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BioChem2 lecture 4 Enzymes

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winniesmith1's version from 2017-03-01 11:09

Section 1

Question Answer
What are enzymes (simply)Catalysts for biological reactions- most are simple proteins. May contain cofactors such as metal ions or organic (vitamins)
How do enzymes workThey lower the activation energy and increase the rate of reactions.
What happens if the enzymes denatureActivity is lost.
What are enzymes (definition)Enzymes are proteins and certain class of RNA (ribozymes) which enhance the rate of a thermodynamically feasible reaction and are not permanently altered in the process.
Why does the body use enzymes?As they are natures catalysts, they speed up reactions 10^16 over un-catalyzed rates, they are specific; only the desired reaction occurs, they permit reactions under mild conditions (less energy required)
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Section 2

Question Answer
How are enzymes named1) end in -ase. 2) Identifies a reacting substance (e.g. lipase-reacts lipids) 3) Describes function of enzyme (oxidase,hydrolase etc). 4) common names of digestion enzymes still use -in (e.g. pepsin)
What are the different classifications of enzymesOxidoreductoases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
Which reaction does this class catalyze: oxidoreductoasesoxidation-reduction (ex. oxidases- oxidize, reductases- reduce)
Which reaction does this class catalyze: TransferasesTransfer group of atoms (ex. Transaminases- transfer amino group, Kinases- transfer phosphate groups)
Which reaction does this class catalyze: HydrolasesHydrolysis (ex. Proteases- hydrolyzed peptide bonds, lipases- hydrolyze lipid ester bonds)
Which reaction does this class catalyze: LyasesAdd/remove atoms to/from a double bond (ex. carboxylases- add CO2, hydrolases- add H20)
Which reaction does this class catalyze: IsomerasesRearrange atoms
Which reaction does this class catalyze: LigasesCombine molecules using ATP
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Section 3

Question Answer
How does the enzyme action: Lock and Key model work•An enzyme binds a substrate in a region called the active site • Only certain substrates can fit the active site • Amino acid R groups in the active site help substrate bind • Enzyme-substrate complex forms • Substrate reacts to form product • Product is released
How does the enzyme action: Induced fit model work• Enzyme structure flexible, not rigid • Enzyme and active site adjust shape to bind substrate • Increases range of substrate specificity • Shape changes also improve catalysis during reaction
What is the model of action of an enzymeSubstrate(s) 'fit' site on enzyme (by lock and key or induced fit) and bind to it, forming the complex, reaction occurs in the complexed state, products released.
Describe 'stickase' pathwaysubstrate---> transition state---> product. If the enzyme just binds substrate then there will be no further reaction. The enzyme must not only recognize substrate but also induce the formation of transition state.
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Section 4

Question Answer
What factors affect enzyme actionTemperature, substrate concentration, pH
How does temperature affect enzyme actionLittle activity at low temp. Rate increases with temp. Most active at optimum temp.(usually 37 degrees in humans). Activity lost with denaturation at (too) high temps.
How does substrate concentration affect temperature Increasing substrate conc. increases the rate of reaction (enzyme conc. is constant). Max activity reached when all of enzyme combines with substrate.
How does pH affect enzyme actionMaximum activity at optimum pH. R groups of amino acids have proper charge. Tertiary structure of enzyme is correct. Narrow range of activity. Most lose activity in low or high pH. (Bonds broken, tertiary shape lost, enzyme denatures)
Give examples of enzymes and there optimum pHpepsin- pH 2, salivary amylase pH 7, Trypsin pH 9
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Section 5

Question Answer
What do inhibitors do• cause a loss of catalytic activity • Change the protein structure of an enzyme • May be competitive or noncompetitive • Some effects are irreversible
What does a competitive inhibitor do• Has a structure similar to substrate • Occupies active site • Competes with substrate for active site • Has effect reversed by increasing substrate concentration
What does a noncompetitive inhibitor do• Does not have a structure like substrate • Binds to the enzyme but not active site • Changes the shape of enzyme and active site • Substrate cannot fit altered active site • No reaction occurs • Effect is not reversed by adding substrate
What does an uncompetitive (anti-competitive) inhibitor do Enzyme inhibitor binds only to the complex formed between the enzyme and the substrate (the E-S complex). Increases the enzymes affinity to substrate,decreases the maximum enzyme activity (Vmax), as it takes longer for the substrate or product to leave the active site.
What is the model of inhibition for non competitive Site obscured by inhibitor in active site or site changed: substrate(s) cannot bind, inhibitor molecule binding elsewhere on enzyme & altering structure as result.
hat is the model of inhibition for competitive Site occupied
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Section 6

Question Answer
How do enzymes speed up metabolic reactions by lowering energy barriers/ activation energy (EA)- The transition state can be reached at moderate temperatures.
What (energy related factor) do enzymes not changeDelta G (change in Gibbs free energy)- only speeds-up reactions that would occur eventually.
What does the high selectability of enzymes allowallows them to determine which chemical processes will occur at any time
how enzymes lower the free energy of activationby binding the transition state of the reaction better than the substrate. The enzyme must bind the substrate in the correct orientation otherwise there would be no reaction – Not a lock & key but induced fit – the enzyme and/or the substrate distort towards the transition state
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Section 7

Question Answer
Describe the activation siteTypically a pocket or groove on the surface of the protein into which the substrate fits
What does the active site allowthe specificity of an enzyme - specific fit between the active site and that of the substrate.
What does the enzyme changing shape allowtighter induced fit, bringing chemical groups in position to catalyze the reaction
Enzyme has catalytic surface- what does this do?stabilizes transition state. transformed transition state to product.
Read over michealis menton equation pg 46/saved in biochem2 notes
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