![]() This supercoiling helps regulate transcription because only certain areas of the DNA are accessible for the production of mRNA by transcription. The nucleosomes (made of histones) will interact further with each other causing the chromosomes to supercoil. The chromosomes have to condense and coil around histone proteins making the chromosome much shorter and fatter. In this condensed form, the DNA is able to be easily segregated however is inaccessible to transcriptional machinery. Since a nucleus is generally less than 5 µm in diameter and some of the DNA molecules are over 50,000 µm in length. In this unravelled form, the DNA is accessible to transcriptional machinery and so genetic information can be translated DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase.ĭuring mitosis chromosomes (tightly wounded strands of DNA) condense prior to division in a process called supercoiling. Metaphase Checkpoint: Ensures proper spindle assembly and correct attachment to centromeres preventing non-disjunction events.Ĭhromatins are loosely packed DNA within the nucleus.Identify replication faults which may have occurred to changes in the DNA sequence distorting genetic fidelity of the daughter cells.Suitable size required for successful cell division. G2 Checkpoint: Determines the state of pre-mitotic cell.Assess the level of DNA damage from ionising radiation or UV. G1 Checkpoint: Determines appropriate growth conditions (nutrients, cell size, presence of growth factors, etc.).Cell cycle checkpoints are mechanisms within Interphase that ensure the fidelity and continued viability of mitotic division in cells G2 – Second intermediate gap stage in which the cell finishes growing and prepares for cell division.S – Synthesis stage in which DNA is replicated.G1 – First intermediate gap stage in which the cell grows and prepares for DNA replication.This phase of the cell cycle is a continuum of three distinct stages: The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules. Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Outline four events that occur during telophase.Outline the process of metaphase, inclusive of the role of microtubules and the kinetochore.Outline four events that occur during prophase.Draw typical eukaryotic cells as they would appear during the interphase and the four phases of mitosis.State the names of the four phases of mitosis.List four processes which involve mitosis.1.6.U.1 Mitosis is division of the nucleus into two genetically identical daughter nuclei (Oxford Biology Course Companion page 51). ![]()
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