Lista Zadań nr 14 – Systemy czucia

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OBLICZENIA BIOCHEMICZNE

do wykładu dr. hab. inż. P. Dobryszyckiego

LISTA ZADAŃ NR 14

SYSTEMY CZUCIA

1. Which would NOT be an indicator that a certain gene codes for an OR?

(a)

codes for 7TM protein

(b)

genes found in cells of nasal epithelium

(c)

part of a large and diverse family of similar genes

2. Is it likely that there is a single OR responsible for a smell like orange peel or chocolate?

3. Functional magnetic resonance focuses on what in the brain?

(a)

electron flow in nerves

(b)

temperature of active brain regions

(c)

speed of blood flow

(d)

hemoglobin versus oxyhemoglobin in the brain

(e)

turnover of neurotransmitters in the brain

4. Which of the following is INCORRECT?

(a)

Like OR, bitter receptors form a large family of 7TM proteins.

(b)

There are many subtle shades of bitter linked with the different receptors.

(c)

Bitter and sweet taste receptors are closely related.

(d)

Bitter receptors are found mostly on the back of the tongue.

5. Match the two main regions of the rod cell in the left column with the appropriate functions or

properties from the right column.

(a) outer segment
(b) inner segment

(1) contains discs
(2) carries out normal cellular processes
(3) contains the photoreceptors that absorb

light

6. Which of the following statements about retinal, the chromophore of rhodopsin, is

INCORRECT?

(a)

The unprotonated Schiff base absorbs maximally at 440 nm and higher.

(b)

In the dark, it is covalently bound to opsin through a Schiff base linkage.

(c)

In the dark, it is present as the 11-cis-retinal isomer.

(d)

When bound to rhodopsin, it absorbs light maximally at 500 nm.

(e)

It becomes the all-cis isomer after absorbing light.

7. Place the following events in the excitation of rhodopsin by light in their correct sequence.

(a)

metarhodopsin II

(b)

conversion of all-trans-retinal to 11-cis-retinal

(c)

triggering enzyme cascade

(d)

conversion of 11-cis-retinal to all-trans-retinal

(e)

activation of transducin G protein

(f)

Bathorhodopsin

Lista Zadań nr 14 – Systemy czucia

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8. Which of the following statements about G

(olf)

, gustducin, and transducin are true?

(a)

All are G proteins.

(b)

All are associated with 7TM sensory receptors.

(c)

All bind calcium ions.

(d)

All bind GTP, which is hydrolyzed to GDP

9. Explain briefly the major roles of the following participants in the enzymatic cascade that is

triggered by the photoexcitation of rhodopsin.

(a)

transducin

(b)

cyclic GMP (cGMP)

(c)

activated phosphodiesterase

10. With its seven transmembrane helices, rhodopsin has a structure similar to that of which of the

following integral membrane proteins?

(a)

nicotinic acetylcholine receptor channel

(b)

Na

+

-K

+

pump

(c)

sarcoplasmic Ca

2+

-ATPase

(d)

hexokinase

(e)

bacteriorhodopsin light-driven pump

(f)

photoreceptors of retinal cones

11. How does the photoexcited system return to the dark state?

12. Which of the following statements about human color vision are correct?

(a)

It is mediated by three different chromophores.

(b)

It is mediated by three different photoreceptors.

(c)

It involves only the cone cells.

(d)

It involves only the rod cells.

(e)

It involves seven-transmembrane-helix proteins.

13. Which colors do not correspond to human visual pigments? What would be different if this

question were about color vision in chickens?

(a)

red

(b)

yellow

(c)

green

(d)

blue

(e)

Violet

14. Which of the compounds in Figure 1. would be expected to have the smallest absorbance per

mole in the visible light range? Give the reason for your choice

FIGURE 1. Four light-absorbing compounds

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Lista Zadań nr 14 – Systemy czucia

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15. Figure 2. shows the absorption spectrum of a light-absorbing pigment that is involved in color

vision.

(a) What color light is absorbed by the pigment?
(b) When the pigment is extracted into an organic solvent, what is the color of the resulting

solution?

FIGURE 2. Absorption spectrum of a color vision pigment.