Chp 10 - Basic concepts of Enzyme Action

what are enzymes?

enzymes are biological catalysts

enzymes ______ reaction rates without _____________

increase, being used up

most enzymes are ______ _______

globular proteins

by how much can enzymes accelerate the rate of a reaction?

by factors of a million or more

what is one of the fastest known enzymes?

carbonic anhydrase

how many molecules of CO2 can carbonic anhydrase hydrate per second?

10^6

carbonic anhydrase catalyzes this reaction and increases what?

the speed of the reaction in both directions

what are reactants in enzyme catalyzed reactions called?

substrates

what is a hydrolysis reaction?

when water is consumed to break the bonds of a larger molecule

what is another name for proteolytic enzymes?

proteases

what do proteases do?

proteases catalyze the hydrolysis of peptide bonds

papain is an enzyme that can…

cleave any peptide bond

papain exhibits broad specificity, meaning…

that papain can bind and catalyze any peptide bond, regardless of what the amino acids are

what does the enzyme trypsin cleave?

trypsin cleaves on the carboxyl side of arginine and lysine residues

trypsin is a digestive enzyme

true

what does the enzyme thrombin cleave?

thrombin cleaves Arg-Gly bonds in particular sequences only (high specificity)

what are the seven major classes of enzymes?

1. oxidoreductases

2. transferases

3. hydrolases

4. lyases

5. isomerases

6. ligases

7. translocases

what type of reaction do oxidoreductases catalyze?

oxidation-reduction reactions

what type of reactions do transferases catalyze?

reactions that transfer functional groups between molecules

what type of reactions do hydrolases catalyze?

hydrolysis reactions

what are examples of hydrolases

• thrombin

• papain

• trypsin

what types of reactions do lyases catalyze?

reactions that include the addition of groups to double bonds or removal of them to form double bonds

what types of reactions do isomerases cleave?

isomerization (intramolecular group transfer)

what type of reactions do ligases catalyze?

a reaction with the ligation of two substrates at the expense of ATP hydrolysis

what type of reaction do translocases catalyze?

reactions that include the movement of ions or molecules across membranes or within membranes

just a helpful chart

yay, thanks :)

what do many enzymes require for activity?

non-protein cofactors

cofactors can be split into what two categories?

1. metal ions (Fe2+, Cu2+, Zn2+)

2. coenzymes (organic molecules)

coenzymes can be split into what two groups?

1. cosubstrates

2. prosthetic groups

how do cosubstrates associate with the enzyme?

transiently → loosely and temporarily

give an example of a cosubstrate

NADH

how do prosthetic groups associate with the enzyme?

permanently (think about heme)

what are some examples of prosthetic groups?

heme, some FADH2 enzymes

here is a chart to break it all down

yay!!

define coenzymes

coenzymes are organic molecules derived from vitamins

metaphor: enzymes are the boss, cofactors are the employees

therefore enzymes ______ cofactors to work for them

employ

an enzyme with its cofactor is called…

a holoenzyme (think HELLO…I WANT TO BE WITH YOU)

an enzyme without the cofactor is called…

an apoenzyme (APOLOGIES, I CANNOT BE WITH YOU)

what are tightly bound coenzymes called?

prosthetic groups

do enzymes alter ΔG of a reaction?

NO

if delta G is positive or negative, does this affect the speed of the reaction?

NO

what part of the S → P reaction does the enzyme affect?

the transition state

delta G is not changed by enzymes because…

delta G is calculated after the transition state

do enzymes effect equlibrium?

NO

enzymes increase ______ ______, which in turn decrease ____

reaction rates (k), ΔG^‡

where do enzyme catalyzed reactions take place?

enzyme catalyzed reactions take place in the pocket on the enzyme called the active site

what is the molecule that is bound in the active site and acted upon by the enzyme?

the substrate

enzymes bring substrates together, forming…

an enzyme-substrate complex

enzyme-substrate complex drives selectivity means…

enzymes are selective, they “choose” the “right” substrate to bind to

what does the interaction of the enzyme and substrate at the active site promote?

the formation of the transition state

(THIS MAKES SO MUCH SENSE, THINK ABOUT THE GRAPH!!, ONCE ENZYME IS A PART OF THE RXN, TRANSITION STATE CHANGES)

active sites may include…

distant residues (amino acids)

overall, enzymes facilitate the formation of…

the transition state

describe the structure of the active site

3D surface created by amino acids from different parts of the primary structure

the active site makes up a ______ portion of the enzyme volume

small

what do active sites create?

unique microenvironments (must be unique for substrate to bind to)

describe the interactions of the enzyme and substrate at the active sites

they are weak!! multiple weak interactions that bind and release reversibly!!

what does enzyme specificity depend on?

the molecular architecture of the active site

enzymes must be _______ a certain way to catalyze the reaction

organized

what is induced fit?

induced fit is when enzymes change shape upon substrate binding

when the substrate binds to the enzyme, the enzyme changes it’s _________ to _____ the substrate

changes, fit

when does the active site form a shape complementary to the substrate?

AFTER the substrate has been bound