Mitosis and Meiosis

Cell Growth and ReplicationWhy Do Cells Divide Instead of Just Growing Bigger and Bigger?The cell's DNA would no longer be able to serve the increasing needs of the growing cell.The cell has more trouble moving enough nutrients and wastes across the cell membrane. Larger cells have a smaller ratio of surface area to volume. Prokaryotic vs. EukaryoticProkaryotic Cell Division:Simple matter of separating the contents of the cell into two parts. Eukaryotic Cell Division:Cell Cycle

Prokaryotic DNA

Eukaryotic DNA

located in the cytoplasmHave a single circular DNA molecule (usually referred to as the cell's chromosome)

Located in the nucleus in the form of chromatin/ chromosomes

Eukaryotic Cell CycleCell Cycle - Series of events that cells go through as they grow and replicate.Interphase - Period of the cell cycle between cell divisions (consists of S, G1, and G2 phase)M Phase Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm)

Cell Cycle- InterphaseG1 Phase Period of intense growth before DNA replicationS Phase DNA (chromosome) replication takes place, still little cell growth G2 Phase Period of more growth and final preparations before cell starts dividing.

There are 3 checkpoints that allow the cells to continue moving through the cell cycle.

G1 = making the key decision of whether the cell should divide, delay division, or enter a resting stage. G0 = resting stage(Livercells, for instance, enter mitosis only around twice a year.)The G1checkpoint is where eukaryotes typically arrest the cell cycle if environmental conditions make cell division impossible or if the cell passes intoG0for an extended period. In animal cells, the G1phase checkpoint is called the restriction point7What do all of these have in common? growth from an infant to an adult 2) repairing or replacing damaged issues/organs3) cancerIs Mitosis Asexual or Sexual?!??Asexual Reproduction = MitosisAsexual Reproduction - Reproduction of genetically identical cells to the parent cell without the fusion of gametes; not necessary to have two parents Examples include: Single-celled organisms Source of new cells when a multicellular organism grows and develops(skin cell, liver cell)

Four Phases of MitosisProphase - Chromosomes visible/centrioles; nuclear envelope disappearsMetaphase Centriole go to opposite ends of the cell; spindle fibers emerge from the centrioles; chromosomes line up in middle of cell Anaphase - Sister chromatids are pulled to opposite ends of cellTelophase - Chromosomes condense back to chromatin and nuclear envelope reappears(The four phases are followed by Cytokinesis)

Four Phases of Mitosis

CytokinesisUsually occurs at the same time as telophase.Cytokinesis - The division of the cytoplasm itself.

Cytokinesis: Plant vs. Animal CellsAnimal Cells: The cell membrane is pinched into two nearly equal parts = cleavage furrow.Plant Cells:A structure known as the cell plate forms midway between the divided nuclei and gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate.

What Phase Of the Cell Cycle Is It?

ABCDEFWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseTelophaseWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseCytokinesisTelophaseWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseInterphaseCytokinesisTelophaseWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseInterphaseCytokinesisTelophaseMetaphaseWhat Phase Of the Cell Cycle Is It?

ABCDEFAnaphaseInterphaseCytokinesisTelophaseProphaseMetaphaseLets take a deeper look at what DNA is before we learn how it replicates...Deoxyribonucleic Acid (DNA) - The material inside the nucleus that carries all the genetic informationResponsible for determining all organisms traitsEye color, body structure, and cellular enzyme production

The Components of DNADNA is a long molecule made up of repeating individual units called nucleotidesNucleotides are made up of three parts:Sugar Phosphate GroupNitrogenous Base

Nucleotides Put Together = DNA

5533Nitrogenous BasesDNA contains four nitrogenous bases:Adenine (A)Guanine (G)Cytosine (C)Thymine (T)

Complimentary BasesChargaff discovered that there were always equal amounts of A & T. And equal amounts of C & G in cells. Adenine pairs with Thymine, and Guanine pairs with CytosineThe complimentary bases are held together by weak hydrogen bonds.(No matter what organism it is!!!!)

[A] = [T][G] = [C]

Purines and PyrimidinesPurines have two rings in their structures.Adenine and guanine belong to this groupPyrimidines have one ring in their structure.Cytosine and thymine belong to this group

Structure of DNAPhosphate Group & Deoxyribose Sugar Form the backbone or sides of the ladder.Nitrogenous Bases Form the rungs of the ladder or middle of the molecule.

The Shape of DNADNA looks like a twisted ladder called a Double Helix.

