How do you get to be 6 ft tall if you started out as a single cell? How do you heal a wound? How do you replace worn out cells?

Cell cycle and Cell Division Ability to reproduce is one characteristic that distinguishes living things from nonliving matter. The continuity of life from one cell to another is based on cell division This division process occurs as part of the cell cycle

cell division Cells come from cells Cell division is needed for growth, replacement and repair Body cells are called somatic cells Sex cells are called gametes

What is Mitosis? Mitosis Takes one cell and produce two cells that are the genetic equivalent of the parent. Mitosis is nuclear division. It is the process by which a new cell receives the identical DNA as its parent cell The new cell is called the daughter cell. Mitosis produces two identical daughter cells

Why is mitosis important? This is how multicellular organisms grow, repair or heal injuries and maintain function. It is also how asexual reproduction takes place

Mitosis accompanied by Cytokinesis Functions in reproduction, growth, and repair –reproduces an entire unicellular organism, increasing the population. –on a larger scale can produce progeny for some multicellular organisms. organisms that can grow by cuttings or by fission.

Is central to the development of a multicellular organism that begins as a fertilized egg or zygote. For repair and renew cells that die from normal wear and tear or accidents. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Prokaryotes( bacteria) reproduce by binary fission –Prokaryotic cells Reproduce asexually by cell division Colorized TEM 32,500  Prokaryotic chromosomes Figure 8.3B

What is a genome? An organism’s complete collection of all its genes DNA is the molecule that makes up your genes DNA is packaged into units called chromosomes in the nucleus of cells

What is DNA? DNA or deoxyribonucleic acid is a large molecule made of chains of repeating units called nucleotides. It contains the information for specifying the proteins that allow life

What kind of information is encoded in DNA? Instructions on how to make proteins. Organisms function as a result of its proteins. Proteins make up structural parts and function as defenses, hormones, enzymes, transport among many others

What is a gene? A segment of DNA on a chromosome containing instruction on how to make a protein

What are chromosomes? A DNA molecule with its associated proteins called histones The number of chromosomes is the same for all the members of a species. Humans have 46 chromosomes

What is the HAPLOID number of chromosomes? What is DIPLOID? What cells have the haploid number? Why? What cells have the diploid number of chromosomes? Why?

–Before a cell starts dividing, the chromosomes replicate –Producing sister chromatids joined together at the centromere TEM 36,000  Centromere Sister chromatids Figure 8.4B

Where are the chromosomes found? Chromosomes are found in the nucleus of eukaryotic cells

one chromosome (unduplicated) one chromosome (duplicated) Chromosome

LM 600  -Chromosomes contain a very long DNA molecule associated with proteins And are visible only when the cell is dividing –If a cell is not undergoing division Chromosomes occur in the form of thin, loosely packed chromatin fibers Figure 8.4A

–Before a cell starts dividing, the chromosomes replicate –Producing sister chromatids joined together at the centromere TEM 36,000  Centromere Sister chromatids Figure 8.4B

What must happen before mitosis? The cell must make exact copies of its chromosomes in the nucleus so each new daughter cell gets the same number and type of chromosomes as its parent cell

Cell division requires the distribution of genetic material - DNA - to two daughter cells. A dividing cell duplicates its DNA, moves the two copies to opposite ends of the cell, and then splits into two daughter cells.

–Cell division involves the separation of sister chromatids results in two daughter cells, each containing a complete and identical set of chromosomes Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8.4C

What is the cell cycle? The cell cycle is an ordered set of events, resulting in cell growth and division into two daughter cells The stages of the cell cycle are : G 1 (stands for Gap 1 ), S ( stands for synthesis, this is when DNA is replicated) and G 2 (stands for Gap 2 )

The Cell Cycle

What are the phases of the cell cycle? Interphase: This takes up most of the cell cycle G1This is a time when a cell doubles organelles in its cytoplasm and grows S is when DNA in the nucleus is doubled G2 each chromosome now consists of two identical sister chromatids and the cell is preparing to divide Mitosis: the nucleus and its duplicated chromosomes divide Cytokynesis: the cytoplasm is divided in two

The mitotic (M) phase of the cell cycle alternates with the much longer interphase. –The M phase includes mitosis and cytokinesis. –Interphase accounts for 90% of the cell cycle. The mitotic phase alternates with interphase in the cell cycle

Interphase Usually longest part of the cycle Cell increases in mass Number of cytoplasmic components doubles DNA is duplicated

Stages of Interphase G1 –Interval or gap after cell division S –Time of DNA synthesis (replication) G2 –Interval or gap after DNA replication

Period of nuclear division Usually followed by cytoplasmic division - Cytokynesis Mitosis

