Chapter Chapter

CELL CYCLE

Why Is Cell Division Important

What do you, an octopus, and an oak tree What do you, an octopus, and an oak tree all have in common?all have in common?

You are all made of many cells, trillions of You are all made of many cells, trillions of them!them!

Many multi-celled organisms start off as just Many multi-celled organisms start off as just one single cell. And this single divides to one single cell. And this single divides to become 2 cells which divide to become 4 become 2 cells which divide to become 4 cells and then 8 and 16 and so forth.cells and then 8 and 16 and so forth.

Why Is Cell Division ImportantWhy Is Cell Division Important

Many celled organisms are able to grow Many celled organisms are able to grow and develop because cell division and develop because cell division increases the total number of cells in an increases the total number of cells in an organism.organism.

Even after we stop growing cell division is Even after we stop growing cell division is very important.very important.

Everyday billions of red blood cells are Everyday billions of red blood cells are replaced by new ones through cell replaced by new ones through cell division.division.

Why Is Cell Division ImportantWhy Is Cell Division Important

Cell division is not just important to multi-Cell division is not just important to multi-celled organisms. It is also important to celled organisms. It is also important to single celled organisms, like bacteria and single celled organisms, like bacteria and algae.algae.All cells go through cell division in what is All cells go through cell division in what is called the cell cycle or the cell life cycle.called the cell cycle or the cell life cycle.The cell cycle begins with the formation of The cell cycle begins with the formation of a cell of an organism. a cell of an organism. This formation is followed by growth and This formation is followed by growth and finally ends in the death of the cell.finally ends in the death of the cell.

Cell CycleCell Cycle

There are 3 There are 3 stages of the cell stages of the cell cycle. And they cycle. And they are: are:

1) Interphase 1) Interphase

2) Mitosis 2) Mitosis

3) Cytokenesis.3) Cytokenesis.

Cell CycleCell Cycle1)1) InterphaseInterphase- during this first stage of the - during this first stage of the

cell cycle, the cell grows and duplicates cell cycle, the cell grows and duplicates its organelles and chromosomes in order its organelles and chromosomes in order to prepare for mitosis.to prepare for mitosis.

2)2) Mitosis- Is stage 2 of the cell cycle. And Mitosis- Is stage 2 of the cell cycle. And mitosis is the way that all of our cell go mitosis is the way that all of our cell go through cell division.through cell division.

3)3) The third stage of the cell cycle is called The third stage of the cell cycle is called cytokenesis. Here the cytoplasm of the cytokenesis. Here the cytoplasm of the parent cell is evenly distributed into the parent cell is evenly distributed into the two new daughter cells or offspring.two new daughter cells or offspring.

InterphaseInterphaseMost of the life of any cell is spent in Interphase, in Most of the life of any cell is spent in Interphase, in which the cell grows and develops.which the cell grows and develops.

Also, during the later part of interphase the cell Also, during the later part of interphase the cell duplicates all of its chromosomes, which hold all of our duplicates all of its chromosomes, which hold all of our genetic material and prepares to undergo a form of genetic material and prepares to undergo a form of cell division called cell division called mitosis. mitosis. When chromosomes duplicate they form 2 chromatids.When chromosomes duplicate they form 2 chromatids.You are able to grow and develop because of You are able to grow and develop because of mitosismitosis, , the process in which one cell splits its nuclei and its the process in which one cell splits its nuclei and its DNA to produce two exact genetic copies of itself.DNA to produce two exact genetic copies of itself.

The cells want to duplicate or copy its chromosomes The cells want to duplicate or copy its chromosomes before mitosis so that the two new cells that are going before mitosis so that the two new cells that are going to be made have an equal amount of chromosomes in to be made have an equal amount of chromosomes in themthem

Cell Division or Mitosis

Cells go through mitosis in order to assure that each new cell receives exactly the same information as the cell it came from.

Also, cells go through mitosis in order to grow and replace dead or damaged cells, like when you get a cut, or break a bone.

5 Stages of Mitosis.

Mitosis occurs in 5 stages, and they are Mitosis occurs in 5 stages, and they are called:called:

1)1) ProphaseProphase

2)2) MetaphaseMetaphase

3)3) Anaphase Anaphase

4)4) TelophaseTelophase

Mitosis1)1) ProphaseProphase- Here, the chromatids become - Here, the chromatids become

visible because the nucleus is breaking visible because the nucleus is breaking down and the down and the spindle apparatusspindle apparatus, which , which is used to separate the chromosomes is is used to separate the chromosomes is formed.formed.

