FMGE 2023 - Biochemistry Practice Questions

Q: A family pedigree chart is given below. Identify the mode of inheritance of this condition. ![img-29.jpeg](img-29.jpeg)

Autosomal dominant. ***Autosomal dominant*** - The trait is seen in **every generation** (vertical transmission), and affected parents (individuals 1 and 2) have an unaffected child (individual 7), which is a hallmark of dominant inheritance. - There is **male-to-male transmission** from the affected father (individual 4) to his son (individual 9), which rules out X-linked inheritance. *Autosomal recessive* - This is incorrect because two affected parents (1 and 2) have an unaffected offspring (7). In autosomal recessive inheritance, two affected parents (genotype **aa**) can only produce affected offspring. - The trait does not **skip generations**, which is a typical feature of recessive inheritance patterns. *X-linked recessive* - This is ruled out because an affected mother (2) has an unaffected son (7). In X-linked recessive traits, an affected mother (genotype **X a X a **) must pass the affected allele to all her sons, meaning all her sons would be affected. - Also, an unaffected couple (7 and 8) would need to have an affected child for this pattern to be considered, which is not the case here. *X-linked dominant* - The presence of **male-to-male transmission** (from father 4 to son 9) makes this mode of inheritance impossible. - In X-linked inheritance, a father passes his **Y chromosome** to his sons and his X chromosome to his daughters, so an affected father cannot have an affected son via this mechanism.

Q: A family pedigree chart is given below. Identify the mode of inheritance of this condition.

Autosomal dominant. ***Autosomal dominant*** - The trait is observed in **every generation** (I, II), which is a hallmark of dominant inheritance, as it does not skip generations. - The presence of **male-to-male transmission** (individual 4 to individual 9) definitively rules out X-linked inheritance. Additionally, affected parents (1 and 2) have an unaffected child (7), indicating the parents are likely heterozygous. *Autosomal recessive* - This is ruled out because two affected parents (1 and 2) have an unaffected child (7). If the trait were recessive, all children of two affected parents **must also be affected**. - Typically, autosomal recessive traits **skip generations**, with carriers being phenotypically normal, which is not the pattern seen here. *X-linked recessive* - An affected mother (individual 2) must pass the recessive allele to **all of her sons**. However, her son (individual 7) is unaffected, which contradicts this inheritance pattern. - The presence of **male-to-male transmission** (4 to 9) is impossible in X-linked inheritance, as fathers pass their Y chromosome to sons, not the X chromosome carrying the trait. *X-linked dominant* - An affected father must pass the trait to **all of his daughters**. In this pedigree, the affected father (individual 4) has an unaffected daughter (individual 8), which rules out this mode. - Similarly, another affected father (individual 9) has an unaffected daughter (individual 11), further disproving this pattern.

Q: A child has elevated liver enzyme levels. A ring-like structure is noted on ocular examination. Which of the following is the cause for this?

Copper. ***Copper***- The combination of elevated **liver enzymes** (hepatitis/cirrhosis) and the characteristic **Kayser-Fleischer (KF) rings** visible on ocular examination is pathognomonic for **Wilson's disease**.- **Wilson's disease** is an inherited disorder involving defective biliary excretion of **copper**, causing its toxic accumulation in tissues, notably the liver, brain, and cornea.*Zinc*- Zinc is an essential trace element, but its deficiency presents primarily with **acrodermatitis enteropathica**, not hepatic failure and KF rings.- Zinc supplementation is sometimes used as a treatment for Wilson's disease because it inhibits the absorption of **copper** in the gut.*Selenium*- Deficiency of **Selenium** is associated with **Keshan disease** (cardiomyopathy) and impaired antioxidant protection, rather than liver disease with corneal rings.- High levels of selenium, though rare, can lead to hair loss and nail changes (**selenosis**).*Iron*- Excessive accumulation of **Iron** causes **hemochromatosis**, which leads to hepatomegaly, cirrhosis, and **bronze diabetes**.- Iron overload does not result in the formation of **Kayser-Fleischer rings**; these rings are exclusively caused by **copper** deposition in the Descemet membrane.

Q: Which of the following is not a microelement?

