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A short class with Sarah and her students. The other ways are under More.
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Before a cell can divide, it has to prepare. What must it copy, so that each new cell gets a full set of instructions?
Its DNA.
Exactly. That happens in interphase. After copying, each chromosome is made of two identical sister chromatids, joined at the centromere.
Is interphase part of mitosis, then?
Not strictly. Mitosis is the division of the nucleus: prophase, metaphase, anaphase and telophase. Interphase comes before, and cytokinesis comes after.
So the full order is interphase, prophase, metaphase, anaphase, telophase, then cytokinesis.
Yes. Remember IPMAT, and then the cytoplasm divides.
In prophase, the chromosomes suddenly become visible. Why?
Because they coil up and get shorter and thicker.
Right. What happens to the nuclear membrane?
It breaks down, and spindle fibres start to form.
Good. Then comes metaphase. Where are the chromosomes now?
Lined up along the middle of the cell, with spindle fibres attached to each centromere.
Exactly, and that makes metaphase the best stage for counting chromosomes.
In anaphase, the spindle fibres shorten. What does that do?
It pulls the sister chromatids apart to opposite ends of the cell.
And in telophase?
A nuclear membrane forms around each set of chromosomes, so there are two nuclei.
Then cytokinesis splits the cytoplasm. Why can't a plant cell just pinch in the middle like an animal cell?
Because it has a rigid cell wall, so it builds a cell plate across the middle instead.
Perfect. The result is two genetically identical cells.
Interphase, prophase, metaphase, anaphase, telophase, then cytokinesis (IPMAT).
The cell grows and replicates its DNA, so each chromosome becomes two sister chromatids.
Chromosomes condense, line up at the equator, are pulled apart, and are enclosed in two new nuclei.
Animal cells pinch in; plant cells form a cell plate that becomes a new wall.
Each new cell gets the same chromosomes as the parent cell, which suits growth, repair and asexual reproduction.
Bacteria have no nucleus and divide by binary fission, not mitosis.
In a stained onion root tip under the microscope, cells can be seen in every stage, from chromosomes lined up at the equator to two new nuclei forming.
When a cut on your finger heals, skin cells near the wound divide by mitosis to replace the cells that were lost.
A strawberry plant grows new plants on its runners by mitosis, so the new plants are genetically identical to the parent.
Interphase prepares, prophase coils, metaphase lines up, anaphase splits the spoils; telophase builds two nuclei new, and cytokinesis splits one cell into two.
Dancers practise all week (interphase), put on their costumes (prophase), line up across the stage (metaphase), split from their partners to opposite wings (anaphase), and form two new groups (telophase) before the curtain falls between them (cytokinesis).
I Prefer My Apples Tasty: Interphase, Prophase, Metaphase, Anaphase, Telophase.
P.M.A.T. - Prophase, Metaphase, Anaphase, Telophase: the four stages of mitosis itself.
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What is the order of the stages?
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What happens in interphase?
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What happens in metaphase?
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What happens in anaphase?
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How does cytokinesis differ in plant cells?
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A thread-like structure of DNA and protein that carries genes.
The two identical copies of a chromosome, made in interphase and joined at the centromere.
The point where two sister chromatids are joined and where spindle fibres attach.
Protein fibres that attach to the chromosomes and pull the chromatids apart.
The stage before division in which the cell grows and replicates its DNA.
The middle of the cell, where chromosomes line up in metaphase.
The division of the cytoplasm that produces two separate cells.
The structure that forms across a dividing plant cell and becomes the new cell wall.
A dividing cell passes through interphase, when it grows and copies its DNA, then the four stages of mitosis (prophase, metaphase, anaphase and telophase), which share the chromosomes equally between two nuclei, and finally cytokinesis, which splits the cytoplasm to make two genetically identical cells.
This lesson walks through each stage of the cell cycle in order. It explains what a cell does to prepare in interphase, what happens to the chromosomes, the nuclear membrane and the spindle in prophase, metaphase, anaphase and telophase, and how cytokinesis differs in animal and plant cells. Worked examples track the number of chromosomes and chromatids through the cycle and use counts from an onion root tip to estimate how long each stage lasts, and the lesson ends with why mitosis matters.
Strictly speaking, mitosis is the division of the nucleus, and it has four stages: prophase, metaphase, anaphase and telophase. It is preceded by interphase, when the cell prepares, and followed by cytokinesis, when the cytoplasm divides. A useful memory aid for the order is IPMAT: Interphase, Prophase, Metaphase, Anaphase, Telophase.
Most cells spend most of their time in interphase. The cell grows, makes new proteins and organelles, and, most importantly, replicates its DNA. Each chromosome becomes two identical sister chromatids, joined at a point called the centromere. During interphase the chromosomes are long, thin threads spread through the nucleus, so they cannot be seen as separate chromosomes under a light microscope.
The cytoplasm divides, usually starting during late anaphase or telophase. In animal cells, the cell membrane pinches inwards around the middle, forming a cleavage furrow, until the cell splits in two. In plant cells, the rigid wall cannot pinch in, so a cell plate forms across the middle of the cell and develops into a new cell wall between the two daughter cells.
A human body cell has 46 chromosomes. After DNA replication in interphase it still has 46 chromosomes, but each now has two chromatids: 92 chromatids in all. At metaphase, 46 chromosomes (92 chromatids) line up at the equator. In anaphase the 92 chromatids separate, so 46 chromosomes move to each pole. After telophase and cytokinesis there are two cells, each with 46 chromosomes, genetically identical to the original cell.
In a stained onion root tip, the fraction of cells seen in each stage reflects the fraction of time that stage lasts. Suppose a count of 200 cells finds 180 in interphase, 10 in prophase, 4 in metaphase, 3 in anaphase and 3 in telophase, and the whole cycle takes 24 hours. Prophase then lasts about 10 ÷ 200 × 24 = 1.2 hours (72 minutes), and metaphase 4 ÷ 200 × 24 = 0.48 hours (about 29 minutes). Interphase takes 180 ÷ 200 × 24 = 21.6 hours, which shows how much of the cycle is spent preparing. The proportion of cells in mitosis, 20 ÷ 200 = 0.10, is called the mitotic index.
Because each daughter cell receives an identical set of chromosomes, mitosis produces genetically identical cells. This is essential for growth (making more cells), repair (replacing damaged cells, as when a cut heals), replacement of cells that wear out, such as skin cells, and asexual reproduction in many plants and some animals and fungi, as when a strawberry plant grows new plants on runners. Bacteria, which have no nucleus, do not carry out mitosis: they divide by a simpler process called binary fission.