- The spindle apparatus is a set of thread - The spindle apparatus is a set of thread like fibers that are made by an organelle like fibers that are made by an organelle called a called a centriolecentriole. .

And it is used to pull the duplicated And it is used to pull the duplicated chromatids apart so that each new cell chromatids apart so that each new cell can have an equal amount of can have an equal amount of chromosomes.chromosomes.

Prophase

Mitosis2) 2) MetaphaseMetaphase- The - The

chromatids line up in chromatids line up in the middle of the cell the middle of the cell and begin to be pulled and begin to be pulled apart from one apart from one another by the spindle another by the spindle apparatus, which is apparatus, which is attached to the attached to the centromerecentromere of the of the chromatid, or where chromatid, or where the chromatids are the chromatids are attached.attached.

Metaphase

Mitosis3)3) Anaphase Anaphase- In anaphase all of the - In anaphase all of the

chromatids that were lined up in the chromatids that were lined up in the middle of the cell are completely pulled middle of the cell are completely pulled apart from on another by the spindle apart from on another by the spindle apparatus.apparatus.

This leaves two sets of equal numbers of This leaves two sets of equal numbers of chromosomes on each end of the cell.chromosomes on each end of the cell.

Anaphase

Mitosis4) 4) TelophaseTelophase- here the - here the

cell wall or cell cell wall or cell membrane of the cell membrane of the cell begins to pinch in and begins to pinch in and the cells divide into the cells divide into two cells of equal size two cells of equal size with the same genetic with the same genetic material.material.

Also here the spindle Also here the spindle starts to disappear starts to disappear and a new nucleus and a new nucleus forms.forms.

Stage 3 of the Cell Cycle:Stage 3 of the Cell Cycle:Cytokenesis Cytokenesis

In animal cells, the cell membrane pinches In animal cells, the cell membrane pinches and the cytoplasm of the parent cell is and the cytoplasm of the parent cell is divided into the two new cells.divided into the two new cells.

In plant cells, after telophase a In plant cells, after telophase a cell platecell plate is formed in order to allow the proper is formed in order to allow the proper formation of the cell wall.formation of the cell wall.

The presence of the cell plate tells you The presence of the cell plate tells you that the cell is in the stage of cytokenesis.that the cell is in the stage of cytokenesis.

Results of MitosisResults of Mitosis

You should remember 2 important facts You should remember 2 important facts about mitosis:about mitosis:

1)1) It is the division of the nucleus.It is the division of the nucleus.

2)2) It produces 2 new nuclei that are It produces 2 new nuclei that are identical to each other and also identical identical to each other and also identical to the original parent cell.to the original parent cell.

Reproduction

The method in which an organism can produce a The method in which an organism can produce a new organism from one parent is called, what?new organism from one parent is called, what?

Asexual reproductionAsexual reproduction

In asexual reproduction, all the DNA in the new In asexual reproduction, all the DNA in the new organism comes from only one parent.organism comes from only one parent.

A potato uses asexual reproduction, so every A potato uses asexual reproduction, so every potato that comes from one parent potato will potato that comes from one parent potato will have the same DNA as that parent.have the same DNA as that parent.

There are 2 ways in which There are 2 ways in which reproduction from one parent reproduction from one parent

occurs.occurs.1)1) By Splitting-bacteria and other single By Splitting-bacteria and other single

celled organisms divide in half, celled organisms divide in half, forming two new cells.forming two new cells.

When the cell divides, each new cell gets When the cell divides, each new cell gets an exact copy of the parents DNA.an exact copy of the parents DNA.

Now the two new cells are exactly alike Now the two new cells are exactly alike and the parent cell no longer exists.and the parent cell no longer exists.

There are 2 ways in which reproduction from There are 2 ways in which reproduction from one parent occurs.one parent occurs.

2) 2) Budding out and Budding out and breaking up- Many breaking up- Many mushrooms, plants, mushrooms, plants, and some animals use and some animals use budding as a form of budding as a form of asexual reproduction.asexual reproduction.

Here a new cell will bud Here a new cell will bud off of the parent cell, off of the parent cell, break away and live break away and live on its own.on its own.

Budding & RegenerationBudding & Regeneration

Ex: If you cut a piece of ivy, that piece that Ex: If you cut a piece of ivy, that piece that you cut can be planted and grow to a new you cut can be planted and grow to a new plant.plant.

