Cell Division: The Process of Mitosis

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication = process whereby DNA is identically copied (before cell division) mitosis = division of the nucleus cytokinesis = division of the cytoplasm chromatin = DNA + protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

one of the major characteristics of living things is the ability to GROW an adult doesn't have bigger cells, they have more cells You can grow too many cells!!!

When do cells divide? Reproduction Replacement of damaged cells Growth of new cells In replacement and growth cell divisions how should daughter cells compare to parent cell? The daughter cells should be identical copies of the parent cell.

3 main stages of the cell cycle: Interphase: longest stage; preparation for cell division Mitosis: nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell Cytokinesis: cytoplasm divides forming 2 distinct cells

Cell Cycle Overview Interphase: quite long (most of the cell’s time spent here) Cell Division: occurs quickly

Interphase 90% of cell cycle is spent in this phase G1 = first growth phase S = synthesis phase, DNA synthesis (replication) occurs here G2 = second growth phase; centrioles are replicated.

Why is it important that the nucleus divides in mitosis? it stores the DNA (information of life) all new cells need this information

Chromosomes Genetic information is passed on from one generation to the next through chromosomes Every organism has a specific number of chromosomes (ex: humans = 46, carrots = 18) Chromosomes are not visible in most cells except in cell division

DNA and protein molecules that make up chromosomes is spread through the nucleus At the beginning of cell division, the chromosomes condense into compact visible structures (chromosomes) Before cell division, each chromosome is replicated (copied) Each chromosome is made up of 2 identical “sister” chromatids held together by a centromere

chromosome centromere chromatin DNA

Prophase Metaphase Anaphase Telophase Mitosis is one, continuous event, but it can be described as happening in 4 phases: Prophase Metaphase Anaphase Telophase

**Remember, the cell is coming out of Interphase…

PROPHASE In the Nucleus: Nucleoli disappear Chromosome fibers condense into discrete chromosomes Each chromosome consists of 2 sister chromatids joined at the centromere

PROPHASE continued… In the Cytoplasm: mitotic spindle begins to form spindle consists of microtubules arranged between the centrioles centrioles move apart due to lengthening of microtubules

PROPHASE

METAPHASE A.) chromosomes line up in the center of the cell;   B.) spindle fibers connect from the poles (end) of the spindle to the centromere of each chromosome

METAPHASE

ANAPHASE A.) centromeres split, causing the sister chromatids to separate, becoming individual chromosomes   B.) chromosomes are pulled apart to opposite ends of the cell (the shape of the cell elongates into an elipse)

ANAPHASE

TELOPHASE A.) chromosomes uncoil into chromatin   B.) new nuclear envelope forms around the chromatin C.) spindle breaks apart D.) nucleolus reappears in each new nucleus

TELOPHASE

Finally… CYTOKINESIS animal cells: cell membrane pinches in & divides (cleavage furrow) plant cells: a cell plate forms (new cell wall) **Begins before telophase has completed**