Post on 10-Jan-2020
Bioenergetics and Enzyme
Jindawan Siruntawineti, Ph.D.Department of Zoology, Faculty of Science,
Kasetsart University
http://pirun.ku.ac.th/~fscijws
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E-mail: fscijws.ku.ac.th/424111
Credit to…http://biology.umt.edu/biol101/lecture.htm#vacation
http://www.hhp.ufl.edu/classes/ess/Summer/pet2350aj04/images/images/ch.04.ppt
http://info.citruscollege.com/LC/SUBJECTS/BIOL/Goodman104/ExamTopics1/ENZYMES.ppt
ReferenceBIOLOGY,
6th/ 7th edition Campbell and Reece
Pearson Education, Inc., publishing as Benjamin Cummings.
At KU-librariesChapter 6
Science, General Stack (2 copies) QH308.2.C34 2002
MainBK, Eng Stack-3rd Fl QH308.2.C34 2002
QH308.2.C34 2005
Objectives for Part II: Enzyme
- Define: enzyme, substrate, active site & enzyme nomenclature
- Describe about enzyme work
- Discuss factors affects enzyme activity
- Describe allosteric regulation & metabolism
Topic Outline: Part II Enzyme• Enzyme speed up metabolic reactions by
lowering energy barriers
• Enzyme are substrate specific• The active site is an enzyme’s catalytic center
• A cell’s physical and chemical environment affects enzyme activity
• Metabolic control often depends on allostericregulation
• The localization of enzymes within a cell helps order metabolism
• What are enzymesenzymes?
C: Data/ biology/ 028F1.mov
1. Proteins:1. Proteins: most enzymesenzymes are proteinsproteins, primarily tertiarytertiary and quaternary quaternary structuresstructures..
2.2. Catalyst:Catalyst: chemical agentchemical agent that acceleratesacceleratesa reaction without being permanently changed in the process.(Enzyme as biocatalyst)
3.3. Selective:Selective: enzymes are specific for which they will catalyzecatalyze (Specificity (Specificity -- depends depends upon 3D shape).upon 3D shape).
4.4. Recycled:Recycled: enzymes are reusable.
5.5. ““asease”” endings: examples:examples: sucrasesucrase
maltasemaltase
lactaselactase
Enzyme Nomenclature
Alcohol dehydrogenase
Substrate Catalytic action -ase suffix
This is an alternative name (for “common use”). In addition, an enzyme has a systematic name (unambigous) and a classification number
(e.g. EC 3.4.17.1 for carboxypeptidase A, whose systematic name is peptidyl-L amino acid hydrolase)
• How do enzymesenzymes work?
Enzyme can decrease the energy barrier
••EnzymesEnzymes speed up the cell’s chemical reactions by lowering the free energy of activationlowering the free energy of activation.
FreeEnergy
Progress of the reaction
Reactants
Products
Free energy of activation (EFree energy of activation (EAA))
Without EnzymeWith Enzyme
SubstrateSubstrate
• The substancesubstance (reactant) an enzymeenzyme acts on.
Enzyme
Substrate
Active SiteActive Site
• A restricted regionrestricted region of an enzymeenzyme molecule which bindsbinds to the substratesubstrate.
Enzyme
Active Site
Substrate
Enzyme-Substrate at active site
C: Data/ biology/ 028F2.mov
“Lock and Key” model
- Enzyme active site is complementary to the substrate
“Induced fit ” model
- Enzyme active site is complementary to the transition state
Lowers activation energy
Enzyme Active Site
Straining bonds
Providing microenvironmentthat favors reaction
Orienting substratescorrectly
byby
bybybyby
Enzymatic ReactionEnzymatic Reactionsubstrate (sucrose)substrate (sucrose) + enzyme (enzyme (sucrasesucrase) ) →→
enzymeenzyme--substratesubstrate complex complex →→
and +sucrasesucrase
glucoseglucose fructosefructose
productsproducts ++ enzymeenzyme
Can enzyme activity be modulated?
Change substrate binding to active site
Change ability of the enzyme to alter the EA
Temperature Covalent modulation
pH
Allosteric modulator
Competitive inhibitor
Campbell; Fig. 6.16a
Can enzyme activity be modulated?
