Biomolecules, metabolism, vitamins, nutrition and porphyrins

71 Kerala PSC Lab Technician Gr II practice questions on Biomolecules, metabolism, vitamins, nutrition and porphyrins, part of Biochemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
In humans, what is the end product of purine catabolism?
1. AUrea
2. BAllantoin
3. CUric acid
4. DBeta-alanine
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Answer: C · Uric acid
Adenine and guanine are broken down through hypoxanthine and xanthine, and xanthine oxidase converts these to uric acid, which is excreted in urine. Humans lack uricase, which in most other mammals turns uric acid into the more soluble allantoin. A high serum uric acid causes gout, and allopurinol lowers it by inhibiting xanthine oxidase.
- A: Urea is the end product of amino acid nitrogen, made in the urea cycle.
- B: Allantoin is formed by uricase, which humans lack.
- D: Beta-alanine comes from the breakdown of pyrimidines.
Question 2 · Easy
Wilson disease is an inherited disorder of the metabolism of which metal?
1. ACopper
2. BIron
3. CCalcium
4. DZinc
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Answer: A · Copper
A defect in the ATP7B copper transporter stops the liver from excreting copper into bile and loading it onto ceruloplasmin. Copper builds up in the liver, the brain (basal ganglia) and the cornea, where it forms Kayser-Fleischer rings. Typical results are a low serum ceruloplasmin, a raised 24-hour urine copper and a high liver copper content.
- B: Inherited iron overload is hemochromatosis.
- C: Calcium disorders involve parathyroid hormone and vitamin D, not ATP7B.
- D: Zinc is used to treat Wilson disease because it blocks copper absorption.
Question 3 · Medium
During prolonged starvation lasting several weeks, the brain meets much of its energy need from:
1. AFree fatty acids
2. BKetone bodies
3. CAmino acids
4. DGlycerol
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Answer: B · Ketone bodies
After a few days of fasting, the liver turns fatty acids into acetoacetate and beta-hydroxybutyrate, which cross the blood-brain barrier. In prolonged starvation these ketone bodies supply a large share of the brain's energy, up to about two-thirds, so less glucose has to be made from muscle protein. Ketonuria is therefore expected in starvation.
- A: Fatty acids bound to albumin do not cross the blood-brain barrier well.
- C: Amino acids are used by the liver for gluconeogenesis, not as direct brain fuel.
- D: Glycerol is a minor substrate for gluconeogenesis, not a direct brain fuel.
Question 4 · Easy
Phenylketonuria is caused by deficiency of:
1. AFumarylacetoacetate hydrolase
2. BHomogentisate oxidase
3. CPhenylalanine hydroxylase
4. DTyrosinase
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Answer: C · Phenylalanine hydroxylase
Phenylalanine hydroxylase converts phenylalanine to tyrosine in the liver, using tetrahydrobiopterin. In PKU, phenylalanine builds up and is converted to phenylpyruvate and other phenylketones, causing a mousy odor and intellectual disability if untreated. Newborn screening and a low-phenylalanine diet prevent the damage; urine phenylpyruvate gives a green color with ferric chloride.
- A: Fumarylacetoacetate hydrolase deficiency causes tyrosinemia type 1.
- B: Homogentisate oxidase deficiency causes alkaptonuria.
- D: Tyrosinase deficiency causes albinism.
Question 5 · Easy
Which is the rate-limiting enzyme of heme synthesis?
1. AALA synthase
2. BHeme oxygenase
3. CFerrochelatase
4. DALA dehydratase
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Answer: A · ALA synthase
Delta-aminolevulinic acid (ALA) synthase in the mitochondria joins glycine and succinyl-CoA to form ALA, using pyridoxal phosphate. Heme represses the enzyme, while drugs such as barbiturates induce it, which can trigger attacks of acute porphyria. Heme oxygenase is the first enzyme of heme breakdown, not synthesis.
- B: Heme oxygenase breaks heme down to biliverdin.
- C: Ferrochelatase inserts iron in the last step; lead also inhibits it.
- D: ALA dehydratase is the second enzyme of the pathway; lead inhibits it.
Question 6 · Medium
A chronic alcoholic is admitted with confusion, ataxia and eye-movement palsy. Red cell transketolase activity is requested to assess:
1. APyridoxine status
2. BRiboflavin status
3. CThiamine status
4. DFolate status
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Question 7 · Hard
A 26-year-old woman given a barbiturate develops colicky abdominal pain, vomiting and confusion. She has no skin lesions. Her urine darkens on standing, and urine porphobilinogen is markedly raised. The most likely diagnosis is:
1. APorphyria cutanea tarda
2. BLead poisoning
3. CCongenital erythropoietic porphyria
4. DAcute intermittent porphyria
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Question 8 · Easy
Pellagra, with dermatitis, diarrhea and dementia, is due to deficiency of which vitamin?
1. ARiboflavin
