Vitamins Biochemistry 2023

Question 1 of 45

Which statement regarding cone cells is true?

Each cell of this type directly gives a signal.
Cone cells can process indirect light.
They need less intense light than rod cells.
They are sensitive mostly to red light.
They need strong direct light to detect colors.

Question 2 of 45

Which statement regarding calcium is true?

It stimulates muscle relaxation.
It can't interact with calmodulin.
It is never hazardous to DNA.
It binds to many proteins as a second messenger.

Question 3 of 45

Which substance usually regenerates the vitamin E used up in the free-radical scavenging process?

Tocopherols
Tocophenols
Vitamin C
Vitamin B
Vitamin K

Question 4 of 45

Which statement regarding vitamin A is correct?

Vitamin A does not play any role in human vision.
β-carotene blocks vitamin A synthesis.
Vitamin A plays an important role in gene expression and cell differentiation during the developmental phase.
Vitamin A is not fat-soluble, and therefore, an excess of this vitamin can lead to toxicity.
Vitamin A plays an important role in hearing and taste.

Question 5 of 45

What is true regarding calcium?

It stimulates muscular contraction.
It stimulates glycogen synthesis.
It inhibits glycogen breakdown.
It promotes the relaxation of skeletal muscle.
When bound to calmodulin, it causes the closing of endoplasmic reticulum channels.

Question 6 of 45

Which of the following statement is not true regarding vitamin B12?

Vitamin B12 plays an essential role in the formation of RBCs, the synthesis of DNA, and the metabolism of fatty acids and amino acids in every cell of the animal body.
Vitamin B12 contains a biochemically rare element cobalt in the center of the planar tetra-pyrrole ring.
Vitamin B12, cobalamin, is a water-soluble vitamin essential for the normal functioning of the nervous system.
A vegetarian diet is a rich source of vitamin B12, followed by dairy products.
The prokaryotic organisms are capable of synthesizing vitamin B12, whereas single-celled and multicellular eukaryotic organisms are unable to synthesize it.

Question 7 of 45

After absorption of a photon by a retinal molecule, structural changes in the opsin protein occur. What is activated after this occurs?

Transducin (G-protein)
Photopsin
Rhodopsin
K ion pump
Na ion pump

Question 8 of 45

Which term is correctly associated with its function?

Parathyroid hormone (PTH) — stimulates the release of calcium from bones
Osteoclast — produces parathyroid hormone (PTH) in the kidneys
Calcitonin — works antagonistically with calcitonin
Parathyroid hormone (PTH) — stimulates phosphate reabsorption in the kidneys
Vitamin D — inhibits calcium absorption from the gut

Question 9 of 45

Pernicious anemia is caused by which of the following?

A deficiency of vitamin B12
High doses of hydroxocobalamin
High doses of vitamin B12
Absorption of an abnormal biochemical type of B12

Question 10 of 45

In what aspect does a retina cell differ from other nerve cells?

In the excited state, a retina cell is hyperpolarized, whereas other nerve cells are depolarized.
Retina cells are not sensitive to photons.
When a retina cell receives a photon, the neurotransmitter is released.
The nerve cells send a signal by blocking the activity of rhodopsin proteins, whereas in retina cells the signal is communicated to the brain via photopsin protein disintegration.
In the excited state, a retina cell becomes hypopolarized, whereas other nerve cells get hyperpolarized.

Question 11 of 45

How does vitamin D differ from steroid hormones?

It stays outside the cell and sends the signal via the second messenger to the nucleus.
It binds to cell surface receptor protein and then moves into the cell.
It does not enter the target cell.
It modulates the DNA activity via second messenger molecules.
Although it crosses the cell membrane, it triggers the second messenger molecule to send a signal to DNA.

Question 12 of 45

Which of the following is not matched correctly?

Adenosylcobalamin — found in the mitochondria of the cells
Vitamin B12 — handles propionic acid metabolism in the cell
N5-methyl tetrahydrofolate — source of extra carbon during methionine synthesis
Methylcobalamin — present in the cytosol of cells
Pernicious anemia — deficiency of vitamin C

Question 13 of 45

Which statement regarding the return of isomerized retinal to its original state is true?

It occurs inside the ciliary body.
It occurs on opsin.
It requires glycolysis.
It requires conversion back to the all-trans state.
It requires ATP.

Question 14 of 45

What does vitamin D-vitamin D receptor (VDR) complex bind to in the DNA?

RAR factor binding unit
PTH genes
Hox genes
Rare genes
Hormone response elements (HREs)

Question 15 of 45

Which of the following is a vitamin B12-dependent enzyme?

