WE EXPRESS OUR DNA • as we need it……….
The ENTIRE DNA MOLECULE can Replicate: Then You have 2 from 1 (DNA REPLICATION---Leads to MITOSIS ..one cell goes to two cells. OR 2. Selected sections of the DNA strand(genes) can be expressed ( transcribed and into mRNA and Translated into proteins)
We know that it is HIGHLY CONDENSED and COMPLEXED WITH PROTEINS Called HISTONES • Into complexes called NUCLEOSOMES …see next 2 SLIDEs. • HINT: REMEMBER the actual DNA molecule is a polymer of nucleotides as you view the next slide keep that in mind and watch the molecule condense and become “complexed” with proteins into nucleosomes.
Duplicating Genetic Information Information about you is in the sequence of nucleotides in the DNA molecule In each of your cells, there is about 2 meters of DNA per nucleus How does the DNA condense into such as small area? DNA histones chromatin
Helicases: Unwind DNA Double Strand • Primers: Short strand of nucleotides • DNA polymerases: position nucleotides along the template DNA strand • DNA Ligases: Splice together short segments of new
Humans Have 46 Chromosomes 23 pairs 2n is called the DIPLOID NUMBER 2n = 46 2 is the number of copies of each chromosome n = the number of different chromosomes 46 is the total number of chromosomes in the cell
The Cell Cycle • Phases include: • Interphase – Preparation phases for mitosis • Mitosis – Cell division or splitting • Interphase Includes: • G1 (Growth) • S- Synthesis ( DNA STRAND IS REPLICATED ) • G2 (Growth) • MITOSIS INCLUDES: SEE SLIDES AHEAD The Cell Cycle
G1 phase, the first gap phase • accumulates materials needed to replicate DNA • S phase, synthesis phase • DNA replication • G2 phase, second gap phase • replicates centrioles • synthesizes enzymes for division • M phase, mitotic phase • nuclear and cytoplasmic division • G0 phase, cells that have left the cycle • Cell cycle duration varies between cell types
The organized series of events that takes place AFTER this DNA replication • It is an event of the homologous chromosomes • It is triggered by various stimuli in some but not all cells during very specific phase of “Cell cycle
We say that cells in the G-0 phase have left the cell cycle. • These cell do not undergo cell division via cell mitosis • Examples: NEURONS, RED BLOOD CELLS,
Cancer genes- stimulates mitosis when we should NOT have it. UNCONTROLLED GROWTH that lead to tumors. • Oncogene is a cancer gene. • Usually has a three letter name (ras)
Your body carefully controls which cells divide and when they do so by using molecular stop and go signals. For example, injured cells at the site of a wound send go signals to the surrounding skin cells • BUT WHAT if these signals are confused? . Mitosis then becomes a weapon turned against the body, spurring the growth of invasive tumors
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WE WILL DISCUSS THE TOPIC OF CANCER in more detail in the next chapter, for now just and introduction to the idea that it is uncontrolled MITOTIC CELL DIVISION
Why Mitosis Growth and Repair Products are identical copies of cells (clones)
APOPTOSIS- programed ( neat and clean) cell death; occurs in fetus. Extra cells are neated destroyed. The lysosomes are organelles that facilitate this destruction. • Bad cells, cells destined to be cancerous are also destroyed this way.
Cells divide when: • Have enough cytoplasm for 2 daughter cells • DNA replicated • Adequate supply of nutrients • Growth factor stimulation • Open space due to neighboring cell death Cells stop dividing when: • Loss of growth factors or nutrients • Contact inhibition
Chromatin coils into genetically identical, paired, sister chromatids • each chromatid contains a DNA molecule • remember: genetic material (DNA) was doubled during S phase of interphase • Thus, there are 46 chromosomes with 2 chromatids/chromosome and 1 molecule DNA per chromatid.
Nuclear envelope disintegrates • Centrioles sprout microtubules that push them apart and towards each pole of the cell • spindle fibers grow towards chromosomes • attach to kinetochore on side of centromere • spindle fibers pull chromosomes towards cell equator
Chromosomes line up on one equator • Mitosis spindles finished • spindle fibers (microtubules) attach centrioles to long centromere • shorter microtubules anchor centrioles to plasma membrane (aster)
Enzyme splits 2 chromatids apart at centromere • Daughter chromosomes move towards opposite poles of cells with centromere leading the way • motor proteins in kinetochore move centromeres along spindle fibers as fibers are disassembled
New nuclear envelopes formed by rough ER • Chromatids uncoil into chromatin • Mitotic spindle breaks down • Nucleus forms nucleoli