Mitotic Cell Division - Exercise 7Objectives

-Know the stages of the cell cycle.-Know why mitosis is important.-Know what types of cells do mitotic division.-Distinguish differences between an animal and a plant cell during mitotic division.-Identify the different stages of mitosis under the microscope and in models.NOTE: YOU DO NOT NEED TO IDENTIFY CELLS IN A POLAR VIEW.

Where one chromosomes is double strandedhelices replicates so that we now have 2 helicesjoined by region called center mere orkinetochore and each of these are now calledtwin chromatid or sister chromatid becauseone DNA double helix replicated itself.

0.5 µm Chromosomes

Chromosomeduplication(including DNAsynthesis)

Chromo-some arm

Centromere

Sisterchromatids

DNA molecules

Separation ofsister chromatids

Centromere

Sister chromatids

MITOSIS is a growth mechanism providing for the production of clone daughter somatic cells and is partially responsible for the processes of embryonic development, growth, and healing. Objective to create two nuclei (cells). Mitosis is to duplicate a set of chromosomes in a parent cell to two daughter nuclei. All cells have identical genome because raise from one fertilize ovule in a process called mitosis.

-Duplication of cells (46 chromosomes)

-Produces somatic cells

AUTOSOMES• Autosomes these are the non sex determining chromosomes.

These are your cells that are involved in mitotic division, such as, liver, skin, bone cells.

• Humans- have a total of 46 chromosomes. Twenty two pairs of autosomes and one pair of sex chromosomes.

• Cell division in eukaryotes typically involves the distribution of duplication sets of chromosomes in a parent cell to two daughter nuclei (Mitosis or karyokinesis) and the division of the cytoplasmic contents of a parent cell into two daughter cells (cytokinesis). Cell division is only one stage (the last (4th) stage – M) of the cell cycle.

• Mitosis is when nuclear material divides (Division of nucleus) and cytokinesis is when cytoplasm divides.

Interphase• G1: First growth event. The newly formed cell actively produces RNA and protein

as it grows – cell growth.

• G0: Period of no growth and it occurs prior to S phase, if it is going to happen.

• S-phase: Cell stops producing RNA and switches to DNA replication. Chromosomes are duplicated during the S-phase of the cell cycle. Think of S as Synthesis of DNA.

• G2: Once the DNA has been duplicated, the cell enters another round of RNA and protein synthesis and growth – more cell growth.

• When cells are in G1, S, and G2, they are often said to be in “interphase” – which literally means, between mitotic division.

• Finally the cell will divide, and this stage is called M phase. Chromosomes are too thin to see in the interphase stage under the microscope.

THE CELL CYCLE• G1 phase- growth phase where cell makes components for DNA

synthesis.• S phase-DNA synthesis, chromosomes replicate. DNA replicates

(synthesis)• G2 phase-growth phase where cell makes components for DNA

synthesis.• G0 phase-non-dividing cells. Neurons stay in this state.

• INTERPHASE-time between cell divisions-everything that is not mitosis.• Mitosis (M-phase)- cell divides: – Prophase– Metaphase– Anaphase– Telophase & CytokinesisInterphase is usually about 90%, and mitosis is the remaining10% of the cell cycle.

MITOSIS• A single (2n,diploid) cell divides to form two

genetically identical (2n,diploid) daughter cells.• 4 stages: Prophase, Metaphase, Anaphase,

&Telophase (Cytokinesis)

Plant cell division• It is necessary to obtain tissues that contain cells that are actively

dividing. One such tissue is the root tip. • Note: The viewpoint your looking at cells is called a lateral view.• Each cell can be considered to be a single frame of a motion picture.

Also know the parts of the cells when dividing.• Onion root tip (Allium cepa). Most of the cells you see will not be in

the M stage of the cell cycle. That is, most cells will be in interphase.

Animal Cell DivisionMitosis is animal cells in most readily seen in early embryonic stages. The blastula stage of an embryo is more or less a spherical ball of cells, and cell division occurs in every imaginable plane of the embryo.

Whitefish blastula.

