Chapter 4-cell division, mitosis, DNA, protein productionPresentation Transcript
Chapter 4 Cell Division and Mitosis
Why Is Cell Division Important 4-1 H.W. pg 102 ques. 1-5
What do you, an octopus, and an oak tree all have in common?
You are all made of many cells, trillions of them!
Many multi-celled organisms start off as just one single cell. And this single divides to become 2 cells which divide to become 4 cells and then 8 and 16 and so forth.
Why Is Cell Division Important
Many celled organisms are able to grow and develop because cell division increases the total number of cells in an organism.
Even after we stop growing cell division is very important.
Everyday billions of red blood cells are replaced by new ones through cell division.
Why Is Cell Division Important
Cell division is not just important to multi-celled organisms. It is also important to single celled organisms, like bacteria and algae.
All cells go through cell division in what is called the cell cycle or the cell life cycle.
The cell cycle begins with the formation of a cell of an organism.
This formation is followed by growth and finally ends in the death of the cell.
There are 3 stages of the cell cycle. And they are:
Interphase - during this first stage of the cell cycle, the cell grows and duplicates its organelles and chromosomes in order to prepare for mitosis.
Mitosis- Is stage 2 of the cell cycle. And mitosis is the way that all of our cell go through cell division.
The third stage of the cell cycle is called cytokenesis. Here the cytoplasm of the parent cell is evenly distributed into the two new daughter cells or offspring.
Most of the life of any cell is spent in Interphase, in which the cell grows and develops.
Also, during the later part of interphase the cell duplicates all of its chromosomes, which hold all of our genetic material and prepares to undergo a form of cell division called mitosis.
When chromosomes duplicate they form 2 chromatids.
You are able to grow and develop because of mitosis , the process in which one cell splits its nuclei and its DNA to produce two exact genetic copies of itself.
The cells want to duplicate or copy its chromosomes before mitosis so that the two new cells that are going to be made have an equal amount of chromosomes in them
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 called:
Prophase - Here, the chromatids become visible because the nucleus is breaking down and the spindle apparatus , which is used to separate the chromosomes is formed.
- The spindle apparatus is a set of thread like fibers that are made by an organelle called a centriole .
And it is used to pull the duplicated chromatids apart so that each new cell can have an equal amount of chromosomes.
2) Metaphase - The chromatids line up in the middle of the cell and begin to be pulled apart from one another by the spindle apparatus, which is attached to the centromere of the chromatid, or where the chromatids are attached.
3) Anaphase - In anaphase all of the chromatids that were lined up in the middle of the cell are completely pulled apart from on another by the spindle apparatus.
This leaves two sets of equal numbers of chromosomes on each end of the cell.
4) Telophase - here the cell wall or cell membrane of the cell begins to pinch in and the cells divide into two cells of equal size with the same genetic material.
Also here the spindle starts to disappear and a new nucleus forms.
Stage 3 of the Cell Cycle: Cytokenesis
In animal cells, the cell membrane pinches and the cytoplasm of the parent cell is divided into the two new cells.
In plant cells, after telophase a cell plate is formed in order to allow the proper formation of the cell wall.
The presence of the cell plate tells you that the cell is in the stage of cytokenesis.
Results of Mitosis
You should remember 2 important facts about mitosis:
It is the division of the nucleus.
It produces 2 new nuclei that are identical to each other and also identical to the original parent cell.
Reproduction sec 4-2 H.W. pg 109 ques. 1-4
The method in which an organism can produce a new organism from one parent is called, what?
In asexual reproduction, all the DNA in the new organism comes from only one parent.
A potato uses asexual reproduction, so every potato that comes from one parent potato will have the same DNA as that parent.
There are 2 ways in which reproduction from one parent occurs.
By Splitting-bacteria and other single celled organisms divide in half, forming two new cells.
When the cell divides, each new cell gets an exact copy of the parents DNA.
Now the two new cells are exactly alike and the parent cell no longer exists.
There are 2 ways in which reproduction from one parent occurs.
2) Budding out and breaking up- Many mushrooms, plants, and some animals use budding as a form of asexual reproduction.
Here a new cell will bud off of the parent cell, break away and live on its own.
Budding & Regeneration
Ex: If you cut a piece of ivy, that piece that you cut can be planted and grow to a new plant.
In a process called regeneration some organisms are able to replace body parts that have been lost because of injury.
In sexual reproduction- a new organism is produced from two parents.
During this process, DNA from both parents combine to form a new individual with its own DNA.
In Chapter 3 we spoke of how there are different cells for different function in the human body.
For sexual reproduction have cells called sex cells.
There are two types of sex cells:
Sperm - a male sex cells that form in male reproductive organs.
Ova or egg- a female sex cell which will form within the female reproductive organs.
Body cells or non sex cells in your body have 46 chromosomes and are called diploid because each chromosome has a pair.
And when they divide the new cells gets all 46 chromosomes that the original had, and we said that this process was called mitosis.
Sex cells are a little different. They go through a process called meiosis , which is the formation of sex cells.
Sex cells only contain 23 chromosomes and are called haploid.
These cells have half the amount that a normal non-sex cell would have.
So when they divide only 23 chromosomes are given to the new cell.
So, each sperm and egg have 23 chromosomes and when they join in a process called fertilization , the result or offspring has a full set of 46 chromosomes.
After these sex cells combine and fertilization occurs the resulting cell that is formed is called a zygote .
