QUESTIONS!ANSWER!KEY!
1.!Using!the!amino!acid!location!numbers!provided!above!the!first!and!last!column!of!each!table,!list!the!locations!
of!the!five!amino!acids!that!contain!a!mutation.!!
The!amino!acid!locations!are!018,!109,!160,!211,!and!233.!!
2.!Of!the!five!mutations!you!identified!in!the!Mc1r!gene,!how!many!are!the!following:!
! 5!substitutions,%0%insertio n s ,%0!deletions%
3.!Of!the!five!mutations!you!identified!in!the!Mc1r!gene,!how!many!are!the!following:!
! 1!silent,%4%missense,%0%nonsense%%
4.'' '
' a.!Which!four!amino!acid!locations!(see!Question!1!above)!contain!the!missense!mutations?!
The!amino!acids!are!018,!109,!160,!and!233.!
b.'Explain!the!link!between!DNA!sequence!and!protein!structure!and!function .!
Students!may!simply!relate!DNA!sequence!to!amino!acid!sequence,!and!amino!acid!sequence!to!the!three-
dimensional!shape!of!the!protein.!More-advanced!students!should!be!able!to!link!the!mutation!to!a!change!in!
the!protein’s!prim a ry!structure,!which!affects!other!levels!of!structure!(secondary!and!tertiary).!All!student!
responses!should!de m onstrate !an!und erstan ding!of!the!link!betw ee n!DN A!an d!the!seq uen ce!of!am ino!acids!
that!determ ine s!the !struc ture ,!and !the re fore !fun ction ,!of!a!pro tein .!
5.!Using!the!information!on!mutations!in!the!introduction!and!your!knowledge!of!proteins,!develop!a!hypothesis!to!
explain!how!the!changes!in!the!MC1R!protein’s!amino!acid!sequence!might!affect!its!function.!
Students!might!suggest!that!since!the!four!missense!mutations!in!the!Mc1r!gene!change!the!amino!acid!
sequence!of!the!MC1R !protein,!the!protein!will!not!function!properly,!as!a!protein’s!function!is!determined!by!
its!struct u re .!
6.!Many!proteins,!including!MC1R,!contain!several!structural!domains!that!can!fold!and!function!inde pe nd en tly!
from!the!rest.!Th e!d omain!names!w ere !pro vide d !for!ea ch!p ortio n!o f!DN A !seq ue nc e!yo u !trans late d!ea rlier.!An sw e r!
the!following!questio ns. !
a.!Where!is!the!MC1R!protein!found,!and!what!is!its!function?!Be!specific.!
It!is!a!rece p tor !pro tein!e m be d de d!in!th e!m e m b ran e!o f!me lan oc ytes .!It!is!specialized !for!pig m en t!pro d uctio n.!
b.!Which!protein!domains!contain!the!four!Mc1r!missense!mutations?!(Refer!to!the!gene!tables!you!completed!
earlier.)!
The!mutation!at!018!is!in!Extracellular!Domain!I,!the!mutation!a t!1 0 9 !is!in !E x t ra c e llu la r!Domain!III,!th e !mutation!
at!160!is!in!Intracellular!Domain!I,!and!the!mutation!at!233!is!in!Intracellular!Domain!III.!
c.!Define!“extracellular.”!
Extracellular!means!“something!outside!of!a!cell.”!
d.!Define!“intracellular.”!
Intracellu la r !means!“something!in sid e !o f!a !c e ll.”!
e.!Why!is!it!significant!that!the!four!missense!mutations!are!found!in!the!extracellular!and!intracellular!domains!of!
the!protein?!Explain!yo ur!an sw er.!(H int:!Think!a bou t!M C1 R’s!fun ction .) !
Specific!answers!will!va r y,!b u t !st u d e n ts !sh o u ld !h a v e !th e !id e a !th a t !a !p ro t ein !t h a t!s p a n s!a !c e ll!membra n e !h as !a !
portion!that!projects!out!of!the!cell!(extracellular)!and!a!portion!that!projects!into!the!cell!(intracellular).!This!
type!of!recep tor!p rote in!u sua lly!functio ns!in!eithe r!cell!trans port!o r!cell!signaling .!Cha nge s!in!the!stru ctu re!of!
extracellular!and!intracellular!portions!can!change!the!function!of!the!protein!in!the!signaling!pathway!or!the!
transport!m ec ha nism .!(N ote :!See !the !lesson !“Th e!B ioch emistry!and!Cell!Signaling!Pathway!of!the!Mc1r!Gene”!
for!more!deta il!on!this!con cep t.)!!