Where we have been.

Cells Organelles

Nucleus DNA

Replication Chromosomes

Let’s Review

Reproduction – 2 types Asexual

Offspring genetically identical to the ONE parent

Quick, many offspring

Sexual Offspring share genetic information from BOTH

parents Creates variation

Curious?

Asexual reproducers Archea Bacteria Protists Starfish

Sexual reproducers (pregnancy length) Birds Humans (9 months) Insects Rabbit (33 Days) Alpine Salamander

(38 months) Elephant (22 months)

Chromosomes

Chromosomes DNA condensed, wrapped around proteins,

called histones Nucleus Only visible during cell division Each organism has its own number

Corn – 20, fruit fly 8, horsetail – 216, Chimp – 48, Dog – 78, humans? Somatic cells? Sex Cells?

Chromosomes

Sister Chromatids The 2 halves of a replicated chromosome

Centromere The place where sister chromatids are

connected

CELL DIVISION

Cell Division

Why? Replace lost cells Repair Growth and development Reproduction

Cell Cycle

“ALL CELLS COME FROM CELLS” The “life cycle” of a cell from the

beginning of one division to the beginning of the next division. The 2 new cells are called Daughter Cells

Cell division 1 cell becomes 2

The Cell Cycle

Interphase G1 – primary growth S – DNA replication G2 – Cell carries out

everyday functions, prepares for division

Mitosis M – Cell divides

Cytokinesis Cytoplasm divides

Starter

1. What is the purpose of cell division?2. What are the 3 major steps and what

happens in each of the cell cycle?3. Why must DNA replication happen

before mitosis and cytokinesis?4. What are the phases of mitosis?5. With a pencil, label your drawings with

the stages of the cell cycle, the phases of mitosis and cytokinesis.

MITOSISThe Break Down

The Phases

Prophase Metaphase Anaphase Telophase Cytokinesis

Prophase

The longest phase Chromatin condenses forming

chromosomes (visible) Centrioles move to opposite sides of the

nucleus Spindle fibers form between them – some

of which attach to centromeres on each side of the chromosome

Nuceolus and nuclear membrane disappear

Metaphase

The shortest phase Chromosomes line up in the center of

the cell Centrioles move to opposite sides of the

cell Spindle fibers are still attached to the

centromeres

Anaphase

Centromeres split Sister chromatids split to make separate

chromosomes Chromosomes move to opposite ends of

the cell This phase ends when the movement

stops

Telophase

Chromosomes begin to uncoil back into chromatin

Nuclear membranes develop around the bundles of chromatin at opposite ends of the cell

Spindle fibers disappear Nucleolus reappear in each new,

daughter cell

Cytokinesis

When the cytoplasm divides, cell division is complete.

Not always the same!

Animals Cell membrane

pinches, forming 2 identical daughter cells

Complete cells that are identical

Plants Cell Plate forms

halfway between the 2 nuclei

Materials for new cell walls and membranes gather and fuse in the middle between the 2 nuclei. Material gradually divides to create 2 cells.