The four stages of mitosis Prophase Metaphase Anaphase telophase

Fig. 12.9

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig left

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig right

On the cytoplasmic side of the cleavage furrow a contractile ring of actin microfilaments and the motor protein myosin form. Contraction of the ring pinches the cell in two. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.8a

Cytokinesis, division of the cytoplasm, typically follows mitosis. In animals, the first sign of cytokinesis (cleavage) is the appearance of a cleavage furrow in the cell surface near the old metaphase plate. Cytokinesis divides the cytoplasm: a closer look Fig. 12.8a

–In plants A membranous cell plate splits the cell in two Figure 8.7B TEM 7,500  Cell plate forming Wall of parent cell Daughter nucleus Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells

Check these web sites: htmlhttp:// html schttp://gslc.genetics.utah.edu/units/stemcells/whatis sc Play this game:

The distinct events of the cell cycle are directed by a distinct cell cycle control system. –These molecules trigger and coordinate key events in the cell cycle. –The control cycle has a built-in clock, but it is also regulated by external adjustments and internal controls. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Control System of the Cell Cycle

Cell cycle control system There are three major checkpoints in the cell cycle. These are “stop and go” signals.(G1, M, and G2) It checks whether or not the cellular processes have been completed up to that point so it can proceed. The G1 check point is very important. Nerve cells and muscle cells switch into a non dividing stage called G0. They do not get a “go ahead” signal and stop dividing.

Regulation of the cell cycle How cell division is regulated is very complex and when there are errors it results in cancer Cancer is a disease where control of cell division is lost. The cells don’t grow or behave normally

An example of a cell cycle control is p53 P53 is a protein that functions to block the cell cycle if the DNA is damaged A p53 mutation ( non functioning or reduced levels)is the most frequent mutation leading to cancer

A variety of chemical and physical factors can influence cell division. Important for mammalian cells are growth factors, proteins released by one group of cells that stimulate other cells to divide. Each cell type responds specifically to a certain growth factor or combination of factors. –For example, platelet-derived growth factors (PDGF), produced by platelet blood cells, bind to tyrosine-kinase receptors of fibroblasts, a type of connective tissue cell. –This triggers a signal-transduction pathway that leads to cell division. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The role of PDGF is easily seen in cell culture. –Fibroblasts in culture will only divide in the presence of medium that also contains PDGF. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

Growth factors appear to be a key in density-dependent inhibition of cell division. –Cultured cells normally divide until they form a single layer on the inner surface of the culture container. –If a gap is created, the cells will grow to fill the gap. –At high densities, the amount of growth factors and nutrients is insuffi- cient to allow cell growth and division stops. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig a

Most animal cells also exhibit anchorage dependence for cell division. –To divide they must be anchored to a substratum, typically the extracellular matrix of a tissue. –Control appears to be mediated by connections between the extracellular matrix and plasma membrane proteins and cytoskeletal elements. Cancer cells are free of both density-dependent inhibition and anchorage dependence. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig b

tumors Growing out of control, cancer cells produces malignant tumors –Cancer cells divide excessively to form masses called tumors Tumors can be benign and malignant (cancerous neoplasm)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

What is a metastasis? 1.Cancer cells break away from tumor 2. Cancer cells migrate to blood vessels. These cells are able to secrete enzymes that open vessel wall and enter the blood stream or lymph. 3. Cells move with the blood, exit vessel and invade a new site. 4. This new growth on a new site is a metastasis

–Radiation and chemotherapy Are effective as cancer treatments because they interfere with cell division

Web sites about cancer: About mitosis: hill.com/sites/ /student_view0/chapter11/animati ons.html

Check these web sites: e/cells2.htmlhttp:/ e/cells2.html Play this game:

Comparison of mitosis and meiosis MITOSIS MEIOSIS -OCCURS IN ALL SOMATIC CELLS -OCCURS ONLY IN SEX CELLS: GAMETES (ova or eggs and sperm) -PRODUCES IDENTICAL COPIES - PRODUCES VARIATION IN OF PARENT CELL. Daughter cell has TRAITS same number of chromosomes as parent. -RESULTS IN 2 DIPLOID (2n) cells - Results in 4 haploid (n) cells complete number of chromosomes reduced number of chromosomes -ONE REPLICATION OF CHROMOSOMES - ONE REPLICATION OF FOLLOWED BY 1 CELL DIVISION CHROMOSOMES FOLLOWED BY 2 CELL - DIVISIONS

FACTORS THAT CONTRIBUTE TO GENETIC VARIATION MUTATIONS CROSSING OVER DURING PROPHASE I OF MEIOSIS INDEPENDENT ASSORTMENT OF CHROMOSOMES during meiosis RANDOM FERTILIZATION OF THE EGG BY SPERM -