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Glycolysis and TCA cycle Quiz
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Quiz #4/5 #4: Glycolysis (Fri, Feb 13th)
#5: TCA cycle (Thurs, Feb 26th)
Quiz will have the entire pathway:
All cofactors will be present
Most intermediate and enzymes removed
You fill in the missing names
Abbreviations are NOT acceptable answers
Draw the structure for 1 intermediate
Indicated by a larger box
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Enzyme Regulation Learning Objectives:
Understand how different conditions affect enzyme activity.
Know the types of genetic control.
Describe how covalent modifications of enzymes affect
activity
Describe how non-covalent modifications of enzymes affect
activity.
Explain how covalent and non-covalent modifications can be
combined to regulate enzyme activity.
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Conditions Affecting Enzyme Activity
pH
temperature
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pH: Enzymes have an optimum pH, based on: required ionization
state of amino acids
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Effects of pH on Enzyme Activity
Protonation state of side chains
Variation in protein structure
Substrate binding
catalysis
Ionization of substrate
Substrate binding
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Temperature
Relative
Activity
ba
Temperature
Protein unfolding
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Control of Enzyme Activity
In response to overall needs of the cell or organism.
Modulate:
Enzyme Availability (Amount)
Enzyme Catalytic Activity
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Control of Enzyme Availability Balance rate of production with
rate of degradation Control of Gene Expression: rate of
production
Constitutive Enzymes: e.g. glycolytic enzymes Inducible Enzymes:
e.g. -galactosidase Repressible Enzymes: e.g. enzymes of
Cholesterol biosynthesis
Control of Proteolysis: rate of degradation based on targeting
to proteosomes (ubiquitin)
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Regulation of Enzyme Catalytic Activity
Modification of protein structure leads to modification of
protein activity
Covalent Modification
Irreversible Reversible
Non-Covalent Modification Allosteric regulators
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Irreversible Covalent Modification: Cleavage of peptide
bonds
Inihibition (Proteolysis)
Proteosomes (ubiquitin)
Activation
+
H2O
"Inactive" "Active"
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Zymogen Inactive precursor protein
Pancreas
Small Intestine
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Reversible Covalent Modification: Modification of amino acid
side chains
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Page 390
Protein Modification (Phosphorylation/Dephosphorylation)
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Non-covalent Modification (Allosteric regulators)
Effectors or Ligands Positive: activators Negative:
inhibitors
Modification of protein structure changes active site structure,
affecting: Substrate Binding Catalytic rate Both
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Negative Effectors (Inhibitors)
"active"
Regulatory Site
Active Site
"inactive" orless active
I
I
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Positive Effectors (Activators)
+
"active" ormore active
"inactive" orpoorly active
++
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Figure 12-16
Glycogen Phosphorylase
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Enzyme activity in cells is controlled by which of the
following? I. modulation of protein degradation rates II.
modulation of protein expression levels III. covalent modifications
IV. allosteric effectors
A) I, II B) II C) III D) III, IV E) I, II, III, IV
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How might the (reversible) attachment of an inorganic phosphate
group to a hydroxyl-containing amino acid side chain (Ser or Tyr)
alter the activity of an enzyme?
A. The phosphate group blocks the active site and prevents the
substrate from binding.
B. Addition of the phosphate group changes the shape of the
enzyme.
C. The binding affinity of the substrate is lowered because of
electrostatic repulsion.
D. Addition of the phosphate group causes the enzyme to
dissociate into its separate subunits which are all in the R
state.
