An Introduction to EnzymesMs. GaynorAP Biology

https://www.youtube.com/watch?v=vTQybDgweiE

• Enzymes are catalytic proteins • A catalyst

–Is a chemical agent that speeds up a reaction without being consumed by the reaction

– http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

ENZYMES

Chemical Reaction• Every chemical reaction between

molecules

–Involves both bond breaking and bond forming

Figure 8.13

H2O

H

H

H

H

HO

OH

OH

OH

O

O OO OHH

H H

H

H

H

CH2OH CH2OH

OHCH2OH

Sucrase

HOHO

OH OH

CH2OH

H

CH2OH

H

CH2OH

H

O

Sucrose Glucose Fructose

C12H22O11 C6H12O6 C6H12O6

+

HOH H

Catabolic vs. Anabolic Reactions• CATABOLIC (an exergonic reaction)

– Reactions that BREAK down LARGE molecules into smaller ones

– Think: “C” for cut apart (make smaller)– RELEASE ENERGY

•POLYMER MONOMER– Ex: Cellular Respiration (glucose O2 + ATP)

• ANABOLIC (an endogonic reaction)– Reactions that PUT TOGETHER down SMALL

molecules into LARGER ones– Think: “A” for add together (make bigger)– ABSORBS/NEEDS ENERGY

•MONOMER POLYMER– Ex: Photosynthesis (sun + CO2 + H2O Glucose)

EXERGONIC vs. ENDERGONIC

• Exergonic reaction– RELEASE ENERGY (exits)– Do NOT need extra energy occurs

spontaneously•OCCUR SLOWLY!!!

• Endogonic reaction– ABSORBS/NEEDS ENERGY (INTO)– Will NOT happen without ENERGY

input– NOT SPONTANEOUS!

Activation Energy, EA

– initial (starting) amount of energy needed to start a chemical reaction

• Amount of energy needed to “PUSH” reactants over a barrier

• Determines the RATE of the reaction– Proportional to difficulty of breaking bonds– All reactions require energy of activation

(EA)–ENZYMES

»Lowers the EA barrier so that chemical reactions can more quickly.

The energy profile for a reaction

(net release of energy)

Fre

e en

erg

y

Progress of the reaction

∆G < O

EAA B

C D

Reactants

A

C D

B

Transition state

A B

C D

Products

• Uphill= EA

required to start reaction.

• Downhill = the loss of energy by molecules in reaction.

G is the difference in energy of products and reactants.

• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Unaffected by enzyme

Substrate Specificity of Enzymes• The substrate

– Is the reactant an enzyme acts on

• The enzyme– Binds to its substrate, forming an

enzyme-substrate complex

ENZYME

SUBSTRATE (REACTANT) PRODUCTS

NOTE: Oxygen gas(O2) forms

BUBBLES

• The active site–Is the region on the enzyme

where the substrate binds

Figure 8.16

Substrate

Active site

Enzyme

(a)

Most enzyme-Most enzyme-substrate substrate

interactions interactions result of result of weakweak

bonds.bonds.

20 Different Amino Acids• Proteins (ex: enzymes) are made up of

amino acids sequences (orders)

• Each amino acid has different functional groups (R groups)

• R groups = red

• POLAR w/ Charges

(+ or -) HYDROPHILIC

• POLAR with NO ChargesHYDROPHILIC

• Non polar HYDROPHOBIC

http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein%20structure.swf

Involves carboxyl and amino groups•Makes covalent

peptide bonds btw amino acids

Involves carboxyl and amino groups•Makes hydrogen

bonds btw carboxyl and amino groups

•Makes hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic or Van Der Waals interactions btw available R groups

Involves R groups

Involves R groups•Same as tertiary structure

• Induced fit of a substrate– “tight” fit creates a “microenvironment” – Enzyme binds to substrate better using amino

acid R groups– Weakens bonds gets to transition state

faster

Figure 8.16 (b)

