Bell Ringer 1.Why do cells need to divide in multicellular organisms? 2.What is the difference between prokaryotes and eukaryotes with regard to chromosomes? 3.What does a human chromosome consist of? Draw one! Label. 4.Describe a role of chromatin in chromosome in your own words.

DNA and Chromosomes Chromatin Histones DN A The function of chromatin is to efficiently package DNA

Cell Cycle Cell Cycle is a sequence of events through which a cell progresses during its lifetime

Cell can be either in dividing (Mitotic Phase) or non-dividing state (Interphase)

Interphase about 90% of the cell cycle

G1 Phase (Gap 1): Cell Growth Protein Synthesis Cell Metabolism Preparation for S Phase

S Phase (synthesis): – DNA is replicated

G2 Phase (Gap 2): Further Cell Growth Protein Synthesis Specialized proteins needed for Cell Division

The cell grows during all three phases, but chromosomes are duplicated only during the S phase

Mitotic Phase

Mitosis: Prophase Metaphase Anaphase Telophase

Cytokinesis is division of cytoplasm/cell: – cleavage furrow forms in animal cells – cell plate (cell wall) forms in plant cells – daughter cells are identical

Figure 12.10a (a) Cleavage of an animal cell (SEM) Cleavage furrow Contractile ring of microfilaments Daughter cells 100  m

Figure 12.10b (b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate New cell wall Daughter cells 1  m

Cell Cycle Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis

Interphase Animal Cell Plant Cell Photographs from:

Prophase Animal Cell Plant Cell Photographs from:

Prophase The cell prepares for nuclear division Animal and Plant Cell – Packages DNA into chromosomes – nuclear envelope breaks down – Centrosomes move apart and forms spindle which guides chr. separation

Metaphase Animal Cell Plant Cell Photographs from:

Metaphase The cell prepares chromosomes for division Animal and Plant Cell – Chromosomes line up at the center of the cell – Spindle fibers attach from daughter cells to chromosomes at the centromere

Anaphase Animal Cell Plant Cell Photographs from:

Anaphase The chromosomes divide Animal and Animal Cell – Spindle fibers pull chromosomes apart – ½ of each chromosome (called chromotid) moves to each daughter cell

Telophase Animal Cell Plant Cell Photographs from:

Telophase The cytoplasm divides Animal Cell – chromosomes uncoil – 2 nuclei form – spindle breaks down – nuclear envelope and – nucleoli reappear