In a process called regeneration some In a process called regeneration some organisms are able to replace body parts organisms are able to replace body parts that have been lost because of injury.that have been lost because of injury.

Sexual ReproductionSexual ReproductionIn In sexual reproduction-sexual reproduction- a new organism is a new organism is produced from two parents.produced from two parents.During this process, DNA from both parents During this process, DNA from both parents combine to form a new individual with its own combine to form a new individual with its own DNA.DNA.

In Chapter 3 we spoke of how there are In Chapter 3 we spoke of how there are different cells for different function in the human different cells for different function in the human body.body.For sexual reproduction have cells called For sexual reproduction have cells called sex sex cells.cells.

Sex cellsSex cells

There are two types of sex cells:There are two types of sex cells:

1)1) SpermSperm- a male sex cells that form in male - a male sex cells that form in male reproductive organs.reproductive organs.

2)2) Ova or egg-Ova or egg- a female sex cell which will form a female sex cell which will form within the female reproductive organs.within the female reproductive organs.

Body cells or non sex cells in your body have 46 Body cells or non sex cells in your body have 46 chromosomes and are called chromosomes and are called diploiddiploid because because each chromosome has a pair.each chromosome has a pair.

And when they divide the new cells gets all 46 And when they divide the new cells gets all 46 chromosomes that the original had, and we said chromosomes that the original had, and we said that this process was called mitosis.that this process was called mitosis.

Sex CellsSex Cells

Sex cells are a little different. They go Sex cells are a little different. They go through a process called through a process called meiosismeiosis, which is , which is the formation of sex cells.the formation of sex cells.

Sex cells only contain 23 chromosomes and Sex cells only contain 23 chromosomes and are called haploid. are called haploid.

These cells have half the amount that a These cells have half the amount that a normal non-sex cell would have.normal non-sex cell would have.

So when they divide only 23 chromosomes So when they divide only 23 chromosomes are given to the new cell.are given to the new cell.

Sex CellsSex Cells

So, each sperm and egg have 23 chromosomes So, each sperm and egg have 23 chromosomes and when they join in a process calledand when they join in a process called fertilizationfertilization, the result or offspring has a full set , the result or offspring has a full set of 46 chromosomes.of 46 chromosomes.

After these sex cells combine and fertilization After these sex cells combine and fertilization occurs the resulting cell that is formed is called a occurs the resulting cell that is formed is called a zygotezygote..

As soon as the zygote is formed, it then begins As soon as the zygote is formed, it then begins to go through cell division.to go through cell division.

Meiosis Meiosis

MeiosisMeiosis only occurs with respect to sex cells. only occurs with respect to sex cells. And meiosis produces more haploid sex cells. And meiosis produces more haploid sex cells.

MeiosisMeiosis ensures that the offspring between 2 ensures that the offspring between 2 organisms will result in an offspring that has the organisms will result in an offspring that has the same amount of chromosomes, 46, as the same amount of chromosomes, 46, as the original parents had.original parents had.

During Meiosis 2 divisions of the nucleus occurs.During Meiosis 2 divisions of the nucleus occurs.

These two divisions are called MThese two divisions are called Meiosiseiosis I and I and Meiosis IIMeiosis II

Meiosis I & IIMeiosis I & IIMeiosis IMeiosis I is very similar to mitosis. is very similar to mitosis. It starts with one diploid cell. They have the It starts with one diploid cell. They have the same steps ( Interphase I, prophase I, same steps ( Interphase I, prophase I, metaphase I, telophase I.metaphase I, telophase I.

However, in Meiosis I the duplicated However, in Meiosis I the duplicated chromosomes in the cells all have chromatids chromosomes in the cells all have chromatids that do not separate at all during the division of that do not separate at all during the division of the cell.the cell.The end result here is that 2 new diploid cells The end result here is that 2 new diploid cells are formed and both have the same genetic are formed and both have the same genetic material as the original parent cell.material as the original parent cell.

Meiosis IMeiosis I

Meiosis IIMeiosis IIThe 2 new diploid cells produced by The 2 new diploid cells produced by Meiosis I are now ready to go through Meiosis I are now ready to go through Meiosis IIMeiosis II..

Again these 2 cells go through Again these 2 cells go through

Interphase II, Prophase II, etc.Interphase II, Prophase II, etc.

However, here the chromatids are However, here the chromatids are separated from the centromere by the separated from the centromere by the spindle apparatus.spindle apparatus.

