The Cell Cycle: Creating Somatic Cells

Why do cells divide? Allow an organism to grow So organisms can replace and repair worn out, damaged, or old cells Some cells can divide every 20 minutes (bacteria) human cells can take up to a day to divide Cell Theory- all cells come from other cells To reproduce (unicellular organisms)

Chromosomes Chromosomes- carry genetic information Somatic Cells- (body cells) have 2 copies of genetic information stored in the nucleus (1 copy from each parent) Diploid- (2n) Humans have 46 chromosomes in each somatic cell Gametes (sex cells) have 1 copy of genetic information Haploid (n) Humans have 23 chromosomes in each gamete

Chromosomes Chromatid- ½ a chromosome Sister Chromosomes Chromatid- ½ a chromosome Sister chromatid- 2 identical DNA molecules attached at a centromere Centromere- holds sister chromatids together

The Cell Cycle 3 Main Steps Interphase- cells work, grow, and prepare to make new cells in this phase Mitosis- cells divide Cytokinesis-cytoplasm splits after a cell divides and 2 new cells are made

Step 1: Interphase Interphase- the cell spends 90% of its time in this phase 3 parts (G1, S, G2) G1- Cell grows, makes new organelles S- (Synthesis Phase) Chromatin (unwound DNA) is copied in the nucleus DNA Replication G2- cell grows, works, prepares to divide

Step 2: Mitosis Mitosis- cell divides into 2 identical daughter cells Also called asexual reproduction 4 steps of Mitosis Prophase Metaphase Anaphase Telophase

Prophase Prophase- chromatin condenses into chromosomes Centrioles move to opposite ends of cells Centrioles- special organelles involved in cell division, makes spindle fibers Nuclear membrane disappears

Metaphase Chromosomes line up in the middle of the cell Spindle Fibers attach to centromeres

Anaphase Spindle Fibers separate sister chromatids and move them to opposite ends of the cell

Telophase Chromosomes decondense (loosen) into chromatin Nuclear membrane reforms Cleavage furrow forms

Step 3: Cytokinesis Cytoplasm divides Cell pinches in half to form 2 new, identical daughter cells In plant cells, a cell plate forms

The Cell Cycle: Creating Sex Cells

Review: Mitosis What types of cells do mitosis? How many cells does mitosis make? Are they the same or different? How many chromosomes are in each cell? Is this haploid or diploid?

Haploid vs. Diploid Somatic Cells are diploid Human somatic cells have 46 chromosomes; 23 from mom and 23 from dad Homologous Chromosomes- a chromosome PAIR, one inherited from the mother and one from the father, containing genes for the same trait

Karyotype In humans there are 23 pairs of homologous chromosomes -A picture of all the chromosomes a person has in their cells In humans there are 23 pairs of homologous chromosomes The first 22 pairs are called autosomes The 23rd pair, the sex chromosome, differs between males and females. Females have 2 X chromosomes and males have one X and one Y chromosome

Female Reproductive System

Male Reproductive System

Cell Cycle: Creating Gametes Interphase, Meiosis, Cytokinesis Meiosis- makes 4 daughter cells that are not genetically identical Used to make gametes (sex cells)

Meiosis I: PMAT 1 Prophase I, Metaphase I, Anaphase I, Telophase I A single cell divides into 2 daughter cells that are not genetically identical The homologous chromosomes come together and swap parts of themselves with each other (called crossing over) Crossing Over ensures that the daughter cells produced after the first cytokinesis are not genetically identical

Meiosis II: PMAT 2 Two diploid cells divide to form 4 haploid daughter cells

Independent Assortment Independent Assortment- each homologous chromosome is randomly assorted into different gametes Result: 4 daughter cells that are genetically different and haploid

Controlling Cell Division Check points- act as stop signs that ensure only healthy cells move forward In G1, S, G2 Regulatory Proteins control information in DNA Contact Inhibition- cells stop growing and dividing when they get too crowded

Uncontrolled Cell Growth Mutant genes prevent cells from being stopped at check points or provide a false positive that allows them to slip through Disrupt normal controls Can cause tumors and cancer to form http://www.youtube.com/wa tch?v=gwcwSZIfKlM

Prokaryotes’ Cell Division Most bacterial genes are located on a single chromosome made up of a circle of DNA and proteins Bacteria do not have as many genes or DNA molecules as long as eukaryotes Prokaryotes reproduce by binary fission, not mitosis In binary fission, chromosome replication begins at one point in the circular chromosome, the origin of replication