CELL CYCLE NOTES
CELL CYCLE – The sequence of events that occur in a cell from the time it is formed until it completes cell division.
INTERPHASE – The cell is not dividing. It consists of three substages.
G1 – A period of cell growth and development. DNA (and proteins) in the nucleus
appears as threadlike chromatin.
S Phase – DNA replicates (makes a copy of itself).
G2 – Cell prepares for mitosis (makes necessary proteins, etc.)
Animal cells have centrioles which are copied.
MITOSIS – Division of the cell nucleus. It consists of four substages.
PROPHASE – Chromatin condenses (shortens) to form chromosomes.
Spindle fibers (protein microtubules) form “bridge” across cell.
Nucleolus and nuclear membrane break down.
METAPHASE – Spindle fibers move chromosomes to the equator of the cell.
ANAPHASE – The sister chromatids of a chromosome are pulled apart.
Sister chromatids (now called chromosomes) move toward the
opposite ends of the cell along the spindle.
TELOPHASE – Chromosomes start to uncoil and form chromatin.
Nucleoli and nuclear membranes reform.
Spindle fibers break down. Cytokinesis has already begun.
CYTOKINESIS – Process where the cytoplasm and cell contents divide to form
two daughter cells.
In animal cells, cell membrane pinches inward (cleavage furrow).
In plant cells, a cell plate forms between the two daughter cells.
M PHASE - Another name for all the phases included in cell division.
It includes mitosis and cytokinesis.
CHROMATIN – DNA and protein in the nucleus of a nondividing cell (during interphase)
CHROMOSOME – DNA and protein in the nucleus of a dividing cell
CHROMATID – One of two identical halves of chromosome
CENTROMERE – Structure that serves as the point of attachment for the two sister
chromatids of a chromosome.
CENTRIOLE – Structure in animal cells that helps to organize spindle fibers during
mitosis.
SPINDLE FIBERS – Protein microtubules that attach to the chromosomes and move
them during mitosis.
HAPLOID (n) – A cell that has only one chromosome from each homologous pair →
(has half of the total # of chromosomes) Ex. in humans, 23 chromosomes
DIPLOID (2n) – A cell that has both chromosomes of each homologous pair.
Ex. in humans, 46 chromosomes
GAMETES – Sexual reproductive cell. Ex. sperm, egg
HOMOLOGOUS CHROMOSOMES - Chromosomes that are similar in size, shape,
and the location of the centromere. They occur in pairs. (one is inherited from the
mother and one from the father)
MEIOSIS - Division of the nucleus that reduces the chromosome number by half.
It occurs in the gametes.
MEIOSIS I - Division in which homologous chromosomes are separated
into different daughter cells.
MEIOSIS II - Division in which sister chromatids are separated into
different daughter cells.
SYNAPSIS - The process of pairing homologous chromosomes during (prophase I
of) meiosis I.
TETRAD - Structure that consists of a paired set of homologous chromosomes that
are intertwined. (during prophase I of meiosis I)
CROSSING-OVER - The exchange of corresponding genes between homologous
chromosomes in a tetrad. (between nonsister chromatids)
It increases genetic variation.
POLAR BODY - Three of the four daughter cells produced during meiosis of the
female gamete receive very little cytoplasm and disintegrate.
(the other daughter cell becomes the egg.