2. BPyridoxine
3. CThiamine
4. DNiacin
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Question 9 · Medium
An infant with vomiting and jaundice after milk feeds has a positive urine Benedict test but a negative glucose oxidase strip. Which disorder is likely?
1. ADiabetes mellitus
2. BRenal glycosuria
3. CGalactosemia
4. DPhenylketonuria
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Question 10 · Medium
A jaundiced patient has no bilirubin in the urine, while urine urobilinogen is increased. This pattern suggests:
1. ADubin-Johnson syndrome
2. BAcute viral hepatitis
3. CHemolytic jaundice
4. DObstructive jaundice
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Question 11 · Medium
A 2-year-old fed mainly on rice gruel has pitting edema, flaky skin and a fatty liver. Serum albumin is 2.1 g/dL and urine protein is negative. What is the condition?
1. AKwashiorkor
2. BMarasmus
3. CNephrotic syndrome
4. DRickets
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Question 12 · Easy
The energy obtained from 1 g of fat is about:
1. A7 kcal
2. B12 kcal
3. C9 kcal
4. D4 kcal
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Question 13 · Hard
A day's diet contains 300 g carbohydrate, 60 g protein and 50 g fat. What is its approximate energy value?
1. A1,890 kcal
2. B1,640 kcal
3. C1,790 kcal
4. D1,940 kcal
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Question 14 · Hard
A 20-year-old student has mild jaundice after fasting during exams. Total bilirubin 2.8 mg/dL (reference up to 1.2), direct 0.3 mg/dL; hemoglobin, reticulocytes, AST, ALT and ALP normal; urine bilirubin negative. The most likely diagnosis is:
1. ADubin-Johnson syndrome
2. BAcute viral hepatitis
3. CGilbert syndrome
4. DHemolytic anemia
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Question 15 · Medium
An adult's urine turns black when left standing, and he has early arthritis of the spine. Which disorder fits?
1. AMaple syrup urine disease
2. BPhenylketonuria
3. CAlkaptonuria
4. DAcute intermittent porphyria
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Question 16 · Medium
A 6-day-old baby feeds poorly, is lethargic and has urine that smells of burnt sugar. Plasma leucine, isoleucine and valine are raised. Which enzyme is defective?
1. AHomogentisate oxidase
2. BCystathionine beta-synthase
3. CBranched-chain ketoacid dehydrogenase
4. DPhenylalanine hydroxylase
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Question 17 · Easy
All of the following are ketone bodies EXCEPT:
1. APyruvate
2. BAcetoacetate
3. CAcetone
4. DBeta-hydroxybutyrate
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Question 18 · Easy
Which metal is present in vitamin B12?
1. AZinc
2. BIron
3. CCobalt
4. DMagnesium
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Question 19 · Medium
A 3-year-old boy has delayed development, writhing movements and bites his lips and fingers. Serum uric acid is very high. Which enzyme is deficient?
1. AXanthine oxidase
2. BAdenosine deaminase
3. CHGPRT
4. DAPRT
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Question 20 · Medium
A 50-year-old man who drinks heavily has fragile, blistering skin on the backs of his hands. His urine fluoresces pink-red under ultraviolet light and urine porphobilinogen is normal. The most likely diagnosis is:
1. APorphyria cutanea tarda
2. BCongenital erythropoietic porphyria
3. CErythropoietic protoporphyria
4. DAcute intermittent porphyria
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Question 21 · Medium
Vitamin C taken with a meal increases the absorption of non-heme iron mainly by:
1. ARaising the pH of the duodenum
2. BIncreasing hepcidin production
3. CReducing ferric iron to ferrous iron
4. DBinding iron to transferrin in the gut
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Question 22 · Easy
In liver cells, bilirubin is conjugated with which compound?
1. ASulphate
2. BGlucuronic acid
3. CTaurine
4. DGlycine
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Question 23 · Medium
A bodybuilder who has eaten many raw egg whites daily for months develops hair loss and a scaly rash. Which vitamin is likely deficient?
1. APyridoxine
2. BBiotin
3. CRiboflavin
4. DVitamin A
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Question 24 · Easy
Von Gierke disease (glycogen storage disease type I) is due to deficiency of which enzyme?
1. ADebranching enzyme
2. BAcid maltase
3. CMuscle phosphorylase
4. DGlucose-6-phosphatase
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Question 25 · Medium
A 4-day-old baby is jaundiced, with serum bilirubin 14 mg/dL, almost all unconjugated, yet the urine has no bilirubin. Why?
1. AThe newborn kidney cannot filter pigments
2. BIt is changed to urobilinogen in the blood
3. CIt is water-insoluble and bound to albumin
4. DIt reaches urine only above 20 mg/dL
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Biomolecules, metabolism, vitamins, nutrition and porphyrins

