TAILIEUCHUNG - Biochemistry, 4th Edition P53

Biochemistry, 4th Edition P53. 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. | What Is the Molecular Mechanism of Muscle Contraction 483 1 to 2 m in diameter. Myofibrils are linear arrays of cylindrical sarcomeres the basic structural units of muscle contraction. Each myofibril is surrounded by a specialized endoplasmic reticulum called the sarcoplasmic reticulum SR . The SR contains high concentrations of Ca2 and the release of Ca2 from the SR and its interactions within the sarcomeres trigger muscle contraction. The muscle fiber is surrounded by the sarcolemma a specialized plasma membrane. Extensions of the sarcolemma called transverse tubules or t-tubules reach deep into the muscle fiber enabling the sarcolemmal membrane to be in contact with each myofibril. Skeletal muscle contractions are initiated by nerve stimuli that act directly on the muscle. Nerve impulses produce an electrochemical signal see Chapter 32 called an action potential that spreads over the sarcolemmal membrane and into the fiber along the t-tubule network. This signal induces the release of Ca2 ions from the SR. These Ca2 ions bind to proteins within the muscle fibers and induce contraction. The Molecular Structure of Skeletal Muscle Is Based on Actin and Myosin Examination of myofibrils in the electron microscope reveals a banded or striated structure. The bands are traditionally identified by letters Figure . Regions of high electron density denoted A bands alternate with regions of low electron density the I bands. Small dark Z lines lie in the middle of the I bands marking the ends of the sarcomere. Each A band has a central region of slightly lower electron density called the H zone which contains a central M disc also called an M line . Electron micrographs of cross sections of each of these regions reveal molecular details. The H zone shows a regular hexagonally arranged array of thick filaments of myosin 15 nm diameter whereas the I band shows a regular hexagonal array of thin filaments of actin together with proteins known as troponin and .

• 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