BIOL 4505 1st EditionExam # 3 Study Guide Lectures: 19 - 24Lecture 19 (October 13)A muscle is a tissue made up of contractile cells. Connective tissues called tendons attach the musces to bones. There are two types: striated (skeletal and heart muscle) and smooth (hollow tubes like blood vessels and intestines). Every muscle consists of a bundle of longitudinal muscle fibersmade of myofibrils that are made up of thick (myosin) and thin (actin) myofilaments that are organized into sarcomeres. The aligned sarcomeres give muscles their striped appearance. Major bands are called A bands, and lighter I bands. The middle of each I band is a narrow, dense Z disc, or Z line. In the center of the A band is the H zone which contains only thick filaments and looks lighter than the rest. The M line bisects the H zone.Titin and nebulin help align and stabilize the thick and thin filaments in the sarcomeres. Actin and myosin polymerize in a polarized fashion to form thin and thick filaments. When the filaments slide by each other during contraction, the heads of myosin molecules bind to sites on actin molecules and draw the thin filaments toward the center of each sarcomere. Each myosin head is also provides energy as an ATPase to power cross-bridge motion. Regulatory proteins troponin (TN) and tropomyosin (TM) on the thin filament, inhibit myosin cross-bridges from interacting with actin, except when cytoplasmic calcium is elevated. When calcium binds to TN-C, it allows myosin cross-bridges to interact with myosin-binding sites on actin molecules.The muscle fiber membrane is known as the sarcolemma. The sarcoplasmic reticulum is a branching network of tubules which sequesters calcium ions to keep a low concentration. The terminal cisternae of it possesses RyR calcium channels. Transverse tubules include voltage-sensitive DHPRs that come into intimate contact with the RyRs of the SR. Skeletal muscle contractions are initiated by action potentials in motor neurons that release acetylcholine, which gives rise to the muscle fiber action potential. The action potential propagates over the cell membrane of the muscle fiber, then depolarizes the DHPRs in the t-tubules. The DHPRs cause the RyR calcium channels to open and allow calcium ions to diffuse out of the terminal cisternae of the SR into the cytoplasm. Calcium ions bind to TN and cause conformational changes of TN and TM that expose the myosin-binding sites of adjacent actin molecules. Myosin heads bind to the actin sites. Repeated cross-bridge cycles continue as long as sufficient calcium is present. The cross-bridges are radial projections that overlap actin thin filaments. move the thick and thin filaments relative to each other, pulling the thin filaments toward the center of the sarcomere. Once the muscle fiber action potential is over, the RyR channels close. The Ca2+-ATPase pumps of the SR sequester Ca2+ back into the SR. As the Ca2+ concentration in the cytoplasm decreases, Ca2+ dissociates from TN, and the TN–TM complex again prevents actin–myosin interactions. The muscle relaxes. Parvalbumin (prevalent in fast muscles) also binds cytoplasmic calcium and thereby enhances the rate of relaxation.Lecture 20 (October 15)Insect metamorphoses illustrates the convergent evolution of endocrine and neuroendocrine functions between vertebrates and invertebrates. Insects change form in the course of their life cycles. Hemimetabolous insects go through gradual metamorphosis, and holometabolous insects go through complete metamorphosis. Environmental and behavioral signals mediated by the nervous systeminitiate molting by providing synaptic input to the PTTH neuroendocrine cells in the brain. These cells secrete PTTH, which stimulates secretion of ecdysone from the prothoracic glands. Ecdysone is converted to 20-hydroxyecdysone by peripheral activation. 20-hydroxyecdysone stimulates thepidermis to secrete enzymes required for the molting process. At each molt, the epidermis lays down a new cuticle beneath the old one. Under the control of PETH and ETH, the insect performs stereotyped pre-ecdysis and ecdysis movements in order to shed the old cuticle. JH, secreted by nonneural endocrine cells in the corpora allata, prevents metamorphosis into the adult form. The relative amounts of JH and 20-hydroxyecdosone in the hemolymphdetermine whether the epidermis will produce juvenile, pupal, or adult structures. In adults, JH functions as a gonadotropin, stimulates the production of sex-attractant pherosomes, and stimulates the secretion of ecdysone, which promotes incorporation of yolk into eggs.The thyroid hormone induces increases in cytochrome c, cytochrome oxidase. Induces increases in uncoupling protein in adipose tissue mitochondrial. Chitin is used in insects to puff themselves up with water which will harden in between molts. Each molt is called an instar or a pupate. A scientist named Wigglesworth discovered that JH is not expressed at every stage, and was able to put his initials into an insect. Factors such as temperature, day length, and food availability will affect the PTTH. The hypothalamus controls sections from the pituitary gland. Neurosecretory cells enter pituitary glands. The anterior lobe: adenohypophysis, nonneuronal, and stimulated by the neurohormone. The posteriorlobe: neurohypophysis, ends of hypothalamus secretory cells, neurohormone is released into blood stream at pituitary lobe. The hypothalamus produces neurohormones that are released into the posterior pituitary gland such as antidiuretic hormone (vasopressin) and oxytocin. Neurohormones are produced in the supraoptic and paraventricular nucleus. These move down the axons, called hypothalamo-hypophyseal neurosecretory tract. Glucocorticoids increase glucose from the adrenal cortex, released in response to stresses, such as aldosterone.Lecture 21 (October 17)The cells in the pancreas release glucagon (A cells) and insulin (B cells) to balance glucose levels in theblood. Insulin promotes the storage of glucose, fatty acids, and amino acids, promotes the production of glycogen. Diabetes mellitus is when there is lower levels of insulin or poor receptor recognition. Glucagon promotes the breakdown of glycogen (gluconeogenesis) and the breakdown of fatty acids, which is secreted in an unfed state.Respiration is the uptake of oxygen plus carbon dioxide dumping, which equals aerobic metabolism. Dry air contains 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, 0.93%