Catalysts and cofactors · Biochemistry
Enzymes & Vitamins MCQ
Enzyme kinetics, coenzymes and cofactors, fat-soluble versus water-soluble vitamins, and the deficiency patterns that show up as oral signs. 25 MCQs and 6 INBDE patient cases.
25 practice MCQsQuick-reference tableMnemonics + clinical pearlsFull distractor explanations
High-yield review
Concept summary and clinical relevance.
Quick-reference structure first, then detailed coverage. Mnemonics in amber, clinical pearls in blue.
Enzymes and vitamins are where biochemistry becomes visible in the mouth. Enzyme kinetics explains how drugs are activated, inhibited, and cleared, including the local anesthetics you inject. Vitamins, working mostly as enzyme cofactors, leave unmistakable signs on the tongue, gums, and lips when they run short, which makes the oral exam a genuine nutrition screen.
Vitamins as cofactors, and the sign when deficient
| Vitamin | Cofactor / role | Classic deficiency sign |
|---|---|---|
| B1 (thiamine) | TPP for pyruvate dehydrogenase | Beriberi; Wernicke (alcohol) |
| B2 (riboflavin) | FAD / FMN | Angular cheilitis, glossitis |
| B3 (niacin) | NAD / NADP | Pellagra (dermatitis, diarrhea, dementia) |
| B6 (pyridoxine) | PLP for transamination | Neuropathy, glossitis (isoniazid) |
| B9 (folate) | THF for DNA synthesis | Megaloblastic anemia; neural tube defects |
| B12 (cobalamin) | Methylation and odd-chain fat | Megaloblastic anemia + neurologic damage |
| C (ascorbate) | Collagen hydroxylation | Scurvy: bleeding gums, poor healing |
| D | Calcium and phosphate absorption | Rickets / osteomalacia |
| K | Clotting factor carboxylation | Bleeding |
Enzyme Kinetics
- Enzymes speed reactions by lowering the activation energy; they do not change the reaction's equilibrium or overall energy.
- Km is the substrate concentration at half of maximum velocity and reflects affinity: a low Km means high affinity for substrate.
- A competitive inhibitor raises the apparent Km (more substrate is needed) but leaves Vmax unchanged; a noncompetitive inhibitor lowers Vmax with Km unchanged.
- Many pathways are controlled by feedback (end-product) inhibition of an early, often allosteric, enzyme, and many enzymes are made as inactive zymogens (trypsinogen, pepsinogen, prothrombin) activated only when needed.
Clinical pearl, Enzymes and your local anesthetic
Ester local anesthetics (procaine, tetracaine, benzocaine) are broken down in the plasma by pseudocholinesterase, while amide anesthetics (lidocaine, articaine) are cleared by the liver. A patient with pseudocholinesterase deficiency, or with liver disease, clears these drugs slowly, which is a real reason to know which class you are giving.
Coenzymes & Cofactors
- A coenzyme is a small organic helper molecule, usually vitamin-derived; a cofactor is often an inorganic metal ion (zinc, magnesium, iron).
- Most B vitamins become coenzymes: niacin gives NAD and NADP, riboflavin gives FAD, thiamine gives TPP, pantothenate gives coenzyme A, and pyridoxine (B6) gives PLP.
- Biotin is the cofactor for carboxylase enzymes; folate becomes tetrahydrofolate for one-carbon transfers in DNA synthesis.
- Because so many enzymes depend on these vitamin cofactors, a single vitamin deficiency can impair several pathways at once.
Mnemonic, Niacin and FAD
“NAD from Niacin (B3), FAD from riboFlavin (B2).” The energy-carrying coenzymes track back to specific B vitamins.
Fat-Soluble vs Water-Soluble Vitamins
- Fat-soluble vitamins are A, D, E, and K. They need bile and dietary fat to be absorbed, are stored in the liver and fat, and can build up to toxic levels.
- Water-soluble vitamins are the B vitamins and vitamin C. They are generally not stored (B12 is the exception, stored in the liver), so deficiencies develop faster and excess is excreted in urine.
- Fat malabsorption (bile obstruction, pancreatic insufficiency, celiac disease) preferentially threatens the fat-soluble vitamins, including the vitamin K needed for clotting.
- Vitamin K is required to carboxylate clotting factors II, VII, IX, and X; warfarin works by antagonizing vitamin K.
