THE CELL CYCLE 

INTERPHASE - This is the time in a cell’s life that it grows and metabolizes (breaks down and creates molecules).  The chromosomes are uncoiled and are known as chromatin.  The cell must also devote some time to preparing the cell for division. 

• During the S phase, it copies its chromosomes to provide genetic material for the new cell.  Now, instead of the chromosomes consisting of a single chromatid, they now consist of two sister chromatids.
• During the G2 phase, the cell makes new organelles and additional cytoplasm for the new cell

MITOSIS - This time in the cell’s life consists of four phases:  prophase, metaphase, anaphase, and telophase.  Remember their order by PMAT.

• Prophase - The chromatin condenses into chromosomes.  The nuclear envelope breaks down.  The centrioles begin to move to each side of the cell and are starting to make spindles.
• Metaphase - The individual chromosomes line up in the middle of the cell and each sister chromatid becomes attached to a spindle
• Anaphase - The spindles pull the sister chromatids to opposite side of the cell.
• Telophase - The spindles break down, the nuclear envelopes reappear, and the chromosomes (now single chromatids) uncoil to form chromatin

CYTOKINESIS - Here is where the cytoplasm divides and two new cells are formed.  The two daughter cells are the same as the parent cell.  Each new cell now enters into G1 of interphase.

MEIOSIS

Meiosis uses two sets of PMAT to divide cells twice:  Meiosis I and Meiosis II.  We start with diploid cells.

• Meiosis I divides each pair of homologous chromosomes into two cells.  Crossing over takes places during Prophase I.  The genes are shuffled between the homologous chromosomes.
• Meiosis II divides the sister chromosomes of each of those cells into two more cells.

The final outcome is four haploid cells.  Each one has ONE of the sister chromatids from each homologue.  In females, only one of the cells will be used as a gamete.  In males, all four will be used.

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GENOMIC IMPRINTING

In genomic imprinting, the phenotypic expression of a gene is going to be determined by whether it is inherited from the mother or the father.  For example, we discussed that Angelman Syndrome and Prader-Willi Syndrome are both caused by the same deletion on chromosome 15.  If the deleted chromosome is inherited from mother, then it is manifested as Angelman Syndrome and, if it is inherited from father, it is manifested as Prader-Willi Syndrome.  These syndromes are distinctively different from each other.  Read more by visiting the websites. 

Click here to get more information on genomic imprinting.

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WHAT IS POLYMERIZATION?

Polymers (poly- meaning “many”) are made up of smaller molecules called monomers (mono- meaning “one”).  These monomers are connected to each other to make up polymers by a condensation reaction (also known as a dehydration reaction, because water is lost from the monomers).   When polymers are broken, a water molecule is broken up to replace the -H and -OH on each of the ends of the monomers.  This process is known as hydrolysis, meaning “water splitting.”