QuestionQuestion

How long do the cells in How long do the cells in your body live?your body live?

AnswerAnswer

It dependsIt depends.

AnswerAnswer

• Different cells live for different lengths of Different cells live for different lengths of time. time.

For example, here’s how often some different For example, here’s how often some different kinds of cell need to be replaced. kinds of cell need to be replaced.

AnswerAnswer

• Skins cells – 20 daysSkins cells – 20 days• Liver cells – 200 daysLiver cells – 200 days• Brain cells – 30 – 50 yearsBrain cells – 30 – 50 years• Intestinal lining – 3 daysIntestinal lining – 3 days• Stomach lining – 2 daysStomach lining – 2 days• Red blood cells – 120 days Red blood cells – 120 days

• If cells have such a short life-If cells have such a short life-span, and you are made of 100 span, and you are made of 100 000 000 000 000 cells, this must 000 000 000 000 cells, this must mean that mean that A LOTA LOT of cells are of cells are dying all the time.dying all the time.

• If cells have such a short life-If cells have such a short life-span, and you are made of 100 span, and you are made of 100 000 000 000 000 cells, this must 000 000 000 000 cells, this must mean that mean that A LOTA LOT of cells are of cells are dying all the time.dying all the time.• In fact, about 300 million of your In fact, about 300 million of your

cells die cells die each minute.each minute.

• This must also mean that This must also mean that A LOTA LOT of cells are being produced to of cells are being produced to replace the ones that are lost.replace the ones that are lost.

• Cells are produced as part of Cells are produced as part of THE CELL CYCLETHE CELL CYCLE

The Cell CycleThe Cell Cycle

So, how do we replace all those cells that we So, how do we replace all those cells that we lose everyday?lose everyday?

The Cell CycleThe Cell Cycle

So, how do we replace all those cells that we So, how do we replace all those cells that we lose everyday?lose everyday?

Cell DivisionCell Division

The Cell CycleThe Cell Cycle

• Most of the cells in your body replace Most of the cells in your body replace themselves in a process calledthemselves in a process called

MITOSISMITOSIS

The Cell CycleThe Cell Cycle

The cell cycle is divided into three stagesThe cell cycle is divided into three stages

The Cell CycleThe Cell Cycle

The cell cycle is divided into three stagesThe cell cycle is divided into three stages

1.1.InterphaseInterphase2.2.MitosisMitosis3.3.CytokinesisCytokinesis

The Cell CycleThe Cell Cycle

• Interphase is the longest stage in the cells life. It is when a cell carries out its various functions within the organism.

• During interphase cells – Grow in size– Prepare for cell division– Replicate their DNA

DNA ReplicationDNA Replication

• DNA makes a copy or DNA makes a copy or “ “replica” of itself duringreplica” of itself during interphase.interphase.• So for a little while the So for a little while the cell has 2 completecell has 2 complete sets of DNA.sets of DNA.

DNA ReplicationDNA Replication

MitosisMitosis

• Mitosis is the next stage in the cell cycle. (But a lot of things happen.)

• Mitosis is divided into 4 phases.1. Prophase2. Metaphase3. Anaphase4. Telophase

MitosisMitosis

The Cell CycleThe Cell Cycle

• The last stage of the cell cycle is The last stage of the cell cycle is Cytokinesis.Cytokinesis.• This is when the original (parent) cell This is when the original (parent) cell

separates into to new (daughter) cellsseparates into to new (daughter) cells

The Cell Cycle - ReviewThe Cell Cycle - Review

• A single cell divides to make two new A single cell divides to make two new cells – this is how our body replaces cells – this is how our body replaces cells.cells.• Most of the cells in our body do this Most of the cells in our body do this

with a process called with a process called MITOSISMITOSIS..

The Cell Cycle - ReviewThe Cell Cycle - Review

• Before mitosis can occur the DNA in Before mitosis can occur the DNA in the cell must the cell must ReplicateReplicate. This happens . This happens during during InterphaseInterphase..• Mitosis results in two new cells that Mitosis results in two new cells that

are are IDENTICALIDENTICAL to the original parent to the original parent cell.cell.