Mitosis and Cytokinesis

Chapter 5.2

KEY CONCEPT Cells divide during mitosis and cytokinesis.

• Show biology presentation film clip mitosis 2

Chromosomes condense at the start of mitosis.

• DNA wraps around proteins (histones) that condense it.

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA

• Overall, DNA has a negative charge. Look at the histone proteins above, what type of overall charge do you think they will have?

• Positive—negative and positive charges attract so if the histones were negatively charged they would repel DNA, instead they coil together.

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA

Vocabulary

• Chromosome—one long continuous thread of DNA• Nucleotides—DNA made of four different subunits • Histones—group of proteins associated with

chromosomes (help to compact DNA)• Chromatin—loose combination of DNA and proteins; ½

is called a chromatid• Centromere—sister chromatids held together at their

center; a region of condensed chromosome that looks pinched.

• Telomeres—don’t form genes—end of chromatin

• DNA plus proteins is called chromatin.• One half of a duplicated chromosome is a

chromatid.• Sister chromatids are held together at the

centromere.• Telomeres protect DNA and do not include genes.

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

• What is the relationship between a molecule and DNA and a Chromosome?

• A chromosome is made of one continuous DNA molecule

Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

• Interphase prepares the cell to divide.

• During interphase, the DNA is duplicated.

Mitosis and cytokinesis produce two genetically identical daughter cells.

• Mitosis divides the cell’s nucleus in four phases.– During prophase, chromosomes condense and spindle fibers form.

• Mitosis divides the cell’s nucleus in four phases.– During metaphase, chromosomes line up in the middle of the cell.

• Mitosis divides the cell’s nucleus in four phases.– During anaphase, sister chromatids separate to opposite sides of the

cell.

• Mitosis divides the cell’s nucleus in four phases.

– During telophase, the new nuclei form and chromosomes begin to uncoil.

• Cytokinesis differs in animal and plant cells.– In animal cells, the membrane

pinches closed.– In plant cells, a cell plate forms.

Cytokinesis--Plant cell vs. animal cell

Question

• How does cytokinesis differ in animal and plant cells?

Answer: in animal cells, the membrane pinches together to separate the cytoplasm. In plant cells, a cell plate forms and divides the cell, along which the cell membrane and cell wall re-form.

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