Why Is Cell Division Important 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 ImportantMany celled organisms are able to growand develop because cell divisionincreases the total number of cells in anorganism.Even after we stop growing cell division isvery important.Everyday billions of red blood cells arereplaced by new ones through celldivision.
Why Is Cell Division ImportantCell division is not just important to multi-celled organisms. It is also important tosingle celled organisms, like bacteria andalgae.All cells go through cell division in what iscalled the cell cycle or the cell life cycle.The cell cycle begins with the formation ofa cell of an organism.This formation is followed by growth andfinally ends in the death of the cell.
Cell CycleThere are 3stages of the cellcycle. And theyare:1) Interphase2) Mitosis3) Cytokenesis.
Cell Cycle1) Interphase- during this first stage of the cell cycle, the cell grows and duplicates its organelles and chromosomes in order to prepare for mitosis.2) Mitosis- Is stage 2 of the cell cycle. And mitosis is the way that all of our cell go through cell division.3) 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.
InterphaseMost of the life of any cell is spent in Interphase, inwhich the cell grows and develops.Also, during the later part of interphase the cellduplicates all of its chromosomes, which hold all of ourgenetic material and prepares to undergo a form ofcell division called mitosis.When chromosomes duplicate they form 2chromatids.You are able to grow and develop because of mitosis,the process in which one cell splits its nuclei and itsDNA to produce two exact genetic copies of itself.The cells want to duplicate or copy its chromosomesbefore mitosis so that the two new cells that are goingto be made have an equal amount of chromosomes in
Cell Division or MitosisCells go through mitosis in order toassure that each new cell receivesexactly the same information as thecell it came from.Also, cells go through mitosis in orderto grow and replace dead ordamaged cells, like when you get acut, or break a bone.
5 Stages of Mitosis. Mitosis occurs in 5 stages, and they are called:1) Prophase2) Metaphase3) Anaphase4) Telophase
Mitosis1) 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.
Mitosis2) 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.
Mitosis3) 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.
Mitosis4) 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: CytokenesisIn animal cells, the cell membrane pinchesand the cytoplasm of the parent cell isdivided into the two new cells.In plant cells, after telophase a cell plateis formed in order to allow the properformation of the cell wall.The presence of the cell plate tells youthat the cell is in the stage of cytokenesis.
Results of MitosisYou should remember 2 important facts about mitosis:1) It is the division of the nucleus.2) It produces 2 new nuclei that are identical to each other and also identical to the original parent cell.
ReproductionThe method in which an organism can producea new organism from one parent is called, what?Asexual reproductionIn asexual reproduction, all the DNA in the neworganism comes from only one parent.A potato uses asexual reproduction, so everypotato that comes from one parent potato willhave the same DNA as that parent.
There are 2 ways in which reproduction from one parent occurs.1) 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) Buddingout 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 & RegenerationEx: If you cut a piece of ivy, that piece thatyou cut can be planted and grow to a newplant.In a process called regeneration someorganisms are able to replace body partsthat have been lost because of injury.
Sexual ReproductionIn sexual reproduction- a new organism isproduced from two parents.During this process, DNA from both parentscombine to form a new individual with its ownDNA.In Chapter 3 we spoke of how there aredifferent cells for different function in the humanbody.For sexual reproduction have cells called sexcells.
Sex cells There are two types of sex cells:1) Sperm- a male sex cells that form in male reproductive organs.2) 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 CellsSex cells are a little different. They gothrough a process called meiosis, which isthe formation of sex cells.Sex cells only contain 23 chromosomes andare called haploid.These cells have half the amount that anormal non-sex cell would have.So when they divide only 23 chromosomesare given to the new cell.
Sex CellsSo, each sperm and egg have 23 chromosomesand when they join in a process calledfertilization, the result or offspring has a full setof 46 chromosomes.After these sex cells combine and fertilizationoccurs the resulting cell that is formed is called azygote.As soon as the zygote is formed, it then beginsto go through cell division.
MeiosisMeiosis only occurs with respect to sex cells.And meiosis produces more haploid sex cells.Meiosis ensures that the offspring between 2organisms will result in an offspring that has thesame amount of chromosomes, 46, as theoriginal parents had.During Meiosis 2 divisions of the nucleus occurs.These two divisions are called Meiosis I andMeiosis II
Meiosis I & IIMeiosis I is very similar to mitosis.It starts with one diploid cell. They have thesame steps ( Interphase I, prophase I,metaphase I, telophase I.However, in Meiosis I the duplicatedchromosomes in the cells all have chromatidsthat do not separate at all during the division ofthe cell.The end result here is that 2 new diploid cellsare formed and both have the same geneticmaterial as the original parent cell.