Clinical pearl, Vitamin K, warfarin, and bleeding
Because warfarin blocks the recycling of vitamin K, it lowers the active vitamin K-dependent clotting factors, and its effect is tracked by the INR. Vitamin K reverses it. For most single extractions in a patient whose INR is in therapeutic range, current guidance is to continue the warfarin and rely on local hemostatic measures rather than stopping it, but always confirm the INR and coordinate with the physician.
Vitamin Deficiency Patterns
- Vitamin C deficiency (scurvy) produces swollen, spongy, bleeding gums, poor wound healing, and easy bruising, because collagen cannot be properly cross-linked.
- Niacin (B3) deficiency causes pellagra, remembered as the three Ds: dermatitis, diarrhea, and dementia, often with glossitis and stomatitis.
- B12 and folate deficiency both cause a megaloblastic anemia with a smooth, sore tongue, but only B12 deficiency causes neurologic damage; folate deficiency in pregnancy risks neural tube defects.
- Riboflavin (B2) deficiency causes angular cheilitis and glossitis, and iron deficiency produces a similar atrophic, pale tongue with angular cheilitis.
Clinical pearl, Why this matters in dentistry
The mouth often shows a deficiency before the patient feels it. A smooth, sore tongue suggests B12, folate, or iron; angular cheilitis suggests B-vitamins or iron; spongy bleeding gums out of proportion to plaque suggest vitamin C; and easy bleeding suggests vitamin K. The dentist's role is to recognize the pattern and refer for blood work, not to diagnose the deficiency outright.
Core Recall Check
25 board-style MCQs.
Active recall is the highest-yield study method. Pick an answer, check it, and read why every distractor is wrong.
0 of 25 answered · 0 correct
Keys: A-E or 1-5, Enter to check
- Question 1EasyEnzymes increase the rate of a reaction by:
- Question 2ModerateThe Km of an enzyme is the substrate concentration at which the enzyme runs at:
- Question 3ModerateA low Km indicates that an enzyme has:
- Question 4HardA competitive inhibitor characteristically:
- Question 5ModerateFeedback inhibition of a metabolic pathway usually means the:
- Question 6ModerateA zymogen is best described as:
- Question 7HardEster local anesthetics (such as procaine) are metabolized mainly by:
- Question 8ModerateA coenzyme differs from a metal cofactor in that a coenzyme is:
- Question 9ModerateNAD+ and NADP+, the major electron-carrying coenzymes, are derived from:
- Question 10ModerateFAD, a coenzyme in the Krebs cycle and electron transport, comes from:
- Question 11HardTransamination reactions require a coenzyme derived from:
- Question 12HardCarboxylase enzymes (such as pyruvate carboxylase) depend on which cofactor?
- Question 13EasyThe fat-soluble vitamins are:
- Question 14ModerateCompared with water-soluble vitamins, fat-soluble vitamins are more likely to:
- Question 15ModerateWhich patient is at greatest risk for fat-soluble vitamin deficiency?
- Question 16HardVitamin K is required to activate which clotting factors?
- Question 17ModerateVitamin D's main role is to:
- Question 18ModerateVitamin C deficiency causes scurvy because vitamin C is required for:
- Question 19ModeratePellagra, with dermatitis, diarrhea, and dementia, results from deficiency of:
- Question 20HardWhich deficiency causes a megaloblastic anemia AND neurologic damage?
- Question 21ModerateAngular cheilitis and glossitis are classically associated with deficiency of:
- Question 22ModerateVitamin A deficiency classically causes:
- Question 23ModerateThiamine (B1) deficiency, common in chronic alcohol use, causes:
- Question 24ModerateAdequate folate before and during early pregnancy is important to prevent:
- Question 25ModerateAmide local anesthetics (such as lidocaine) are cleared mainly by the:
Clinical Reasoning Cases
INBDE patient cases.
6 ADA INBDE-format patient cases on enzymes & vitamins. Each case is a shared patient box plus linked questions with full distractor explanations.
INBDE Patient Cases
Enzymes & Vitamins INBDE Patient Cases →
6 patient cases · 30 linked questions
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Author
Dr. Isaac Sun, DDS
Founder, KYT Dental Services. These MCQs are reviewed by a practicing clinician and offered as an educational reference for dental students.
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