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Lecture 12 objectives in progress
Lecture 12 objectives in progress
Terms in this set (96)
What are enzymes?
A special class of proteins that function as catalysts, and increase the rate of reaction without being changed or consumed
What is a catalyst?
A chemical that increases the rate of a chemical reaction
What is a substrate?
A substance on which an enzyme acts
What does the first part of an enzyme's name represent?
It is derived from the name of the substrate
What does the second part of an enzyme's name represent?
The type of reaction that the enzyme controls
What are the six categories of enzymes? (List)
What is an oxidoreductase?
An enzyme that catalyzes oxidation-reduction reactions
What is a transferase?
An enzyme that catalyzes the transfer of functional groups from one molecule to another
What is a hydrolase?
An enzyme that catalyzes hydrolysis reactions in which a substance is broken down into simpler compounds through reaction with water molecules
What is a lyase?
An enzyme that catalyzes the addition reactions of water, ammonia or carbon dioxide
What is an isomerase?
An enzyme that catalyzes the rearrangement of functional groups within a molecule, enabling the conversion of one isomer to another
What is a ligase?
An enzyme that catalyzes the condensation or joining of two small biomolecules to form one larger molecule
What is the protein portion of the enzyme called?
What is the name for the enzyme cofactor?
What is an active site?
A water-free cavity or cleft on the surface of an enzyme, which is the position on the enzyme where the substrate binds
What is a diagrammatic illustration of how an enzyme reaction takes place?
E + S ⇔ ES ⇔ E + P
Where E is the enzyme, S is the substrate, ES is the enzyme-substrate complex, and P is the product
What are the six factors that determine whether a forward or a reverse reaction is favored?
1. Substrate concentration
2. Enzyme concentration
What is energy of activation?
The amount of energy required to initiate or "jump start" a reaction
What effect do enzymes have on the energy of activation?
They lower the energy of activation so that less free energy is needed to initiate the reaction
What are the reaction conditions when an enzymatic reaction is occurring at first order kinetics?
~ From the onset of the reaction until it has reached maximum velocity
~ the rate of the reaction is dependent on substrate concentration, which is gradually increased approaching equilibrium (maximum velocity)
What are the reaction conditions when an enzymatic reaction is occurring at zero order kinetics?
~ Once equilibrium (maximum velocity) is reached, the rate of the reaction is no longer dependent on substrate concentration, and the reaction rate is constant
~ increases in substrate concentration will not yield further increases in reaction velocity
Are enzymatic reactions performed in the clinical laboratory performed at first or zero order kinetics, and why?
Zero order kinetics, because the reaction rate is constant
What pH range is optimum for enzyme function?
pH of between 7 and 8
What temperature is optimum for enzyme function?
What is a cofactor?
A non-protein substance that binds to the enzyme before the enzymatic reaction takes place
How is NADH used as a cofactor in many enzymatic reactions?
~ The rate of conversion of NADH to NAD+ is directly proportional to enzyme activity
~ it absorbs UV light in the reduced state (NADH), so a UV spectrophotometer is used to monitor reaction rate changes by measuring absorbance at 340 nm over a period of time
What is an inhibitor?
Any substance that interferes with an enzymatic reaction
What are 3 ways inhibitors may be introduced into a test system?
1. A heavy metal introduced as a contaminant from inadequately washed glassware
2. Insufficiently purified water
3. Some anticoagulants used in the collection of plasma
How are product production or substrate depletion used to determine enzyme activity?
An enzyme assay does not directly measure the concentration of enzyme in serum, but measures the amount of catalytic activity performed by the released enzyme, by measuring increases in either product formation or substrate depletion
What is the fixed-time method for analyzing enzyme reactions?
The reactants are combined, the reaction proceeds for a fixed time, and is then stopped, and the measurement is recorded
What is the kinetic method for analyzing enzyme reactions?
~ it is a continuous monitoring method in which multiple measurements (usually of change in absorbance or ΔA) are made during the reaction at specific time intervals by a spectrophotometer
Which method, kinetic or fixed-time, is more often used and why?
Kinetic, because the linearity of the reaction can be more adequately verified
What units of measure are used for reporting enzyme results?
IU/L or U/L
What is an international unit (IU) of enzyme activity?
The quantity of an enzyme that will catalyze the conversion of one micromole of substrate per minute under optimal conditions
What enzyme does ACP stand for?
What enzyme does ALT stand for?
What enzyme does ALP stand for?
What enzyme does AMS stand for?
What enzyme does AST stand for?
What enzyme does CK stand for?
What enzyme does GGT stand for?
What enzyme does G-6-PD stand for?
What enzyme does LD stand for?
What tissues contain the highest levels of creatine kinase (CK)?
~ skeletal muscle
~ cardiac muscle
~ brain tissue
What are conditions that display elevation of CK enzyme?
~ All forms of muscle disease including muscular dystrophy
~ Following acute myocardial infarction
~ brain tumors
What are the three CK isoenzymes, and where is each predominately found?
