Biology 30 Cell Division

Where is DNA found? Put these terms in order from biggest to smallest Gene -DNA Organism -Cell Chromosome -Nucleus

Where is DNA found?

Terminology Chromosome = compressed string of DNA Sister chromatids Chromosome = compressed string of DNA Chromatin = DNA that is unwound (not compressed into a chromosome); found when cell is not dividing Sister chromatids = a chromosome duplicates to make 2 identical copies (DNA replication) Telomere Centromere - where chromatids join together

Chromosomes, genes and DNA <> Chromosomes, genes and DNA Genes are DNA sequences located on chromosomes Strand 1: A T G C C G A A Strand 2: T A C G G C T T

Chromosomes, Genes and DNA Chromosomes are just tightly wound chromatin Only visible during mitosis Otherwise, exist as a stringy mass called chromatin Chromatin = DNA + Histones (protein)

DNA + Histones = Chromatin

Human DNA Fun Facts: - Human DNA is 3 billion base pairs and about 2 m in length. 50% of the genes found in humans are also found in bananas We have 65% genetic similarity to fruit flies

Why do cells divide? Cells grow because proteins and organelles accumulate in the cytoplasm Cells divide because the surface area of the cell membrane becomes inadequate (volume vs. surface ratio) Cells die and need to be replaced In order to reproduce the cell must pass on it’s genetic information

What happens next? Our cells must be able to divide. There are 2 types of cell division: Asexual cell division – occurs in somatic (body) cell division = Mitosis 2. Sexual cell division – occurs in sex cells (germ cells) = Meiosis

Asexual Reproduction The cells in our bodies started from a single cell called a ________ (think back to reproduction) We constantly replace old/dying cells and are able to heal wounds, thanks to cell division

The Cell Cycle The Cell Cycle has 4 major stages broken into 2 parts (Interphase and Mitosis) Interphase: - Cell spends 90% of time in Interphase prepares cell for division; cell grows and makes organelles DNA is in the form of chromatin DNA replication occurs

Cell Cycle - Interphase Interphase has 3 parts G1 (Gap 1) –rapid growth phase where cells grow and new organelles are made, protein synthesis occurs S (Synthesis) – genetic material in the cell doubles (DNA replication); therefore each daughter cell receives a full set of genetic material G2 (Gap 2) – growth and preparation for division

The Cell Cycle: Summary G1, S and G2 make up interphase This is the process of cell activity between cell division Cells grow and prepare for division in this stage ~ 90% of the cell cycle is interphase Mitosis (M) is the process by which the cell divides ~ 10% of the cell cycle is mitosis