Topic 5 - Enzymes Flashcards
What is an enzyme and what is it’s function?
A Catalyst. Speed up reactions w/out being used up or changed
Most enzymes are what kind of protein?
globular => soluble in H20, hydrophobic outside, hydrophilic inside
To bind to an enzyme and cause a reaction the substrate’s structure and stereochemistry must fit the entire active site exactly. T or F?
True
Enzyme function is determined by their….?
primary aa sequence
What is a simple enzyme?
all protein, no cofactor
What is a complex enzyme?
protein and cofactor/coenzyme
What is a holoenzyme?
A complete complex enxyme
What is a Apoenzyme?
Protein component of holoenzyme. Require a cofactor or prosthetic group for activity
What is a cofactor?
one or more weakly bound metal ions, or a weakly bound organic (e.g. NADH) or metalloorganic molecule
What is a prosthetic group?
tightly or covalently bonded cofactor (e.g. heme)
What is a metallo-enzyme?
metal always bound to active site
What is a metal-activated enzyme?
metal not part of native structure, but required for activity.
What is the main difference b/w a cofactor and a prosthetic group?
A prosthetic G is tightly bound
Are coenzymes consumed during a reaction?
yes
Are coenzymes a substrate?
yes
What is an isozyme? What do they allow?
different enzymes that catalyse the same reaction. Can have related aa sequence or very different. allow metabolic pathways to follow different courses in different cells: same metabolites, different fates
How do enzymes act, what do they induce and what does this allow
Enzymes act by binding substrates, allowing development of kinetic equations. Induce transition state.
What is the transition state?
midway b/w substrate & product
PLEASE READ SLIDES 44-56 FOR TRANSITION STATE INFO
Draw transition state graph
PLEASE PLEASE PLEASEE!!!
State the equilibrium constant (Keq) equation for products & substrates
Keq = [P]/[S] for multiple: Keq = ([C].[D])/([A].[B])
State the equation which describes the direct relationship b/w Keq and the free energy change (ΔG) => answer gives how much energy is given off changing a substrate into a product
ΔG = -RT R= universal gas constant (1ap) T = absolute temp (298K=25C) PLEASE SEE TRANSITION SLIDES 44-56
Enzymes do not bind transition states better than substrates. T or F?
False
Enzymes do not effect equilibrium (ΔG). T or F?
True
Define enzyme specificity.
The ability of an enzyme to selectively bind to and catalyse a specific substrate(s) is termed enzyme specificity.
Catalytic reactions @ active site: What is general acid-base catalysis?
A number of aa side chains can act as H+ donors or acceptors (Glu, Asp, Lys, Arg, His)
Catalytic reactions @ active site: What is covalent catalysis?
A transient bond is formed b/w substrate & enzyme. Requires a nucleophile
Catalytic reactions @ active site: What is metal ion catalysis?
can electrostatically polarise atoms, or change oxidation state to donate/receive electrons (H+). Involves a metal ion bound to enzyme. -stabilisies -ve charges -participates in oxidation reactions
Define enzyme activity?
rate of enzyme catalysed reaction
Define specific enzyme activity?
measure of enzyme purity = number of enzyme units per mg of total protein i.e. the purer, the higher the specific activty
List the factors that influence enzyme activity.
enzyme [] -linear relationship pH -can denature enzyme; have optimal pH Temp. -see pH Substrate [] inhibitors
What is the study of enzyme kinetics?
study of rate of enzyme catalysed reactions -how rates are affected by enviro -[] of substrate
FOR ENZYME KINETICS, LINEWEAVER-BURKE PLOT, MICHAELIS-MENTEN EQUATION AND ENZYME INHIBITION PLEASE REVISE HAND WRITTEN NOTES
DO IT DO IT DO IITTT!!!
Qrite the equation for the reaction where substrate (S) is converted into product (P) by enzyme (E)
For the enzyme-substrate complex reaction, what is:
k1?
k-1?
k2?
Where does the transition state occur within the enzyme-substrate complex reaction?
within the ES complex
(not E or P or S)
What is Vmax? When does it occur?
maximum rate of enzyme-catalysed reactions
Occurs when all enzyme exists as ES complex => when E is saturated
Write the Michaelis-Menten Equation and what it describes and what it allows us to determine.
Draw the graph it reciprocates
Low km = ?
(km=michaelis constant)
E has higher affinity for S & vice versa
What is Kcat? Write the equation.
Measures enzyme efficiency (catalytic production of product)
Kcat= number of substrate molecules converted per enzyme molecule per second
Kcat = Vmax/[E]
Kcat & Km together determine rate of catalysis.
High Kcat, low Km =?
reactions catalysed the fastest
Draw the Lineweaver-Burke Plot
FOR ENZYME INHIBITION ALSO READ NOTES
PLEASE PLEASE PLEASE!!!!!!
Describe irreversible enzyme inhibitors
react w/ enzyme
One inhibitor molecule can permanently shut off one enzyme molecule
Describe reversible inhibitors
bind to & can dissociate from enzyme
-prevent reaction or binding of substrate
Describe competitive inhibition, its affects on Vmaz and Km. Draw it’s LWB plot.
Competes w/ substrate for binding
- binds active site
- does NOT affect catalysis
No change in Vmax, apparent increase in Km
LWB lines intersect y axis
Describe uncompetitive inhibition, its affects on Vmax and Km. Draw it’s LWB plot.
Only binds to ES complex
- does not affect S binding
- Inhibits catalytic function
Decrease in Vmax, apparent decrease in Km
in LWB lines are parallel
Describe mixed inhibition, its affects on Vmaz and Km. Draw it’s LWB plot.
Binds enzyme w/ or w/out substrate
- binds regulatory site
- inhibits both S binding & catalysis
Decrease in Vmax, change in Km
LWB lines intersect left of y axis
List the types of enzyme regulation
irreversible
reversible
covalent modification
noncovalent mod
