Chapter 8: The Cell Cycle Cytokinesis Reading sequence: 8.1, 8.3, 8.4, 8.5, 8.2, 8.6, 8.7

8.1 Cells Divide & Cells Die Reproduction Review: – Asexual Binary fission or mitosis – Sexual Gametes (egg/sperm) Meiosis (next chapter) Fertilization Mitosis (8.5) Apoptosis (8.7) embryo

8.3 Binary Fission

8.4 Replicated Chromosomes Condense as a Eukaryotic Cells Prepares to Divide

DNA- Review Double helix H bonds Nucleotide Complementary pairs Purine Pyrimidine Antiparallel

Chromatin – Histones – Nucleosomes Chromosome – Chromatid – Centromere

Chromosomal confusion Chromosome = set of genes After it’s been copied, looks like an “X” – Each copy is called a chromatid During cell division, copies (chromatids) are separated

Centriole- review and expand

8.5 The Cell Cycle 2 Major Phases – Interphase – M Phase Each phase has substages

Interphase Longest part of cell cycle – Can’t see distinct chromosomes (chromatin) 3 Substages: – G1 = cell growth, makes proteins, normal cell activities – S* = copies DNA – G2 = more growth, prepares for cell division *additional notes to follow (8.2)

G 0 phase

Why cells divide… Eukaryotes- growth, repair, maintenance – Note- some cells don’t ever divide and instead remain in G 0. Prokaryotes- reproduction (binary fission) Triggers for a cell to divide – Can come from inside or outside of the cell Hormones/growth factors, cyclins (8.6) Cell size (SA:V ratio / efficiency of cell transport) Lack of contact with other cells

M Phase Broken into 2 parts: – Mitosis = division of nucleus – Cytokinesis = division of cytoplasm

Mitosis Has 4 substages: – Prophase – Metaphase – Anaphase – Telophase – Remember “PMAT” – Some resources include prometaphase as a stage; we won’t (lump in with prophase)

Prophase Major events: – Nuclear envelope breaks down – Chromosomes condense (individual chromosomes are now visible) – Spindles begin to form and attach to chromosomes

Metaphase Major events: – Chromosomes line up along the middle of the cell

Anaphase Major events: – Sister chromatids are separated as spindles pull chromosomes apart

Telophase Major events: – Chromosomes return to chromatin – Nuclear envelopes reform – Spindles disintegrate

Cytokinesis Cytoplasm divides Animals- cells “pinch” apart Plants- form a cell plate to divide the 2 new cells

What stages are these? Whitefish (animal)Onion (plant)

Onion root tip

Donut Mitosis