Question

Multiple choice questions. Need answers asap. Human nutrition

When you enter a dark room from a brightly lit area; a) Vision is poor until retinol is oxidized to all trans retinal b) Vision will be optimal for the first 15 seconds, and then rhodopsin will degrade under the low-light conditions c) Vision is poor until opsin can be synthesized d) Vision is poor until significant levels of opsin and 11-cis retinal bind together It is safer to consume large amounts of beta carotene than retinol because: a) Beta-carotene is readily excreted in the urine b) Beta-carotene cannot be converted to retinoic acid c) Large stores of retinyl palmitate in the liver inhibit 15,15'-doxygenase in the small intestine d) Retinol is a strong detergent that can harm the stomach lining Which of the following molecules is not important in the pathway to formation of retinoic acid? a) Retinyl palmitate b) Retinol c) All-trans retinal d) 11-cis retinal There are specific molecules that represent the blood homeostatic set points for vitamin A and Which of the following statements about this is true? a) 11-cis retinal levels in the blood stream are carefully maintained b) Blood calcitriol levels never vary by more than a few percent c) Blood retinoic acid levels are a good way to estimate vitamin A status d) Low blood retinol (bound to retinol binding protein) feeds back to activate retinyl esterase Which of the following statements about blood calcium is false? a) Blood calcium can be increased by resorption of bone b) Blood calcium is maintained at a low concentration relative to intracellular calcium c) Blood calcium will be increased by secretion of parathyroid hormone (PTH) d) High blood calcium will cause secretion of calcitonin Which of the following is a difference between vitamin D from sun and vitamin D produced from diet? a) Only vitamin D from diet is carried by the vitamin D binding protein (DBP) b) Only vitamin D from diet is carried by a lipoprotein c) Only vitamin D from diet is converted to calcidiol (25-OH-vit D) d) Only vitamin D from diet is converted to calcitriol (1, 25-OH-vit D) Which of the following statements about vitamin K is false? a) Vitamin K is required for the gamma-carboxylation of proteins b) Vitamin K is produced by bacteria in the colon c) Following gamma-carboxylation, the vitamin K molecule can bind divalent calcium (Ca++) d) Regeneration of the active form of vitamin K is inhibited by warfarin (rat poison)

Answer 1

43). d). Vision is poor until significant levels of opsin and 11-cis retinal bind together.

Retinol produces pigments in the retina (rhodopsin), which is essential for eye sight. Rhodopsin is the visual pigment present in the rods, and absorption of light by this pigment brings conformational changes to its structure and activates it.

Absorption of light by rhodopsin converts the cis-retinal to trans-retinal, and opsin, the colour of retinal changes from purple to yellow, this reaction is called bleaching or isomerization. In dark, trans-retinal is converted to cis-retinal and is called regeneration of photopigment.

44). c). Large stores of retinyl palmitate in the liver inhibit 15,15'dioxygenase in the small intestine.

It is safer to consume large amounts of beta carotene because large stores of retinyl palmitate in the liver inhibit 15,15'dioxygenase in the small intestine, thereby preventing the vitamin A toxicity.