Difference Between DNA and Chromosome

Replication fork (French : fourche de réplication) A Y shaped point at which two strands of a DNA molecule are unwound and separated during replication. Replicon (French : réplicon) Any genetic element - bacterial chromosome, virus, genome, plasmid - that behaves as an autonomous unit of replication. Repressor (French : répresseur) Protein synthesised by a regulator gene, which, by binding to a specific site on DNA, the operator gene of an operon, prevents the formation of messenger RNA by the operon's other structural genes and hence stops protein -enzyme- synthesis. Reproduction, assisted technology ART (French : reproduction assistée, ART) (assisted reproduction technology, ART) Technology that concerns one or several steps of intervention during the process of in vitro reproduction. Resistance factor, R factor, R plasmid, resistance plasmid (French : facteur de transfert de résistance) Plasmid that codes for one or more enzymes inactivating one or more toxic agents or antibiotics.


03/01/2014 · Chromosomes: Structure, Functions and other details about Chromosomes

Ionizing radiation-induced DNA injury and damage …

The lesions induced in the DNA of lymphocytes by chemical exposure that lead to formation of structural chromosome aberrations, sister chromatid exchange, and micronuclei must persist in vivo until the blood is withdrawn and then in vitro until the cultured lymphocyte begins DNA synthesis. It is, therefore, important to score cells directly after the first division (in the case of chromosome aberrations or micronuclei) or after the second division (sister chromatid exchanges) in order to obtain the best estimate of induced damage.

Molecular Biology | Biochemistry for Medics – Lecture …

SMC6 is proximal to the centromeres during both meiotic metaphases in mouse (Gomez et al. ; Verver et al. ) and human (Verver et al. ). As well as during prophase I stages, SMC6 co-localizes at the centromeres with Topo IIα during metaphase I and II (Gomez et al. ). More specifically, in metaphase I and anaphase I, SMC6 was present as two foci proximal to the sister kinetochores, and only one signal near the kinetochores at metaphase II and anaphase II (Gomez et al. ). Additionally, in metaphase II spermatocytes, in which the centromeres are subjected to tension from opposite poles, SMC6 appeared as a strand connecting the sister kinetochores (Gomez et al. ). The finding that SMC6 co-localizes with Topo IIα, together with the fact that the strand of SMC6 joining sister kinetochores persists even after redistribution of Aurora-B, suggests that the SMC5/6 complex may regulate sister chromatid centromere cohesion and dissolution of DNA catenates that form after DNA replication (Gomez et al. ). This role for SMC5/6 was further appointed when Topo IIα was inhibited by etoposide, inducing lagging chromosomes during the second meiotic division. Both SMC6 and Topo IIα co-localized at stretched strands connecting these lagging chromatids at the site of the kinetochores (Gomez et al. ). Complementary data was acquired using budding yeast, where localization of Smc5 depends on meiotic DNA replication, and in the absence of TopoII, Smc5 localization is aberrant (Copsey et al. ).

Chapter 27 - Biological Monitoring

Timely organization of the different steps of meiotic DSB repair depends on tight regulation of the meiotic prophase I, which can be subdivided in four stages: leptonema, zygonema, pachynema, and diplonema. During leptonema, the chromatin condenses and formation of axial elements between sister chromatids begin to form. Simultaneously, DSBs are induced by the endonuclease SPO11, triggering the meiotic DNA damage response. During zygonema, homologous chromosomes begin to synapse, characterized by the formation of the SC, a proteinaceous structure which comprises axial proteins (now termed lateral elements) linked by central components. Single-strand invasion occurs, followed by resection and DNA synthesis, resulting in recombination intermediates. Recombination events are neither randomly nor equally distributed throughout the genome but are preferentially located at hotspots at which DSBs are more frequently formed (reviewed in (Keeney et al. )). At pachynema, the homologous chromosomes are fully synapsed along their entire length. DSB repair via HR continues by the resolution of recombination intermediates into either a non-crossover or a crossover event. Only a minority of recombination intermediates are resolved as crossovers, but there are processes which ensure that at least one crossover is formed per homolog pair (reviewed in (Youds and Boulton )). Finally, in diplonema, the synaptonemal complex gradually dissociates and most recombination intermediates are completely resolved. Importantly, crossovers remain as chiasmata in order to keep homologous chromosomes locally tethered and, together with proper chromosome cohesion, ensure bi-orientation and accurate segregation during meiosis I (reviewed in (Petronczki et al. )).

Vito Foà and Lorenzo Alessio

Meiosis is a specialized cell division during which one round of DNA replication is followed by two successive rounds of chromosome segregation. First, the homologous chromosomes, each consisting of one pair of sister chromatids held together by cohesin complexes, move to opposite poles (meiosis I). Second, the sister chromatids are segregated, resulting in the formation of four haploid cells (meiosis II). During prophase I, the homologous chromosomes align and, in most organisms, chromosome synapsis is achieved by formation of the synaptonemal complex (SC). Correct synapsis of the homologous chromosomes is required to facilitate meiotic recombination and the subsequent formation of meiotic crossovers. These meiotic crossovers, or chiasmata, introduce genetic variation among the resulting gametes. Additionally, together with proper sister chromatid cohesion, they also ensure correct chromosome orientation and segregation during meiosis I (reviewed in (Petronczki et al. )).

Mitosis | Cell Cycle | Cell Division | PMF IAS

This chromosome number stays the same after chromosome replication during S phase: each chromosome entering cell division now consists of a pair of sister chromatids joined together at the centromere. Then in mitosis, the sister chromatids of each chromosome separate, so each daughter cell receives one chromatid from each chromosome. The result of mitosis is two identical daughter cells, genetically identical to the original cell, all having 2N chromosomes. So during a mitotic cell cycle, the DNA content per chromosome doubles during S phase (each chromosome starts as one chromatid, then becomes a pair of identical sister chromatids during S phase), but the chromosome number stays the same.