Mitosis & Meiosis Diploid cells- (2n)- a cell that has 2 of each chromosome - 1 from mom, 1 from dad = 1 pair The pair is called homologous chromosomes The homologous chromosomes contain the same gene placement, but do not carry identical gene codes Humans have 23 pairs or 46 chromosomes Haploid cells- (n)- contains 1 of each kind of chromosome (1/2 of a homologous pair)
Cell Size Diffusion limits cell size the organism would die before the center of the cell got the materials it would need Amount of DNA limits cell size if the cell was bigger, the nucleus could not keep up with the cell s protein demands Surface area to volume ratio limits cell size as volume increases surface area increases, but surface area does not increase as much as needed
Mitosis Cellular Reproduction Chromosomes are dark staining structures that contain genetic information - X Chromosomes are condensed chromatin (the chromatin becomes tightly packed for ease in division) Chromatin is loosely coiled DNA in the nucleus
Mitosis Cellular Reproduction The Cell Cycle made up of interphase, mitosis and cytokinesis
Interphase The cell spends the majority of its life in interphase 3 parts of interphase gap 1 phase- cell undergoes intense growth cell grows in size, busiest phase synthesis phase- chromatin (DNA) copied gap 2 phase- cell prepares for cell division extra mitochondria and other organelles are made
Interphase
Mitosis period of nuclear division 4 stages: Prophase, Metaphase, Anaphase, Telophase The end result is 2 daughter cells that are identical to the parent cell
Prophase first and longest phase of mitosis chromatin coils to form chromosomes (they look like X under the scope) each half of the chromosome (X) is called a sister chromatid sister chromatids are exact copies of each other sister chromatids are held together by a centromere centromeres help with movement of the chromosomes during mitosis (cohesins) the centrioles begin to migrate to opposite poles of the cell the spindle forms (spindle- football shaped structure made of thin microtubule fibers)
Prophase
ProMetaphase chromatin continues to coil the nuclear envelope & nucleolus disintegrate microtubules of the spindle invade the nuclear area some microtubules attach to the kinetochore at the centromere
Prometaphase
Metaphase chromosomes attach to the spindle fibers by their centromeres chromosomes line up on the equator each sister chromatid is attached to its own spindle fiber; the spindle fiber is attached to a pole
Metaphase
Anaphase separation of sister chromatids centromeres split the spindle shortens and pulls apart the sister chromatids (pulls the X s apart) the sister chromatids begin migration to opposite poles
Anaphase Telophase
Telophase final phase: the reverse of Prophase sister chromatids reach opposite poles chromosomes unwind to chromatin spindle breaks down nucleolus reappears cytoplasm pinches to form 2 cells: this is called cytokinesis (animal cell only) cell plate forms across the cell s equator in a plant cell; the cell membranes and cell walls then form
Results of Mitosis 2 new identical cells unicellular organisms can also use mitosis for reproduction multicellular organisms can form tissues, organs, organ systems Cancer- uncontrolled reproduction of cells that destroy surrounding cells Mutations in the DNA can cause cancer What substances can cause cancer? Cyclins
Apoptosis Apoptosis is programmed cell death. The process includes blebbing, cell shrinkage & breakdown of the DNA material. Between 50 and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day
Telomeres - protective caps at the end of chromosomes Shorten after each cell division limits the number of times a cell can divide Prevents genome from shortening and cancers from forming Stops growing, senescences (cell grows old), goes into apoptosis Can also lead to genomic instability (mutations) and cancer Cancer cells tend to have shorter telomeres Factors that increase cancer have also been linked to shorter telomeres smoking, inactivity, food choices, increased stress Telomerase promotes telomere repair Protecting DNA
Mitosis in Action
