Lecture 1 - Mitosis

• The amount of DNA changes, but not the ploidy level in mitosis
• A diploid somatic cell after the S-phase is still considered a diploid cell, even though there are 4 complete sets of chromosomes. This is a short and transient phase. Note that the amount of DNA has doubled.
• 1 chromosome from dad's germ cell is haploid, 1 chromosome from mom's germ cell is haploid. When these combine they form a diploid cell with two unique chromosomes.
• A diploid cell has two complete sets of chromosomes. One copy from the mother and one copy from the father. An example would be a somatic cell such as a leaf cell, skin cell or a stem cell within the colon.
• A cell with one complete set of chromosomes is haploid. An example of a haploid cell would be a sperm or egg cell.
• The number of complete sets of chromosomes in a cell is known as its ploidy.
• In cytokinesis in animal cells, the contractile ring divides the two cells.
• In telophase, the nuclear envelop re-forms and chromosomes decondense.
• In anaphase, the sister chromatids (which become individual chromosomes when the centromere splits) separate and travel to opposite poles.
• In metaphase, chromosomes align in the center of the cell.
• Kinetochores are protein complexes.
• In pro-metaphase, the microtubules of the mitotic spindle attach to chromosomes. The nuclear envelop starts to break down.
• In prophase, the chromosomes condense. Centrosomes radiate microtubules and migrate to opposite poles.
• Sister chromatids are two identical chromosomes that are joined at the centromere.
• Centromeres are the central part, that is essential for attaching the spindle fibres in chromosomes.
• A neuron with its axon and dendrites would be quiescent with respect to the cell cycle. They will not re-enter the cell cycle.
• Cells that are not actively cycling may exit the cell cycle. From G1 they enter a state called G0. These cells are said to be quiescent.
• In the M phase (mitosis) chromosomal separation and cytokinesis occurs
• In the G2 phase (Gap 2) it is the preparation for mitosis.
• During the S phase (synthesis) DNA replication occurs (chromosome duplication)
• G1 phase (Gap 1) - The first phase of the cell cycle. The cell grows and prepares to divide. (extra mitochondrial DNA and ribosomes are made).
• Interphase is the time between successive mitoses (G1 + S + G2)
• The main stages on the cell cycle are G1 phase, S phase, G2 phase, M phase
• If a stem cell divides once a day for 75 years, it will have divided over 27,000 times, without making a mistake.
• In prokaryotes mitotic cell division the genome is small and circular and the DNA is found in the cytoplasm.
• In eukaryotes mitotic cell division the genome is large and linear and the DNA is found in the nucleus.
• Mitotic cells in an adult that would be considered stem cell are: neural, follicle hair, mammary, muscle, intestinal, epithelial, and hematopoietic stem cells.
• Cell division occurs by either: mitosis or meiosis
• Cell division occurs for: growth, cell replacement, healing, reproduction.
• Mitosis occurs in stem cells in the colon.
• Homologous chromosomes are identical chromosomes that carry the same genes.
• Sister chromatids are two copies of one chromosome joined at their centromere.