Cell Division

Mitosis

Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA)

DNA Deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main component of chromosomes. It is the carrier of genetic information.

Chromatids are two identical copies of a single chromosome that are connected by a centromere. They occur as a result of a chromosome that duplicates during the prophase stage of the cell division

Vocabulary

What is cell division?

What phase is not included in mitosis?

Which phase of cell division last the longest? Why?

How many chromosomes are in a normal human cell? How does this change during mitosis?

What are centrioles and what role do they play in mitosis?

In what phase does the membrane of the nucleus begin to break down?

What are spindle fibers and what role do they play in mitosis?

How is the cytokinesis phase different from the other phases of mitosis?

What happens that causes cancer cells to grow and how does this effect the organism?

Copy the following questions your science notebooks and provide a complete answer for each

What is the difference between meiosis and mitosis?

Cell Division

Cell division is the process that cells go through in order to divide. Cells may divide for several reasons, and there are two types of cell division depending on the purpose. The cell division associated with sexual reproduction is one type, called meiosis. The other type, the cell division associated with growth and cell replacement or repair, is called mitosis. In both types of cell division, the nucleus splits and DNA is replicated.

The cell division called mitosis produces daughter cells that have all the genetic material of the parent cell — a complete set of chromosomes. However, chromosomes are not the only material that needs to be divided and transferred to the daughter cells: there are cytoplasm and the cell membrane to divide as well.

Cytokinesis is the process of dividing the cytoplasm and the cell membrane, and this process may follow immediately after mitosis or occur separately, depending on the organism involved. Together, these two processes make up the mitotic phases of the cell cycle.

Cell division consist of a series of steps or phases. These phases are Interphase, prophase, metaphase, anaphase, telophase, and cytokinesis

Interphase, which is the foundation building stage during, the parent cell, or original cell makes a copy of its genetic material so that each daughter cell can have a complete set. Therefore, mitosis is an ongoing and repetitive process, that begins with interphase over and over again..

Instructions:

As you go through this lesson, identify in your science notebook each phase of mitosis and explain what is occurring in each phase. Along with your explanation of each phase, make and label an illustration of each phase.

You will be expected to identify organelles within the cell, state what mitosis phase a cell is in by observing an image and / or by a given explanation of what is occurring in the cell.

Begin by continuing to the next slide.

This lesson will illustrates mitosis—the division of a cell's nucleus. Along with cytokinesis (the division of the rest of a cell), mitosis results in a parent cell dividing into two daughter cells. The genetic information within each of these daughter cells is identical.

A human cell contains 46 chromosomes. However, to simplify your illustration, you will only see four..

Interphase is the period between cell divisions. It is the longest phase. During this time, chromosomes replicate—each DNA strand unzips into two strands while free-floating bases attach to the unzipped strands. The chromosomes are loosely packed and not visible with a microscope.

Two pair of centrioles lie just outside the nucleus, next to each other. A centriole is a cylinder type structure within the cell that plays a part in cell reproduction.

Interphase

Centrioles are short cylinders with a 9+0 microtubule triplet that helps in organizing spindle fibers and direct organization of microtubles

Chromosomes begin to condense, taking on the form that they are usually depicted in: four arms connected at a point. Each chromosome is, at this time, actually two identical copies. Each copy is called a chromatid.

A spindle begins to form from the centrioles. This spindle is made of fibers. The centrioles begin to separate and the membrane of the nucleus, or nuclear envelope, fragments and disperses.

Prophase

Chromatid

The centrioles are now at opposite ends of the cell. The spindle fibers from both of the centrioles attach to each one of the chromosomes.

MetaphaseSometimes referred to as Prometaphase

Spindle fibers are protein structures that pull apart the genetic material in a cell when the cell divides.

The chromosomes line up on the metaphase plate, an imaginary line that divides the cell in two. The spindle fibers begin to tug each chromosome toward opposite ends of the cell.

Metaphase

The spindle fibers pull the chromatids toward opposite ends of the cell.

Anaphase

The chromatids (now also considered chromosomes) arrive at the opposite ends of the cell, and new nuclear membranes form.

Mitosis, which describes only the division of the nucleus, is now complete.

Telophase

In cytokinesis the rest of the cell divides and the division of the cell's cytoplasm, is now complete. The entire process of has been complete with a result of two identical cells.

Cytokinesis

Now, review the entire mitosis process again by clicking the link below. In addition pay particular attention about the discussion of cancer cell.

Video Clip: Mitosis and Cancer Cells

Cell Division

Meiosis

Meiosis

How is Interphase II different from Interphase in mitosis and Interphase I in meiosis?