Mitosis concept check 1. Explain 3 reasons why cells must be small. - Diffusion takes too long if cells are too large - The volume increases at a greater rate than the surface area. The cell membrane (surface area) does not have enough channels and receptors to be able to handle the increased nutrient demand of the organelles. - If a cell was larger, it would have more organelles which would need instruction from the DNA. The DNA would not be able to keep up with the demands of the organelles. 2.What are the stages of the cell cycle? - interphase, mitosis and cytokinesis 3.Name & describe the events of the 3 sub-phases of interphase. - G1- grow & do normal cell processes - S duplicate DNA - G2- final preparations for cell division
Mitosis concept check 4.Describe the events of prophase. - Nuclear envelope disappears - Nucleolus disappears - Centrioles migrate to the poles - Spindle fibers begin to form - Chromatin condenses to chromosomes 5.Describe the events of metaphase. - Chromosomes line up on the equator of the cell 6.Describe the events of anaphase. - Chromosomes separate into sister chromatids and the chromatids are pulled to opposite poles 7.Describe the events of telophase. - Nuclear envelope reappears - Nucleolus reappears - Spindle fibers break down - Chromosomes uncoil
Mitosis concept check 8.Explain the difference between cytokinesis in a plant cell vs. an animal cell. - A plant cell builds a cell plate that turns into a cell wall and an animal cell pinches inward and forms a cleavage furrow eventually splits the cytoplasm into two cells. 9.What is cancer? How are cyclins and apoptosis related to cancer? -Cancer is uncontrolled cell division that invades and disturbs the function of nearby cells. Cyclins are chemicals that regulate cell division. If cyclins are not present or work well, then the cell divides too often and can lead to cancer. Apoptosis is programmed cell death. If apoptosis does not occur, cancer could result.
Onion Mitosis
Animal mitosis Prophase Prometaphase Metaphase Anaphase Telophase
Meiosis Meiosis- the formation of gametes (haploid cells) Gametes are sex cells- egg or sperm Why does meiosis occur? Why do we need to half the number of chromosomes given to our offspring? - If we received 46 chromosomes from mom and 46 chromosomes from dad, we would have 92 chromosomes!!!
Chromosomes replicate Interphase
Prophase I spindle forms DNA condenses to form tight chromosomes Synapsis occurs = tetrads formhomologous chromosomes pair up crossing over occurs exchange of genetic material between homologous pairs provides genetic variability = genetic recombination
Crossing Over
Metaphase I centromere of each chromosome attaches to the spindle spindle fibers pull tetrads to the equator (tetrads line up together)
Anaphase I Anaphase I & Telophase I tetrads (homologous pairs) separate Telophase I chromosomes uncoil to form chromatin spindle breaks down cytoplasm divides
Meiosis Overview
Prophase II spindle forms spindle attaches to chromosomes at the centromeres
chromosomes line up at the equator Metaphase II
Anaphase II centromeres split sister chromatids separate & move to opposite poles
spindles break down nucleus reforms and cytoplasm divides Meiosis produces 4 haploid cells. The 4 cells are genetically different Telophase II
Meiosis Overview
Meiosis Overview Meiosis Hoedown Play
Male Meiosis
Female Meiosis
Meiosis Mistakes Nondisjunction- failure of homologous chromosomes to separate during meiosis. Trisomy- the zygote produced has an extra chromosome Ex: down syndrome Monosomy- the zygote produced lacks a chromosome Ex: turner syndrome (1 X chromosome); death Triploidy- the zygote has 3 sets of chromosomes Polyploidy- the zygote has more than 1 copy of the chromosomes; results in death in most animals, but is beneficial in some plants
Meiosis
Meiosis Mistakes Triploidy Karyotype- An organized picture of the chromosomes of an organism Homologous chromosomes are paired together and arranged from largest to smallest
Karyotype
Sexual Reproduction Sexual reproduction uses sex cells and results in a zygote. A zygote is the fusion of an egg cell and a sperm cell.
Asexual Reproduction Binary Fission Budding Fragmentation
Binary Fission Process by which bacteria cells reproduce. 1. DNA attaches to cell membrane 2. DNA duplicates 3. Second DNA strand attaches to cell membrane 4. Cell continues to grow 5. Cell splits into two separate cells