1. CK-MM: found predominately in skeletal muscle
2. CK-BB: found primarily in brain tissue
3. CK-MB: found in heart muscle
What is the enzyme that rises first following AMI?
What CK levels can be seen at time frames including 4-6 hours, 18-24 hours, and 36-48 hours following AMI?
Levels > 9 ng/mL within 4-6 hours, peaking at 18-24 hours, and falling to normal by 36-48 hours after AMI
What is the ratio of CK-MB to total CK that is diagnostic for AMI?
CK-MB : total CK > 2.5
(Also stated as CK-MB greater than or equal to 6% of total CK)
What is the reference range for CK in males?
What is the reference range for CK in females?
What tissues is LD found in?
~ skeletal muscle
~ red blood cells
How many LD isoenzymes are there, and which is normally found in highest concentration?
5 LD isoenzymes, LD-2 normally found in highest concentration
What is a "flipped" LD isoenzyme pattern?
When the level of LD-1 concentration is greater than LD-2 concentration
What is the diagnostic significance of a flipped LD isoenzyme pattern?
When seen in conjunction with elevated cardiac troponin or CK-MB, it is suggestive of a heart attack
What are typical LD levels at 12 hours and 14 days following AMI?
LD levels rise 12 hours after an AMI and may remain elevated for 14 days
Which LD isoenzyme fractions are elevated in hemolytic disease?
LD-1 and LD-2
How does hemolysis affect LD results?
Causes a false increase in the LD-1 fraction
What is the reference range for serum LD?
80-280 U/L (but generally found within 45-90 U/L)
What does an aminotransferase do?
Catalyzes the exchange of amino and keto groups between α-amino and α-keto acids
In which tissue is AST found in the highest concentration?
What happens to AST levels at 6 hours, 24 hours, and 5 days after an AMI?
Increases within 6 hours, peaks at 24 hours, and returns to normal after about 5 days after an AMI
What is the reference range for AST?
In which tissue is ALT found in the highest concentration?
What are two types of hepatic disease that show elevated ALT?
Hepatitis and cirrhosis
What is the reference range for ALT?
What tissues have the highest levels of ALP?
Liver and bone
What is the typical ALP finding in obstructive liver diseases?
Significantly elevated levels of ALP
What does an elevation in the heat labile fraction of ALP signify?
What is the ALP isoenzyme produced by the placenta during late pregnancy?
How is Regan ALP isoenzyme used in the diagnosis of germ cell tumors?
Certain germ cell tumors, including testicular cancer and certain tumors of the brain, produce the same type of alkaline phosphatase produced by the placenta (Regan isoenzyme)
What is the reference range for serum ALP?
In what gland is acid phosphatase found in the highest concentration, and what is its level compared with other body tissues?
Prostate gland, has 100x more acid phosphatase than any other body tissue
What specific condition is acid phosphatase used to monitor?
Metastatic prostate cancer
What substance can be used to inhibit the prostatic fraction of acid phosphatase?
What is the reference range for acid phosphatase?
What tissues have the highest concentration of GGT?
What conditions show elevated or markedly elevated GGT levels?
~ Biliary tract obstruction (elevated levels)
~ alcoholism (markedly elevated levels)
What enzyme is the most sensitive marker of alcohol toxicity?
What tissues secrete amylase?
Pancreas and salivary glands
What is the primary way amylase functions?
To break down starches in food into glucose and maltose so they can be used by the body
What is a condition that shows significantly elevated amylase levels?
What specimens may amylase testing be performed on?
Blood and urine
What is the reference range for serum amylase?
60-180 Somogyi units/dL (or 95-290 U/L)
What is the most specific enzyme for diagnosis of acute pancreatitis?
What is the reference range for serum lipase?
What tissues have high levels of aldolase?
Skeletal muscle, liver, and brain tissue
What condition shows markedly elevated levels of aldolase?
Early stages of muscular dystrophy
What is a circumstance in which an elevated level of pseudocholinesterase could be seen?
What effect does a genetic deficiency of pseudocholinesterase sometimes show?
An extended reaction to succinyldicholine (individual doesn't wake up from surgery as quickly as normal)
What enzymes are observed in patients following AMI, in order of appearance?
Elevated total CK appears first, then elevated AST, and last elevated LD. Also elevated CK-MB isoenzyme (>6% of total CK) and LD-1 > LD-2 (flipped LD)
What enzymes are elevated in hepatic conditions?
ALT, AST, LD (especially of LD-4 and LD-5), GGT, and ALP
What enzymes are elevated in skeletal muscle disorders, including muscular dystrophy?
CK, CK-MM (especially in muscular dystrophy), aldolase (especially in muscular dystrophy), AST, and LD
What is an enzyme that is elevated in bone disease?
The heat-labile fraction of alkaline phosphatase
What is an enzyme that is elevated in metastatic prostate cancer?
What are two enzymes that are elevated in acute pancreatitis?
Amylase (serum and urine) and lipase
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