CHROMOSOMES

Chromosomes are composed of DNA, and are found in the nucleus of cells.

DNA contains the genetic material, or genes.

Genes are lined up on chromosomes like the cars on a freight train.

Organisms have tens of thousands of genes that control different traits. Genes play an important role in determining how a person’s body develops and functions.

Human body cells have 46 chromosomes.

How does DNA fit inside the nucleus of a cell? If you took one of your cells and stretched out the chromosomes and laid them end to end, the DNA would be about 3 meters long. How does DNA fit inside the nucleus of a cell?

DNA wraps around proteins that help organize and condense it. The DNA strands are highly coiled.

REVIEW!!

THE CELL CYCLE

All organisms have a life cycle: birth growth reproduction death

Within all organisms, cells are also “born”, grow, reproduce/divide, and die. CELL TYPE LIFE SPAN Lining of the intestine 4-5 days Skin cell 2 weeks Red blood cell 4 months Liver cell 300-500 days Brain cells 100 years Brain cells do not divide… you are born with all your brain cells you will ever have!

Cell Cycle - cells are born - cells grow and work - cells divide to make new cells - cells die

The cell cycle A repeating sequence of cellular growth, DNA replication, and cell division .

The cell cycle can be divided into three stages: Interphase Mitosis Cytokinesis

During interphase….. The cell grows. Cells also increase in size, and organelles increase in number.

During interphase….. The cell works…and works The cell carries out its normal functions. Red blood cells-- Carry oxygen Muscle cells--- contract to move joints

During interphase….. The cell copies its DNA . At the end of this stage, the nucleus contains two complete sets of DNA.

CELL CYCLE The cell spends most of its life in interphase.

Interphase is followed by cell division.

Cell division involves: Mitosis Cytokinesis.

Mitosis occurs first. CELL DIVISION

2. Mitosis: The division of the cell nucleus into two identical nuclei. one nucleus two nuclei

Mitosis is followed by cytokinesis. CELL DIVISION

3. Cytokinesis: The division of the cytoplasm.

REVIEW CELL CYCLE Cell Division

CELL DIVISION MITOSIS & CYTOKINESIS Making new cells

Why does cell division occur? To make new cells… To replace old or dead cells To replace cells destroyed by injury Skin cells

for growth and development.

to produce a new individual --- asexual reproduction the production of genetically identically offspring from a single parent…a clone.

This protist is reproducing asexually. http://www.youtube.com/watch?v=kexgNglKeWU

YOU are here because of cell division. The one cell divided to produce 2, then 4, then 8, 16, 32, ….. cells You began life as one cell And continued to divide… zygote

As old cells die, new cells are produced. New cells are produced by cell division. One cell divides to form two new cells. cell division one cell two identical cells

How do cells divide? Is this a problem???? What can a cell do???? 23 46 23 Is this a problem???? What can a cell do????

Before a cell can divide, it must duplicate/copy its DNA. 4 chromosomes 4 4 DNA is duplicated 8 cell divides 4 Identical! New cells identical to original cell.

4 4 8 4 Identical! New cells have same number of 4 chromosomes 4 chromosomes 4 4 DNA is duplicated 8 cell divides 4 Identical! New cells have same number of chromosomes as the original cell.

A cell duplicates its DNA during interphase. 4 chromosomes 8 chromosomes DNA is duplicated

During interphase, a cell duplicates its DNA…. 4 chromosomes 8 chromosomes DNA duplicates nucleus

Interphase….DNA is duplicated chromosomes 4 chromosomes …..double nucleus cell DNA in chromosomes DNA is duplicated nucleus cell chromosomes in cell 4 chromosomes ….single

the cell proceeds to divide. After Interphase, the cell proceeds to divide. Cell division

Cell division involves: Mitosis Cytokinesis.

MITOSIS pmat There are four phases in mitosis: 1. prophase Remember me! There are four phases in mitosis: 1. prophase 2. metaphase 3. anaphase 4. telophase pmat

1. Prophase DNA condenses into tightly coiled chromosomes. Duplicated chromosomes consist of two identical copies. pro = chromosomes condensed cell

Condensed duplicated chromosomes are x - shaped

2. Metaphase Chromosomes line up along the middle/center of the cell. meta = middle

3. Anaphase Chromosomes are pulled apart and move to opposite ends of the cell.

3. Anaphase Chromosomes are pulled apart and move to opposite ends of the cell. Ana = Apart Chromosomes pull apart

4. Telophase The chromosomes gather at opposite poles of the cell forming two nuclei.

4. Telophase The chromosomes have reached opposite ends of the cell telo = two nuclei The nuclear membrane starts to form. Two nuclei form.

Cytokinesis The cytoplasm divides, forming two identical cells.

Cytokinesis The cytoplasm divides, forming two identical cells. DNA The cells can now go about their business.

After the cell undergoes mitosis and cytokinesis, the two new cells produced are identical to the original cell.

Recap….Making more cells Organisms are always in need of more cells. Organisms make more cells by cell division. Cell division = mitosis + cytokinesis

Recap…..Mitosis Mitosis is Division of the nucleus

P M A T Recap…..Mitosis Which are the phases? --- prophase Remember me! Which are the phases? P M A T --- prophase pro = chro - chromosomes condensed --- metaphase meta = middle - chromosomes in middle --- anaphase ana = apart - chromosomes move apart --- telophase telo = two - two nuclei

MITOSIS 4 chromosomes One cell 4 chromosomes Two cells

MITOSIS produces two cells with the same number of chromosomes as the original cell … produces two identical cells

Regulating the Cell Cycle Some cells divide every few hours…cells lining stomach. Some cells never divide….brain cells How do cells know when to divide?

There are many different proteins that regulate the cell cycle and cell division. Proteins…workhorses of the cell!!!

Regulating the Cell Cycle Most cells will divide until they come in contact with other cells. Once the cells come in contact with other cells, the cells stop dividing. Example: Injury

CANCER: Uncontrolled Cell Growth a disorder in which body cells lose the ability to control cell growth and cell division. Cancer cells do not respond to signals that regulate their cell cycle; As a result cells divide uncontrollably.

Cancer cells divide forming a mass of cells called a tumor. Benign tumors do not spread. Malignant tumors spread and destroy healthy tissue.

Cancers are caused by defects in the genes that regulate the cell cycle and cell division. The defect or mistake in the gene (DNA) results in the production of a defective protein that is unable to regulate the cell cycle. As a result, the cell divides uncontrollably.