M-line

Examples of M-line in the following topics:

• ATP and Muscle Contraction

  • As myosin expends the energy, it moves through the "power stroke," pulling the actin filament toward the M-line.
  • When the actin is pulled approximately 10 nm toward the M-line, the sarcomere shortens and the muscle contracts.

• Sliding Filament Model of Contraction

  • A sarcomere is defined as the segment between two neighbouring, parallel Z-lines.
  • Actin myofilaments attach directly to the Z-lines, whereas myosin myofilaments attach via titin molecules.
  • The I-band is spanned by the titin molecule connecting the Z-line with a myosin filament.
  • Within the H-band is the M-line, which is composed of myosin myofilaments and titin molecules crosslinked by myomesin.
  • Titin molecules connect the Z-line with the M-line and provide a scaffold for myosin myofilaments.

• Antibody Structure

  • BCRs on naïve B cells are of the IgM class and, occasionally, the IgD class.
  • IgM molecules comprise approximately ten percent of all antibodies.
  • Conversely, some IgM is secreted into bodily fluids of the mucosa.
  • (a) As a germ-line B cell matures, an enzyme called DNA recombinase randomly excises V and J segments from the light chain gene.
  • Splicing at the mRNA level results in further gene rearrangement.

• mRNA Processing

  • Eukaryotic pre-mRNA receives a 5' cap and a 3' poly (A) tail before introns are removed and the mRNA is considered ready for translation.
  • The additional steps involved in eukaryotic mRNA maturation create a molecule with a much longer half-life than a prokaryotic mRNA.
  • Eukaryotic mRNAs last for several hours, whereas the typical E. coli mRNA lasts no more than five seconds.
  • Pre-mRNAs are first coated in RNA-stabilizing proteins; these protect the pre-mRNA from degradation while it is processed and exported out of the nucleus.
  • This moiety protects the nascent mRNA from degradation.

• Class Scyphozoa

  • Members of this species range from 2 to 40 cm in length, but the largest scyphozoan species, Cyanea capillata, can reach a size of 2 m across.
  • These animals possess a ring of muscles lining the dome of the body, which provides the contractile force required to swim through water.

• Regulating Immune Tolerance

  • MALT is a collection of lymphatic tissue that combines with epithelial tissue lining the mucosa throughout the body .
  • Foreign particles that make their way to MALT are taken up by absorptive epithelial cells called M cells and delivered to APCs (antigen-presenting cells) located directly below the mucosal tissue.
  • M cells are located in the Peyer's patch, which is a lymphoid nodule.
  • Pathogens are taken up by M cells in the intestinal epithelium and excreted into a pocket formed by the inner surface of the cell.

• Digestive System: Small and Large Intestines

  • These structures are lined with epithelial cells on the luminal side to allow the nutrients from the digested food to be absorbed into the blood stream on the other side .
  • The human small intestine, over 6 m long, is divided into three parts: the duodenum, the jejunum, and the ileum.
  • Here, hydrolysis of nutrients is continued while most of the carbohydrates and amino acids are absorbed through the intestinal lining.
  • Villi are folds on the small intestine lining that increase the surface area to facilitate the absorption of nutrients.

• Class Cubozoa and Class Hydrozoa

  • The polyp form in these animals often shows a cylindrical morphology with a central gastrovascular cavity lined by the gastrodermis.
  • M. kingi is one of two species of jellies known to cause Irukandji syndrome, a condition characterized by excruciating muscle pain, vomiting, increased heart rate, and psychological symptoms.

• Elongation and Termination in Prokaryotes

  • Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain.
  • The interaction with rho releases the mRNA from the transcription bubble.
  • The mRNA folds back on itself, and the complementary C–G nucleotides bind together.
  • The complementary U–A region of the mRNA transcript forms only a weak interaction with the template DNA.
  • This, coupled with the stalled polymerase, induces enough instability for the core enzyme to break away and liberate the new mRNA transcript.

• The Initiation Complex and Translation Rate

  • A shift in the reading frame results in mistranslation of the mRNA.
  • Once bound to the mRNA's 5' m7G cap, the 43S complex starts travelling down the mRNA until it reaches the initiation AUG codon at the start of the mRNA's reading frame.
  • Sequences around the AUG may help ensure the correct AUG is used as the initiation codon in the mRNA.
  • Next, eIF5 with GTP bound binds to the 40S ribosomal subunit complexed to the mRNA and the tRNAi-Met.
  • Discuss how eukaryotes assemble ribosomes on the mRNA to begin translation