DNA Replication, Mitosis, and Cell Cycle PDF

DNA Replication, Mitosis, and Cell Cycle Chapter 8  Cells Cells are the fundamental unit of life and life consists of one or more cells. One of the chief characteristics of life is that life reproduces. Life reproduces, because life dies....

DNA Replication, Mitosis, and Cell Cycle Chapter 8  Cells Cells are the fundamental unit of life and life consists of one or more cells. One of the chief characteristics of life is that life reproduces. Life reproduces, because life dies. Cells reproduce and cells die. Your bodies cells die and are replaced by other cells through cell reproduction. We will be going through the process of the cell cycle, which is the life a Bacteria going through cell from its inception to the point binary fission, a form where it produces two new cells of asexual through cell reproduction. reproduction.  Multicellular reproduction Children continue to develop into For simple unicellular organisms, adults through mitosis. reproduction is often asexual. Easy and requires finding no partners to reproduce with Multicellular organisms reproduce through sexual reproduction. Consists of two parents exchanging sex cells (gametes) with one another Meiosis is the formation of sex cells or gametes Sperm and ova Will be discussed further in chapter 9 Mitosis produces new cells which leads to a Meiosis produces Fertilization is the union of the sperm new organism Sperm and ova and the ova. Mitosis (one of the featured process of Fertilization produces this chapter) results in duplicated DNA a zygote being transferred from one cell to two Fig. 8.1 and 8.2 cells.  Death is a part of life Development of an organism from a single cell includes cell division (or cell reproduction means the same thing)… …but development includes apoptosis or The sculptor programmed cell death. shapes the rock Apoptosis shapes by removing bits organisms by cells of the rock. dying in a similar In the picture there is a mouse paw that is way that chiseling developing. In the red helps shape rocks box there are cells for sculpture. which are going to go through apoptosis Life is about a balance reducing the amount between cell of “webbing” between death/apoptosis and cell the toes. reproduction (mitosis).  DNA Replication Two important steps for cell reproduction: Original DNA 1. DNA Replication 2. Replicated DNA must be moved DNA being opened to each cell. We are going to be talking about DNA Replication DNA becomes replicated when it is opened up (or unzipped) and new nucleotides are added to each old New DNA being added strand of DNA. One piece of DNA becomes two. Each with a copy of the old material and a copy of the new  Nucleotide Structure Nitrogenous containing base Phosphate This one happens to be cytosine. 5 Carbon sugar The position 5’ Carbon of carbon 1’ Carbon atoms in the sugar molecule 4’ Carbon play a big factor in the formation of 3’ Carbon 2’ Carbon new DNA molecules.  DNA Structure Antiparallel means the strands are opposite but oriented in different directions. Antiparallel? Notice in the picture the two strands are opposite of each other. The 5’ carbon points upward on the right strand and the 3’ carbon points upwards on the left strand. The two strands are said to be antiparallel with one another.  How DNA Replicates Helicase is the first enzyme and it unzips or opens up the DNA molecule. Binding proteins are put into stabilize the separation. On each strand of the unzipped DNA, Primase adds a short RNA primer to the template to facilitate DNA polymerase which is going to add the new nucleotides.  DNA is built in a 5’ 3’ direction What this means is that new On the left side of the DNA nucleotides gets added by DNA molecule, the new strand of polymerase with the 5’ side DNA (in blue) is being buildt with the 5’ first and the 3’ oriented in a downward following. This is called the projection leading strand. One primer is used and DNA polymerase just works its way up continuously. This is called the the On leading other strand. side, as the helicase unzips the DNA, Primase has to add a primer. And DNA polymerase works its way down. But it doesn’t start at the beginning and as helicase unwinds more, then a new primer must be added and DNA polymerase must start anew. This is called the lagging strand.  Okazaki Fragments The RNA primers placed by Primase eventually are lost. This creates fragments on the lagging strand called Okazaki Fragments. Where there are Okazaki Fragments there are gaps in between the fragments. Ligase fixes these gaps by putting the DNA nucleotides in and On the leading strand there finishing the construction are no problems. DNA of the DNA molecule. polymerase follows the helicase and replicates the old strand of DNA.  