Mitosis is simply described as having four stages—prophase, metaphase, anaphase, and telophase; the steps follow one another without interruption. The entire four-stage division process averages about one hour in duration, and the period between cell divisions, called interphase or interkinesis, varies greatly but is considerably longer.
During interphase the chromosomes are dispersed in the nucleus and appear as a network of long, thin threads or filaments, called the chromatin. At some point before prophase begins, the chromosomes replicate themselves to form pairs of identical sister chromosomes, or chromatids; the deoxyribose nucleic acid (DNA) of the chromosomes is synthesized only during interphase, not while mitosis is in process.
During prophase the two chromatids remain attached to one another at a region called the centromere, but each contracts into a compact tightly coiled body; the nucleolus and, in most cases, the nuclear envelope break down and disappear. Also during prophase the spindle begins to form. In animal cells the centrioles separate and move apart, and radiating bundles of fibers, called asters, appear around them. Some sets of fiber run from one centriole to the other; these are the spindle fibers. In plant cells the spindle forms without centrioles.
During metaphase the chromosomes congregate at a plane midway between the two ends to which the spindle tapers. This is called the equatorial plane and marks the point where the whole cell will divide when nuclear division is completed; the ends of the spindle are the poles to which the chromatids will migrate. The chromatids are attached to the spindle fibers at the centromeres.
During anaphase the two chromatids of each chromosome separate and move to opposite poles, as if pulled along the spindle fibers by the centromeres. During telophase new nuclear envelopes form around the two groups of daughter chromosomes (as they are now called), the new nucleoli begin to appear, and eventually, as the formation of the two daughter nuclei is completed, the spindle fibers disappear. The chromosomes uncoil to assume their dispersed distribution within the interphased nucleus. Cytokinesis, which may begin before or after mitosis is completed, finally separates the daughter nuclei into two new individual daughter cells.
A considerable variance in the degree and timing of these stages exists across species, and cells can be classified by their mitotic characteristics. Despite the relative ease of observation of the physical stages of mitosis under the microscope (primarily because the chromosomes stain readily when in their coiled state), the exact chemical and kinetic nature of mitosis is not yet fully understood. For instance, the spindle has been determined to consist largely of thin, elongate tubules called microtubules, but their functions have yet to be understood.
Lactase refers to an enzyme that can dissociate lactose sugar into glucose and galactose. This enzyme plays an important role in the digestion of milk that comprises high lactose sugar. In case, if a mutation occurs in the gene codon of lactase, then two possibilities can take place. These are as follows:
1. Loss of mutation: In this case, the person becomes lactose intolerant because of mutation in lactase gene codon. Due to this, there is low mRNA expression and thus low production of the enzyme lactase. This is also known as lactase non-persistent phenotype.
2. Gain in mutation: In this case, the person gain an increase in mRNA expression of the lactase gene, thus more production of lactase takes place than usual. This kind of individual exhibits lactase persistent phenotype.
A mutation in the lactase gene could lead to changes in the structure and function of the lactase enzyme, affecting the organism's ability to process lactose. Depending on the type and location of the mutation, the effects can range from mild to severe, possibly causing diseases related to lactase deficiency.
A mutation in the coding region of the lactase gene could have several potential effects, depending on the nature of the mutation. Mutations could include insertions, deletions or other changes in the DNA sequence that could alter the structure and function of the resulting protein. Such changes could increase the possibility of the protein having extra bends and loops, potentially altering its effectiveness in metabolizing lactose.
For example, in the case of E. coli, mutations in the lactase gene could disrupt the operon's regulation of lactose metabolism.
With a functioning lactase gene, when lactose is present, it triggers the transcription of genes that allow the bacterium to metabolize lactose. However, if the lactase gene were mutated, it could prevent this from happening, leaving the cell unable to process lactose as a food source.
Therefore, considering the potential range of effects, a mutation in the lactase gene could cause significant changes in an organism's ability to process lactose, and it could also cause diseases linked to either the lack of lactase or to structurally abnormal lactase proteins.
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Answer:
A muscle which is connected to the skeletal to move are body is know as skeletal muscle