Module 04: Enzymes (Comprehensive) Flashcards
These are specialized proteins with catalytic properties
Enzymes
This specificity pertains to stereoisomer
stereochemical specificity
This specificity pertains to substrate it will act upon
absolute specificity
This specificity pertains to the type of bond/linkage
linkage specificity
Chemical reactions need an initial input of energy to reach this.
Activation Energy
During the activation energy, the molecules are said to be in what?
Transition state
This provides an alternate route, one with lower energy of activation and it stabilizes the transition state
Enzyme Controlled Pathway
Describe the structure of the active site.
Cleft or pocket on the enzyme’s surface, With catalytic and binding sites, where catalysis occurs (at catalytic residues)
Where is the active site located?
Located at the interface between subunits of multimeric enzymes (Shields the substrate from solvent)
An additional non-protein molecule that is needed by some enzymes to help the reaction. These are small organic or metalloorganic molecules or metal ions.
Cofactor
Tightly bound cofactors are called _______________..
prosthetic groups (heme in hemoglobin)
Organic cofactors that are bound and released easily are called ____________ and are commonly activated by vitamins.
coenzymes
These can associate and disassociate from enzymes between reactions cycles thus behaving like substrates.
Weakly bound coenzymes (cosubstrates)
This is the protein part of an enzyme that is inactive. It requires a cofactor to be active.
Apoenzyme
This is the complete catalytically active enzyme
Holoenzyme
This is the enzymes requiring metal ions as cofactor
Metalloenzyme
These function as group transfer agents, Transport substrates from port of generation to port of utilization. They are usually derived from vitamins.
Coenzymes
These coenzymes transfer H atoms or Hydrides
NAD+ (Nicotinic acid/niacin/B3 )
These coenzymes transfer methyl group.
folates
These coenzymes transfer acyl group.
Pantothenic acid/B5 (Coenzyme A)
These coenzymes transfer oligosaccharides.
dolichol
These coenzymes transfer Electrons .
Riboflavin/B2 (FAD and FMN)
These coenzymes transfer aldehyde group transfer.
Thiamine/B1 (thiamin pyrophosphate/TPP)
These coenzymes transfer Activated CO2 group transfer
Biocytin (Biotin)
These coenzymes transfer One C group transfer
Folic acid (Tetrahydrofolate/THF)
These coenzymes transfer H and alkyl groups
Electrons & acyl groups
(1) Deoxyadenosyl cobalamin (B12)
(2) Lipoic acid (lipoate) is not required in the diet
These are the reactants that are acted upon/activated by the enzyme
substrates
The specificity is determined by the “________________”
active site
In this theory of specificity, the fit between the substrate and the active site of the enzyme is exact Like a key fits into a lock very precisely. The key is analogous to the substrate and the enzyme analogous to the lock
The Lock and Key Hypothesis
What is the temporary structure of the lock and key hypothesis?
Temporary structure called the enzyme-substrate complex /ES complex formed
What happens when the enzyme-substrate is formed/
Once formed, they are released from the active site leaving it free to become attached to another substrate
Dehydrogenase, oxidase are examples of what
Oxidoreductase enzymes
Kinase, amino transferase are examples of what
Transferase
Esterase, glycosidase, peptidase, phosphatase, phospholipase are examples of what?
Hydrolase
Decarboxylase, synthase are examples of what
Lyase
Epimerase, mutase are examples of what
Isomerase
Synthetase, carboxylase are examples of what
Ligase
The substrate concentration in non-enzymatic reactions is directly proportional to what
The increase in velocity is proportional to the substrate concentration (Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied)
Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied, this stage is called the
Vmax
What happens when you alter the concentration
If you alter the concentration of the enzyme then Vmax will change too.
What happens when there is Extreme pH levels
Extreme pH levels will produce denaturation (The active site is distorted and the substrate molecules will no longer fit in it)
These changes affects binding of the substrate with the active site.
small changes in the charges of the enzyme and its substrate molecules will occur ( change in ionization)
What is the temperature coefficient?
Q10 (the temperature coefficient) - the increase in reaction rate for every 10°C rise in temperature.
What does the Q10 = 2 to 3 mean?
(the rate of the reaction doubles or triples with every 10°C rise in temperature)
BUT at high temperatures (beyond the optimum) proteins denature at around _______
70°C
In terms of enzyme concentration, the increase in velocity is proportional to what?
The increase in velocity is proportional to the enzyme concentration
What are the uses of the double reciprocal plot?
(1) The biggest advantage to using the double reciprocal plot is a more accurate determination of VMax, and hence KM.
(2) The x intercept value is equal to -1/KM.
(3) It is also useful in characterizing the effects of enzyme inhibitors and distinguishing between different enzyme mechanisms.
What are the different types of irreversible inhibition?
(1) group specific covalent modifying agents
(2) Affinity labels
(3) Transition state analogs
(4) Suicide inhibitors
These react with specific type of functional group or any enzyme protein.
group specific covalent modifying agents
These are enzymes in nucleotide biosynthesis (new nucleic acids required for cell division)
dihydrofolate reductase
This inhibits vertebrae DHRF and selectively kills rapidly dividing cells.
Methotrexate
This inhibits prokaryotic DHFR.
Trimethoprim
This pertains as to how Eukaryotic cells are divided into organelles which often allows for separation of opposing processes.
Compartmentation
Fatty acid oxidation occurs in the
mitochondria
synthesis occurs in the .
cytosol
These are different forms of an enzyme found in different organelles or different tissues but Catalyze the same reaction
Isozymes
A tetramer whose subunits occur in two forms (H for heart) and (M for muscle)
Isozymes of Lactate DH(LDH)
How do Isozymes differ?
(1) Substrate affinity (glucokinase and hexokinase)
(2) Sensitivity to regulatory factors
This isozymes predominates in the heart
I1 or H4
This isozymes predominates in the liver
I5 or M4
Elevation in I1 or I5 is detected by
separating oligomers of LDH by electrophoresis
Dimeric CK has two types of protomers:
muscle (M) and brain (B).
Heart muscle has
CK2 (MB) and CK3 (MM).
This is found exclusively in heart muscle.
CK2
When is CK2 released?
CK2 is released 6 hrs. after chest pain and reaches a maximum after 18 hrs.
These are enzymes tested for the diagnosis of MI
Troponin, lactate dehydrogenase and creatine kinase
This is the more definitive diagnostic test because it is more cardiac specific than the others
Troponin
