The Cell Cycle& Mitosis

Why are Cells so Tiny? Your body contains 60 trillion cells. Cells take in nutrients and dispose of waste through the cell membrane.

Why are Cells so Tiny? As cells grow larger, the volume grows faster than the membranes’ surface area. When the cell becomes too large to absorb enough nutrients it must divide.

Why Do Cells Divide? The larger a cell becomes, the more demands the cell places on it's DNA. It also has more trouble moving enough food and wastes across its cell membrane.

Food goes in The bigger the cell gets the harder it becomes to move food and waste across the membrane Waste goes out

Protein Pumps This happens because the surface area and volume ratio does not stay the same as the cell size increases.

The cell's ability to either get substances from the outside or eliminate waste from the inside is related to the surface area of the cell membrane. (outside)

How much food and other material is required, and how much waste the cell produces and has to get rid of, is related to the volume of the cell. (inside)

As a cell gets bigger there comes a time when its surface area is not large enough to meet the demands of the cell's volume and the cell stops growing.

So, once cells reach a certain size they must divide in order to continue to function – or they will no longer be able to take in nutrients and eliminate waste.

Why do Cells Divide? Growth: Repair: Reproduction: To increase the number of cells in the body. Repair: To replace dead, damaged or old cells. Reproduction: Can make exact copies (clones).

The Cell Cycle Every hour, about 1 billion of your cells die and another 1 billion are made. Body cells go through several stages in their lifetime called the Cell Cycle. In most Eukaryotic cells, mitosis takes about 80 minutes. Embroynic cells can divide every 15-20 minutes.

How long do cells live? Type of Body Cell Average Life Span Brain 30-50 years Red blood 120 days Stomach lining 2 days Liver 200 days Intestine lining 3 days Skin 20 days

The Cell Cycle The Cell Cycle has 2 parts: 1. Interphase: Cell repairs any damages, re-energizes, grows and prepares for division. 2. Mitosis & Cytokinesis: Division of the cell into 2 identical “daughter” cells. * Note : Mitosis only takes place in Somatic (Regular Body) Cells

Interphase Longest stage of the cell cycle. Divided into three phases.

Interphase First Gap Phase (G1): Cells grow in size. New proteins and organelles are made. Synthesis Phase (S): DNA is replicated (known as chromatin). Second Gap Phase (G2): Cells prepare for division. Serves as a checkpoint to make suer that the DNA is correct.

Cell Division Mitosis (division of the nucleus) Prophase Metaphase Anaphase Telophase Cytokinesis (division of the cytoplasm)

The Nucleus

Chromosomes Hereditary information. Contained within the nucleus. Human cells contain 23 pairs of chromosomes. When a cell divides, each daughter cell gets the same 23 pairs of chromosomes.

Chromosomes Composed of DNA and proteins. A gene is a segment of DNA that codes for a particular trait.

Just to Clarify… One Chromosome Centromere

Prophase Chromatin condenses to form paired chromosomes (sister chromatids). Centrioles move to each pole. Nucleolus disappears. Nuclear membrane breaks down.

The nuclear membrane breaks apart

The chromosomes become visible The spindle apparatus forms and attaches to the centromeres of the chromosomes

Metaphase The Nuclear Membrane is Completely gone Spindle fibers attach to centromere. Duplicated chromosomes line up at metaphase plate ( aka the equator)

The Nuclear Membrane is completely gone The duplicated chromosomes line up along the cell's equator.

Anaphase Spindle fibers shorten. Sister chromatids separate and move to opposite poles.

Diploid sets of daughter chromosomes separate They are pushed and pulled toward opposite poles of the cell by the spindle fibers

Spindle Fibers

Telophase & Cytokinesis Nuclear membrane and nucleoli reform Cell membrane pinches inwards. Cytoplasm splits in half. Cells return to interphase.

The nuclear membrane and nucleoli (nucleus) reform. Cytokinesis is nearly complete,

The Cell Plate begins to form The Cell prepares for finial division

Cytokinesis – The final stage of Mitosis The cytoplasm, organelles, and nuclear material are evenly split and two new cells are formed. Cell Plate

The two new cells – each exactly like the other – are called Daughter Cells

Quick Review – Place Cells in Mitosis Order A B C D E

Interphase Quick Review: Identify What happens in each phase of Mitosis: Prophase Metaphase Anaphase Telophase

Plant vs. Animal Cell

Cell Cycle Checkpoints A point in the life of a cell when proteins determine whether cell division should or should not occur Cell division WILL NOT happen if: there is not enough nutrients to support cell growth DNA is not replicated DNA is damaged

Go Phase Cells can enter a resting phase called Go. E.g., nerve cells in the brain stop dividing when the brain is developed and cannot reenter the cell cycle.

Cell Death Necrosis: Apoptosis: Cells may die due to external factors. E.g., Toxins, infections, trauma. Apoptosis: The controlled death of old cells. E.g., White blood cells divide to fight viral infections. When they are no longer required, they undergo apoptosis.