Cell Reproduction Chromosomes, Cell Cycle and Mitosis

DNA Structure  Double stranded with backbone made of  Sugar (deoxyribose)  Phosphate (PO ₄)  Nitrogenous base  Adenine  Thymine  Guanine  Cytosine

DNA Organization  Chromosomes  rod-like structures of compacted DNA and proteins  In eukaryotic cells:  DNA is wrapped tightly around histone proteins

DNA in Prokaryotic Organism  Single circular genome (1 chromosome)  Coiled and surrounded by proteins

Chromosome Structure

Chromosomes (in dividing cells)  Chromatid = ½ chromosome (2 identical halves)  Centromere = holds two chromatids together  Only in dividing cells!!!

Chromosome Numbers  Different organisms have different numbers of chromosomes  Diploid = full set  Haploid = half set (found in sex cells)  2 types of chromosomes:  sex & autosomes

Autosomes vs Sex Chromosomes  Sex chromosomes can be X or Y  XX = female  XY = male  Normal humans each have 2 sex chromosomes

Homologous Chromosomes  Humans have 2 copies of each autosome 1-22 (one from each parent)  Two copies of each chromosome are called homologues  Same size, shape and genes

Karyotype Photomicrograph of chromosomes in a dividing cell Haploid = n Diploid = 2n In humans: Haploid = 23 Diploid = 46

Cell Division – Prokaryotes  Binary fission

Cell Division - Eukaryotes  2 types:  Mitosis  Identical cells  Meiosis  Cells with ½ the genetic info (sex cells)

Cell Cycle Series of steps that make up the life cycle of a cell Cytokinesis

Interphase  Cells spend most of their time in interphase  Includes G ₁, S and G₂  G ₁ = Gap 1  Cell grows to mature size (originally ½ size of parent cell)  S = Synthesis  DNA is synthesized (made) in preparation for cell division.  G₂ = Gap 2  Cell prepares for division  G₀ = resting phase  Cell does NOT copy DNA or prepare for division

Mitosis = division of the NUCLEUS!!  4 parts to division of nucleus  Prophase  Metaphase  Anaphase  Telophase  Division of remainder of the cell  Cytokinesis

Stages of Mitosis

Regulating the Cell Cycle

Review of Cell Cycle  G ₁ - increase in size, new proteins and organelles  S – DNA is replicated  G₂ - organelles and molecules for mitosis produced  M – cell division  Remember:  G ₁ + S + G₂ = interphase!

Some review questions… 1. What happens during the S phase of the cell cycle? 2. What happens to the number of chromosomes in the cell before mitosis occurs? 3. Why is the DNA condensed into chromosomes before mitosis occurs? 4. A replicated chromosome is made up of 2 _______________________________ (fill in the blank). 5. What are the two main parts of cell division? 6. What is the purpose of the spindle fibers during mitosis?

What’s happening here?  Two athletes are brought before an investigating committee because both tested positive for growth hormones. One athlete, a record holder, denies ever knowingly taking the growth hormone. The other recently had knee surgery and was taking the drugs prescribed by the doctor.  Consider the following  Hypothesize - How were the growth hormones being used by the athletes?

What regulates the cell cycle?  Cell cycle is regulated by proteins called cyclins.  Different cyclins signal cell to move from phase to phase.

Other regulators…  Other regulatory proteins also help to control the cell cycle from both the inside and outside the cell.  External regulators – respond to events OUTSIDE the cell  Can speed up or slow down cell cycle  Ex: Growth factors – stimulate growth and division of cells  Internal regulators – respond to events INSIDE cell  Ex: Prevents mitosis until chromosomes have replicated

Back to our scenario…  How does the story of the two athletes relate to the cell cycle?

Apoptosis  Apoptosis = programmed cell death!  Cell slowly breaks down and is “digested” by lysosomes in nearby cells.  Occurs normally in most cases  Certain diseases cause too much apoptosis  AIDs  Parkinson's

Cancer  A disease in which body cells lose the ability to control growth.

Cancer and the Cell Cycle  Cancer cells do not respond to signals that regulate the growth of most cells and divide uncontrollably.  The mass of cells that result from rapid cell division are called tumors.  Once a tumor gets too large, it can metastasize or move to other parts of the body.  Cancer can cause a whole host of problems – blocking blood vessels, using nutrients needed by other cells and prevent proper function of organs.

Contact Inhibition

What causes cancer?  Growing older  Tobacco  Sunlight  Ionizing radiation  Certain chemicals and other substances  Some viruses and bacteria  Certain hormones  Family history of cancer  Alcohol  Poor diet, lack of physical activity, or being overweight

Cancer Treatments  Surgery  Radiation  Chemotherapy  Prevention

And a few more questions… 1. What is the name of the group of proteins that regulate the cell cycle? 2. What is the difference between internal and external regulators? (…yes…it seems obvious…explain!) 3. What is apoptosis and why is it important? 4. What is cancer? 5. How are cancer cells different from regular cells? 6. What are some ways that cancer can be prevented?