This separation of the chromatids in these This separation of the chromatids in these 2 cells produces 4 new sex cells that only 2 cells produces 4 new sex cells that only contain 23 chromosomes.contain 23 chromosomes.

Mistakes in MeiosisMistakes in Meiosis

Sometimes mistakes occur during meiosis. Sometimes mistakes occur during meiosis.

One mistake could be that a cell might be One mistake could be that a cell might be produced with too many or too few produced with too many or too few chromosomes.chromosomes.

If this cell becomes fertilized it might not If this cell becomes fertilized it might not survive and if it does the organism that survive and if it does the organism that forms may not develop or grow properly.forms may not develop or grow properly.

DNADNA- Deoxyribonucleic acidDNA- Deoxyribonucleic acid contains all contains all the information that an organism needs to the information that an organism needs to grow and develop.grow and develop.DNA, as we know, is contained inside all DNA, as we know, is contained inside all cells in their nuclei. And when a cell cells in their nuclei. And when a cell divides, DNA is copied and passed on to divides, DNA is copied and passed on to the new cells, or daughter, cells that are the new cells, or daughter, cells that are formed.formed.Cells do this to ensure that all new cells Cells do this to ensure that all new cells receive the same coded information that receive the same coded information that was in the original cell.was in the original cell.

Discovery of DNADiscovery of DNAIn the In the 1800’s1800’s scientists knew that inside the scientists knew that inside the nucleus of all cells were large molecules called nucleus of all cells were large molecules called nucleic acids, however they did not know what nucleic acids, however they did not know what they were used for.they were used for.In the In the 1950’s1950’s, scientists identified what the , scientists identified what the nucleic acids were and named them Adenine, nucleic acids were and named them Adenine, Thymine, Guanine, and Cytosine. But they still Thymine, Guanine, and Cytosine. But they still didn’t know how they were arranged or put didn’t know how they were arranged or put together.together.In In 1952, a scientist named Rosalind Franklin1952, a scientist named Rosalind Franklin discovered that DNA was composed of 2 chains discovered that DNA was composed of 2 chains of molecules in a spiral shape or a twisted of molecules in a spiral shape or a twisted ladder shape.ladder shape.This twisted ladder or spiral staircase shape is This twisted ladder or spiral staircase shape is called a called a helixhelix. And DNA, since it has 2 chains is . And DNA, since it has 2 chains is called a called a double helix.double helix.

Discovery of DNADiscovery of DNA

In 1953, two scientists In 1953, two scientists named James named James Watson and Francis Watson and Francis Crick created the first Crick created the first 3-D model of a DNA 3-D model of a DNA molecule.molecule.

DNA StructureDNA Structure

DNA ModelDNA ModelEach side of the DNA ladder is made up of Each side of the DNA ladder is made up of a 5 carbon sugar molecule with a a 5 carbon sugar molecule with a phosphate molecule attached to it.phosphate molecule attached to it.

Because of this, we call the sides of the Because of this, we call the sides of the ladder the sugar-phosphate backbone of ladder the sugar-phosphate backbone of DNA.DNA.

The sugar here in the backbone is a The sugar here in the backbone is a deoxyribose sugar. Meaning it has 2 deoxyribose sugar. Meaning it has 2 oxygen molecules and a ribose sugar.oxygen molecules and a ribose sugar.

DNA ModelDNA Model

The rungs of this ladder that connect the The rungs of this ladder that connect the two sides are the nucleic acids Adenine, two sides are the nucleic acids Adenine, guanine, cytosine, and thymine.guanine, cytosine, and thymine.

Another name for a nucleic acid is Another name for a nucleic acid is nitrogenous base, because all 4 of them nitrogenous base, because all 4 of them contain nitrogen.contain nitrogen.

When these nitrogen bases interact they When these nitrogen bases interact they are called base pairs.are called base pairs.

DNA ModelDNA Model

These nucleic acids are very specific when it These nucleic acids are very specific when it comes to binding.comes to binding.Adenine will only bind to ThymineAdenine will only bind to ThymineGuanine will only bind to CytosineGuanine will only bind to CytosineA-T & G-C We now this because when A-T & G-C We now this because when scientists measured the amounts of these scientists measured the amounts of these nucleic acids they found that in every cell the nucleic acids they found that in every cell the amount of Adenine was always the same as the amount of Adenine was always the same as the amount of thymine.amount of thymine. And the amount of Guanine was always equal And the amount of Guanine was always equal to the amount of cytosineto the amount of cytosine

Copying DNACopying DNA

We said that before mitosis, in interphase, We said that before mitosis, in interphase, chromosomes inside the nucleus are chromosomes inside the nucleus are duplicated.duplicated.The Watson and Crick model shows that The Watson and Crick model shows that when this happens each side of the DNA when this happens each side of the DNA unwind from each other. unwind from each other. Now the two separate sides each become Now the two separate sides each become a template for a new piece of DNA to be a template for a new piece of DNA to be made from. made from.