Mutations DNA polymerase is amazingly accurate in Occasionally DNA Polymerase, that it very rarely adds even with the proofreading, makes the wrong nucleotide. a mistake. These mistakes DNA Polymerase also include: has a proofreading 1. Substitution mutation where mechanism which only one nucleotide is substituted allows for one mistake for another for every billion a) Usually a purine for a nucleotides on average. purine or a pyrimidine for a pyrimidine b) Sometimes a pyrimidine for a purine or a purine for a pyrimidine. 2. Deletion is where a DNA nucleotide is not added and skipped. 3. Insertion is where a DNA nucleotide is squeezed in  DNA in the Nucleus A chromosome is a polymer of DNA and its associated proteins which organize the DNA molecule. Most humans have 46 chromosomes. Other animals have different amounts of chromosomes. Chromatin is the term which represents the collective amount of DNA in the human cell can DNA (Chromosomes) stretch 2 meters, but is and all the proteins. In organized by proteins called this case the proteins nucleosomes. include enzymes Nucleosomes are collections of involved with building, chromatin organized around repairing, and using proteins called histones. Each  Chromosomes condense after replication The nucleosomes begin to condense after DNA replication and begin to become so large that they are now visible in a light microscope. DNA replicating The duplicated chromosomes now consists of two identical (save for a few mutations) stretches of replicated DNA. These two identical pieces of DNA are called sister chromatids. The two sister Fully chromatids are joined together replicated at the centromere. chromoso me  Mitotic Division Creates Identical Cells (Asexual) Mitosis is a part of the cell cycle which redistributes the sister chromatids into two new cells when the cell divides. Mitosis is a part of the Cell Cycle. The Cell Cycle is the collection of events which occur in between cell divisions. There are three main processes: 1. Interphase a) Regular cellular metabolism 2. Mitosis 3. Cytokinesis a) The splitting of the cell’s cytoplasm into two cytoplasms (two cells).  Interphase 90% of the time between cell divisions is spent in Interphase. This is a period of growth, metabolism, and protein synthesis. Interphase is split up into two to three Gap Phases (G1, G0, and G2). There is also a synthesis During phase (S). Interphase the chromatin is in a very diffuse form and is unnoticeable in the light microscope. In the picture to the right the nucleus appears as a solid red circle with a darker nucleolus. You cannot see the chromosomes.  Normal Cell Metabolism During the G1 Phase the cell carries out: 1. Cell grows 2. Basic metabolic functions a) Glycolysis, etc. 3. Produces molecules to form organelles and other chemical components. During G0 Phase the cell is fully grown but does not enter DNA replication or prepares to divide. Most of the cells in the human body are in G0 phase. The machinery necessary for cell division are broken down. Most cells can reverse this phase, but a few, like nerve cells in the brain, cannot go through cell division. Not all cells enter G phase  Preparation of Cell Division Two main phases to prepare for cell division S Phase G2 Phase S phase is when DNA is replicated. DNA is replicated so two copies are made. Eventually the two copies will be separated from one another two the two new cells. G2 Phase the proteins necessary for cell division and the other machinery are manufactured. Once Mitosis begins the DNA will be inaccessible for protein formation.  Mitosis Mitosis is the process of separating the sister chromatids (identical pieces of DNA) from one another and into two new There nuclei. are three main functions of Mitosis/Cell Division: 1. Asexual Reproduction 2. Growth and Development 3. Repair and Cell Replacement Mitosis consists of 4 main phases and Cytokinesis. 1. Prophase a) Prometaphase 2. Metaphase 3. Anaphase 4. Telophase Cytokinesis occurs after Telophase  Prophase and Prometaphase Prophase: DNA Condenses (is now visible under a light microscope) Spindle fibers begin to form. Nuclear Envelope begins to dismantle Prometaphase Nuclear envelope is dismantled. Spindle fibers attach to the kinetochore. The kinetochore is a protein on the centromere. A spindle fiber attaches from both sides of the cell.  