Download Enzymes

Figure 2-3
Table 2-2
Figure 2-7 (1 of 3)
Figure 2-7 (2 of 3)
Figure 2-7 (3 of 3)
Figure 2-8 (2 of 6)
Figure 2-8 (3 of 6)
Figure 2-8 (4 of 6)
Figure 2-8 (5 of 6)
Figure 2-8 (6 of 6)
Figure 2-9 (2 of 7)
Figure 2-9 (3 of 7)
Figure 2-11 - Overview (1 of 3)
Figure 2-14
Figure 2-15
METABOLISM
• Energy Transformations
– What determines how much energy is transferred?
• What factors can influence whether a chemical reaction (or set
of chemical reactions) produces a product?
• What is the difference between an exergonic and an endergonic
reaction?
• What does it mean when reactions are coupled?
• Where does the energy to make ATP come from?
• Why do we make ATP (DG= -30.9kJ/mole) rather than PEP (DG=60.9 kJ/mole)?
High Energy Compounds
Compound
DGo'of phosphate hydrolysis (kJ/mol)
Phosphoenolpyruvate (PEP)
- 61.9
Phosphocreatine
- 43.1
Pyrophosphate
- 33.5
ATP (to ADP)
- 30.5
Glucose-6-phosphate
- 13.8
Glycerol-3-phosphate
- 9.2
1
2
Gibbs Free Energy Changes
Rxn#Enzyme
ΔG°'(kJ/mol)
1 Hexokinase
-16.7
2 Phosglucoisom
+1.7
3 Phosfructkinase
-14.2
4 Aldolase
+23.9
5 TriosphosIsom
+7.6
6 G-3-PDH
+12.6
7 Phosglyc kinase
-37.6
8 Phosglyc mutas
+8.8
9 Enolase
+3.4
10 Pyruvate kinase
-62.8
ΔG(kJ/mol)
-33.5
-2.5
-22.2
-1.3
+2.5
-3.4
+2.6
+1.6
-6.6
-33.4
ΔG°‘ = under standard temperature and pressure
with equal concentrations of reactants
ΔG = non standardized conditions (physiological)
3
4
5
6
7
8
9
10
Figure 4-4 - Overview
Enzymes
• What kind of biomolecule is an enzyme?
• What does an enzyme do to make a reaction go faster?
• How do the substrates bind to the enzyme?
• What happens to the enzyme when the reaction is complete?
Figure 2-16
Figure 4-8
Table 4-3
Some Important Characteristics of Enzymes:
• Some enzymes must be “activated” before they can interact with
their ligand
Figure 2-17
• Some require a cofactor or coenzyme in order to make the
reaction proceed
Glucose +ATP
Mg2+
Glucose-6-Phosphate
hexokinase
Figure 2-18
Coenzymes:
NADH+ H+
Pyruvate
NAD+
Lactate
Lactate dehydrogenase
Coenzyme
Table 2-3
FAD+
Succinate
Malonate or oxaloacetate
FADH2
Fumarate
Succinate dehydrogenase
Figure 2-19
ATP
Glucose
Glycogen
ADP
Glucose-6-phosphate
Glycogen phosphorylase
Glycolysis
Figure 2-20a
ATP
ADP
Glucose
Glucose-6-phosphate
hexokinase
Figure 2-20b
Covalent modulation – generally an addition or removal of a
phosphate group; can either increase or decrease the
activity of the enzyme
Triglyceride
fatty acid + diglyceride
Hormone sensitive lipase
P
2nd messenger activation of kinase
epinephrine
Modulation by temperature
Figure 2-21
Modulation by pH –
How? What is the mechanism?
pH for Optimum Activity
Enzyme
Lipase (pancreas)
pH
Optimum
8.0
Lipase (stomach)
4.0 - 5.0
Lipase (castor oil)
4.7
Pepsin
1.5 - 1.6
Trypsin
7.8 - 8.7
Urease
7.0
Invertase
4.5
Maltase
6.1 - 6.8
Amylase (pancreas)
6.7 - 7.0
Amylase (malt)
4.6 - 5.2
Catalase
7.0
Given a set concentration of substrate, more enzyme makes a
reaction proceed faster
Enzyme
Figure 2-22
With a fixed concentration of enzyme, increasing the substrate
concentration will lead to the enzyme becoming saturated, and the
reaction will go no faster (maximum rate).
enzyme
Figure 2-23
Many enzymes can bind more than one substrate. How can we tell
which substrate binds more efficiently? Determine Km (binding
affinity)!
*Rule = the smaller the Km, the tighter the binding
You have a mixture of several metabolic intermediates in a test tube. The
intermediate compound A is the substrate of enzyme ZZ. Additional compounds
include B, C, D, F, and G. Look at the following conditions and explain what is
happening.
Condition 1: A and B are in in the test tube in equal concentrations. A is found to
occupy the active site 3X as often as B, but when both are present, the reaction
rate slows down. Draw what the activity of the enzyme might look like in the
presence of compound A, and then when A and B are both present.
Condition 2: Enzyme ZZ is in the test tube with intermediates A, C and F. The
activity of the enzyme is lower than expected. What is possibly happening and how
would you determine whether your theory is true or not? Graph your experimental
results.
Condition 3. Enzyme ZZ is in the test tube with intermediates B and D. The
activity is higher than expected. What is possibly happening and how would you
determine whether your theory is true or not? Graph your experimental results.
Activity of enzyme
?
[Substrate]