NOTE!!!• A professor could ask you what are the

different stages of mitosis? In that case, you would write down prophase, metaphase, anaphase, and telophase.

• A professor could ask you the different stages of the cell cycle? In that case, you would include interphase (G1, S, G2), and mitosis (P,M,A,T).

Question

How can you tell whetheryou’re looking at a plantcell or an animal cell?

THE CELL CYCLE

Growth period: production of proteins and cytoplasmic

organelles

INTERPHASE

• The only significant genetic event occurring here is the replication of DNA (all the chromosomes duplicate).

• In interphase the chromosomes are not visible. They exist in thread-like strands known as CHROMATIN

• Cell is not diving. Very prominent nucleus (no chromosomes) cell makes protein and lots of RNA.

Interphase

These cells have obvious nuclear membranes and thenuclear material is still dispersed as chromatin.

PROPHASE CELLS

interphase prophase

-Chromosomes condense and become visible-Nuclear membrane breaks down-Nucleoli vanish

When mitosis begins, several changes occur in the cell. The chromosomal material (called chromatin) in the nucleus starts to condense, and eventually reaches thickness that makes them visible under the light microscope.

As prophase proceeds, the chromosomes continue to get shorter and thicker, and eventually begin to move toward the equator of the cell, midway between the poles. Prophase is typically the longest phase of mitosis.

Prophase

Several cells are seen in various stages of prophase. Note thepresence/absence of a nuclear membrane and the spindle apparatus,and the chromatin beginning to condense as visible chromosomes.

METAPHASE CELL

-chromsomes line up on the center line of the cell-centromeres duplicate-spindle fibers attach to centromeres

Chromosomes are short and thick will reach the center of the cell called the equatorial plane or metaphase plate. The duplicated chromosomes are separated from one another, except at one point called the kinetochore (centromere). When the duplicate chromosomes are in this attached condition, as they have been since they were duplicated, each strand is called a sister chromatid.

At the conclusion of metaphase each centromere, holding two identical sister chromatids, is attached to two spindle fibers, one from each pole.

Metaphase

The two cells in the center are in metaphase. In each, notice thechromosomes are aligned at the cell’s equator and the wellformed spindle apparatus.

ANAPHASE CELL

• -Sister chromatids move to opposite poles of the cell• -Spindle fibers pull the chromosomes apart by the

centromeres

Anaphase begins with the separation of sister chromatids of each duplicated chromosome. Each chromatid is moved by motor molecules that ratchet along the spindle fibers toward the polar ends.

The original chromosome and its exact duplicate are pulled to opposite poles of the cell. This happens for each different chromosome that the cell possesses; thus, each pole will eventually obtain exactly the same set of chromosomes that were in the original nucleus. In anaphase the chromatids are separated.

Early Anaphase

The spindle apparatus has begun to separate thechromosomes in the upper cell. The cell near the bottom of thefield as in metaphase.

Late Anaphase

• The chromosomes are close to the centrosomes, which means they have moved apart just about as far as they will go.

TELOPHASE CELL

Plant cell Animal cell

The events of telophase are essentially the reverse of the those of prophase. At the end of this, there are two nuclei, each having identical sets of chromosomes.

TELOPHASE

• Sister chromatids reach the opposite poles and begin returning to the interphase state.

• Nuclear membrane and nucleoli reform.• Spindle fibers disperse.• Cytokinesis occurs.• A cell plate (plants) or a cleavage furrow

(animals) forms.

Cytokinesis : division of cytoplasm

• Animal cells : cleavage– Cleavage furrow

• Division begin as a shallow groove in the cell surface near the metaphase plate

– Contractile ring (on the cytoplasmic side of the furrow)• Composes of actin microfilaments and the protein myosin

– Cleavage furrow deepens until the parent cell is pinched in two

• Plant cells : cell plate formation– Vesicles from the Golgi collect at the middle of the cell

producing a cell plate– Cell wall material carried in the vesicles is deposited on the

plate as it grows, until it fuses with the membrane along the perimeter of the cell

Late Telophase and Cytokinesis

The cleavage furrow has nearly divided the two cells, so cytokinesis isalmost complete. Telophase will continue with the chromosomesdispersing as chromatin and the nuclear envelope reforming.

