Ground Rules of Metabolism

CHAPTER 6

Antioxidants

You’ve heard the term.

What’s the big deal?

Antioxidants

�Found naturally in many fruits and vegetables

�Added to many products�What do they actually do?

Antioxidants help us get ridof Free Radicals!

� Free Radicals are highly reactive molecules� Example: Oxidants like O2

-

� Formed by natural reactions in our bodies to break down fats & amino acids.

� Very destructive to macromolecules (proteins, lipids, DNA)

� Major contributor to the aging process and diseases like:◦ Cancer◦ Heart Disease◦ Failing Immune System

Dealing with Free Radicals

� Cells deal with O2- by using a series of

reactions.◦ A series of reactions is a pathway

� The pathway for the removal O2- from a

cell uses two enzymes: ◦ Superoxide Dismutase◦ Catalase

Reaction Basics

� Reactant – substance that enters a metabolic reaction or pathway; also called an enzyme’s substrate.

� Intermediate – Substance formed between reactants and end products of a reaction or pathway.

� Product – Substance left at end of reaction or pathway.

� Cofactors – Coenzyme or metal ion; assists enzymes or taxis electrons, hydrogen, or functional groups between reaction sites.◦ Metal Ions, NAD+, FAD2+, NADP+

Reaction Basics

� Energy carrier – Mainly ATP in cells; couples energy-releasing reactions with energy-requiring ones.

� Transport Protein – Protein that passively assists substances across a cell membrane or actively pumps them across.

AB + CD à AD + CB

Metabolism- Pathways

� Metabolism: Cell’s capacity to acquire energy and to use it to build, degrade, store, & release substances in controlled ways.

� Metabolic Pathway: Enzyme-mediated series of reactions

� Catabolism = metabolic pathways that release energy by breaking down compounds

� Anabolism = metabolic pathways that consume energy to build compounds

Equilibrium

� Equilibrium = state of maximum stability

� Metabolism as a whole is never at equilibrium because of the constant flow of materials in & out of the cell

Energy

� Kinetic Energy – energy of motion

� Potential Energy – stored energy

� Chemical Energy – the potential energy available for release in a chemical reaction

� Thermal Energy – kind of energy that is related to and/or caused by heat

Cells utilize chemical & electrochemical energy, and often release thermal energy

Laws of Energy Transformation (Thermodynamics)

� First Law of Thermodynamics – energy can be transferred & transformed, but it cannot be created or destroyed

� Second Law of Thermodynamics –energy transfer or transformation increases the entropy (disorder or randomness) of the universe

Energy Flow through Ecosystem

� Free Energy (G)◦ portion of a system’s energy than can perform work

-when temperature and pressure are uniform throughout the system◦ measure of a system’s instability (tendency to change to

a more stable state)

� Chemical reactions that…◦ lose free energy (DG < 0) are spontaneous or

exergonic

◦ absorb free energy (DG > 0) are endergonic

Chemical reactions that…◦ lose free energy(DG < 0) are

spontaneous or exergonic◦ Ex: Cellular respiration

◦ absorb free energy(DG > 0) are

endergonic◦ Ex: Photosynthesis

ATP (Adenosine Triphosphate)

� Immediate source of cellular energy� Common to ALL living things� Responsible for mediating most energy-

coupling reactions (use of exergonic reaction to drive an endergonic reaction)

� 10 million consumed & regenerated per second per cell

� The hydrolysis of ATP powers cellular work◦ the bond between the 2nd & 3rd phosphate groups breaks◦ the phosphate group is transferred to another molecule (=phosphorylation)

Phosphate group is easily lost due to the

concentration of negative charges in phosphate tail.

� 3 Kinds of Cellular Work:

◦ Mechanical� ex: beating of cilia, muscle contraction, movement of chromosomes during cell division

◦ Transport� ex: active transport

◦ Chemical� ex: endergonicreactions

Cellular Work

ATP Cycle

ATP synthesisrequires energy

ATP hydrolysisyields energy

Enzymes

� Many chemical reactions in the cell are slow (even spontaneous reactions)

� Cells use enzymes (catalytic proteins) to speed up reactions

� Enzymes lower the energy required to start a reaction (activation energy – EA)

Enzymes Show Specificity

� The active site of an enzyme has a specific shape that is specific to the shape of the substrate that binds to it

� Induced Fit Hypothesis – substrate induces a change in the shape of the active site to create a snug fit

How Enzymes Work

� Enzymes emerge from reactions in their original form

� Enzymes can catalyze both the forward & reverse reactions

How Enzymes Lowering EA

1. Active site can help substrates come together in the proper orientation for a reaction to occur

2. Enzyme may stretch substrates toward their transition-state conformation

3. Active site may provide a microenvironment that is more conducive to a particular type of reaction

4. Active site may participate directly in the chemical reaction

Substrate Concentration

� As substrate concentration increases, reaction rate will increase to a point

� When enzyme becomes saturated (all enzymes have their active sites engaged), the rate of the reaction will be determined by the rate at which the active site can convert substrate to product

Temperature

� Enzyme reaction rate increases with an increase in temperature to a point◦ Initially, an increase in temperature makes

substrates move faster and they are more likely to collide with the active sites of enzymes

◦ When temperatures get too high, the enzyme denatures and the reaction stops

� Most human enzymes have optimal temperatures between 35-40°C

pH

� The optimal pH for most enzymes is between 6-8

� When the pH deviates from the optimum, the enzyme denatures and the reaction stops

� 2 exceptions: pepsin & trypsin

Enzyme Inhibitors

� Competitive – mimics the substrate; binds to & blocks the active site

� Noncompetitive – binds away from the active site; causes the enzyme to change shape which changes the shape of the active site

� Inhibitors can play a regulatory role

Regulation of Enzyme Activity

� Allosteric regulation – binding of an activator or inhibitor molecule to a regulator site on an enzyme which stabilizes the functional or inactive form of the enzyme, respectively� Ex: ADP acts as an activator & ATP acts as an

inhibitor for several catabolic enzymes� Cooperativity – one substrate binds to an

enzyme and primes the enzyme to accept additional substrates

� Feedback inhibition – product of a metabolic pathway binds to & inhibits an enzyme that acts early in the pathway

EnzymeVideos• http://www.youtube.com/watch?v=PILzvT3spCQ&feature=related

– (GeneralFunctionandCompetitiveInhibition)• http://www.youtube.com/watch?v=MpcnkBE6FS0

– (studentmadeclaymation toPacMantheme- watchsmileturntofrown)• http://www.youtube.com/watch?v=CZD5xsOKres&feature=related

– (studentmade- quirkybutgood)• http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html– (MCGraw Hillshowsconformationchangeleadingtoproductformation)

• http://www.youtube.com/watch?v=Ms_ehUVvKKk&feature=related– (Interleukin-1bindng tosurfaceprotein receptor,leadstoconformational

change- good3Dshapes)• http://www.youtube.com/watch?v=uRbdpYEagbs&feature=related

– (showsproteinstructureandstickfiguremolecularbinding)

EnzymeE.C.!!!!!!

Byyourselforwithagroup,createandfilmanenzymevideo,postitonYouTubeandsendmethelink.

AmountofE.CwillbebasedonMr.Newton’sSUBJECTIVEopiniononthequalityofthevideoANDthesheernumberofYouTubehits!