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At least 739 records · Page 41Linked to original sources
PubMed1983

Anatomy and biomechanics of the shoulder in throwing, swimming, gymnastics, and tennis.

As the most mobile joint in the body, the shoulder is structurally insecure. The ball-shaped humeral head rotates and glides on a shallow scapular cup. A limited amount of passive stability is provided by the glenoid labrum, which slightly deepens the scapular cup, and by ligaments reinforcing the capsule on its superior and anterior surfaces. At peak maturity ligamentous restraint equals 50 to 80 kg. These structural limitations indicate that the primary source of joint stability must be balanced muscle control. Joint compression is the major factor. This is supplemented by active tangential restraint, which selectively opposes anterior, posterior, or superior displacement. The large external muscles used for purposeful motion and speed often create subluxating shear forces in addition to the desired actions. Impingement and attrition syndromes are common consequences. To counter this, as well as to provide selective rotation, there are the four muscles that constitute the rotator cuff. Joint compression is the major force generated by the supraspinatus and infraspinatus. The latter (accompanied by the teres minor) also provides a downward pull to oppose the upward displacement of early deltoid action. Anterior protection against excessive external rotation or extension is offered by the subscapularis. Athletic who use the arm for a propelling force strain the extremes of joint range in their drive for maximum performance. The threat of injury can be minimized by two actions, namely, modifying motion patterns, which may avoid impingement or make it a less frequent experience, and active protection, which is gained through specific strengthening of the rotator cuff muscles.

Athletic Injuries↗
PubMed2006

Molecular gymnastics: serpin structure, folding and misfolding.

The native state of serpins represents a long-lived intermediate or metastable structure on the serpin folding pathway. Upon interaction with a protease, the serpin trap is sprung and the molecule continues to fold into a more stable conformation. However, thermodynamic stability can also be achieved through alternative, unproductive folding pathways that result in the formation of inactive conformations. Our increasing understanding of the mechanism of protease inhibition and the dynamics of native serpin structures has begun to reveal how evolution has harnessed the actual process of protein folding (rather than the final folded outcome) to elegantly achieve function. The cost of using metastability for function, however, is an increased propensity for misfolding.

Animals↗
PubMed2005

Molecular gymnastics: distortion of an RNA polymerase sigma factor.

A recent structure obtained by nuclear magnetic resonance (NMR) spectroscopy shows that the binding of a small phage factor to the sigma(70) subunit of Escherichia coli RNA polymerase induces an unprecedented remodeling of a region of sigma(70), converting a DNA-binding helix-turn-helix into a continuous pseudohelix. This conformational change suggests how the phage factor can function both as an inhibitor and co-activator of transcription.

Bacteriophage T4↗
PubMed2004

Viral DNA polymerase scanning and the gymnastics of Sendai virus RNA synthesis.

mRNA synthesis from nonsegmented negative-strand RNA virus (NNV) genomes is unique in tht the genome RNA is embedded in an N protein assembly (the nucleocapsid) and the viral RNA polymerase does not dissociate from the template after release of each mRNA, but rather scans the genome RNA for the next gene-start site. A revised model for NNV RNA synthesis is presented, in which RNA polymerase scanning plays a prominent role. Polymerase scanning of the template is known to occur as the viral transcriptase negotiates gene junctions without falling off the template.

DNA-Directed RNA Polymerases↗
PubMed2000

Genome gymnastics: unique modes of DNA evolution and processing in ciliates.

In some ciliates, the DNA sequences of the germline genomes have been profoundly modified during evolution, providing unprecedented examples of germline DNA malleability. Although the significance of the modifications and malleability is unclear, they may reflect the evolution of mechanisms that facilitate evolution. Because of the modifications, these ciliates must perform remarkable feats of cutting, splicing, rearrangement and elimination of DNA sequences to convert the chromosomal DNA in the germline genome (micronuclear genome) into gene-sized DNA molecules in the somatic genome (macronuclear genome). How these manipulations of DNA are guided and carried out is largely unknown. However, the organization and manipulation of ciliate DNA sequences are new phenomena that expand a general appreciation for the flexibility of DNA in evolution and development.

Animals↗