Metaphase and Anaphase Metaphase The duplicated chromosomes are a lined up along the equator of the cell. Anaphase Once there is even tension amongst all the duplicated Anaphase chromosomes the cell will enter Anaphase. During Anaphase the kinetochores move each of the two chromatids to a different side of the cell One chromatid goes to the “right” One chromatid goes to the “left”  Telophase & Cytokinesis Telophase New nuclei New Nuclear envelopes and Nucleous form in the two areas the sister chromatids each moved to. Cytokinesis Cytoplasm splits into two cytoplasms resulting in two new cells. This ends the previous cell’s cell cycle and begins two new cell cycles.  Plant and Animal Cytokinesis Animal cytokinesis begins with a Cleavage Furrow. A indentation of the cell membrane (or a pinching) which will eventually follow through to separating the two new cells from one another. Plant cells form a rigid cell plate. Golgi Bodies travel along the spindle fibers and place new cellulose, polysaccharides, and proteins to form a cell plate. Cell Plate  Cells out of control!!! Cancer is the result of cells dividing out of control. Cells normally have checkpoints to keep No, cell I cell division under control. told you to stop During G1 there are checkpoints for dividing!!! damaged DNA. p53 protein promotes genes involved with DNA repair to be expressed if the DNA is damaged. Apoptosis is triggered by p53 if therehas S phase is too much damage. checkpoints if there is not enough nucleotides to build the new DNA molecules or if the DNA molecule breaks. Cell cycle may pause or stop  Further Checkpoints G2 checkpoints are the last checkpoints before cell division. If the cell does not contain two I am thinking this p53 gene sounds very complete sets of DNA or if the important. If the gene spindle machinery are not set up which is responsible for it properly the cell cycle maybe is dysfunctional this could delayed or the p53 protein will lead to problems!! trigger apoptosis. Metaphase is the last checkpoint. If the chromosomes don’t align properly or the spindle machinery is not set up properly cell division will halt.  Cancer Cancer is nasty, because it is the result of cells getting past all the Cancer is hard to defeat, checkpoints and continuing to divide. because every cancer is Your own body recognize the cells as unique. The body doesn’t part of your body, even though they recognize the cells as have gone haywire. foreign, because they aren’t foreign. But I won’t A benign tumor is a cancer which stop doing research to grows slowly and doesn’t invade other figure out a cure!!! parts of the body. May grow big enough to inhibit other organs A malignant tumorfrom operating invades adjacent effectively. tissues and spreads. The dysfunctional cells take the place of regular cells. Malignant tumors which have metastasized can spread through the blood stream.  Cell Fuses Chromosomes have noncoding DNA called telomeres at the end of the chromosomes. Without Every time cells divide they lose a bit telomerase cell of the telomeres division will stop Telomeres are usually long enough for eventually. I wish 50 cell divisions. cancer cells lacked Once the telomere is lost the cells telomerase!! usually cease Telomerase to divide. is an enzyme which fixes telomeres. Some cells have active telomerase so they can divide beyond 50 cell divisions. Cancer cells often have active telomerase.  Cell Growth Cancer cells continue to grow when normal cells would stop. So cancer cells are Growth Factors are proteins which cells without any promote cell division. controls!! Cancer cells often have lots of growth factors promoting the growth of the cancer. In cultures most cells stop growing once contact is made, this action has been titled contact inhibition by scientists. Cancer cells will grow on top of one another. Demonstrating that cancer cells will not conform to the shapes of organs. Normal cells only divide if anchored to a structure, but cancer cells will grow  Genes that affect cancer Oncogenes are mutated genes that normally control cell division. Proto-oncogenes are the normal Cell growth isn’t always a good thing version and control many proteins which are involved with controlling cell division. Oncogenes speed up the rate of cell division, which may lead to cancerous cells being produced. Tumor Suppressor Genes encode genes that block cancers. p53 is an example, but there are others as well. When these genes are mutated and no longer functional cells will not complete apoptosis.  Environment The more oncogenes and mutated tumor suppressor genes a person has, the higher the chances of cancer. This is not the only factor. The environment plays a key factor. Exposure to U/V light Chemicals in tobacco Radiation from nuclear fall out Lack of exercise Molecular oxygen is our friend Viruses Cancers are the result of a large and is our foe. We need it for category of different health cellular respiration, but it is conditions and situations and also a carcinogen. each cancer has its own set of risk factors.