Enzymes 2 Flashcards
What are co-factors?
Non-protein factors which are essential for enzyme activity
What are coenzymes?
Carbon containing cofactors (organic) derived from water soluble vitamins
What are prosthetic groups?
Tightly bound cofactors
some covalently bound
What are co-substrates?
Loosely + transiently bound cofactors
What is a haloenzyme?
Enzyme w/ prosthetic group
What is an apoenzyme?
Enzyme w/out prosthetic group
What are the 3 cofactor examples and their roles in catalysed reactions?
Iron & copper
- REDOX
Zinc
-helps bind NAD
What are the 4 coenzyme examples?
Biotin
Coenzyme A
NAD
-carries electrons
FAD
-carries electrons
What are the 3 prosthetic groups?
Heme
Flavin
Retinal
What is the overall pattern in the structure of coenzymes?
Adenine + ribose + 2 phosphates + vitamin
What is the general structure of a cofactor?
Common motif of adenine + ribose + another group
What do coenzymes do?
Bind to active site of enzyme + are involved in catalysis
By how much to enzymes increase the rate of reaction?
10^5 to 10^17 fold
What are steady-state kinetics?
The state reached a short time after mixing an enzyme + a substrate
What is a katal?
SI unit
Amount of enzyme that gives 1 Mol/sec
What is added to an enzyme assay to stop a reaction?
Acid
- denatures enzyme
How can product be measured in a direct assay?
If P is coloured - measure colour change via spectrophotometer
P could fluoresce or be a gas
Measure continuously
How is rate of reaction measured in a discontinuous direct assay?
Stop reaction (using acid/alkali) at set time points + measure P or S
What are the 4 factors that affect enzyme rate?
Conc of enzyme
Conc of substrate
Temp
pH
When is there a linear relationship between rate + amount of enzyme?
When substrate is not limiting or product in excess
What happens as substrate conc increases?
Rate increases by lesser amounts
–> eventually reaches plateau
= Vmax
What is the Michaelis-Menten equation?
V = Vmax[S] / (Km +[S])
What is Km?
Michaelis constant
= the [S] that gives 1/2 maximal rate
= 1/2Vmax
The higher the Km…?
The higher the [S] needed to reach Vmax
Why could the real Km of some enzymes be different to those found in experiments?
In labs, artificial substrates added to enzymes
- could be different for natural substrates
What is the issue with the Lineweaver-Burk equation rearrangement?
The lowest [S] gives the highest values on the graph
–> but lowest [S] are most inaccurate values
Why does reaction rate increase w/ temp up to optimum?
Increases enzyme’s internal mobility
–> allows substrate to enter + exit active site
as allows formation of transition state complex
Why does rate of reaction decrease w/ temp beyond optimum?
Enzyme too mobile
–> loses structure
= denatured
What are isozymes?
Different forms of enzymes w/ same function but diff structure
How does pH affect enzymes?
H+ ions bind to/are released from carboxyl groups + amino groups present in side chains of amino acids
–> charges on amino acids are important for structure
What are the water soluble vitamins?
B1, B2, B3, B6 + B12 Vit C Folic acid Biotin Pantothenic acid
What are the water insoluble vitamins?
A
D
E
K
Which type of vitamins form co-factors?
Water soluble
Which test is used to measure glucose?
Hardings test
in a discontinuous direct assay
(measure green colour)
