Ch 2 - Enzymes Flashcards
1
Q
catalyst
A
- do not impact thermodynamics
- increase reaction rate
- lower activation energy
- does not alter equilibrium constant
- not consumed
- ph/temperature sensitive
- does not effect overall gibbs free energy
- specific
2
Q
oxidoreductases
A
- catalyze redox reactions
- cofactor electron carrier
- reductant - electron donor
- oxidant - electron acceptor
- named “dehydrogenase” or “reductase”
- oxygen at final electron acceptor is named “oxidase”
3
Q
transferases
A
- movement of functional group from one molecule to another
- kinases - transfer of phosphate group
4
Q
hydrolases
A
- break compound using addition of water
- phosphatase - cleave phosphate group off
- peptidase - break down protein
- nuclease - break down nucleic acid
- lipase - break down lipid
5
Q
lyases
A
- cleavage of single molecule into 2 products
- does not require water
- no redox
- can also cause synthesis of 2 molecules to 1
- synthases
6
Q
isomerase
A
- rearrangement of bonds within molecule
- stereo and constitutional isomers
- can be classified as oxidoreductases, transferases, lyases
7
Q
ligases
A
- addition or synthesis reactions
- between larger molecules
- ofen require ATP
- smaller synthesis via lyases
- nucleic acid synthesis and repair
8
Q
enzyme substrate complex
A
- active site
- favorable microenvironment
- charge/pH
- stabilize transition state
- bring reactive groups together
- account for selectivity and regulatory mechanism
- hydrogen bonds
- ionic interactions
- transient covalent bonds
9
Q
lock and key theory
A
- enzymes active site is already in correct conformation for substrate
- no alteration to 3 or 4 structure
10
Q
Induced fit model
A
- substrate and enzyme change shape to fit together perfectly
- requires energy and is endergonic
- release substrate and return to original shape
- releases energy and is exergonic
- incorrect substrate will not cause correct shift in conformation of enzyme
11
Q
Cofactors and coenzymes
A
- cofactors - inorganic molecules or metal ions
- ingested from diet
- coenzymes - small organic
- vitamins, NAD+, FAD, CoA
- B complex vitamins and vitamin C need to be replenished
- nonprotein molecules that the enzyme requires
- kept at low conc in cells
- apoenzyme - enzyme without them
- holoenzyme - with cofactor/coenzyme
- prosthetic group - tightly bound and required for function
- may require several cofactors or coenzymes
12
Q
vmax
A
- when enzyme reaches saturation
- adding more substrate will NOT increase the reaction rate
- only increasing [E] will increase the rate of reaction
- unit of moles of enzyme per second
- vmax = [E] kcat
- kcat : number of substrate molecules converted to product per enzyme per second
13
Q
Michaelis Menten
A
- v = vmax [S] / (Km + [S]
- Km = [S] when v = vmax / 2
- Km : substrate conc when half of the enzymes active sites are full
- Michaelis constant
- used to compare enzymes
- higher means lower affinity and more substrate needed to be half saturated
- lower means higher affinity because less substrate needed to fill half active sites
- not altered by changing [E] or [S]
- when [S] << Km then rate is highly effected by changes in [S]
- when [S] << Km then rate is barely effected by changes in [S]
14
Q
catalytic efficiency
A
- kcat / Km
- efficiency of the enzyme
- low Km and/or high kcat
15
Q
Lineweaver - Burk Plot
A
- double reciprocal of michaelis menten
- x axis intercept : -1 / Km
- y intercept : 1 / vmax
- used to determine type of inhibition
- plot of 1 / V (y axis) vs 1 / [S] (x axis)
16
Q
Cooperativity
A
- do not follow michaelis menten
- sigmoidal curve
- low affinity tense state (T)
- high affinity relaxed state (R)
- binding of substrate encourages transition of other subunits from T to R state
- increases substrate binding
- also loss of substrate causes other subunits to change from R to T state and decrease binding
- often regulatory enzymes
- quantified by Hill’s coefficient
17
Q
Hill’s Coefficient
A
- quantifies cooperativity
- nature of cinding of molecule
- < 1 then positive cooperative
- < 1 negative cooperative
- = 1 does not exhibit cooperative properties
18
Q
temperature effect on enzyme
A
- rate doubles every 10 deg C until reaching optimal then sharply drops off
- falls sharply due to denaturation
- only some enzymes can regain function if cooled
19
Q
pH on enzymes
A
- effects ionization of active site
- can cause denaturation
- optimal pH varies depending on environment
- stomach, blood, small intestine
20
Q
salinity effect
A
- small physiological effect
- in vitro - increase in salt can disrupt hydrogen bonds and ionic bonds
- denaturation
21
Q
feedback regulation
A
- regulation by products further down the pathway
- feed forward regulation - regulated by intermediates that precede the enzyme in the pathway
- negative feedback - feedback inhbition, maintain homeostasis. Level of product determines enzyme activity
- product may bind competitively bind to active site of first enzyme in the pathway
22
Q
Competitive Inhibition
A
- occupancy of the active site
- can be overcome by addition of substrate
- does not alter vmax
- increases Km
- [S] must be higher in order to reach half of mac velocity
- LB plot - same y intercept, different X intercept
23
Q
Noncompetitive inhbition
A
- bind to allosteric site NOT active site
- change enzyme conformation
- cannot be overcome by additional substrate
- bind equally well to enzyme or enzyme-substrate complex
- decrease v max
- does not alter Km
- same x intercept
- different y intercept
24
Q
mixed inhibition
A
- inhibitor can bind to enzyme or enzyme-substrate complex
- different affinity for each
- bind to allosteric site
- alter Km
- if prefers enzyme then increase Km
- if prefers ES-complex then decrease Km
- either case, Vmax decrease
- on LB plot the inhibitor and no inhbitor lines cross off the axes
25
Q
Uncompetitive inhibitor
A
- only bind to ES complex
- prevent release of S from E
- bind to allosteric site
- lower Km AND v max
- conformational change when S binds to E allows for uncompetitive inhibitor to bind
- parallel lines on LB plot
26
Q
irreversible inhibition
A
- prime drug mechanism
- active site made unavailable for long time or enzyme permanently altered
- not easily overcome
- may have to transcribe and translate a new enzyme
27
Q
allosteric enzymes
A
- multiple binding sites
- alternate between active and inactive form
- allosteric activators or inhibitors bind to the allosteric site
28
Q
covalently modified enzymes
A
- activated or deactivated by phosphorylation or dephosphorylation
- ex. glycosylation - covalent attachment of sugar
29
Q
zymogens
A
- enzymes that are secreted in an inactive form
- catalytic domain and regulatory domain
- regulatory domain is removed or altered to expose active site
- ex. apoptotic enzymes and trypsinogen
- suffix -ogen