Glutamate carboxylase
Methionine reductase
Catalase
Methylmalonyl-CoA mutase
Vitamin K epoxide reductase

Question 16 of 45

Which statement regarding vitamin D is true?

Its active form promotes calcium excretion.
It increases bleeding time.
Cholecalciferol (D3) is created by exposure to oxygen.
Deficiency causes scurvy.
Its active form is carefully regulated in the body.

Question 17 of 45

Which statement is not true regarding folic acid?

Vitamin B9 plays an essential role in the synthesis of thymidine from the uridine-containing nucleotides.
Folate deficiency leads to excessive hemorrhage in adults.
Folic acid is an essential vitamin and is required for the synthesis of nucleic acids and amino acid metabolism.
Folate deficiencies can lead to severe megaloblastic anemia in adults.
Folic acid is given to pregnant women as a supplement to prevent neural tube defects.

Question 18 of 45

Which statement regarding cholecalciferol is true?

It is hydroxylated in the liver to calcitriol.
It is a precursor of ergocalciferol.
It is a precursor of retinol.
It is hydroxylated in the liver to calcifediol.
The dietary supplement cholecalciferol must be phosphorylated.

Question 19 of 45

The folate derivatives act as substrates in which of the following reactions?

Single-carbon transfer reaction
Nitrogen-containing ring transfer reactions
Cyclic hydrocarbon transfer reactions
Two-carbon transfer reactions
Three-carbon transfer reactions

Question 20 of 45

Which statement regarding calcium is true?

It is stored in the Golgi apparatus.
Vitamin C closely regulates calcium.
It readily passes through the lipid bilayer.
It is stored in cells in the sarcoplasmic reticulum.
Vitamin A stimulates its uptake from the intestine.

Question 21 of 45

What is the main complication faced in case of an overdose of warfarin?

Dangerously hyperdense bones
Thrombosis, due to overproduction of proteins C and S
Uncontrolled bleeding
Decrease in albumin production by the liver

Question 22 of 45

Dihydrofolate reductase (DHFR) is often targeted in cancer treatment. Why?

DHFR inhibition interferes with cell membrane synthesis in cancer cells.
DHFR inhibition causes lysis of the nuclear membrane in cancer cells.
The inhibition of DHFR by folate antagonists (e.g., methotrexate) results in a deficiency in the cellular pools of thymidylate and purines and thus in a decrease in DNA synthesis.
DHFR inhibition interrupts the formation of the mitotic spindle of cancer cells.
DHFR inhibition causes lysis of cancer cell membranes.

Question 23 of 45

Which statement regarding dietary calcium is true?

It promotes vitamin D synthesis.
It is released from the mitochondria into the blood.
It is bound in the intestinal cell by calbindin.
At high levels it causes tetany.
It binds to collagen in the blood.

Question 24 of 45

Which enzyme participates in the recycling of vitamin K?

Vitamin K epoxide reductase
Vitamin K peroxide reductase
Vitamin K epoxide hydrolase
Vitamin K oxide reductase
Vitamin K epoxide carboxylase

Question 25 of 45

Which of the following reactions correctly describes the production of N5, N10-methylene-tetrahydrofolate?

THF + glycine → serine + N5, N10-methylene-THF
Thymidylate + THF → serine + N5, N10-methylene-THF
Serine + dihydrofolate ↔ glycine + N5, N10-methylene-THF
Glycerol + dihydrofolate → serine + N5, N10-methylene-THF
Serine + tetrahydrofolate (THF) ↔ glycine + N5, N10-methylene-THF

Question 26 of 45

Which vitamin is not correctly associated?

Vitamin K5 — tocopherol
Vitamin K3 — menadione
Vitamin K2 — menaquinone
Vitamin K1 — phylloquinone
Vitamin MK4 — menatetrenone

Question 27 of 45

Which of the following is NOT correctly matched regarding folate metabolism?

N5 – methyl THF → THF — via methionine synthesis from homocysteine
N5, N10 – methenyl THF → N10 – formyl THF — via hydrolysis reaction
THF → N5 – formyl THF — via glycine/serine metabolism
THF → N10 formyl THF — via combination with formate
THF → N5, N10 – methylene THF — via glycine/serine metabolism

Question 28 of 45

Which statement regarding vitamin A is true?

Its primary form is retinol.
It has 2 forms: retinol and retinal.
It has 3 primary forms: retinol, retinal, and retinoic acid.
It is water-soluble.
It is stored in the kidney.

Question 29 of 45

Which enzyme participates in the recovery of the 11-cis retinal form during the visual cycle?