Discovering DNA

Rosalind Franklin - Used X-ray diffraction; Showed the X-shaped pattern of DNA (helix shape)

Watson and Crick Two scientists that discovered the double helix shape in 1953

31ChromosomeGenesLong, continuous single piece of DNA, contains many genesSequence of DNA that codes for a protein and thus determines a trait

ChromosomesIn eukaryotic cells, the genetic information that is passed on from one generation of cells to the next is carried by chromosomes. The cells of every organism have a specific number of chromosomesThe cells of fruit flies have 8 chromosomes.Human cells have 46 chromosomes.Carrot cells have 18 chromosomes.

ChromosomesWell before cell division, each chromosome is replicated, or copied.

ChromosomesEach chromosome consists of two identical sister chromatids. When the cell divides, the sister chromatids separate from each other. One chromatid goes to each of the two new cells.

ChromosomesEach pair of chromatids is attached at an area called the centromere.

Chromosome StructureDNA molecules are surprisingly long The chromosome of the prokaryote E. coli, which can live in the human colon, contains 4,639,221 base pairs!Analogy: Imagine trying to pack a 300-meter length of rope into your school backpack! DNA must be dramatically folded and tightly packed to fit within the cellCell Cycle- InterphaseG1 Phase Period of intense growth before DNA replicationS Phase DNA (chromosome) replication takes place, still little cell growth G2 Phase Period of more growth ; organelles replicate; final preparations before cell starts dividing.

Cell Cycle M Phase (cell division)Cell Division - The process by which a cell divides into two new daughter cells.M Phase Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm) Before cell division occurs, the cell replicates, or copies, all of its DNA. Each daughter cell gets one complete set of genetic information.

CHROMATINCHROMOSOMESWhat does the DNA look like?Present in what stage of the cell cycle?CHROMATINCHROMOSOMESWhat does the DNA look like?

Present in what stage of the cell cycle?

Interphase

Cell Divison (M Phase)

DNA ReplicationBefore a cell divides, it duplicates its DNA via a process called DNA Replication During the S phase of cell division Ensures that each resulting cell will have a complete set of DNA moleculesResult: Two identical DNA molecules (each DNA molecule has one original strand and one new strand)How DNA Replication OccursStep 1: Helicase, an enzyme, unzips the DNA moleculeHydrogen bonds between the base pairs are brokenResult = 2 separated strands of DNA

How DNA Replication OccursStep 2: A replication fork is formed.

How DNA Replication OccursStep 3: Free floating nucleotides pair up with complimentary basesEach strand of DNA serves as a template, or model, for the new strand DNA Polymerase Enzyme that joins individual nucleotides to produce a DNA molecule and also proofreads each new DNA strand

You Try It!What is the complimentary DNA strand if the original DNA strand is AGTCTA? You Try It!What is the complimentary DNA strand if the original DNA strand is AGTCTA?

Original Strand: AGTCTAComplimentary Strand: TCAGATIf a meerkats parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkats daughter skin cells contain?17 chromosomes34 chromosomes68 chromosomesNone because skin cells dont go through cell divisionIf a meerkats parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkats daughter skin cells contain?17 chromosomes34 chromosomes68 chromosomesNone because skin cells dont go through cell division

Asexual reproduction produces cells that are genetically identical to their parents for reasons of growth, repair and replacement.

Regulating the Cell CycleNot all cells move through the cell cycle at the same rate.Cell growth and cell division are controlled.Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells.

G1 0-5 hrsS 6-8 hrsG2 2-5 hrsMitosis 1 hr

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Regulating the Cell CycleIf cells are placed in a petri dish containing food:Cells will grow until they come in contact with other cells then they stop growing.

If cells are removed from the center of the dish: The cells bordering the open space will begin dividing until they have filled the empty space.

Regulating the Cell CycleThis occurs in an injury as well:If a cut in the skin or a break in a bone occurs, cells at the edges of the injury are stimulated to divide rapidly.When the healing process nears completion, the rate of cell division slows down.

CancerCancer - Disorder in which some of the body's own cells lose the ability to control growth.Cancer cell divide uncontrollably and form masses of cells (tumors) Cancer cells may spread throughout the body: Disrupts normal activities and causes serious medical problems or even death

There are many reasons that cells can divide and grow out of control:* exposure to environmental causes (such as carcinogens or ultraviolet (UV) radiation from the sun)*nutritional deficiencies* genetic causes*some infections(All of these will result in DNA mutations)