Calcium. ***Calcium***- Calcium is classified as a **macroelement** (or major mineral) because the body requires it in large quantities, often exceeding 100 mg daily.- It is essential for **bone mineralization**, muscle contraction, and is the most abundant mineral in the human body.*Copper*- Copper is a **microelement** (or trace mineral) and is required in amounts less than 100 mg per day.- It functions as a cofactor for several antioxidant and electron transport enzymes, crucial for **iron metabolism**.*Zinc*- Zinc is a **microelement** vital for immune function, protein synthesis, and is required in trace daily amounts.- It is a necessary cofactor for the function of over 300 enzymes, playing a key role in **gene expression** and wound healing.*Selenium*- Selenium is a **microelement** known for its antioxidant properties and is required in minute quantities (micrograms) daily.- It is structurally central to **glutathione peroxidase**, an enzyme that protects cells from oxidative damage.

Q: Which enzymes use molecular oxygen as a hydrogen acceptor to produce water?

Cytochrome c oxidase. ***Cytochrome c oxidase*** - This enzyme (Complex IV of the ETC) is responsible for the final step of cellular respiration, where it accepts electrons from **Cytochrome c**. - It catalyzes the four-electron reduction of molecular oxygen (**O₂**) to two molecules of **water** (**H₂O**), utilizing O₂ as the terminal hydrogen/electron acceptor. *Catalase* - Catalase breaks down **hydrogen peroxide** (**H₂O₂**) into water and molecular oxygen, acting as a peroxidase and protecting cells from reactive oxygen species. - It facilitates the breakdown of an existing toxic product and does not use O₂ as a hydrogen acceptor in a reduction reaction. *Superoxide dismutase* - This enzyme converts the hazardous **superoxide radical** (**O₂⁻**) into molecular oxygen and hydrogen peroxide. - It is critical for antioxidant defense but is involved in dismutation reactions, not in using O₂ as the final acceptor to form water. *Pyruvate dehydrogenase* - The pyruvate dehydrogenase complex links glycolysis to the Krebs cycle by converting **pyruvate** to **acetyl-CoA** (oxidative decarboxylation). - Its electron acceptors are **NAD⁺** and **lipoic acid** (which accept hydrogens/electrons to form NADH and reduced lipoic acid), not molecular oxygen.

Q: A 34-year-old male whose staple diet primarily consisted of only maize presents with diarrhea, dementia, and photosensitive dermatitis in sun-exposed areas. Which vitamin is most likely deficient in this patient?

Niacin. **Correct: Niacin** - The constellation of **dementia**, **diarrhea**, and **photosensitive dermatitis** (the 3 Ds) is the hallmark presentation of **Pellagra**. - A diet reliant on **maize** (corn) is a classic cause of Pellagra because maize is deficient in **tryptophan**, a vital precursor to Niacin (Vitamin B3). - Pellagra can progress to a fourth D (**Death**) if untreated. *Incorrect: Vitamin B6* - Deficiency typically manifests as **peripheral neuropathy**, **seborrheic dermatitis** (non-photosensitive), and microcytic anemia (**sideroblastic anemia**). - It is not associated with the severe chronic diarrhea or the characteristic sun-exposed rash seen in Pellagra. *Incorrect: Ascorbic acid* - Deficiency causes **Scurvy**, characterized by **bleeding gums**, **perifollicular hemorrhages** (petechiae), and **impaired wound healing**. - Neurological symptoms typical of dementia and pronounced gastrointestinal symptoms are not primary features of Scurvy. *Incorrect: Biotin* - Biotin (Vitamin B7) deficiency is rare, usually presenting with **alopecia**, non-specific dermatitis, and sometimes hypotonia or developmental delay. - It is differentiated by the absence of characteristic photosensitive rash and the severe central nervous system symptoms (dementia) that define this case.

Q: A female patient complains of swelling and pain in her great toe. Her uric acid level is found to be high. A drug that reduces uric acid levels is prescribed. Which of the following enzymes should the drug inhibit?

