an enzyme and a substrate within the active site form a ?

Enzyme-Substrate complex

20.2 How do enzymes make chemical reactions in the body proceed at faster rates?

Enzymes bind to substrates at the optimal position, allow for catalyzation to occur efficiently.

20.1 Why do chemical reactions in the body require enzymes?

Enzymes catalyze reactions at extremely fast rates, up to a billion, a trillion, or even a hundred million trillion times more faster than uncatalyzed reactions. Optimal for survival.

What is a substrate?

The molecule that reacts in the active site in an enzyme-catalyzed reaction. In short, the substance being broken down

20.29 Indicate if the following statements describe enzyme regulation by (1) an allosteric enzyme, (2) a zymogen, or (3) covalent modification: a. The enzyme activity increases due to phosphorylation. b. Fibrinogen in the blood forms fibrin in damaged tissues. c. A positive regulator stimulates enzyme action.

a. covalent modification b. zymogen c. allosteric enzyme

20.3 Match the terms, (1) enzyme-substrate complex,(2) enzyme, and (3) substrate, with each of the following: a. has a tertiary structure that recognizes the substrate b. the combination of an enzyme with the substrate c. has a structure that fits the active site of an enzyme

a. enzyme b. enzyme-substrate complex c. substrate

20.5 a. Write an equation that represents an enzyme-catalyzed reaction. b. How is the active site different from the whole enzyme structure?

a. enzyme + substrate (reversible to) enzyme-substrate complex -> enzyme-product complex -> enzyme + product b. the active site refers to the tertiary portion of that enzyme that binds to the substrate for optimal catalyzation.

20.4 Match the terms, (1) active site, (2) induced-fit model, and (3) lock-and-key model with each of the following: a. an active site that has a rigid shape b. the portion of an enzyme where catalytic activity occurs c. an active site that adapts to the shape of a substrate

a. lock and key model b. active site c. induced fit

20.21 Trypsin, a protease that hydrolyzes polypeptides, functions in the small intestine at an optimum pH of 7.7 to 8.0. How is the rate of a trypsin-catalyzed reaction affected by each of the following conditions? a. lowering the concentration of polypeptides b. changing the pH to 3.0 c. running the reaction at 75 °C d. adding more trypsin

a. reaction will be slower b. this will denature the tertiary and quaternary structure. Disrupts r group amino acid residues, causing reaction to be slowed or stopped. c. this high temperature will be excessive, causing it the tertiary structure and the active site to denature. d. will increase rate of reaction, as more enzymes are available to bind and catalyze substrate.

What is the function of the active site in an enzyme?

active site is the location in which the enzyme binds the substrate to catalyze the substrate efficiently. R group of the amino acids from active site form hydrogen bonds, salt bridge and form hydrophobic interactions against the functional groups of the substrate.

20.27 In feedback control, how does the end product of a reaction sequence regulate enzyme activity?

acts as a negative regulator. when end product needs are met, the end product binds the allosteric site of the first enzyme in the reaction series, preventing the substrate from being able to bind it and continue catalyzation.

Briefly name the ways enzyme activity can be regulated?

allosteric enzymes, feedback control, and covalent modifications

Why does an increase in enzyme concentration at a particular substrate concentration lead to greater activity?

at higher enzyme concentrations, there are more enzymes available to catalyze the substrates.

20.31 Why is the active form of thrombin, which helps blood clot, produced from prothrombin only when injury and bleeding occur?

because thats when it is needed most, to prevent excessive blood loss. If active when not needed, blood clotting can occur in vessels and obstruct them. this can lead to many complications, high blood pressure and organ failure.

What happens to the rate of reaction when all the available enzymes are attached to substrate molecules?

maximum enzyme activity is achieved, because all enzymes have bound substrate.

20.25 How does an allosteric enzyme function as a regulatory enzyme?

most enzymes are allosteric enzymes. They work by regulating enzyme activity, increasing reaction rate when more of substance is needed. Decreasing reaction rate when a substance is no longer needed.

Do the intermediate enzymes in a reaction sequence have regulatory sites?

no, only the first enzyme. when end product binds first enzyme, all intermediate products ceased.

what happens when more substrate is added to a concentration of enzymes that have achieved maximum activity?

nothing, activity cannot be increased because all enzymes are occupied.

Briefly list the classes of enzymes.

oxidoreductases transferases hydrolases lyases isomerases ligases

Why does the digestive enzyme pepsin have an optimum pH of 2.0?

pepsin is an enzyme that catalyzes proteins in the stomach. when food enters stomach, HCl acid is secreted, causing the empty stomach pH of 4 or 5 to drop to 2pH. This allows pepsin to function in this environment

How does the lock-and-key model explain the binding of the substrate at an active site?

the substrate fits perfectly into the active site of the enzyme similar to a key fitting into a lock. this disproves the flexibility of the tertiary structure, as they do not have a rigid active site. Instead the active site flexes to accommodate the chemical reaction being catalyzed.

in feedback control, what happens when level of end product is low once again?

this would indicate more end product is needed, thus the end product bound to the first enzyme inhibiting binding of the substrate is released. Substrate now able to bind, catalyzation can occur.