Kendall Preece 307 Honors Meats February 12, 2019ANSC 307 HonorsExam A Take-home Portion (worth 25 points)Submitted through eCampus by 8am Wednesday, February 13, 2019Use notes, book Internet, etc, for answers but please reference what sources you used. Each question is worth 5 points each. Expected answer should be between a half-pageand full-page, single-spaced type (do not overwrite your answers).1. How are muscle contraction and rigor mortis formation similar and different?A muscle contraction starts off as an impulse that travels along the motor neuron and down to the neuromuscular junction. At the neuromuscular junction, the action potential causes the release of acetylcholine across the synaptic cleft. Acetylcholine causes the resting potential tochange, causing an action potential to happen in the muscle fiber. This signal travels in both directions and when the action potential reaches a transverse tubule surrounding the myofibrils, the action potential causes the release of Ca++ ions into the sarcoplasm from the transverse tubules. The calcium ions cause a change in the thin filaments by binding to troponin and causingtropomyosin to shift and expose binding sites for myosin on the actin thin filaments. Myosin grabs onto an ATP that is available and breaks it down into ADP and inorganic phosphate (Pi), releasing energy. The myosin then becomes stretched and binds to actin and the filaments slide. This leads to the sarcomere length shortening and the muscle contracting. Myosin then lets go of the ADP and Pi and is still connected to the actin. To release from actin, myosin binds again to another ATP and the myosin head changes shape and releases from actin. This new ATP can then be broken down all over again and made into the ADP and Pi the myosin needs to “grab and swivel” again. This cycle repeats itself over and over again, making the sarcomere length shorter and shorter until the C++ ions are re-obtained by the transverse tubules after the loss of the action potential. When C++ ions leave troponin, tropomyosin shifts and covers actin. ATP and magnesium ions, form a complex, causing the myosin heads to return to relaxation. The process of muscle contraction requires huge amounts of ATP which are mostly made through aerobic respiration and takes place as an animal is alive. Rigor mortis, however, takes place when the animal is deceased and is no longer making enough ATP to keep muscles in a relaxed state. In thebeginning of rigor mortis (called the delay phase), the formation of ATP and Mg++ ion complex remains in place as there is plenty of ATP in the glycogen stores of the muscle. As all of the ATP and Creatine phosphate stores are used up, myosin and actin form rigor bonds as the myosin is no longer relaxed and is using the remaining ATP to contract the muscle. After this onset phase, completion phase happens when all of the creatine phosphate is used up and there is no way to make ATP. When ATP cannot be synthesized, the myosin head cannot let go of the actin and can no longer relax. Resolution can then take place as proteolytic enzymes are released that cause thebreakdown of proteins. This causes softening of the muscle and rigor mortis is complete. Both muscle contraction and rigor mortis involve the use of ATP to cause contractions. Rigor mortis, on the other hand, runs out of ATP and is no longer able to relax.References used for question 1:Beef Quality Research (2013). Rigor Mortis. [video] Available at: https://www.youtube.com/watch?v=mO6a9UZmtag [Accessed 12 Feb. 2019].Carroll, W. (2018). Rigor Mortis; An Examination of Muscle Function. [online] Serendipstudio.org. Available at: https://serendipstudio.org/biology/b103/f02/web2/wcarroll.html [Accessed 12 Feb. 2019].Animalbiosciences.uoguelph.ca. (n.d.). Contraction and rigor mortis. [online] Available at: http://animalbiosciences.uoguelph.ca/~swatland/ch5_1.htm [Accessed 12 Feb. 2019].Meat Science. (2019). Conversion of Muscle to Meat - Meat Science. [online] Available at: https://meat.tamu.edu/ansc-307-honors/conversion-muscle-to-meat/ [Accessed 12 Feb. 2019].Crash Course (2015). Muscles, part 1 - Muscle Cells: Crash Course A&P #21. [video] Available at: https://www.youtube.com/watch?v=Ktv-CaOt6UQ [Accessed 12 Feb. 2019].2. Why do short-term and long-term stress impact meat quality so differently.The cause of short-term stress is genetic and from stress-susceptible animals. Swine are an example of genetic influence as they can have the gene for porcine stress syndrome and can easily become short-term stressed after excitement. Short-term stress can result from even mild stressors and the animal will deplete its glycogen stores. Short-term depletion of glycogen resultsin rapid glycolysis and lactate production becomes extremely high. Extremely high lactate production causes the pH to become too low. Low pH causes the meat to become exudative and unable to hold water. The meat is no longer firm and is soft and light pink in color from increase of acidity. After cooking, the meat is dry and shrinks and has poor flavor. Long-term stress can do the opposite to meat quality but not make it better. Animals that are stress resistant, like prey animals such as sheep and cattle, can maintain a normal temperature and remain homeostatic in their muscles. To keep a normal temperature and maintain homeostatic they must use up their glycogen stores. These animals do this when they have stress resulting from sickness, loss of feed, excitement, and even exhaustion. The adrenaline produced causes them to deplete glycogenstores and have limited glycolysis after death. Limited glycolysis makes lactate production low and results in a high ultimate pH of 6.0 to 6.5. This causes the meat hold on to too much water and makes the meat sticky when raw. The color of the meat does not go through normal color transformation postmortem due to the high pH and thus remains dark colored. When cooked, the meat is wet, firm, and has less flavor. The results of both of these are unattractive in appearance and are less flavorful products. These products are hard to sell and are often avoided. To avoid short-term stress effects, animals are selected for having looser frames and lower degree of muscling. To avoid long-term and help short-term stress effects on meat, animals are handled in calmer environments with as little stress as possible placed on them. References used for question 2:Fao.org. (n.d.). CHAPTER 2: Effects of stress and