Xanthine oxidase. ***Xanthine oxidase*** - **Xanthine oxidase** catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid in the purine degradation pathway - **Xanthine oxidase inhibitors** (allopurinol, febuxostat) are the mainstay drugs for chronic management of hyperuricemia and gout - By inhibiting this enzyme, these drugs reduce uric acid production, lowering serum uric acid levels and preventing crystal deposition in joints - The clinical presentation of **podagra** (acute pain and swelling of the great toe) with elevated uric acid is classic for **acute gouty arthritis** *Lysyl oxidase* - Involved in cross-linking collagen and elastin in connective tissue formation - Not related to purine metabolism or uric acid synthesis - Inhibition would affect collagen strength, not uric acid levels *Homogentisate oxidase* - Enzyme in the tyrosine degradation pathway - Deficiency causes alkaptonuria (accumulation of homogentisic acid) - Not involved in purine metabolism *Urease* - Bacterial enzyme that hydrolyzes urea to ammonia and carbon dioxide - Found in bacteria like *Helicobacter pylori* and *Proteus* species - Not involved in human uric acid synthesis or metabolism

Q: A patient presented to the OPD with liver damage. The picture depicts the patient having their eyes examined. Which of the following substances is responsible for this condition?

Copper. ***Copper*** - The image displays a **Kayser-Fleischer ring**, a greenish-gold ring at the corneal limbus, which is a hallmark sign of **Wilson's disease**. This condition, combined with liver damage, points to an issue with copper metabolism. - Wilson's disease is an autosomal recessive disorder caused by a mutation in the **ATP7B gene**, leading to impaired biliary excretion and subsequent toxic accumulation of **copper** in the liver, brain, and cornea. *Glucose* - Elevated **glucose** levels, as seen in diabetes mellitus, can cause ocular complications such as **diabetic retinopathy** and **cataracts**, but not Kayser-Fleischer rings. - While diabetes can be associated with liver disease (e.g., **NAFLD**), the combination of this specific eye finding and liver damage is not characteristic of glucose-related pathology. *Galactose* - Excess **galactose** is characteristic of **galactosemia**, an inherited metabolic disorder that can cause liver failure and cirrhosis, similar to Wilson's disease. - However, the classic ocular finding in galactosemia is the formation of **"oil-droplet" cataracts**, not the Kayser-Fleischer rings shown in the image. *Mannose* - Disorders of **mannose** metabolism are typically classified as **congenital disorders of glycosylation (CDGs)**. - These rare genetic disorders present with a wide spectrum of multi-systemic symptoms, including neurological and developmental issues, but are not associated with the development of Kayser-Fleischer rings.

Q: A patient who was in excruciating pain all over his body was taken to the hospital. In recent years, he has experienced these episodes frequently. When exercising vigorously, the pain begins. Anemia was detected on blood examination along with sickled RBCs as opposed to normal biconcave ones. It was determined that he had sickle cell anemia. What substitution takes place in sickle cell anemia?

Substitution of glutamic acid by valine at the 6th position. ***Substitution of glutamic acid by valine at the 6th position***- This is the defining molecular defect in **sickle cell anemia** (HbS), resulting from a point mutation (GAG $\rightarrow$ GTG) in the $\beta$-globin gene.- The replacement of the hydrophilic amino acid **glutamic acid** by the hydrophobic amino acid **valine** at the **6th position** facilitates the polymerization of **deoxy-HbS** under low oxygen tension, causing RBC sickling.*Substitution of valine by glutamic acid at the 6th position*- This change is the **opposite** of the mutation causing HbS; HbS involves the substitution of a hydrophilic residue (Glutamic acid) with a **hydrophobic** one (Valine).- This particular reverse substitution would not lead to the formation of the **deoxy-HbS polymers** responsible for the sickling phenomenon.*Substitution of valine by glutamic acid at the 5th position*- The amino acid at the 5th position of the $\beta$-globin chain is typically **proline**, and the crucial molecular abnormality in HbS involves the **6th position**, not the 5th.- The defining mutation involves Glutamic acid being replaced by Valine, not Valine being replaced by Glutamic acid.*Substitution of glutamic acid by valine at the 5th position*- While the amino acid change (Glutamic acid $\rightarrow$ Valine) is correct for the type of substitution, the characteristic mutation of **sickle cell anemia** occurs specifically at the **6th position**.- Substitutions at different positions (like the 5th) usually result in other, distinct hemoglobin variants.