Polar view

The cell in the center doesn’t fit any of the descriptionbecause it is begin viewed from one end (pole) rather than fromabove.

Cleavage furrow

The cleavage furrow (CF) has begun to form.

Cytokinesis in animal and plant cells

Cell Division• Reproduction

– Equal distribution of genetic material to two daughter cells

• Growth– Sexually reproducing

organisms develop from a single cell (zygote)

• Repair– Replace cells that die from

normal wear and tear or accidents

A single-celled

eukaryote (amoeba)

reproduces

Sand dollar embryo after

the egg divided to

form 2 cells

Dividing bone marrow cells produce new

blood cells

Interphase

Early Prophase

Late Prophase

Metaphase

Early Anaphase

Late Anaphase

Telophase - Cytokinesis

Interphase 2

Animal Vs. Plant Cells

-What are some differences between an animal cell and a plant cell?

Animal Vs. Plant Cells

-What are some differences between an animal cell and a plant cell? Plants have a cell wall, after telophase plant cells divide by forming a cell plate, and animal cells form a cleavage furrow. Plant cells are rectangular, and animal cells are more circular.

Mitosis - Review

Page 8 – Lab Book• 1. Why are the onion root tip and the whitefish blastula useful tissues

for the study of cell division?

• 2. Distinguish between mitosis and cytokinesis.

• 3. If a cell has 16 chromosomes when it is in G1, how many chromosomes will there be in each daughter cell following a mitotic cell division?

• 4. What are the genetic consequences of mitotic cell division for the resulting daughter cells?

• 6. How do plant and animal cells differ in the execution of cytokinesis? Why don’t plant cells undergo cytokinesis in the same manner as animal cells?

Page 8 – Lab Book• 1. Why are the onion root tip and the whitefish blastula useful tissues for the study

of cell division? These two tissues were actively dividing, so we (classmates) could find cells under going mitosis at different phases.

• 2. Distinguish between mitosis and cytokinesis. Mitosis is the division of the nucleus (nuclear division) produces 2 identical nuclei. Cytokinesis is the division of the cytoplasm – produces 2 cells.

• 3. If a cell has 16 chromosomes when it is in G1, how many chromosomes will there be in each daughter cell following a mitotic cell division? 16

• 4. What are the genetic consequences of mitotic cell division for the resulting daughter cells? Every cell is genetically identical to each other. Produces 2 identical nuclei, each with the same number and types of chromsomes as the parent cell.

• 6. How do plant and animal cells differ in the execution of cytokinesis? Why don’t plant cells undergo cytokinesis in the same manner as animal cells?

Figure 12.8 Cytokinesis in animal and plant cells

Page 9 – Lab Book• 7. List several important values or attributes that

mitotic cell division provides to multicellular life. In other words, in what ways is mitotic cell division useful for life?

• 8. List the 4 stages of the cell cycle and describe the primary cellular activity in each stage.

Cell Division• Reproduction

– Equal distribution of genetic material to two daughter cells

• Growth– Sexually reproducing

organisms develop from a single cell (zygote)

• Repair– Replace cells that die from

normal wear and tear or accidents

A single-celled

eukaryote (amoeba)

reproduces

Sand dollar embryo after

the egg divided to

form 2 cells

Dividing bone marrow cells produce new

blood cells

Questions1. How many daughter cells are produced by mitosis? 2. How does the number of chromosomes in eachdaughter cell compare with the number ofchromosomes in the original parent cell after mitosis? 3. When are chromosomes replicated? 4. During cytokinesis plant cells form a _________while animal cells form a ____________.

Questions1. How many daughter cells are produced by mitosis? 2

2. How does the number of chromosomes in eachdaughter cell compare with the number of chromosomesin the original parent cell after mitosis? Same numberand type of chromosomes.

3. When are chromosomes replicated? Interphase, specifically S-phase

4. During cytokinesis plant cells form a cell plate whileanimal cells form a cleavage furrow.