As soon as the zygote is formed, it then begins to go through cell division.
Meiosis only occurs with respect to sex cells. And meiosis produces more haploid sex cells.
Meiosis ensures that the offspring between 2 organisms will result in an offspring that has the same amount of chromosomes, 46, as the original parents had.
During Meiosis 2 divisions of the nucleus occurs.
These two divisions are called M eiosis I and Meiosis II
Meiosis I & II
Meiosis I is very similar to mitosis.
It starts with one diploid cell. They have the same steps ( Interphase I, prophase I, metaphase I, telophase I.
However, in Meiosis I the duplicated chromosomes in the cells all have chromatids that do not separate at all during the division of the cell.
The end result here is that 2 new diploid cells are formed and both have the same genetic material as the original parent cell.
The 2 new diploid cells produced by Meiosis I are now ready to go through Meiosis II .
Again these 2 cells go through
Interphase II, Prophase II, etc.
However, here the chromatids are separated from the centromere by the spindle apparatus.
This separation of the chromatids in these 2 cells produces 4 new sex cells that only contain 23 chromosomes.
Mistakes in Meiosis
Sometimes mistakes occur during meiosis.
One mistake could be that a cell might be produced with too many or too few chromosomes.
If this cell becomes fertilized it might not survive and if it does the organism that forms may not develop or grow properly.
DNA Section 4-3 H.W. pg 115 ques. 1-4
DNA- Deoxyribonucleic acid contains all the information that an organism needs to grow and develop.
DNA, as we know, is contained inside all cells in their nuclei. And when a cell divides, DNA is copied and passed on to the new cells, or daughter, cells that are formed.
Cells do this to ensure that all new cells receive the same coded information that was in the original cell.
Discovery of DNA
In the 1800’s scientists knew that inside the nucleus of all cells were large molecules called nucleic acids, however they did not know what they were used for.
In the 1950’s , scientists identified what the nucleic acids were and named them Adenine, Thymine, Guanine, and Cytosine. But they still didn’t know how they were arranged or put together.
In 1952, a scientist named Rosalind Franklin discovered that DNA was composed of 2 chains of molecules in a spiral shape or a twisted ladder shape.
This twisted ladder or spiral staircase shape is called a helix . And DNA, since it has 2 chains is called a double helix.
Discovery of DNA
In 1953, two scientists named James Watson and Francis Crick created the first 3-D model of a DNA molecule.
Each side of the DNA ladder is made up of a 5 carbon sugar molecule with a phosphate molecule attached to it.
Because of this, we call the sides of the ladder the sugar-phosphate backbone of DNA.
The sugar here in the backbone is a deoxyribose sugar. Meaning it has 2 oxygen molecules and a ribose sugar.
The rungs of this ladder that connect the two sides are the nucleic acids Adenine, guanine, cytosine, and thymine.
Another name for a nucleic acid is nitrogenous base, because all 4 of them contain nitrogen.
When these nitrogen bases interact they are called base pairs.
These nucleic acids are very specific when it comes to binding.
Adenine will only bind to Thymine
Guanine will only bind to Cytosine
A-T & G-C We now this because when scientists measured the amounts of these nucleic acids they found that in every cell the amount of Adenine was always the same as the amount of thymine.
And the amount of Guanine was always equal to the amount of cytosine
We said that before mitosis, in interphase, chromosomes inside the nucleus are duplicated.
The Watson and Crick model shows that when this happens each side of the DNA unwind from each other.
Now the two separate sides each become a template for a new piece of DNA to be made from.
The nucleic acids in our DNA are used to make proteins.
Genes are the specific instructions for making specific proteins.
And proteins are made of hundreds of thousands of things called amino acids.
The genes tells what amino acids to make and in what order to make them in.
RNA is made in the nucleus on a DNA pattern.
It is very similar to DNA, but instead of looking like a ladder, it looks like half a ladder. And instead of deoxyribose it has a ribose sugar.
There is also one other major chemical difference. Instead of having thymine like DNA. RNA has a nucleic acid called Uracil.
So in RNA A binds to U not to T.
G will always bind to C, even in RNA
Main types of RNA
mRNA- messenger RNA
rRNA- ribosomal RNA
tRNA- transverse RNA
How Proteins are Made
Proteins are made in a couple of steps:
First, tRNA makes a copy of the DNA section that is needed for the production of a protein, in the form of mRNA. ( this occurs inside the nucleus)
Next, the mRNA, which is an exact copy of the DNA, is shipped to a ribosome in the cytoplasm.
The mRNA attaches to the ribosome, which is made of rRNA. The ribosome now reads the mRNA and begins to make the amino acids that the nucleic acids tell it to make.
Lastly, tRNA takes the amino acids made by the ribosome and puts them together in the order in which the ribosome made them.
Mutations a source of trait variation.
A mutation is a permanent change in a gene or a chromosome due to some error during cell division.
Some mutations could be caused from outside sources like UV light from the sun or smoking.
Some mutations occur because they are present on the parent DNA and it is passed down to the offspring. Or, the DNA is not copied correctly during cell division.
Not all mutations are of the negative variety. Some are good. Like a 4 leaf clover. Normally it will have 3 leaves but due to a mutation it has 4. This is good because the extra leaf can trap more sunlight for photosynthesis.
H.W. pg 121 ques. 1-10 & Look though your notes and see if you have any questions about the Chapter.