DNA ReplicationDNA Replication

GenesGenes

The nucleic acids in our DNA are used to The nucleic acids in our DNA are used to make proteins. make proteins.

Genes are the specific instructions for Genes are the specific instructions for making specific proteins.making specific proteins.

And proteins are made of hundreds of And proteins are made of hundreds of thousands of things called amino acids.thousands of things called amino acids.

The genes tells what amino acids to make The genes tells what amino acids to make and in what order to make them in.and in what order to make them in.

Ribonucleic acidRibonucleic acid

RNA is made in the nucleus on a DNA pattern.RNA is made in the nucleus on a DNA pattern.

It is very similar to DNA, but instead of looking It is very similar to DNA, but instead of looking like a ladder, it looks like half a ladder. And like a ladder, it looks like half a ladder. And instead of deoxyribose it has a ribose sugar.instead of deoxyribose it has a ribose sugar.

There is also one other major chemical There is also one other major chemical difference. Instead of having thymine like DNA. difference. Instead of having thymine like DNA. RNA has a nucleic acid called Uracil. RNA has a nucleic acid called Uracil.

So in RNA A binds to U not to T.So in RNA A binds to U not to T.

G will always bind to C, even in RNAG will always bind to C, even in RNA

Main types of RNAMain types of RNA

mRNA- messenger RNAmRNA- messenger RNA

rRNA- ribosomal RNArRNA- ribosomal RNA

tRNA- transverse RNAtRNA- transverse RNA

How Proteins are MadeHow Proteins are MadeProteins are made in a couple of steps:Proteins are made in a couple of steps:

1)1) First, tRNA makes a copy of the DNA section that is First, tRNA makes a copy of the DNA section that is needed for the production of a protein, in the form of needed for the production of a protein, in the form of mRNA. ( this occurs inside the nucleus)mRNA. ( this occurs inside the nucleus)

2)2) Next, the mRNA, which is an exact copy of the DNA, Next, the mRNA, which is an exact copy of the DNA, is shipped to a ribosome in the cytoplasm.is shipped to a ribosome in the cytoplasm.

3)3) The mRNA attaches to the ribosome, which is made The mRNA attaches to the ribosome, which is made of rRNA. The ribosome now reads the mRNA and of rRNA. The ribosome now reads the mRNA and begins to make the amino acids that the nucleic begins to make the amino acids that the nucleic acids tell it to make.acids tell it to make.

4)4) Lastly, tRNA takes the amino acids made by the Lastly, tRNA takes the amino acids made by the ribosome and puts them together in the order in ribosome and puts them together in the order in which the ribosome made them.which the ribosome made them.

Protein productionProtein production

MutationsMutationsMutations a source of trait variation.Mutations a source of trait variation.A mutation is a permanent change in a gene or A mutation is a permanent change in a gene or a chromosome due to some error during cell a chromosome due to some error during cell division. division. Some mutations could be caused from outside Some mutations could be caused from outside sources like UV light from the sun or smoking.sources like UV light from the sun or smoking.Some mutations occur because they are Some mutations occur because they are present on the parent DNA and it is passed present on the parent DNA and it is passed down to the offspring. Or, the DNA is not copied down to the offspring. Or, the DNA is not copied correctly during cell division.correctly during cell division.Not all mutations are of the negative variety. Not all mutations are of the negative variety. Some are good. Like a 4 leaf clover. Normally it Some are good. Like a 4 leaf clover. Normally it will have 3 leaves but due to a mutation it has will have 3 leaves but due to a mutation it has 4. This is good because the extra leaf can trap 4. This is good because the extra leaf can trap more sunlight for photosynthesis.more sunlight for photosynthesis.

H.WH.W& Look though your notes and & Look though your notes and see if you have any questions see if you have any questions

about the Chapter.about the Chapter.

Test on Chapter 4 in one Test on Chapter 4 in one Week!!!!!Week!!!!!