Enzymes Flashcards
What are enzymes
- catalysts (speed up chemical reactions without themselves being altered)
- do not alter equilibrium, only increases the rate of reaction/ time it takes to reach equilibrium
Why are enzymes important
- catalyse chemical reactions in our metabolic system
- many roles in living organisms
Two types of enzyme mechanisms
Lock and key
Induced fit
Key words when describing how enzymes function
- enzyme
- enzyme substrate complex
- substrate
- product
- active site
Enzyme are what type of biological molecules
- proteins
- special ones include riboenzymes ( catalytic rna molecule)
What affects enzymes 3D structure
Ph
Temp
Inhibitors (non-competitive can bind at allosteric site)
What is standard free energy change (delta g)
Standard free energy change is the energy difference between reactants (enzyme and substrate) and products
Describe the mechanism of action of lysozyme
- cleaves the bacterial cell walls between carbon 1 of NAM and carbon 4 of NAG in the peptidoglycan cell wall of bacteria (beta 1-4 glycoside bond)
What affects the rate of reaction?
Ph
Temp
Inhibitor presence
Enzyme conc
Substrate conc
Covalent modifications
What is optimum temp of human enzymes
37
Optimum temp of heat tolerant bacterial enzymes ?
77
Optimum ph of trypsin?
8
Optimum ph of pepsin?
2
What is thermodynamic activation or inactivation?
Thermodynamic activation is when there is an increase in free energy
Thermodynamic inactivation is when the temp is too high and protein starts to denature
Describe the effect of enzyme conc on reaction rate?
Enzyme conc increase, rate of reaction increases until equilibrium is reached
What is the Michaelis constant?
Km = Vmax / 2
What is Vmax
Vmax is the maximum rate of reaction
(Enzymes are fully saturated)
What is Km
Michaelis constant
High affinity Low Km
Low affintiy high Km
Describe the affinities linked with Km
When Km is high, affinity of enzyme FOR its substrate is Low
Draw the graph of high and Low Km
Labels on each axis
Refer to slides for answers
Rate of reaction At Low Km
The enzyme is usually saturated so the rate of reaction is fairly constant
Rate of rxn at high Km
Low affinity so enzyme is usually not saturated with substrate, activity will vary as substrate conc varies. Rate of product formation depends on substrate availability
Explain what is the Michaelis- Menten equation and give the equation
V = Vmax . [S] / (Km + [S])
Michaelis menten equation is a representation of the graph of V against [S]
The Km of dextran surcease is 4nm. When is this enzyme saturated?
8nm because Vmax is when an enzyme is saturated and Km= Vmax over 2 so the enzyme is saturated when 4x2=8nm
Draw the Lineweaver-Burk plot and describe when is it used
Graph of 1/V against 1/[S].
Used to see a linear graph
The y intercept is 1/Vmax
The x intercept is NEGATIVE 1/Km
Gradient is Km/Vmax
Allosteric site def
Site away from the active site
Describe how the non competitive inhibitor works
Binds at the allosteric site, causes a conformational change, active site is no longer functional
Feedback inhibiton
Control metabolic pathways
Basically, when a lot of the product has formed, it can act as an inhibitor and bind to the enzyme in the earlier step of the metabolic pathway, stopping the pathway from continuing
What inhibitor is this? Km changes Vmax stays same
Km increases or decreases? Explain why and also draw the graph
- Competitive inhibitor
- Vmax stays same because increasing the substrate concentration can outcompete the inhibitors
- Km increases because affinity decreases
- Y intercept same x intercept shifts to the RIGHT
What inhibitor is this? Km stays the same Vmax changes.
Vmax increases or decreases? Explain why and also draw the graph
Non competitive inhibitor
Km stays the same because binding of substrates can still occur
Vmax decreases because a proportion of enzymes are inactive due to it binding to inhibitor
The x intercept stays the same and y intercepts increases ( remember that even though the Vmax decreases, the y axis Is 1/Vmax so the intercept goes up)
What are Allosteric enzymes NOT allosteric binding sites
Allosteric enzymes possesses multiple subunits
Allosteric enzymes are enzymes which have an additional site for an effector to bind to, as well as the active site
Efforts regulate the activity of the enzyme – they can either activate or inhibit
Allosteric enzymes are larger and more complex than normal enzymes
They are regulated through homotropic regulation or heterotropic regulation
Graph of allosteric enzymes
CANNOT use Michaelis menten equation! CANNOT use Lineweaver-Burk plot!!
Graph is sigmoidal shape
Covalent modification of enzymes
Adding example phosphate group can activate or inactive an enzyme
How does an allosteric enzyme function?
Binding of substrate, inhibitor or modulator/ activator to one subunit of the allosteric enzyme causes a conformational change in all subunits of the allosteric enzyme
What are the two types of modulators and what do they do?
Positive - increases affinity for substrate
Negative - decreases affinity for substrate