Q: Vitamin A deficiency leads to?

Xerophthalmia. ***Xerophthalmia***- **Vitamin A** (retinol) is essential for the formation of **rhodopsin**, the photopigment necessary for low-light vision, making deficiency a primary cause of **night blindness** (nyctalopia).- Deficiency leads to **keratinization** of the *corneal and conjunctival epithelium*, resulting in dryness of the eye (*xerosis*), progressing to corneal ulcers and potentially blindness (*keratomalacia*).*Beriberi*- Caused by a deficiency of **Vitamin B1** (**thiamine**), which is crucial for carbohydrate metabolism.- Symptoms include **peripheral neuropathy** (dry beriberi) or high-output cardiac failure (wet beriberi).*Pellagra*- Caused by a deficiency of **Vitamin B3** (**niacin**), or its precursor **tryptophan**.- Classically presents with the '3 Ds': **dermatitis**, **diarrhea**, and **dementia** (and eventually death).*Neuropathy*- While severe Vitamin A deficiency can cause secondary issues, primary **neuropathy** is mainly associated with deficiencies of B-vitamins like **B1** (thiamine), **B6** (pyridoxine), or **B12** (cobalamin).- *Neuropathy* is a symptom and not the specific disease term commonly linked directly and primarily to Vitamin A deficiency, which is **xerophthalmia**.

Question 1

A family pedigree chart is given below. Identify the mode of inheritance of this condition. ![img-29.jpeg](img-29.jpeg)

Accepted Answer

Autosomal dominant

Answer

Autosomal recessive

Answer

X-linked recessive

Answer

X-linked dominant

Question 2

A family pedigree chart is given below. Identify the mode of inheritance of this condition.

Accepted Answer

Autosomal dominant

Answer

X-linked dominant

Answer

Autosomal recessive

Answer

X-linked recessive

Question 3

A child has elevated liver enzyme levels. A ring-like structure is noted on ocular examination. Which of the following is the cause for this?

Accepted Answer

Copper

Answer

Zinc

Answer

Selenium

Answer

Iron

Question 4

Which of the following is not a microelement?

Accepted Answer

Calcium

Answer

Copper

Answer

Selenium

Answer

Zinc

Question 5

Which enzymes use molecular oxygen as a hydrogen acceptor to produce water?

Accepted Answer

Cytochrome c oxidase

Answer

Catalase

Answer

Superoxide dismutase

Answer

Pyruvate dehydrogenase

Question 6

A 34-year-old male whose staple diet primarily consisted of only maize presents with diarrhea, dementia, and photosensitive dermatitis in sun-exposed areas. Which vitamin is most likely deficient in this patient?

Accepted Answer

Niacin

Answer

Vitamin B6

Answer

Ascorbic acid

Answer

Biotin

Question 7

A female patient complains of swelling and pain in her great toe. Her uric acid level is found to be high. A drug that reduces uric acid levels is prescribed. Which of the following enzymes should the drug inhibit?

Accepted Answer

Xanthine oxidase

Answer

Lysyl oxidase

Answer

Homogentisate oxidase

Answer

Urease

Question 8

A patient presented to the OPD with liver damage. The picture depicts the patient having their eyes examined. Which of the following substances is responsible for this condition?

Accepted Answer

Copper

Answer

Glucose

Answer

Galactose

Answer

Mannose

Question 9

A patient who was in excruciating pain all over his body was taken to the hospital. In recent years, he has experienced these episodes frequently. When exercising vigorously, the pain begins. Anemia was detected on blood examination along with sickled RBCs as opposed to normal biconcave ones. It was determined that he had sickle cell anemia. What substitution takes place in sickle cell anemia?

Accepted Answer

Substitution of glutamic acid by valine at the 6th position

Answer

Substitution of valine by glutamic acid at the 5th position

Answer

Substitution of glutamic acid by valine at the 5th position

Answer

Substitution of valine by glutamic acid at the 6th position

Question 10

Vitamin A deficiency leads to?

Accepted Answer

Xerophthalmia

Answer

Beriberi

Answer

Neuropathy

Answer

Pellagra

FMGE 2023 — Biochemistry