Sarcomeres In Fruit Flies

-Sarcoplasmic Reticulum (SR) then releases Calcium which binds to troponin in the thin filament, exposing myosin-binding sites;

For muscle to contract, actin and myosin filaments need to slide past each other, causing the sarcomere to shorten in length . Each myosin filament has a protruding bulbous head, which can bind with the binding sites on the

Rationale, Significance and Hypothesis. An extrinsic factor, which exerts a dominant influence on skeletal muscle fiber phenotype, is the nervous system. Buller et al. (1960) elegantly demonstrated the plastic nature of skeletal muscle fibers in response to changes in innervation type. Later, Lφmo and Westgaard (Lφmo and Westgaard, 1974; Westgaard and Lφmo, 1988) demonstrated that depolarization of muscle with specific patterns and frequencies of electrical activity are sufficient to cause changes in mature muscle fiber phenotypes. However, how myofibrillar gene expression and structural organization is affected by the frequency of impulses during activity, the amount of activity over time, or other characteristics of patterned activity is essentially unknown. To answer these questions will require the isolation and study of subsets of muscle-specific proteins in relation to different electrical activation patterns in vivo, an issue that cannot be easily addressed in preparations currently used in the study of muscle development and maintenance. However, using novel in vivo approaches can, in part, circumvent this difficulty.

Myofibrils are made up of long proteins that include myosin, titin, and actin while other proteins bind them together. These proteins are arranged into thin and thick filaments that are repetitive along the myofibril in sectors known as sarcomeres. The sliding of actin and myosin filaments along each other is when the muscle is contracting. Dark A-bands and light I-bands reappear along myofibrils. The alignment of myofibrils causes an appearance of the cell to look banded or striated. A myofibril is made up of lots of sarcomeres. As the sarcomeres contract individually the muscle cells and myofibrils shorten in length. The longitudinal section of skeletal muscle exhibits a unique pattern of alternating light and dark bands. The dark staining, A-bands possess a pale region in the middle called the H-zone. In the middle of the H-zone the M-line is found, that displays filamentous structures that can join the thick filaments. The light-staining bands also known as I-bands are divided by thin Z-line. These striated patterns appear because of the presence of myofibrils in the sarcoplasm (IUPUI, 2016).

Pasternak C, Wong S, Elson EL. (1995). Mechanical function of dystrophin in muscle cells. The Journal of Cell Biology, 128(3), 355-361. doi:10.1083/jcb.128.3.355

Actin and myosin are contractile proteins that are essential for muscle contraction (Powers). A contraction is triggered by a series of events called the crossbridge cycle. In a muscle fiber, the functional unit of contraction is called a sarcomere (Powers). A sarcomere contains myofibrils, which consist of actin and myosin myofilaments. The sarcomere shortens when myosin heads and thick myofilaments form crossbridges with actin molecules and thin myofilaments. The formation of a crossbridge is initiated when calcium ions released from the sarcoplasmic reticulum bind to troponin. An action potential triggers this release of these ions. The binding of calcium ions causes troponin to change shape. Tropomyosin moves away from the myosin binding cites on actin, allowing the myosin head to bind actin and form a crossbridge. When ATP on the myosin head has not been hydrolyzed yet, the myosin head is inactivated, or in the uncocked position. The myosin head has to be activated before a crossbridge cycle can begin (Powers). This occurs when ATP binds to the myosin head and is hydrolyzed to Adenosine Diphosphate (ADP) and an inorganic phosphate. The enzyme that breaks this ATP down is called myosin ATPase, which is located on the myosin head. The energy from the hydrolysis activates the myosin head putting it into the cocked position. The activated myosin head binds to actin forming a crossbridge. Then inorganic

Dystrophin is a pole molded cytoplasmic protein and an indispensable part of a protein complex that associates the cytoskeleton of a muscle fiber to the encompassing extracellular grid through

Muscles contract through an action potential moving along a motor neuron toward the skeletal muscle and they connect to a neuromuscular junction  acetylcholine vesicles being released  binding on the sarcolemma  causes Na+ influx in the muscle fiber generating an action potential within the muscle fiber  action potential moves through the T-tubules Calcium channels open calcium is released into the cytoplasm  actin-myosin binding sites and cross-bridges are activated by calcium ions between the actin/ myosin heads  ATP is hydrolyzed to flex myosin head  this flexion makes the actin filaments move close to the middle of the sarcomere  The length of the sarcomere becomes shorter  contraction. I would like to define a few terms discussed within this

As per the sliding fiber hypothesis, the myosin thick fibers of muscle strands slide past the actin thin fibers amid muscle compression, while the two gatherings of fibers stay at generally steady length.a new idea called cross-connect hypothesis traditionally swinging cross-connect, now for the most part alluded to as cross-connect cycle which clarifies the atomic system of sliding fiber. Cross-connect hypothesis expresses that actin and myosin frame a protein complex traditionally called actomyosin by connection of myosin head on the actin fiber, accordingly shaping a kind of cross-connect between the two fibers. These two corresponding speculations ended up being the right depiction, and turned into a generally acknowledged clarification

Skeletal muscle contractions play a pivotal role in our day-to-day lives. Their main function is to generate force and provide our bodies with structural integrity. For many of us, muscle contractions seem effortless, but there’s actually quite a bit going on under the surface. Our muscles are composed of sarcomeres, units of skeletal muscle fibers, which are made up of actin and myosin contractile filaments. These filaments need to bind to each other in order to lengthen and shorten the sarcomere. However, the binding sites for actin and myosin are blocked by troponin and tropomyosin proteins. In order to get them off of the binding sites, calcium needs to bind to the troponin, which then lifts

Bownes, M., Roberts, S. 1981. Analysis of vestigialw (vgw): a mutation causing homoeosis of haltere to wing and posterior wing duplications in Drosophila melanogaster. Journal of Embryology and Experimental Morphology 65: 49-76.

Drosophila melanogaster commonly known as a fruit fly is an oviparous animal with a short generation time of approximately two weeks, during this time the insect hatches into a larva and goes through the developmental larval instar stages, and finally evolves into an adult fly. This species has become an important resource for biologists to better understand different organisms, such as other insects, and even humans. By understanding a simple living organism such as a fruit fly, researchers have been able to comprehend more complex organisms and their behaviors, brain processes, development and other important details. Some examples of the previous research done on this species have provided information about the sense organs in animals

The sliding filament theory of muscle contraction is basically saying the myosin thick filaments slide past actin thin filaments during muscle contraction. I believe the sarcomere would be an example of this occurring.

Microfilaments are the thinnest/finest of all the filaments and are about 3-6 nm in diameter. Microfilaments are composed of contractile globular protein known as actin. They are also responsible for movement as it is associated with myosin which is a protein responsible for muscle contraction. Intermediate filaments are mid-sized proteins as the name suggests usually measuring 8-12nm in diameter. These filaments are constructed from a number of different subunit proteins namely desmins, keratins, laminins and vimentin. Intermediate filaments play a structural role by providing strength to cells and tissues instead of cell motility. Tubulin proteins have a cylindrical shape, comprising alpha and beta subunits polymerized into microtubules.

1. Ok so the sliding filament theory is basically the contraction of the sacromere. Calcium released from an ion channel bind to troponin which lies on the thick filament known as the actin. This then causes the tropomyosin to reveal on the actin. The myosin head then releases a phosphate from an ATP which causes then forms a cross bridge attaching both thick and thin filament. Causing one muscle contraction.