Retinol polymerase
Retinol isomerase
Retinol cyclase
Retinol depolymerase
Retinase

Question 30 of 45

Vitamin K is a co-factor for which enzyme?

Tyrosine kinase
Vitamin K epoxide reductase
Polymerase
Glutamate carboxylase
Nuclease

Question 31 of 45

Which of the following is associated with folate deficiency?

Neural tube defects
Subdermal hematoma
Tongue infection
Retinal hemorrhage
Lymphedema

Question 32 of 45

Which statement regarding vision is true?

Triple bonds play critical roles in light detection.
Retinol is the light-sensing pigment.
Double bonds play critical roles in light detection.
The absorption of a photon leads to the conversion of 11-trans retinal to 11-cis retinal.
Light detection occurs as a result of rotation of a single bond.

Question 33 of 45

Which statement regarding retinoic acid is true?

It leads to dedifferentiation of the differentiated cells, thus acting as a major cause in cancer development.
It regulates the Sox gene during the development phase of the organism’s life.
It has a very strong anti-oxidant effect because it impacts the differentiation genes.
It is a storage form of vitamin A.
It is obtained from retinal via a nonreversible oxidation reaction.

Question 34 of 45

What is the most biologically active form of vitamin E?

α-tocopherol
γ-tocopherol
β-tocopherol
δ-tocopherol
λ-tocopherol

Question 35 of 45

Which statement regarding specialized retinal cells is true?

They are devoid of opsin.
They contain opsin, which holds retinal.
They are devoid of photopigments.
Stimulated optic nerve cells are unpolarized.
They include cones, which detect light.

Question 36 of 45

What leads to the conversion of 7-dehydrocholesterol to cholecalciferol?

Boiling temperatures
X-rays
Freezing temperatures
Visible light
Ultraviolet light

Question 37 of 45

Vitamin E acts as a fat-soluble antioxidant by doing what?

Preventing the propagation of reactive oxygen species and reactive lipid radicals through biological membranes
Facilitating the propagation of reactive proton species through biological membranes
Facilitating the propagation of reactive oxygen species and reactive lipid radicals through biological membranes
Facilitating the propagation of reactive metal ion species through biological membranes
Facilitating the propagation of reactive chlorine species through biological membranes

Question 38 of 45

Which statement regarding rod cells is true?

They contain the protein opsin, which isomerizes in the light.
They become depolarized when stimulated by light.
They become hyperpolarized when stimulated by light.
Rod cells need at least 10 photons to detect light.
They start out all-trans-retinal.

Question 39 of 45

What does calcitriol control?

Calcium pump activity
Calcium excretion into the gut
PTH efficacy
Sequestration of Ca+2 ions within the small intestine
Calbindin gene expression

Question 40 of 45

Vitamin E acts antagonistically against what other vitamin?

Vitamin K, by facilitating the external blood clotting
Vitamin K, by facilitating the internal blood clotting
Vitamin K, by interfering with blood clotting
Vitamin C, by reducing its antioxidant effect
Vitamin A, by bleaching the opsin protein in the retina cells

Question 41 of 45

What process occurs during light stimulation in rod cells?

Retinal converts to the all-trans form.
Retinal converts to the all-cis form.
cGMP causes ion channels to close.
cGMP phosphodiesterase converts GMP to cGMP.
A g-protein called transducin is inactivated.

Question 42 of 45

Which of the following statements regarding calcitonin and parathyroid hormone (PTH) is true?

PTH and Calcitonin have identical effects.
Calcitonin promotes reabsorbtion of calcium.
Calcitonin decreases blood calcium levels.
PTH stimulates bone formation.
PTH increases phosphate levels.

Question 43 of 45

What process occurs when retinal in opsin isomerizes?

This process causes depolarization.
Calcium gates open.
Transducin binds to opsin.
cGMP phosphodiesterase is activated.
Ion channel gates close.

Question 44 of 45

Which statement regarding vitamin D is true?

It favors angiogenesis.
It controls the transcription of specific genes involved in mineral metabolism and immune function.
It stimulates receptor tyrosine kinase signaling.
It moves across cellular membranes.

Question 45 of 45

What are atherosclerotic plaques usually linked to?

Damaged cell membranes due to tunnel protein peroxidation of nonpolar regions
Damaged cell membranes due to membrane-embedded protein oxidation of nonpolar regions
Damaged cell membranes due to lipid peroxidation of nonpolar regions
Damaged cell membranes due to transmembrane protein oxidation of polar regions
Damaged cell membranes due to protein peroxidation of nonpolar regions

Vitamins Biochemistry 2023

Vitamins Biochemistry 2023

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