An Introduction to Enzymes Ms. Gaynor AP Biology https://www.youtube.com/watch?v=vTQybDgweiE
Dec 13, 2015
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
Substrate Specificity of Enzymes• The substrate
– Is the reactant an enzyme acts on
• The enzyme– Binds to its substrate, forming an
enzyme-substrate complex
• 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
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
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)
• 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