Transcript Chapter 5 Section 2

5.2 Mitosis and Cytokinesis
KEY CONCEPT
Cells divide during mitosis and cytokinesis.
5.2 Mitosis and Cytokinesis
Objectives
• Describe the structure of a chromosome.
• Follow chromosomes through the process of mitosis and
cytokinesis.
5.2 Mitosis and Cytokinesis
Vocabulary
• Chromosome
– Long, continuous thread of DNA that consists of
numerous genes and regulatory information.
• Histone
– Protein that organizes chromosomes and around
which DNA wraps.
• Chromatin
– Loose combination of DNA and proteins that is
present during interphase.
• Chromatid
– One half of a duplicated chromosome.
5.2 Mitosis and Cytokinesis
Vocabulary
• Centromere
– Region of condensed chromosome that looks pinched;
where spindle fibers attach during meiosis and
mitosis.
• Telomere
– Repeating nucleotide at the ends of DNA molecules
that do not form genes and help prevent the loss of
genes.
• Prophase
– First phase of mitosis when chromatin condenses, the
nuclear envelope breaks down, the nucleolus
disappears, and the centrosomes and centrioles
migrate to opposite sides of the cell.
5.2 Mitosis and Cytokinesis
Vocabulary
• Metaphase
– Second phase of mitosis when spindle fibers align the
chromosomes along the cell equator.
• Anaphase
– Third phase of mitosis during which chromatids
separate and are pulled to opposite sides of the cell.
• Telophase
– Last phase of mitosis when a complete set of identical
chromosomes is positioned at each pole of the cell,
the nuclear membranes start to form, the
chromosomes begin to uncoil, and the spindle fibers
disassemble.
5.2 Mitosis and Cytokinesis
Chromosomes condense at the start of mitosis.
• DNA wraps around proteins (histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
5.2 Mitosis and Cytokinesis
• DNA plus proteins is called chromatin.
chromatid
• 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.
telomere
centromere
telomere
Condensed, duplicated chromosome
5.2 Mitosis and Cytokinesis
Mitosis and cytokinesis produce two genetically identical
daughter cells.
Parent cell
• Interphase prepares
the cell to divide.
• During interphase,
the DNA is
duplicated.
centrioles
spindle fibers
centrosome
nucleus with
DNA
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During prophase, chromosomes condense and
spindle fibers form.
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During metaphase, chromosomes line up in the
middle of the cell.
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During anaphase, sister chromatids separate to
opposite sides of the cell.
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During telophase, the new nuclei form and
chromosomes begin to uncoil.
5.2 Mitosis and Cytokinesis
• Cytokinesis differs in animal and plant cells.
– In animal cells, the
membrane pinches
closed.
– In plant cells, a cell
plate forms.
5.2 Mitosis and Cytokinesis
Question/Answer
• What is the relationship between a molecule of DNA and
a chromosome?
– A chromosome is made of one continuous DNA
molecule
• How many chromosomes does the cell have at the start
of mitosis? How many does it have after cytokinesis?
– Four (duplicated) chromosomes ; four (unduplicated)
chromosomes.
• How does cytokinesis differ in animals and plant cells?
– 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.