Cell Growth & Division

Mitosis

Why do Cells Reproduce?

• Growth of an organism

• Replacement of old or damaged cells

Chromosomes• Each cell has lots of DNA, but it must be

condensed in order to fit in the nucleus

• DNA is organized and packaged into structures called chromosomes

• Prokaryotic Chromosome:

– Single circular strand of DNA that is condensed through many twists

• Eukaryotic Chromosome…

Eukaryotic Chromosomes• Most eukaryotes have between 10 & 50

chromosomes in their body cells, but…

• Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

Eukaryotic Chromosomes• When cells are ready

to divide, the chromatin condenses into chromosomes

• Each of the 2 thick strands is called a chromatid

• Identical chromatids (sister chromatids) are held together at centromere

Preparing for Cell Division• All newly-formed cells require DNA, so

before a cell divides, a copy of DNA is made for each new cell (daughter cell)

• This assures that new cells will work in the same way as the cells they came from

• In prokaryotic cells, it’s simple!! DNA is copied, then cell divides

• In eukaryotic cells, it’s more complex…

Preparing for Cell Division

Eukaryotic Cell Cycle: Overview 1.)

Interphase: when cell

grows and prepares to

divide

2.) Mitosis: when

nucleus divides

3.)

Cytokinesis: when cytoplasm divides and two new cells are complete

Interphase• Growth stage

• Cells mature by making more cytoplasm

• Organelles and Centrioles duplicate

• DNA is copied

Two Two identicidentic

al al copies copies of DNAof DNA

Original Original DNADNA

• Prophase

• Metaphase

• Anaphase

• Telophase

• PMAT!!

Mitosis

Prophase• Chromatin in nucleus condenses to form

visible chromosomes

• Spindle fibers form from the centrioles and attach to centromeres

Metaphase• Chromosomes that are attached to spindle

fibers move to the center of the cell and line up

Anaphase• Occurs Rapidly

• Sister chromatids are pulled apart to opposite poles of cell by spindle fibers

Telophase• Sister chromatids are at opposite poles

• Spindles disassemble

• Nuclear envelope forms around each set of sister chromatids

Cytokinesis• Division of cytoplasm

• Division of cell into two, identical cells called daughter cells

• Daughter cells have the same # of chromosomes as each other and as the parent cell from which they were formed

• Must still grow in size to become mature

Onion Root TipInterphase

Interphase

Prophase

Prophase

Prophase

Metaphase

Anaphase

Anaphase

Telophase

Cytokinesis

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