Campbell and Reece, Chapter 12 p , Edulink and learning guide notes

 Chromosomes form when the chromatin network in the nucleus of the cell, coils up, shortens and thickens.  Each organism has a specific amount of chromosomes.  All humans have 46 chromosomes.  These chromosomes are arranged in identical pairs called homologous chromosome pairs –  Therefore humans have 23 homologous pairs of chromosomes.  These chromosomes are only visible during cell division processes.  One chromosome consist of 2 chromatids and one centromere that attach the chromatids together.  Each chromatid consist of genes which in turn consist of DNA.

X and Y chromosomes: gonosomes/sex-chromosomes Colored bands represents different genes

 Allow an organism to grow.  Repairs damaged cells/tissue.  Replace dead cells/tissue.  Reproduction in some simple organisms.

 In all somatic cells (include all body cells and excludes the sex cells – sperm/egg cells)

 CONSIST OF A FEW PHASES:  INTERPHASE  PROPHASE  METAPHASE  ANAPHASE  TELOPHASE

The cell cycle includes the following phases:  Interphase (include G1-, S- [DNA synthesis] and G2 phase)  Mitosis  (divides nucleus)  Cytokinesis  (divides cytoplasm)  Growth The result is 2 identical cells.

 Cell builds up enough energy for division process (preparation).  Nuclear envelope bounds the nucleus  DNA replication occurs (during S phase) – chromosomes not condensed yet  Cell look normal, like before division

 Nuclear envelope and nucleolus disappear.  Chromatin become more tightly coiled, and condenses into individual chromosomes. Chromosomes arrange randomly in the cell.  Centrioli (centrosomes) move to opposite poles, with spindle fibers stretching between them (mitotic spindle).

 Chromosomes become even more condensed  Each of two chromatids has kinetochore  Specialized protein structure located at centromere  Some microtubules attach to kinetochores – kinetochore microtubules  Pull chromosomes back and forth

 The centrioli reached the opposite poles with the spindle fibers in between.  The chromosomes arrange randomly on the equator (metaphase plate), each single chromosome attaching to a separate spindle fiber by means of the centromere.

 The spindle fibers pull tight.  The centromers attaching the chromatids of the chromosomes split in half.  Daughter chromosomes move to opposite poles as kinetochore microtubules shorten.

 Daughter chromosomes reach poles.  Nuclear envelope surrounds chromosomes.  Nucleolus reappear at each pole.  Chromosomes become less condense forming chromatin.  Two identical nuclei have been formed

 Invagination of the cytoplasm and plasma membrane occurs. (Cleavage furrow forms in animal cells; and a cytoplasmic plate forms in plant cells)  Continues until the cell in divided into 2 separate cells. (Identical to one another and to the original cell)