Cellular Division

Purpose of Cell Division: In prokaryotes: Asexual reproduction In eukaryotes: Make new cells for growth and replace damaged or old cells

Keeping Cells Identical The instructions for cells are in the DNA. Each new cell must get a complete set of the DNA.

Two new, identical DNA strands DNA Replication DNA must be copied or replicated before cell division Each daughter cell will receive an identical copy of the DNA Original DNA strand Two new, identical DNA strands

Identical Daughter Cells Two identical daughter cells Parent Cell

Chromosomes

Prokaryotic Chromosome In prokaryotes (bacteria), DNA is one, circular piece of DNA also have plasmids – small, extra pieces of DNA.

Cell Division in Prokaryotes

Cell Division in Prokaryotes Prokaryotes divide by binary fission First, the single piece of DNA makes a copy of itself The cell splits A cell wall forms between the new cells Parent cell Chromosome relicates Cell splits 2 identical daughter cells

Prokaryotic Cell Undergoing Binary Fission

Eukaryotic Cells have chromosomes Most eukaryotes have 10 - 50 chromosomes in their body cells Human body cells have 46 chromosomes (23 pairs)

Eukaryotic Chromosomes Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

Compacting DNA into Chromosomes Before division, DNA tightly coils around histone proteins

Chromosomes in Dividing Cells Before division, chromosomes replicate. Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids

Karyotype A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male

The Y Chromosome Decides Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome

Cell Reproduction in Eukaryotes

The events in eukaryotic cell division are described as the Cell Cycle

Phases of the Cell Cycle Phase 1 – Interphase 3 parts: G1 - primary growth phase S – synthesis; DNA replicated G2 - secondary growth phase Phase 2 – mitosis Phase 3 - cytokinesis

Interphase - G1 Stage Cells grow and mature by making more cytoplasm & organelles

Two identical copies of DNA Interphase – S Stage Synthesis stage DNA is copied or replicated Two identical copies of DNA Original DNA

Interphase – G2 Stage 2nd Growth Stage All the cell structures that are needed for division are made (e.g. centrioles)

Mitosis

Mitosis Doesn’t occur in some cells such as brain cells Has four stages

Four Mitotic Stages Prophase Metaphase Anaphase Telophase

Early Prophase Chromatin in nucleus condenses (gets thick) to form visible chromosomes Mitotic spindle forms Cytoplasm Nucleolus Nuclear Membrane Chromosomes

Late Prophase Nuclear membrane & nucleolus are broken down Spindle fibers attach to the centromere of each chromosome

Nucleus & Nucleolus have disintegrated Late Prophase Chromosomes Nucleus & Nucleolus have disintegrated

Metaphase Chromosomes move to the center of the cell and line up at the equator Equator of Cell Pole of the Cell

Metaphase Asters at the poles Spindle Fibers Chromosomes lined at the Equator

Chromosomes at Equator Metaphase Aster Chromosomes at Equator

Anaphase Sister chromatids are pulled apart to opposite poles of the cell

Sister Chromatids being separated Anaphase Sister Chromatids being separated

Telophase Sister chromatids reach opposite poles Nuclear envelope forms around each set of sister chromatids Nucleolus reappears CYTOKINESIS occurs

Cytokinesis Means division of the cytoplasm Division of cell into two, identical halves called daughter cells In plant cells, cell plate forms at the equator to divide cell In animal cells, cleavage furrow forms to split cell

Cleavage furrow in animal cell Cell plate in plant cell Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell

Mitotic Stages

Daughter Cells of Mitosis Have the same number of chromosomes as the parent cell Identical to each other, but smaller than parent cell Must grow in size to become mature cells (G1 of Interphase)

Review of Mitosis

Review: Interphase Name this? Prophase Telophase Name this? Metaphase Anaphase

Eukaryotic Cell Division Cells are diploid (2n) Cytokinesis Anaphase Prophase Metaphase Telophase

Name each stage as you see it occur? Mitosis Animation Name each stage as you see it occur?

Mitosis in Onion Root Tips Do you see any stages of mitosis?

Draw & Learn these Stages

Draw & Learn these Stages

Test Yourself over Mitosis

Mitosis Quiz

Mitosis Quiz

Name the Stages of Mitosis: Early prophase Early Anaphase Metaphase Interphase Early Telophase, Begin cytokinesis Late Prophase Late telophase, Advanced cytokinesis Mid-Prophase Late Anaphase

Early, Middle, & Late Prophase Telophase & Cytokinesis Identify the Stages ? Early, Middle, & Late Prophase ? ? ? Metaphase Anaphase Late Prophase ? ? ? Telophase & Cytokinesis Late Anaphase Telophase

Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase Prophase

Uncontrolled Mitosis Cancer cells If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are genes that increase the chance that a normal cell develops into a tumor cell Cancer cells

Meiosis Formation of Gametes (Eggs & Sperm)

Facts About Meiosis Two meiotic divisions --- Meiosis I and Meiosis II Called Reduction division Original cell is diploid (2n) Four daughter cells produced that are haploid (1n)

Facts About Meiosis Daughter cells contain half the number of chromosomes as the original cell Produces gametes (eggs & sperm) Occurs in the testes in males (Spermatogenesis) Occurs in the ovaries in females (Oogenesis)

After division - 23 chromosomes (1n) Start with 46 double stranded chromosomes (2n) After division - 23 chromosomes (1n)  

Why Do we Need Meiosis? Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

Fertilization – “Putting it all together”

Replication of Chromosomes Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere Occurs in Interphase Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.

Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number from mom from dad child too much! meiosis reduces genetic content The right number!

Each diploid cell contains a pair of matching chromosomes – one from mom and one from dad. These are called HOMOLOGOUS CHROMOSOMES or HOMOLOGS.

Meiosis: Two Part Cell Division Sister chromatids separate Meiosis I Meiosis II Homologs separate Diploid Haploid Haploid

Prophase I Early prophase Homologs pair. Crossing over occurs.

Homologous chromosomes (each with sister chromatids) Homologs form Tetrads Homologous chromosomes (each with sister chromatids)   Join to form a TETRAD Called Synapsis

Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring

Crossing-Over Crossing-over multiplies the already huge number of different gamete types

Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome

Oogenesis or Spermatogenesis Gametogenesis Oogenesis or Spermatogenesis

Spermatogenesis Meiosis in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day

Spermatogenesis in the Testes Spermatid

Oogenesis Meiosis in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days

Oogenesis in the Ovaries

Comparing Mitosis and Meiosis

Comparison of Divisions Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction