Enzymes Flashcards
Enzyme effect on activation energy
Lowers it
Enzyme effect on reaction rate
Increases it
Enzyme effect on equilibrium constant
No effect
Is an enzyme used in a reaction?
No
Enzymes must have ________ to function.
Optimal temperature and ph ranges
Enzyme effect on free gibbs energy
No effect
How do enzymes know which reaction to catalyze?
They are specific for reactions
Oxidoreductases
They catalyze oxidation-reduction reactions by transferring electrons. They usually have cofactors to carry electrons.
Reductant
Donates electrons
Oxidant
Accepts electrons
Transferases
They catalyze the transfer of functional groups from one molecule to another. Kinases are an example and they transfer phosphate from ATP to a molecule.
Hydrolyase
They break down compounds by adding water. Examples include phospotases, peptidases, lipases, and nucleases.
Lyase
Cleave single molecule into two without adding water
Synthase
Make compound by joining two molecules; reverse action of lyase
Isomerase
They rearrange bonds in a molecule. They can be oxidoreductases, transferases, and lyases. They can do reactions between stereoisomers as well as consituitional isomers.
Ligases
Synthesis of large molecules and often require ATP
Endergonic
Free gibbs energy of products is higher and reaction requires energy
Exergonic
Free gibbs energy of products is lower and reaction releases energy
How many copies of an enzyme do you need for a reaction?
You don’t much because they do not get used up in reactions and can be reused.
Enzymes lower the activation energy to get to _______
transition state
Active site
Site on enzyme where substrate is held
How does a substrate know which enzyme to bind to?
The active site has a defined spatial arrangement that dictates specificity of that enzyme for a substrate
What interactions stabilize the active site?
Hydrogen bonding, ionic bonding, transient covalent bonds
Lock and key theory
Enzyme is lock and substrate is key. There is no change in tertiary and quaternary structure.
Induced model fit
Substrate and enzyme do not seem to fit. Substrate induces a conformational change in the enzyme which requires energy. When the substrate is released, energy is released.
According to the induced model fit, what will happen to the enzyme if the wrong substrate tries to bind to it?
No conformation change
Cofactors and conezymes
They are small, bind to the active site of an enzyme, can carry charge, and usually there is a low concentration of them.
Apoenzymes
Enzymes without cofactors
Haloenzymes
Enzymes with cofactors
Cofactors
Inorganic molecules e.g. metal ions
Coenzymes
Small organic molecules, mostly vitamins
Saturation
When all active sites are occupied.
What will happen to Vmax if more substrate is added?
Nothing will happen because all active sites are occupied
How do you raise Vmax?
Increase enzyme concentration by increasings its gene expression
Michaelis-Menten Equation
Look this up for clear picture buts its V=(Vmax*[S])/(Km+[S])
What is V when Km=[S]
V=0.5Vmax
Km
Substrate concentration at which 0.5 of enzyme active sites are full
Low Km
Enzyme has higher affinity for substrate
High Km
Enzyme has lower affinity for substrate
Vmax equation
Vmax=[E]kcat
Kcat
Number of substrate molecules “turned over” into product
ES –> E+P
Catalytic efficiency
Kcat/Km
Lineweaver burk plots
Linear version of Michaelis-Menten equation. It is 1/[S] vs 1/v. The x and y intercepts represent the 1/vmax and 1/kmax.
[S] vs V shape for cooperativity
Sigmoidal
T
Low affinity tense state
R
High affinity relaxed state
Hill’s coefficient
Measures cooperativity
Hills cooefficient < 1
Negative cooperativity
Hill’s coefficient > 1
Positive cooperativity
Hill’s coefficient = 1
No cooperativity observed
Human temperature
37 C, 98.6 F, 310 K
What happens to enzyme activity as temperature increases?
Activity increases but after certain temperature, the enzyme starts to denature and so activity lowers.
What happens to enzyme activity is there is change in pH?
It lowers because enzymes denature.
What happens to enzyme activity if there is change in [salt] in vitro?
This disrupts hydrogen and ionic bonds and change in enzyme structure and denaturation.
Feedback regulation
Enzymes regulated by products made later
Forward regulation
Enzymes regulated by products made before
Negative feedback
Enough product created so turn off synthesis pathway; product may bind to active site and compete with substrates
Competitive inhibition, it’s effects on Vmax and Km
Substrates cannot access actives site if inhibitor is in the way
- Vmax does not change
- Km increases because you have to add more S
How can you overcome competitive inhibition?
By increasing [S] so S is more likely to encounter E rather than the competitive inhbitor
Noncompetitive inhibitor, its effects on Vmax and Km
It binds to allosteric site on enzyme which induces enzyme conformational and substrate is unable to bind.
- Vmax decreases
- Km does not change because adding [S] won’t do anything
Mixed inhbition
Has unequal affinity for enzyme or enzyme-substrate complex
Binds to allosteric site
If it binds to enzyme, Km increases and Vmax decreases
If it binds to complex, Km decreases and Vmax decreases
Uncompetitive inhibitor
It binds to allosteric sites on enzyme-substrate complex and increases affinity for substrate and so enzyme complex does not release it. Kmax decreases and so does Vmax
How do you overcome irreversible inhibition?
Make new copies of enzyme to get function back
Irreversible inhbition
Enzyme permanently altered or not easily reversible.
Allosteric sites
Binding here affects affinity of binding sites
Allosteric activators
Make the active site for available
Allosteric inhibitors
Inhibit active site
Zymogen
They have catalytic (active) domain and regulatory domain. Regulatory domain must be altered to expose active site.
Which has more affinity? A cooperative enzyme or cooperative enzyme with substrate bound?
In cooperative enzymes, as susbtrates bind, cooperativity (+ or -) increases so an unbound nezyme has less afinity than one bound to one < 2< 3
Can triglycerides be cofactors?
No, they are too big.
What happens to ideal temperature if a catalyst is added to a reaction?
It is lowered
