Cell Cycle and Mitosis a.k.a. Cell Reproduction Biology is the only subject in which multiplication is the same thing as division

Introduction All organisms start with a single cell. All new cells are produced from other, already existing cells. Millions of cell divisions take place in our bodies every day to replace the cells that have died Cell Type Approximate Life Span Skin Cells 2 weeks Red Blood Cells 4 months Liver Cells 300-500 days Intestine-internal lining 4-5 days Intestine-muscles and other tissue 16 years Source: Spaulding et al., Cell 122:1.

Type of Cells it occurs in 3 Types of Cell Division Type of Cell Division Type of Cells it occurs in Function Binary Fission Prokaryotes Asexual Reproduction Mitosis Eukaryotes Growth of Individual Repair/Maintenance of Tissues Meiosis Sexual Reproduction

Binary fission Asexual reproduction of a Prokaryotic cell Bacteria (Ex E. coli = every 20 minutes) How many bacteria will result from 1 bacteria 7 hours (optimal conditions)? 1 million!

Binary Fission Begins with the duplication of the genetic material A plasma membrane splits the cell in two, with each side containing a single copy of the DNA The resulting two daughter cells replace the single parent cell and are genetically identical

Eukaryotes Use Mitosis to Generate Identical Daughter Cells Multiphase process in which the cell divides from 1 parent cell to 2 identical daughter cells. Occurs in all cells except reproductive cells Mitosis is how asexual cell are replicated. Meiosis is how sex cells are produced (we will look at this process later in the term)

The Cell Cycle Interphase is not part of mitosis!! This is when the cell is doing its “everyday” jobs and getting ready for mitosis Interphase is divided into 3 phases: G1 = 1st Gap cell doing its “everyday job” cell grows S = DNA Synthesis copies chromosomes G2 = 2nd Gap prepares for division produces organelles, proteins, membranes Length of G1 differs the most from cell type to cell type S, G2 and mitosis take about 12 hours in human cells In embryos and children go through the cell cycle faster

The Cell Cycle Many adult cells enter a non-dividing phase called G0 The G0 phase can last from a few days to the lifetime of the organism Ex: liver cells stay in G0 for approximately a year, then reenter the cycle

Organization of Genetic Material For equal division of the DNA to occur it has to be organized In interphase each DNA double helix is packaged with special proteins to form long strands of chromatin Chromatin is further compacted during mitosis to form chromosomes DNA Packaging DNA during Interphase DNA during Mitosis

Organization of Genetic Material One Chromosome DNA is replicated during S phase, resulting in two identical pieces of DNA, known as sister chromatids Each human cell has twice the usual amount of DNA at the end of S phase and the start of mitosis The identical sister chromatids are held together at a region called the centromere

The Karyotype Describes All the Chromosomes in a Nucleus Every species has its own characteristic number of chromosomes The display of all the chromosomes in a somatic (non-sexual) cell is called the karyotype Each of us has two of each chromosome, one from mom and one from dad. This pair of chromosomes, one from mom and one from dad, are similar but not identical They are called homologous chromosomes

Karyotypes Before and After S-phase of Cell Cycle Before S-Phase After S-Phase

Karyotype of The Human Genome Let’s not get Chromosomes, Homologous Chromosomes, and Sister Chromatids Confused!! Copied Homologous Chromosomes Homologous Chromosomes This is part of a karyotype looking at just chromosome 1 Sister Chromatids

Prophase Metaphase Anaphase Telophase Video 4 Stages of Mitosis: Prophase Metaphase Anaphase Telophase Video

Prophase Beginning of mitosis DNA compacts into chromosomes Centrosomes appear and begin to move to opposite ends of cell making the poles of the cell The nuclear envelope breaks down The mitotic spindle forms. It is made up of microtubules attached to each centrosome What is a microtubule? Remember from cytoskeleton? Centrosomes (centro- center, some- body)

Metaphase Sister chromatids attach to the spindle fibers at the centromere through the kinetochore The kinetochores are patches of proteins that attaches to the microtubules Each centromere has two kinetochores that attach to the spindle fibers, one from each centrosome This causes the chromosomes to line up on the metaphase plate

Anaphase Sister Chromatids separate and begin to move to opposite ends of the cell The centrosomes shorten the spindle fibers dividing the sister chromosomes and bringing them to opposite side of the cell Each chromatid is now considered a new chromosome

Telophase Begins when the new chromosomes reach the centrosome The spindle fibers break down Two new nuclei form and the nuclear envelope forms around the chromosomes at each pole of the cell Chromosomes appear as chromatin After telophase cytokinesis occurs

Cytokinesis in Animal Cells Not considered a phase in mitosis Follows telophase The cell membrane moves inward to create two daughter cells Occurs at the metaphase plate

Cytokinesis in Plant Cells Since plants have cell walls they also have to build this between daughter cells. Vesicles containing cell wall components move to the metaphase plate where the cell wall forms

How can you remember the order???? Answer this question....Where would you like your cat or dog to pee? On a PMAT of course

The Cell Cycle Is Highly Regulated Cells divide in response to internal and external signals In humans, cell cycle regulatory proteins are activated by external signals to divide, advancing the cell from G1 to S phase and initiating DNA replication Cell cycle regulatory proteins can stop or pause the cell cycle if conditions are not favorable for cell division What is this condition called? What happens when the cell does not stop at a checkpoint?

Cancer 6 key mutations Turn on cell division Ignore checkpoints Turn on promoter genes Ignore checkpoints Turn off suppressor genes Avoid programed cell death Turn off “suicide” genes Unlimited divisions Turn on chromosome maintenance genes Promotes blood vessel growth Turn on blood vessel genes Cell attachment, anchor and density dependence genes Turn off touch censor gene

Some people love mitosis a little too much!