TAILIEUCHUNG - Biochemistry, 4th Edition P81

Biochemistry, 4th Edition P81. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | How Are Steroid Hormones Synthesized and Utilized 763 HO -Estradiol corticoid are also derived from progesterone. Pregnenolone and Progesterone Are the Precursors of All Other Steroid Hormones Pregnenolone is transported from the mitochondria to the ER where a hydroxyl oxidation and migration of the double bond yield progesterone. Pregnenolone synthesis in the adrenal cortex is activated by adrenocorticotropic hormone ACTH a peptide of 39 amino acid residues secreted by the anterior pituitary gland. Progesterone is secreted from the corpus luteum during the latter half of the menstrual cycle and prepares the lining of the uterus for attachment of a fertilized ovum. If an ovum attaches progesterone secretion continues to ensure the successful maintenance of a pregnancy. Progesterone is also the precursor for synthesis of the other sex hormone steroids and the corticosteroids. Male sex hormone steroids are called androgens and female hormones estrogens. Testosterone is an androgen synthesized in males primarily in the testes and in much smaller amounts in the adrenal cortex . Androgens are necessary for sperm maturation. Even nongonadal tissue liver brain and skeletal muscle is susceptible to the effects of androgens. Testosterone is also produced primarily in the ovaries and in much smaller amounts in the adrenal glands of females as a precursor for the estrogens. j8-Estradiol is the most prominent estrogen Figure . 764 Chapter 24 Lipid Biosynthesis Steroid Hormones Modulate Transcription in the Nucleus Steroid hormones act in a different manner from most hormones we have considered. In many cases they do not bind to plasma membrane receptors but rather pass easily across the plasma membrane. Steroids may bind directly to receptors in the nucleus or may bind to cytosolic steroid hormone receptors which then enter the nucleus. In the nucleus the hormone-receptor complex binds directly to specific nucleotide sequences in DNA increasing transcription of DNA

• Sinh học
• Nền tảng của hóa sinh học
• trao đổi chất protein
• RNA trao đổi chất
• nguyên tắc của hóa sinh
• Axit amin
• công nghệ DNA