Figure 1C: The S1 and S1 sub fragments of the HMM fragment. Source: (Lodish, et al.), labels edited for paper. As seen in Figure 2, many different myosin’s cluster together to form a bipolar filament. Figure 2: Myosin proteins together to form a “bipolar” filament with head domains together and both ends. Source: Actin assembles into a polymer, F-actin that is made up of many linear G-actin monomers, can be seen in Figure 3 below. Actin has functionally distinct ends, (+) end and (-) end. The difference in the ends of actin is that actin monomers favor the addition to the (+) end over the (-) end. Cross-Bridge Cycle: When no ATP is present, the myosin head is tightly bound to actin. When one ATP molecule binds to the myosin head domain, the myosin loses affinity for actin, thus myosin and actin are no longer bound. The myosin head then hydrolyzes the ATP to ADP and Pi, which rotates the myosin head into a “cocked state.” In this cocked state, the myosin head stores the energy released during ATP hydrolysis. Also in this cocked
state, the myosin head binds to actin. Upon the release of ADP and Pi the stored energy is also released, resulting in a “power stroke” which essentially moves the myosin head along the actin. The exponential repetition of this cycle generates muscle contraction. This interaction that occurs can also be known as a “cross-bridge cycle”, shown in Figure 3. Figure 5: Cross bridge cycle of actin and myosin in the presence of ATP. Source: In each cardiac muscle cell, there are many myofibrils that are composed of a repeating array of sarcomeres, which are the basic unit of contraction. Each sarcomere is made up of the thick and thin filaments, as shown in Figure 4. The thick filaments are composed of the myosin II bipolar filaments. The thin filaments are composed of the actin filaments which are assembled with their (+) ends orientated in the same direction, towards the Z disk. During the cross-bridge cycle, the myosin heads move toward the Z-disk and essentially shorten the sarcomere and thus the muscle contracts. Figure 6: Sarcomere contracted and relaxed. Source:
Calseq F ACG ATG GGA AAG ACC GAG TG 100% Mus musculus calsequestrin 2 (Casq2), mRNA 100% 100% Calseq R GGC CAC AAG CTC CAG TAC AA Mus musculus calsequestrin 2 (Casq2), mRNA 100% 100% Mcyclo F TGG TGA CTT TAC ACG CCA TAA Mus musculus peptidylprolyl isomerase A (Ppia), mRNA 100% 100% Mcyclo R CCA TCC AGC CAT TCA GTC TT Mus musculus peptidylprolyl isomerase A (Ppia), mRNA 100% 100% β actin F AGT CCT GTC GCA TCC ACG AAA CTA Mus musculus actin, beta (Actb), mRNA 91% 91% β actin R ACT CCT GCT TGC TGA TCC ACA TCT Mus musculus actin, beta (Actb), mRNA 100% 100% NCX F AGT CTC CCA CCC AAT GTT TC Mus musculus solute carrier family 8 (sodium/calcium exchanger), member 1 (Slc8a1), transcript variant B, mRNA 100% 100% NCX R CTC CTG TTT CTG CCT CTG TAT Mus musculus solute carrier family 8 (sodium/calcium exchanger), member 1 (Slc8a1), transcript variant B, mRNA 100% 100% PLB F TAT CAG GAG AGC CTC CAC TATT Mus musculus phospholamban (Pln), transcript variant 1, mRNA 100% 100% PLB R CAG ATC AGC AGC AGA CAT ATC Mus musculus phospholamban (Pln), transcript variant 1, mRNA 100% 100% Table 2: Blast results of all primers.