Cell Division Multicellular organisms –Important in growth and development Single celled organisms –Important for reproduction Goals –To create 2 identical daughter cells

Genetic Material Equally Distributed What has to occur in order for genetic material to be equally distributed? –Each new cells contains the total number of chromosomes as the parent cell –DNA has to replicate Before we talk about replication we need to understand more about DNA

Double Helix Sugar Phosphate Backbone Made of nucleotides

sugar base sugar p p p p Bases Guanine – Cytosine Thymine - Adenine NUCLEOTIDES

Before we go on to cell division: What is the structure of DNA? How are the bases paired? What is the function of DNA? Replicate the following chain: –TAC TTG AAA TGA CCC ACG ACT –AUG AAC TTT ACT GGG TGC TGA

Back to Cell Division Cells pass through a life cycle of 5 phases In single-celled eukaryotes, – cell cycle is the major mechanism for asexual reproduction In multicellular eukaryotes, –Development –Growth

Cell Cycle Overview Key Events –Cell grows (interphase) –DNA doubles(interphase) –Nucleus divides(prophasetelophase) –Cyotplasm divides(telophase)

Mitosis an Overview Interphase each chromosome is uncoiled and in an unreplicated state

Mitosis an Overview interphase, each chromosome is replicated. The replicated chromosome consists of two sister chromatids attached at the centromere.

Mitosis an Overview At the beginning of mitosis, the chromosomes coil and become visible (still Interphase). Note that the chromosome is still in a replicated state, with a sister chromatids attached at the centromere.

Mitosis an Overview Anaphase: the centromere splits, the sister chromatids separate and become daughter chromosomes, the daughter chromosomes move to opposite sides of the cell.

Mitosis an Overview At the end of mitosis, the chromosomes on each side of the cell uncoil and form two new, identical nuclei. (telophase)

A. Prophase 1. Chromosomes coil up and become individually visible. 2. The nuclear membrane disappears 3. The mitotic spindle will form between the centrosomes. 5. microtubules attach to the centromere of each sister chromatid

A. Metaphase 1. Chromosomes line up on the middle of the spindle. 2. Each chromosome has microtubules attached to the centromere of each of its sister chromatids.

B. Anaphase 1. Chromosomes move to opposite ends of the cell. One chromatid from each chromosome goes to each end of the cell. Use spindel fibers to do this –a) Why can’t DNA fragments without a centromere be passed on to further generations? –b) Why can’t chromosomes have more than one centromere?

A. Telophase 1. Chromosomes reach the opposite ends of the cell. 2. Chromosomes uncoil 3. The spindle disintegrates, 4. The nucleolus reappears 5. The cytoplasm divides in a process known as cytokinesis. –a) using either a cell plate or cleavage furrow –b). This produces two cells each identical to the original cell (except, of course for errors in DNA duplication).

Mitosis an Overview During what stage of the cell cycle do the drawings take place? What is a chromosome? A chromatid? A sister chromatid? A daughter chromosome? And in what stage of the cell cycle do we find each?