2. Chapter 1–2: Enzymes
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87 Terms
What are enzymes?
Biological catalysts that speed up chemical reactions without being consumed.
How do enzymes speed up reactions?
They lower the activation energy.
What is the basic enzyme reaction?
Substrate is converted into product with help of an enzyme.
What is enzyme specificity?
An enzyme usually works only with one or a few specific substrates.
What are most enzymes made of?
Proteins.
What is a simple enzyme?
An enzyme composed only of amino acids.
What is a conjugated enzyme?
A protein enzyme combined with a non-protein group.
What is an endoenzyme?
An enzyme that acts where it is produced.
What is an exoenzyme?
An enzyme produced in one place but acting somewhere else.
What are isoenzymes?
Enzymes that catalyze the same reaction but have different physical and chemical properties.
What is the active site?
The specific part of the enzyme where the substrate binds.
What is the lock and key model?
The active site already fits the substrate perfectly.
What is the induced fit model?
The enzyme changes shape slightly to fit the substrate better.
What are contact amino acids?
Amino acids that help bind the substrate.
What are catalytic amino acids?
Amino acids that directly participate in the chemical reaction.
What is the Michaelis-Menten theory?
The enzyme and substrate form an enzyme-substrate complex, then product is formed and the enzyme is released unchanged.
What is the enzyme-substrate complex?
A temporary complex formed when enzyme and substrate bind.
What happens to the enzyme after the reaction?
It is released unchanged and can be reused.
Which factors affect enzyme reaction rate?
Temperature, pH, enzyme concentration, substrate concentration, activators, and inhibitors.
What happens when temperature increases?
Reaction rate increases until the optimum temperature is reached.
What happens above the optimum temperature?
The enzyme denatures and loses function.
What is optimum pH?
The pH at which an enzyme works best.
What happens in very acidic or alkaline conditions?
Most enzymes denature and lose activity.
How does enzyme concentration affect reaction rate?
If enough substrate is present, more enzyme means faster reaction.
How does substrate concentration affect reaction rate?
The rate increases until enzymes are saturated and Vmax is reached.
What is Vmax?
The maximum reaction rate of an enzyme reaction.
What is Km?
The substrate concentration at which reaction rate is half of Vmax.
What does low Km mean?
Strong enzyme-substrate binding.
What does high Km mean?
Weaker enzyme-substrate binding.
What are enzyme activators?
Substances that increase enzyme activity.
Which ions can act as enzyme activators?
Mg²⁺, Ca²⁺, Cu²⁺, Zn²⁺.
What are enzyme inhibitors?
Substances that decrease enzyme activity.
What is competitive inhibition?
Inhibitor competes with the substrate for the active site.
What is non-competitive inhibition?
Inhibitor binds outside the active site and reduces enzyme activity.
What is acompetitive inhibition?
Inhibitor binds only to the enzyme-substrate complex.
What is allosteric inhibition?
Inhibitor binds to an allosteric site and reduces enzyme activity.
What is irreversible inhibition?
Inhibitor permanently blocks the enzyme.
Why are enzymes important in clinical diagnosis?
Changed enzyme levels can show tissue or organ damage.
Why do enzyme levels increase in blood?
Increased synthesis, membrane leakage, cell necrosis, impaired secretion, or impaired elimination.
What is enzyme half-life?
Time needed for enzyme activity to decrease to half of its original value.
Why is enzyme half-life clinically important?
It helps doctors choose the right testing time and interpret results.
What is the half-life of AST?
12–22 hours.
What is the half-life of ALT?
37–57 hours.
What is the half-life of CK?
About 15 hours.
What is the half-life of alpha-amylase?
3–6 hours.
How is enzyme activity measured in laboratory medicine?
By measuring the rate of a reaction catalyzed by the enzyme.
What is the single-point method?
Enzyme activity is measured at one fixed time point.
What is the kinetic method?
The reaction is monitored continuously over time.
What does the optical test use?
The absorbance difference between NADH/NADPH and NAD⁺/NADP⁺.
At which wavelength does NADH absorb strongly?
Around 340 nm.
What happens to absorbance when NADH is oxidized?
Absorbance decreases.
Which enzyme assay is a classic example of the optical test?
LDH activity determination.
What are common clinical enzymes?
AST, ALT, CK, alpha-amylase, GGT, LDH, ALP, lipase, cholinesterase.
What is AST mainly found in?
Liver, heart, and skeletal muscle.
What is AST used for?
Hepatobiliary disease, myocardial infarction, and skeletal muscle disease.
What does AST/ALT ratio > 1 suggest?
Progressive or more severe liver disease.
What does AST/ALT ratio < 1 suggest?
Milder liver disease.
What is ALT mainly specific for?
Liver damage.
Why is ALT more liver-specific than AST?
It has its highest concentration in the liver.
When do ALT and AST rise in viral hepatitis?
They rise early, often before bilirubin.
What is CK important for?
Muscle and heart damage.
What are the CK isoenzymes?
CK-MM, CK-MB, and CK-BB.
Where is CK-MM found?
Skeletal muscle.
Where is CK-MB found?
Heart.
Where is CK-BB found?
Brain.
Is CK-MB the best marker for myocardial infarction today?
No, troponin is the gold standard.
What does alpha-amylase do?
Hydrolyzes alpha-1,4 glycosidic bonds in starch and glycogen.
Where is alpha-amylase mainly found?
Pancreas and salivary glands.
In which disease is alpha-amylase increased?
Acute pancreatitis.
Why is amylase not completely specific?
It can also increase in salivary gland disease, kidney disease, ileus, appendicitis, and other conditions.
What is GGT used for?
Marker of hepatobiliary damage.
When is GGT strongly increased?
Obstructive jaundice, chronic active hepatitis, cirrhosis, and liver cancer.
What does LDH do?
Converts pyruvate to lactate and lactate to pyruvate.
Why is LDH not specific?
It is present in many tissues.
How many LDH isoenzymes exist?
Five.
Where are LDH1 and LDH2 mainly found?
Heart and erythrocytes.
Where are LDH4 and LDH5 mainly found?
Liver and skeletal muscle.
What is ALP important for?
Bone disease and hepatobiliary disease.
Where is ALP physiologically elevated?
Children, puberty, pregnancy, and fracture healing.
Which bone diseases increase ALP?
Paget disease, osteomalacia, bone tumors, and rickets.
Which liver condition strongly increases ALP?
Extrahepatic biliary obstruction.
What does lipase do?
Hydrolyzes triglycerides into fatty acids and glycerol.
Where is lipase mainly produced?
Pancreas.
Why is lipase useful in acute pancreatitis?
It remains elevated longer than amylase.
What is cholinesterase used for clinically?
Marker of liver function and organophosphate poisoning.
What happens to cholinesterase in liver dysfunction?
It decreases.
What happens to cholinesterase in organophosphate poisoning?
It is inhibited.