What does the term Cross-over refer to?

How many chromosomes does a egg cell and sperm cell have?

In meiosis, what phase does the chromosomes share genetic information

List all the phases of meiosis in the correct order.

Copy the following questions your science notebooks and provide a complete answer for each

In meiosis, how is prophase I and prophase II different?

Before We SplitThough the genetic code of a human being is contained within 46 chromosomes, only half of this number exists within the cell of a sperm or egg. If the cells didn't have half, a fertilized egg would contain 92 chromosomes and be untenable. Meiosis, a type of cell division specific to reproduction, avoids this by halving the number of chromosomes in a cell.

The cell shown here will divide twice, resulting in four cells. Each of these cells will have only half the number of chromosomes, but each chromosome will contain genetic information from both parents.

Meiosis

The activities within this cell are the same as in the mitosis-dividing cell.

NOTE: Blue indicates chromosomes from the father; orange indicates chromosomes from the mother. The titles used for each step—e.g., "Interphase," Interphase I"—are those used in biology textbooks.

Interphase I

The activities are the same as in mitosis, except that in this cell the chromosomes attach to the membrane of the nucleus and then pair up with their corresponding chromosome.

While paired up, enzymes cut sequences of DNA (genes) from the chromosomes. These sequences are exchanged between the chromosomes, which allows for an exchange of genes between the two

Prophase I

Blue indicates father chromosomes

Orange indicates mothers chromosomes

Notice that the fathers chromosomes are paring up with a pair of chromosomes from the mother. It is at this point where genetic information is shared between mother and father and the pairing creates a new chromosome pattern which results in the creation of a new unique individual. This type of pairing and sharing of genetic material is referred to as Crossing-over

Same as in mitosis, except that the spindle fibers from each centriole attach to one chromosome of a matching chromosome pair.

In other words, the fibers from one centriole attach to 23 chromosomes, and the fibers from the other centriole attach to the other 23 chromosomes. (Again, only four chromosomes are shown here in order to simplify the illustration.)

Metaphase I

Same as in mitosis, except that the chromosome pairs line up on either side of the metaphase plate.

Metaphase I

Father’s chromosomes

Father’s chromosomes

Mother’s chromosomes

Mother’s chromosomes

The chromosome pairs separate; half of the chromosomes move toward one end of the cell, the other half, to the other end. The chromosomes' sister chromatids do not separate as they do in mitosis.

Anaphase I

Now as you view each chromatid, you can see a trace of the other parent genetic material on the new chromosome. This process reoccurs each time a cell divides which leads to enormous variety with the genetic code.

Mother & Father

Mother & Father

As in mitosis, the chromosomes arrive at opposite ends of the cell, and new nuclear membranes form.

The dividing cell shown here is a male's sperm cell. With meiosis in a female, most of the cell's cytoplasm will be concentrated in one of the two emerging cells, which will result in one large cell and one small cell.

Telophase I

Identical to mitosis.

Cytokinesis

This concludes the first part of Meiosis.View the video clip and complete your information with what is being said in the video. They should be similar.

Video Clip: Part 1 on Meiosis

The chromosomes do not replicate during this phase, as they do in interphase in mitosis and interphase I in meiosis

Interphase II

As in prophase I, the chromosomes condense, spindles form, the centrioles begin to separate, and the nuclear membrane fragments and disperses.

Unlike prophase I, the chromosomes do not attach to the nuclear membrane in order to exchange genetic information.

Prophase II

In this phase the DNA does not get copied. The chromosomes do not pair up and do not exchange information as they did in prophase I

The spindle fibers attach to the chromosomes. The centrioles are now at opposite ends of the cell. As in mitosis in this part of metaphase, fibers from both ends of the cells attach to each one of the four chromosomes.

Metaphase II

The chromosomes align along the metaphase plate. As in mitosis metaphase, (and unlike meiosis metaphase I), fibers from the centrioles begin to pull on each one of the chromosomes from both directions.

Metaphase II

As in anaphase in mitosis (and unlike anaphase I in meiosis), the fibers pull the chromatids apart and toward opposite ends of the cells.

Anaphase II

The chromatids arrive at the either end of each cell and new nuclear membranes form.

Telophase II

End of cytokinesisThe rest of the cell continues to divide. Only when two, distinct cells form will cytokinesis, the division of the cell's cytoplasm, be complete.

There are now four daughter cells. Each cell has one set of chromosomes, or one half the number of the initial cell.

Cytokinesis

This completes the 2nd part of meiosis. As you did with the first part, compare your data with information from the video clip. They should be similar.

Video Clip: Meiosis: Part two