Active Sites & Specificity
What is the active site (or active center) of an enzyme?
The region of the enzyme where substrate binding and catalysis occur
Which primary enzyme class cleaves chemical bonds using water, encompassing most human digestive enzymes?
Hydrolases
What is the definition of the Michaelis Constant (๐พ๐) on a substrate saturation curve?
The substrate concentration [๐] at which reaction velocity ๐ is equal to 1/2 ๐max
What defines Competitive Inhibition regarding the inhibitor's binding site?
Inhibitor molecules compete directly with the substrate for binding at the active site
A 24-year-old female presents with abdominal bloating, cramps, and watery diarrhea after consuming milk products. What enzyme deficiency is responsible for this condition?
Shortage of lactase enzyme preventing breakdown of milk sugars
Which catalytic amino acid triad is located at the active site of Chymotrypsin?
His (57), Asp (102), Ser (195)
Which primary enzyme class joins two separate molecules together using energy derived from ATP?
Ligases
How do enzymes affect the equilibrium constant (๐พeq) and free energy change (ฮ๐บ) of a chemical reaction?
Enzymes do NOT change ๐พeq or ฮ๐บ; they only accelerate the rate at which equilibrium is reached
How does a Competitive Inhibitor alter the kinetic parameters ๐พ๐ and ๐max?
Apparent ๐พ๐ increases; ๐maxremains unchanged
A 58-year-old male presents to the ER with crushing substernal chest pain. Diagnostic blood work reveals markedly elevated serum Aspartate Aminotransferase (AST). What cellular event causes AST to rise in serum during Myocardial Infarction?
Heart cells die from lack of oxygen, spilling intracellular AST into circulation
How does the Lock-and-Key model of substrate binding differ from the Induced-Fit model?
Lock-and-Key posits the substrate fits perfectly into a rigid active site; Induced-Fit posits the active site conforms its shape upon substrate binding
How do Lyases differ from Hydrolases in their mechanism of bond cleavage?
Lyases break chemical bonds by means other than hydrolysis or oxidation
What effect does accumulating high product concentration have on enzyme reaction velocity?
It decreases velocity by causing product inhibition, slowing forward catalysis, and shifting equilibrium backward
What defines Non-competitive Inhibition regarding binding site and kinetic parameters?
Inhibitor binds to an allosteric site (not the active site); ๐พ๐ remains unchanged while ๐max decreases
A 48-year-old patient with chronic pancreatitis presents with bulky, foul-smelling, fatty stools (steatorrhea) and weight loss. What condition is present, and what is its cause?
Exocrine Pancreatic Insufficiency (EPI); failure to release enough pancreatic enzymes like lipase or amylase
Human enzymes exhibit strict stereochemical specificity. Which specific optical isomers do human enzymes recognize?
L-amino acids and D-carbohydrates
Match the group-transferring co-enzymes Pyridoxal phosphate (PLP), Biotin, and Coenzyme-A (Co-A) to their respective transferred groups.
PLP (Amino group), Biotin (Carbon dioxide), Co-A (Acyl groups)
Why does enzyme activity display a bell-shaped curve across varying pH levels?
pH determines the charge on amino acid residues at the active site, influencing substrate binding and catalysis
What is Allosteric Regulation?
A regulatory molecule binds at a site other than the active site (allosteric site), changing shape and turning activity on or off
A newborn infant screens positive for Phenylketonuria (PKU). Which enzyme is deficient, and what dangerous accumulation occurs if left untreated?
Phenylalanine Hydroxylase (PAH) deficiency; dangerous buildup of phenylalanine that harms brain development
A research isolate synthesizes a peptidoglycan layer composed exclusively of D-amino acids. A human proteolytic enzyme added to the culture fails to degrade the cell wall. What is the primary biochemical explanation for this failure?
Human proteases exhibit strict stereochemical specificity for L-amino acids and cannot bind D-optical isomers
In glycolysis, Hexokinase catalyzes the conversion of Glucose to Glucose-6-phosphate. Which group-transferring co-enzyme is required for this reaction, and which enzyme class carries out this reaction?
ATP (transfers Phosphate); Transferases
An astrocyte reaction has a positive enthalpy change (ฮ๐ป>0) and a positive entropy change (ฮS>0). Under which conditions will this enzyme-catalyzed reaction occur spontaneously (ฮ๐บ<0)?
At high temperatures
A researcher studying a novel enzyme finds that a specific inhibitor binds ONLY to the enzyme-substrate (๐ธโ๐) complex. How will this inhibitor affect the apparent ๐พ๐ and ๐max?
Apparent ๐พ๐ decreases and ๐max decreases
A patient presenting with jaundice and right upper quadrant abdominal pain has elevated serum AST and ALT. Besides cardiac tissue, which organ contains high concentrations of AST that spill into blood during cellular injury?
Liver