Unit 6: AP classroom questions /
Strategies Review of Key Quizzes & Correct Answers.Quiz____?In mammals, the dark color of skin, hair, and eyes is due to a pigment called melanin. Melanin is produced by specialized skin cells called melanocytes. The melanin is then transferred to other skin cells called keratinocytes. Melanocytes synthesize melanin in a multistep metabolic pathway (Figure 1). The amount of melanin produced is dependent on the amount of the enzymes TYR, TRP2, and TRP1 present inside melanocytes.Figure 1. Melanin synthesis pathway The peptide hormone α-melanocyte stimulating hormone (α-MSH) activates a signal transduction pathway leading to the activation of MITF. MITF is a transcription factor that increases the expression of the TYR, TRP2, and TRP1 genes (Figure 2).Some mammals increase melanin production in response to ultraviolet (UV) radiation. The UV radiation causes damage to DNA in keratinocytes, which activates the p53 protein. p53 increases the expression of the POMC gene. The POMC - Answer✓✓ The TYR, TRP2, and TRP1 genes may be located on different chromosomes but are activated by the same transcription factor.Quiz____?Which of the following claims best explains why keratinocytes do not produce melanin? - Answer✓✓ Keratinocytes do not express the MITF gene.Quiz____?Page 1 of 9 1 / 2
Mice have melanocytes in the skin on their ears and show a tanning response to UV radiation. Researchers were studying a mutant population of mice that do not show a tanning response. Genetic testing of these mutant mice showed that the pathway causing the production of α-MSH by keratinocytes in response to UV radiation was fully functional. Thus, the researchers claimed that the lack of tanning response was due a nonfunctional MC1R.Which of the following pieces of evidence would best support the researchers' claim above? - Answer✓✓ When researchers applied a drug that activates adenylyl cyclase to the mutant mice's ears, the level of melanin increased.Quiz____?Based on the information provided in Figure 1 and Figure 2, which of the following best predicts the effects of a mutation in the promoter of the TYR gene that prevents it from being transcribed? - Answer✓✓ Skin pigmentation will not be able to change, resulting in a negative selection pressure.Quiz____?Which of the following best explains a process occurring between point 1 and point 2 in Figure 3 ? - Answer✓✓ A poly-A tail is added to RNA.Quiz____?Researchers discovered a mutant form of the TYR gene with a deletion of a single guanine nucleotide in the beginning of the coding sequence.Which of the following best predicts the phenotype of an individual who is homozygous for this TYR mutation? - Page 2 of 9
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