In humans, what is the end product of purine catabolism?

Wilson disease is an inherited disorder of the metabolism of which metal?

During prolonged starvation lasting several weeks, the brain meets much of its energy need from:

Phenylketonuria is caused by deficiency of:

Which is the rate-limiting enzyme of heme synthesis?

A chronic alcoholic is admitted with confusion, ataxia and eye-movement palsy. Red cell transketolase activity is requested to assess:

A 26-year-old woman given a barbiturate develops colicky abdominal pain, vomiting and confusion. She has no skin lesions. Her urine darkens on standing, and urine porphobilinogen is markedly raised. The most likely diagnosis is:

Pellagra, with dermatitis, diarrhea and dementia, is due to deficiency of which vitamin?

An infant with vomiting and jaundice after milk feeds has a positive urine Benedict test but a negative glucose oxidase strip. Which disorder is likely?

A jaundiced patient has no bilirubin in the urine, while urine urobilinogen is increased. This pattern suggests:

A 2-year-old fed mainly on rice gruel has pitting edema, flaky skin and a fatty liver. Serum albumin is 2.1 g/dL and urine protein is negative. What is the condition?

The energy obtained from 1 g of fat is about:

A day's diet contains 300 g carbohydrate, 60 g protein and 50 g fat. What is its approximate energy value?

A 20-year-old student has mild jaundice after fasting during exams. Total bilirubin 2.8 mg/dL (reference up to 1.2), direct 0.3 mg/dL; hemoglobin, reticulocytes, AST, ALT and ALP normal; urine bilirubin negative. The most likely diagnosis is:

An adult's urine turns black when left standing, and he has early arthritis of the spine. Which disorder fits?

A 6-day-old baby feeds poorly, is lethargic and has urine that smells of burnt sugar. Plasma leucine, isoleucine and valine are raised. Which enzyme is defective?

All of the following are ketone bodies EXCEPT:

Which metal is present in vitamin B12?

A 3-year-old boy has delayed development, writhing movements and bites his lips and fingers. Serum uric acid is very high. Which enzyme is deficient?

A 50-year-old man who drinks heavily has fragile, blistering skin on the backs of his hands. His urine fluoresces pink-red under ultraviolet light and urine porphobilinogen is normal. The most likely diagnosis is:

Vitamin C taken with a meal increases the absorption of non-heme iron mainly by:

In liver cells, bilirubin is conjugated with which compound?

A bodybuilder who has eaten many raw egg whites daily for months develops hair loss and a scaly rash. Which vitamin is likely deficient?

Von Gierke disease (glycogen storage disease type I) is due to deficiency of which enzyme?

A 4-day-old baby is jaundiced, with serum bilirubin 14 mg/dL, almost all unconjugated, yet the urine has no bilirubin. Why?