Meiosis II The 2 new diploid cells produced by Meiosis I are now ready to go through Meiosis II. Again these 2 cells go throughInterphase 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 MeiosisSometimes mistakes occur duringmeiosis.One mistake could be that a cell might beproduced with too many or too fewchromosomes.If this cell becomes fertilized it might notsurvive and if it does the organism thatforms may not develop or grow properly.
DNADNA- Deoxyribonucleic acid contains allthe information that an organism needs togrow and develop.DNA, as we know, is contained inside allcells in their nuclei. And when a celldivides, DNA is copied and passed on tothe new cells, or daughter, cells that areformed.Cells do this to ensure that all new cellsreceive the same coded information thatwas in the original cell.
Discovery of DNAIn the 1800’s scientists knew that inside thenucleus of all cells were large molecules callednucleic acids, however they did not know whatthey were used for.In the 1950’s, scientists identified what thenucleic acids were and named them Adenine,Thymine, Guanine, and Cytosine. But they stilldidn’t know how they were arranged or puttogether.In 1952, a scientist named Rosalind Franklindiscovered that DNA was composed of 2 chainsof molecules in a spiral shape or a twistedladder shape.This twisted ladder or spiral staircase shape iscalled a helix. And DNA, since it has 2 chains iscalled a double helix.
Discovery of DNAIn 1953, two scientistsnamed JamesWatson and FrancisCrick created the first3-D model of a DNAmolecule.
DNA ModelEach side of the DNA ladder is made up ofa 5 carbon sugar molecule with aphosphate molecule attached to it.Because of this, we call the sides of theladder the sugar-phosphate backbone ofDNA.The sugar here in the backbone is adeoxyribose sugar. Meaning it has 2oxygen molecules and a ribose sugar.
DNA ModelThe rungs of this ladder that connect thetwo sides are the nucleic acids Adenine,guanine, cytosine, and thymine.Another name for a nucleic acid isnitrogenous base, because all 4 of themcontain nitrogen.When these nitrogen bases interact theyare called base pairs.
DNA ModelThese nucleic acids are very specific when itcomes to binding.Adenine will only bind to ThymineGuanine will only bind to CytosineA-T & G-C We now this because whenscientists measured the amounts of thesenucleic acids they found that in every cell theamount of Adenine was always the same as theamount of thymine. And the amount of Guanine was always equalto the amount of cytosine
Copying DNAWe said that before mitosis, in interphase,chromosomes inside the nucleus areduplicated.The Watson and Crick model shows thatwhen this happens each side of the DNAunwind from each other.Now the two separate sides each becomea template for a new piece of DNA to bemade from.
GenesThe nucleic acids in our DNA are used tomake proteins.Genes are the specific instructions formaking specific proteins.And proteins are made of hundreds ofthousands of things called amino acids.The genes tells what amino acids to makeand in what order to make them in.
Ribonucleic acidRNA is made in the nucleus on a DNA pattern.It is very similar to DNA, but instead of lookinglike a ladder, it looks like half a ladder. Andinstead of deoxyribose it has a ribose sugar.There is also one other major chemicaldifference. 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 RNAmRNA- messenger RNArRNA- ribosomal RNAtRNA- transverse RNA
How Proteins are Made Proteins are made in a couple of steps:1) 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)2) Next, the mRNA, which is an exact copy of the DNA, is shipped to a ribosome in the cytoplasm.3) 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.4) Lastly, tRNA takes the amino acids made by the ribosome and puts them together in the order in which the ribosome made them.
MutationsMutations a source of trait variation.A mutation is a permanent change in a gene ora chromosome due to some error during celldivision.Some mutations could be caused from outsidesources like UV light from the sun or smoking.Some mutations occur because they arepresent on the parent DNA and it is passeddown to the offspring. Or, the DNA is notcopied correctly during cell division.Not all mutations are of the negative variety.Some are good. Like a 4 leaf clover. Normally itwill have 3 leaves but due to a mutation it has4. This is good because the extra leaf can trapmore sunlight for photosynthesis.
H.W& Look though your notes andsee if you have any questions about the Chapter.