Growth & Development Cell Reproduction

Why do cells have to divide?

2 Reasons – 1. To grow 2. Replace old/damaged/dead cells

2 Reasons – Surface area to volume ratio is an issue

What is the most important part of the cell that has to be divided?

A bunch of words for all the same stuff: chromatids chromatin Chromatin

Chromosome # (Diploid) Organism Chromosome # (Diploid) Buffalo 60 Lion 38 Llama 74 Donkey 62 Horse 64 Camel Cow Tiger Cabbage, Broccoli, Cauliflower 18 Cockroach 23 or 24 Chimpanzee 48 Earthworm 36 Kangaroo 16 Mango 40 Human 46 How many chromosomes do we have?

Karyotype

CELL CYCLE Three parts: Then you do it all over again. Interphase Mitosis Cytokinesis Then you do it all over again.

INTERPHASE Most of the cell’s life is spent here. Divided into three parts: G1 S G2

INTERPHASE G1 – Gap 1 Offspring cells grow to mature size.

INTERPHASE S – Synthesis The cell’s DNA is copied (synthesized).

INTERPHASE G2 – Gap 2 More cell growth and preparation for cell division.

INTERPHASE G0 – Gap 0 Cells can exit the cell cycle at G1 and go into G0. They stop preparation for division and do not divide.

MITOSIS Broken into 4 steps: Prophase Metaphase Anaphase Telophase Video: A plant cell going through mitosis

MITOSIS 1st phase of mitosis DNA forms chromosomes nuclear membrane breaks down centrosomes move to opposite ends of the cell spindle fibers start to form Prophase

MITOSIS 2nd phase of mitosis chromosomes easy to see Metaphase 2nd phase of mitosis chromosomes easy to see kinetochore fibers move chromosomes to the center of the cell

MITOSIS 3rd phase of mitosis chromatids separate at the centromere Anaphase 3rd phase of mitosis chromatids separate at the centromere chromatids begin moving towards opposite sides

MITOSIS 4th phase of mitosis chromosomes reach opposite sides of cell spindle fibers disassemble chromosomes uncoil nuclear membrane forms around the DNA Telophase

CYTOKINESIS mitosis divides the nucleus cytokinesis divides the cytoplasm cleavage furrow pinches the cell in two using microfilaments plats also need to form a cell plate

Animal and Plant Cell Cytokinesis

MITOSIS What’s the end result? ONE 2n* (diploid) cell produces TWO identical 2n* (diploid) daughter cells *”n” is considered haploid, or the number of unique chromosomes/chromosome pairs in a given species “n” for humans is 23 “2n” for humans is 46

MITOSIS What’s the end result? ONE 2n (diploid) cell produces TWO identical 2n (diploid) daughter cells

Controlling Cell Division G1 checkpoint – proteins control division. If the cell is large and healthy, proteins initiate DNA synthesis G2 checkpoint – DNA repair enzymes check the results of DNA synthesis. If everything is good, proteins will let mitosis begin.

When Control is Lost Cancer is uncontrolled cell division. Mutations can cause increased amounts of growth promoting molecules or prevent proteins from slowing or stopping cell division.

When Control is Lost

When Control is Lost Benign Malignant