The Cell Cycle

Reproduction Organisms can reproduce: 1. Sexually AND/OR 2. Asexually

Cell Division Multicellular organisms undergo asexual cellular division (mitosis) for growth and repair.

Asexual Reproduction Cloning Binary fission Mitosis Regeneration Fragmentation Any variations that arise are due to mutations.

Sexual Reproduction Requires gametes Gametes form through meiosis Fertilization of gametes creates a genetically unique individual.

Chromosomes DNA and proteins iare organized into chromosomes. Somatic cells (non-sex cells) have two of each type of chromosome. The set is called a homologous pair. Somatic cells are diploid or 2n cells. Humans have 23 homologous pairs of chromosomes or 46 total.

Gametes Sex cells- egg and sperm Haploid or n cells. 23 chromosomes in humans.

Fertilization Union of gametes to form a zygote. Restores the diploid number of chromosomes.

Diplonic Life Cycle Animals and some plants The only haploid cells are the gametes. Gametes unite to form the diploid organism.

Haplonic Life Cycle Fungi and some protists Only diploid cell is the zygote Gametes are formed through mitosis, and spores are produced through meiosis which germinate to form the organism.

Alternation of Generations Most plants and some protists Diplonic and haplonic life forms Spores formed through meiosis and grow into the gametophyte. Gametes formed through mitosis which unite to form the sporophyte.

The Cell Cycle Interphase (preparation for cell division) Mitosis (Splitting of the chromosomes) Cytokinesis (Splitting of the cytoplasm)

Interphase Chromatin Visible nucleus 3 Subphases G1 S (DNA replication) G2 Take up the majority of the cell cycle

Mitosis Prophase Metaphase Anaphase Telophase Chromatin condenses Spindle and centrosomes appear Metaphase Chromosomes align at the equator Anaphase Sister chromatids are pulled apart, Telophase Nuclear envelope reforms around daughter chromosomes.

Cytokinesis Splitting of the cytoplasm to form two identical cells. Animal cells form a contractile ring and pinch. Plant cells form a cell plate and then a cell wall originating from golgi apparatus vesicles.

Regulation Cells divide due to growth factors. Check points regulate timing. Cdks, or cyclin-dependent kinases, phosphorylate proteins using ATP to allow the cell cycle to proceed from one step to the next.

Important Proteins G1-S cyclin binds to Cdk which then inhibits RB (retinoblastoma protein) so that transition to the S phase can occur. M phase cyclin binds to Cdk which allows separase to hydrolyze cohesin so that chromatids can separate. Cytoplasmic dynein hydrolyzes ATP for chromosomes to move to poles. RB prevents cell division.

Meiosis Creation of gametes 2 nuclear divisions Reduction division Genetic variation Meiosis I separates homologues Meiosis II separates sister chromatids

Genetic variation Mutations Crossing over resulting in recombinant chromosomes Independent assortment

Prophase I Crossing over Males-lasts about a week Females- occurs prior to birth Crossing over between non-homologues is called a translocation. Leukemia is causes by a translocation.

Nondisjunction Meiotic error resulting in abnormal chromosome numbers. Aneuploidy Polyploidy

Cell Death Necrosis Apoptosis