Enzymes Flashcards
What is an enzyme?
A protein molecule which catalyses chemical reactions without being destroyed or altered.
How do biological catalysts differ from chemical catalysts?
-Catalyses very high reaction rates
-Shows great reaction specifity
-Works in mild temperatures/pH conditions
-Can be regulated
Define substrate.
A reactant catalysed in a chemical reaction.
Define active site.
The part of the enzyme that binds the substrate to form the enzyme-substrate complex
Define product.
The substance produced by the enzyme-catalysed conversion of a substrate
Define cofactor.
Non-protein component needed for the reaction e.g. magnesium
Define coenzyme.
Heat-stable substance that can aid enzyme reactions e.g. FAD from riboflavin
Define isoenzyme.
Enzymes that catalyse the same reaction but vary in structure and other biochemical properties
What is activation energy?
The amount of energy required for a reaction to take place.
How do rnzymes increase the rate of reaction?
By lowering activation energy.
How do enzymes increase the rate of reaction?
By lowering activation energy.
Name the three ways enzymes can lower the activation energy.
Entropy reduction, desolvation, induced fit.
How does entropy reduction take place?
Enzymes “force” the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
How does desolvation take place?
Weak bonds between the substrate and enzyme essentially replace most or all of the H-bonds between substrate and aqueous solution.
How does induced fit take place?
Conformational changes occur in the protein structure when the substrate binds.
Write down the Michaelis-Menten equation.
V0=V(max) x S
—————–
Km
V0=initial reaction velocity
V(max)=maximum reaction velocity
S=substrate conc.
Km=the substrate concentration when the reaction is at ½ the maximum velocity (Vmax)
What does a high/low Km measurement tell us?
How specific an enzyme is for a substrate
High-poor fit
Low- good fit
What does V(max) tell us?
How fast a reaction is proceeding when the enzyme is saturated w substrate.
Higher the value, faster the reaction.
Name five things that can effect enzyme activity.
-pH
-Temperature
-Inhibitors
-Enzyme conc.
-Substrate conc.
Define competitive inhibition.
An inhibitor binds to the active site of an enzyme. to prevent the substrate from binding.
In the presence of a competitive inhibitor, what is required to reach V(max)?
A higher substrate conc. is required to achieve the same velocity as if there was no inhibition.
What happens to the V(max) in the presence of a competitive inhibitor?
Stays the same.
What happens in non-competitive inhibition?
Inhibitor binds to the allosteric site changing the conformation and preventing the substrate from binding.
What happens to V(max) in non-competitive inhibition?
Decreases
What happens to Km in non-competitive inhibition?
Stays the same.
Give a few reasons why we measure enzymes.
Detection of suspected disease at pre-clinical stage
Organ function assessment
Detection of vitamin deficiencies.
What factors determine enzyme activities in serum/plasma?
-age
-gender
-pregnancy
-race
-time of day
-genetics
-drugs
-disease process, progress and treatment e.g. surgery
When do serum enzyme concs rise?
If there is damage to cells and release of contents.
List some processes which may trigger the release of enzymes from cells.
Cellular damage
Physical damage
Immune disorders
Genetic defects
Nutritional disorders
Define hypoxia.
Loss of oxygen supply due to occlusion, or inadequate oxygenation, or loss of oxygen carrying capacity
Are enzymes specific to certain tissues?
No- they can be found in many different organs and tissues.
The rate of an enzyme-catalysed reaction is directly proportional to?
The amount of enzyme present.
Name two methods of analysing enzymes.
Electrophoresis
Spectrophotometry
Name some problems of taking enzyme measurments.
Not specific i.e. can be found in more than one tissue in the body so if conc is up, does not tell us where in the body it is coming from.
Particular requirements – temperature, pH etc.
Assays must be optimised to the conditions of the enzyme.
Where can alkaline phosphate be found?
Bone, liver, kidney, intestine, placenta.
List some of the reasons for a raised CK (creatine kinase) as a marker of skeletal muscle damage.
-Acute muscle injury
-Surgical operations
-Vigorous exercise
Rhabdomyolysis (breakdown of damaged skeletal muscle).
-Chronic neuromuscular disease e.g. Duchenne muscular dystrophy
-Acute myocardial infarction
-Statins
-Macro-CK
What is a statin?
Any of a group of drugs that lower the amount of cholesterol and certain fats in the blood. Statins inhibit a key enzyme that helps make cholesterol.
If levels of enzyme Thiopurine S-methyltransferase (TPMT) are low, what might this indicate?
Patient at risk of toxicity.
If levels of enzyme Thiopurine S-methyltransferase (TPMT) are high, what might this indicate?
Patient might need a higher dose of the drug as it gets metabolised very quickly.
Name some symptoms of Fabry disease.
Pain in hands and feet
Angiokeratomas (dark red spots on the skin).
Decreased sweating
Corneal opacity
GI problems
Hypertrophic cardiomyopathy
Renal failure
What level of enzyme conc. is consistent w Fabry diease?
Low enzyme conc.
