Where the magic happens! Cell Division Where the magic happens!

Remember Cell Theory? Q: What was cell theory? A: All living things are made of cells AND that all cells come from other cells. This part of the unit is going to be about HOW cells come from other cells.

Basic idea: get bigger and split The cell’s overall goal is to divide into two cells. To do this it needs to give each new ‘daughter’ cell: - all the necessary organelles - a copy of the entire genome Q: What is the ‘genome?’ A: The entire set of genetic information in an organism

The Eukaryotic Genome In each of our bodies’ cells (with some exceptions) there are 46 chromosomes. Each chromosome can have tens of thousands of genes. Each gene can be composed of more than a hundred thousand base pairs.

Difference between Mitosis and Meiosis? Eukaryotic cell division (mitosis) consists of: Mitosis, the division of the nucleus Cytokinesis, the division of the cytoplasm In meiosis Sex cells are produced after a reduction in chromosome number

Separation of sister chromatids Each duplicated chromosome Has two sister chromatids, which separate during cell division 0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centromeres A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

Chromosomes Our genome is composed of Chromosomes (‘colored bodies’) Each chromosome can range from 25 million to 250 million base pairs.

Some chromosomal vocabulary Chromosome Chromatid Centromere Centriole Spindel Fibers

The Cell Cycle Two main phases: Interphase: replicating chromosomes and growth Mitotic Phase: separating chromosomes and splitting the cell

BAM!!! What's going on in the cell in respect to time. INTERPHASE G1 S (DNA synthesis) G2 Cytokinesis Mitosis MITOTIC (M) PHASE

Interphase is broken up into 3 phases. G1: Growth S: ‘synthesis’ (replication of chromosomes) G2: more growth, making the molecules needed for cell division

Kinetochore microtubule Mitosis consists of five distinct phases Prophase Prometaphase G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nonkinetochore microtubules

TELOPHASE AND CYTOKINESIS 3. Metaphase 4. Anaphase 5. Telophase Centrosome at one spindle pole Daughter chromosomes METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Figure 12.6

Mitotic Phase The process of a single cell splitting into two daughter cells.

Prophase Chromatin condenses into identifiable chromosomes Mitotic spindle begins to form (yay for microtubules) Centrosomes move apart Q: What are the structures in the centrosomes that form microtubules? A: Centrioles! Remember- they are not found in plants! Prophase

Prometaphase Nuclear envelope fragments Kinetochore microtubules attach to centromere region Centrosomes are at or near poles of cell

Metaphase Mitotic spindle has lined the chromosomes up at the metaphase plate. Centrosomes are at poles and begin to elongate cell

Anaphase Kinetochore microtubules begin to pull apart sister chromatids Spindle apparatus continues to elongate cell Q: How are sister chromatids different? A: they aren’t! Barring mutation, they should be identical!

Telophase Kinetochore microtubules detach Nuclear envelopes reappear Chromosomes begin to unpack Cleavage furrow begin to form Q: What is actin? A: a globular protein monomer

Cytokinesis Cleavage furrow (made of actin – microfilaments) contracts to pinch cell in half. Results in two daughter cells. Q: How is cytokinesis different in plant cells? A: they need to form a new cell wall – they do this by forming a ‘cell plate’

(b) Cell plate formation in a plant cell (SEM) In plant cells, during cytokinesis a cell plate forms Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (b) Cell plate formation in a plant cell (SEM)

Summary Interphase: grow and replicate Prophase: condense Prometaphase: nucleus bye bye Metaphase: line up on the plate Anaphase: pull ‘em apart Telophase: nucleus hello and decondense Cytokinesis: cleavage

Got it!?!?! You ok? Or feel like this?

Question Your homework will ask you about prokaryotic cell division. How is eukaryotic cell division similar to prokaryotic and how is it different? Discuss with people on your table.

Binary Fission Prokaryotes (bacteria) Reproduce by a type of cell division called binary fission

In binary fission: The bacterial chromosome replicates The two daughter chromosomes actively move apart Origin of replication E. coli cell Bacterial Chromosome Cell wall Plasma Membrane Two copies of origin Origin Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1 Replication continues. One copy of the origin is now at each end of the cell. 2 Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. 3 Two daughter cells result. 4

Coming attractions… We will next discuss HOW the cell cycle is REGULATED and what kinds of things happen when that regulation is not working properly. (HINT: cancer)