Enzyme- substratecomplex

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf

Enzyme is RECYCLED!!Never used

up or destroyed

EFFECTS OF TEMPERATURE & pHEFFECTS OF TEMPERATURE & pH• Enzymes have an optimal temperature

and pH in which it can function

Figure 8.18

Optimal temperature for enzyme of thermophilic

Rat

e o

f re

actio

n

0 20 40 80 100Temperature (Cº)

(a) Optimal temperature for two enzymes

Optimal temperature fortypical human enzyme

(heat-tolerant) bacteria

– Enzymes have an optimal pH in which it can function

Figure 8.18

Rat

e o

f re

actio

n

(b) Optimal pH for two enzymes

Optimal pH for pepsin (stomach enzyme) Optimal pH

for trypsin(intestinalenzyme)

10 2 3 4 5 6 7 8 9

What factors denature proteins?Denaturation = take away (or

lower) the function of protein

• pH

• Salt concentration

• Temperature

Why does pH denature proteins?In either excess H+ or excess OH- ions,

protein's shape is alteredActive site is distorted/blocked

alters ionic bonds that contribute to its functional shape

Enzyme cannot catalyze reactions at all or as well

+

H+ ( pH) in acids+/- +/-

-

Why does SALT [ ] denature proteins?REMEMBER: SALTS are IONIC

COMPOUNDS!!! THEY HAVE +/- ionsIn either excess + or excess - ions, protein's

shape is alteredR-groups/side chains of amino acids

distorted/blocked by affecting ionic bondingEnzyme cannot catalyze reactions at b/c it

forms a precipiceLess salt= R groups form extra bonds with

each other More salt= disrupt R groups from normal

bonding patterns

Why does TEMPERATURE denature proteins?

Kinetic energy changes with temperature

Atoms move differently and affects the bonding patterns that hold the protein together

A higher temperature generally results in increase activity b/c molecular motion increases resulting in more molecular collisionsIf, however, temp rises above a certain point, the heat

will denature molecules move too fast and can’t H-bond

Cold temp’s SLOW DOWN or stop activityb/c molecular motion decrease

[Enzymes]

• http://www.sumanasinc.com/webcontent/animations/content/proteinstructure.html

• Denaturation and eggs

[SUBSTRATE] ALSO EFFECTS ENZYME ACTIVITY

• If [ ] of enzyme is constant… – at lower [substrate] [substrate]= limiting

factor – As [substrate] increases, RATE of enzyme

activity also increases– However, at very high [substrate]

enzymes become saturated with substrate and a higher concentration of substrate does NOTHING to increase the reaction rate• All the enzymes are already in use

Cofactors• Cofactors

– Are non-protein enzyme helpers

– Bind to active site to enhance enzymatic rxns

• Cofactors may be inorganic metals such as zinc, iron, or copper.

• Coenzymes– Are organic cofactors

– Coenzymes example= vitamins

Enzyme Inhibition

•Competitive inhibitors – mimic the substrate and compete for the

active site.

•Non-competitive inhibitors– bind to the enzyme away from the active

site, and indirectly cause a change in the active site (i.e.-changing the function)

– https://www.youtube.com/watch?v=PILzvT3spCQ– https://www.youtube.com/watch?v=VQVPlmzf-iY

Enzyme Inhibitors

Allosteric Enzymeshttps://www.youtube.com/watch?v=d5fDEUhjo-M

•A specific type of enzyme •Helps regulate cell processes•Can change their conformational shape

• Have 2 states (ACTIVE vs. INACTIVE)

Allosteric Enzymes

• CooperativityCooperativity– Is a form of allosteric regulation that

can amplify enzyme activity

Figure 8.20

Binding of one substrate molecule toactive site of one subunit locks all subunits in active conformation.

Substrate

Inactive form Stabilized active form

(b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.

https://www.youtube.com/watch?v=fyww37XOrXo

Cooperativity