mitotic cell cycle

• what is a chromosome?

  threadlike structure containing DNA and genes
• what is a chromatin?

  a combination of DNA wound around histone proteins (basic)
• Chromosomes condensed, so DNA is tightly packed ∴ easier to separate chromatids at the centromere into daughter cells.
• Telomeres: repeated short base sequence at end of the chromosome (by telomerase).
• function of telomeres?

  permit continued replication, prevent loss of genes, protect ends of chromosomes from being degraded
• Centromere: The region where chromatids are held together.
• Kinetochore: protein structure found on centromere of chromatid to which microtubules attach. Two kinetochore at centromere on each chromatid during metaphase
• Microtubules extend from kinetochore to the poles of spindle.
• Centrosome: poles of spindle and act as MTOC with a pair of centriole that are surrounded by proteins that make microtubules.
• 3 phases: Interphase → nuclear division → cell division.
• what happens in interphase?


  the cell grows to its normal size after cell division, and synthesizes important substances ex: proteins
• what are the three stages of interphase?

  g1, s phase, g2 phase
• Growth 1 phase: gap after cell division and before S phase. 46 chromosomes and chromatids at this phase. Prepares for growth and DNA synthesis (S phase) by producing RNA, proteins and enzymes.
• S phase: synthesis of DNA so each chromosome consists of two identical chromatids. 46 chromosomes and 92 chromatids at this stage. Chromatin also replicates along with DNA so histones are replicated (for M phase
• Growth 2 phase: gap after S phase and before nuclear division (prepares for mitosis) New DNA checked, and errors are repaired. Sharp increase in the production of tubulin to make microtubules for the formation of mitotic spindle. Nuclear envelope envelopes nucleus.
• Nuclear division: division of nuclei at M phase. Growth stops temporarily during mitosis
• Cytokinesis: division of cytoplasm between daughter cells, last stage of cell division
• : nuclear envelope breaks down into vesicles during prophase and reassembles when the vesicles fuse to form the envelope back at telophase
• what happens in prophase?

  Chromosomes condense and become visible, the nuclear membrane breaks down, and the spindle fibers form from the centrosomes
• what happens in the prometaphase?

  chromosomes continue to condense, kinetochores appear at the centrosomes, microtubules attach to the kinetochores and centromeres move toward opposite poles
• what happens in metaphase?

  spindle fibres fully developed, centrosomes are at opposite poles of the cell, chromosomes are lined up at the metaphase plate and each sister chromatid is attached to a spindle fiber originating from opposite poles
• what happens at anaphase?

  cohesin proteins binding to the sister chromatids together break down, sister chromotids (now chromosomes) are pulled towards opposite poles and non-kinetochore spindle fibers lengthen which elongates the cell
• what happens in telophase?


  chromosomes arrive at opposite poles and begin to decondense, nuclear envelope surrounds each set of chromosomes and the mitotic spindle breaks down
• what happens in cytokinesis?

  in animal cells, a cleavage furrow separates the daughter cells and in plant cells, a cell plate separates the daughter cells
• Importance of Mitosis: replacement of cells, repair of tissue, growth/increase in cell numbers, asexual reproduction, maintains / same number of chromosomes genetically identical to parents, produces daughter cells that are genetically identical, Cloning of B and T-lymphocytes during immune response
• Stem cells: cells that divide repeatedly by mitosis, and differentiate into specialized cells or remain as stem cells
• what are the three types of stem cells?

  totipotent, pluripotenent and multipotent
• Totipotent: cells that can divide repeatedly to form any other cell in the body, e.g.: zygote
• Pluripotent: embryotic stem cells that lead to development of the embryo and later the adult. They are not specialized into placenta
• Multipotent: Adult stem cells that are only able to produce a few types of cells e.g. stem cells in bone marrow
• Cancer: mutation occurs in genes that control cell division, an oncogene, that results in uncontrolled mitosis. Cancerous cells divide repeatedly and form a tumour, which is an irregular mass of cells.
• Malignant tumour: tumours that spread through the body, invade other tissues and destroy them. These cells break off from the tumour and form secondary growth, known as metastasis