Temperature
Campbell; Fig. 6.16b
Can enzyme activity be modulated?
pH
Can enzyme activity be modulated?
“helpers” for
catalytic activity
Some enzymesmust be ‘activated’
Cofactors Prosthetic groups
Inorganic molecules or
nonprotein organic molecules (Ca2+,
Mg2+)
Organic molecules, small & Covalently linked to protein
Coenzymes
Organic molecules (precursors are vitamins) e.g. NAD, FAD
Apoenzyme + Cofactor = Holoenzyme
Can enzyme activity be modulated?
Reduce productivity of enzymes by blocking
substrates from enteringthe active site
Enzyme Inhibitors
Directly Indirectly
Competitive Inhibitors
Noncompetitive Inhibitors
Uncompetitive Inhibitors
Enzyme Inhibition (Mechanism)
I
I
S
S
S I
I
I II
S
Competitive Non-competitive Uncompetitive
EE
Different siteCompete for
active siteInhibitor
Substrate
Car
toon
Gui
deEq
uatio
n and
Des
cripti
on
[II] binds to free [E] only,and competes with [S];increasing [S] overcomesInhibition by [II].
[II] binds to free [E] or [ES] complex; Increasing [S] cannot overcome [II] inhibition.
[II] binds to [ES] complex only, increasing [S] favorsthe inhibition by [II].
E + S→ES→E + P+II↓EII
←
↑
E + S→ES→E + P+ +II II↓ ↓EII+S→EIIS
←
↑ ↑
E + S→ES→E + P+II↓
EIIS
←
↑
EI
S X
Juang RH (2004) BCbasics
Can enzyme activity be modulated?
Reduce productivity of enzymes by blocking
substrates from enteringthe active site
Enzyme Inhibitors
Competitive (Direct) Inhibitors
Campbell; Fig. 6.17b
Cannot be overcome byhigh concentration
of substrate
Competes with substratefor binding to active site
Allosteric complexes oscillatebetween two conformational
states
AllostericRegulationHow is metabolism
controlled?
Campbell; Fig. 6.18a
Allosteric complexes oscillatebetween two conformational
states
AllostericRegulation
Binding of activator
Binding of inhibitor
Catalyticallyactive
Catalyticallyinactive
How is metabolismcontrolled?
Switching off ofa metabolic
pathway by itsend product
Feedback InhibitionHow is metabolism
controlled?
Switching off ofa metabolic
pathway by itsend product
Feedback InhibitionHow is metabolism
controlled?
Campbell; Fig. 6.19
Substrate molecules stimulate the catalyticpowers of an enzyme
CooperativityHow is metabolismcontrolled?
Campbell; Fig. 6.20
Campbell; Fig. 6.20
Cooperativity
http://images.google.com/imgres?imgurl=www.blc.arizona.edu/courses/181gh/rick/energy/graphics2/competitive.gif&imgrefurl=http://www.blc.arizona.edu/courses/181gh/rick/energy/regulation.html&h=262&w=317&prev=/images%3Fq%3Dcompetitive%2Binhibition%26svnum%3D
10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG
And…the localization of enzymes within the cellhelps order metabolism.
Campbell; Fig. 6.21
Remember the importanceof compartmentalization?
Questions?
54
สวัสดีคะ
Jindawan Siruntawineti , Ph.D., Assistant Professor
ผศ.ดร. จินดาวรรณ สิรันทวิเนติ
หองชีว. 402A ตึกชีววิทยา คณะวิทยาศาสตร
E-mail: fscijws@ku.ac.th http:// course.ku.ac.th/424111
หองทํางานชั่วคราวชั้น 2 อาคารสโมสรคณะวิทยาศาสตร (ขางตกึชีววิทยา)
Office: 1) Room 402A Biology-Building, Fac. of Science
2) 2nd Floor, Sc. faculty Society-Building, Fac. of Science
http:// pirun.ku.ac.th/~fscijws
Thank you!This semester: Tuesday, 11.00 – 12.30 am
Wednesday, Thursday 11.00 – 12.30 pm
18 July, 2006