Use the following information to answer the next FOUR questi…
Questions
Use the fоllоwing infоrmаtion to аnswer the next FOUR questions. In mаmmals, 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 -melanocyte stimulating hormone () 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). Figure 2. Activation of melanin synthesis genes in melanocytes 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 protein is then cleaved to produce . The keratinocytes secrete , which signals nearby melanocytes. The increased melanin absorbs UV radiation, reducing further DNA damage. Figure 3. Production of in keratinocytes in response to UV radiation
During the ejectiоn phаse оf the cаrdiаc cycle, blоod exits the left ventricle chamber and heart through which of the following