Lesson 1: Foundations to Set the Stage:
Focusing on Cellular Structure and Function:
- The Normal Cell Cycle: -The cell cycle refers to the ordered seres of processes of DNA
replication and mitosis, or cell division
-Cell nucleus regulates these processes by gathering and processing complexes
molecular information - Interphase and Mitotic Phase: Cell division produces two identical cells
through these two major phases - During interphase:: Cell grows and DNA is replicated through the following three
steps:
1: First growth phase (G1 or first gap) 2:
Synthesis phase (S phase) 3:Mitotic Phse
(M phase) - First Growth Phase (G1 or first gap): -cells increase in size
-reproduce RNA
-“quality assurance” test that the cell will be ready to synthesis DNA
-Length of time is variable, can be from hours to days - Synthesis Phase (S phase): -DNA replicates
-Results in the formation of identical pairs of DNA (chromatids)
-which are attached a t the centromere
-lasts 2-10 hours - Mitotic Phase (M phase): -Replicated chromosomes are aligned, separated, and
move into 2 new, identical daughter cells
-takes about 30-60 minutes
- Major points of cell regulation are entry and exit from: -G1 checkpoint
-S Phase
-G2 checkpoint
-M phase - Restriction Point: -The transition from the resting phase into an actively
dividing phase (G0-G1) is a point where cellular transformation can occur
-During this time, cells pass through a transition phase known as a restriction point
-Extracellular growth factors trigger reentry into G1, and GF are required to send the
cells past the restriction point, or the point of no return - G0 Phase (resting phase): -After mitosis, cells may enter back into the G1 phase
or go into a resting phase, known as G0
-Most cells in the human body reside in G0 - -Exceptions to this are those that are (Resting in G0 phase): -Exceptions to this are
those that are metabollically active, such as
-granulocytes
-and the epithelium of the GI tract - Cell Cycling Time: Amount of time from mitosis to mitosis
- Cell cycle video and
image: http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation how_the_cell_cycle_works.html - Check points in the Cell Cycle: Keeping it All Under Control: -The cell cycle is
carefully controlled through a series of checkpoints
-Variation in duplication or distribution of chromosomes during cell division can alter the
genetic information passed on to daughter cells, leading to cellular dysfunction and
disease, such as cancer
- Progression through the cell cycle is controlled through two proteins:: 1. cyclines
(D, E, A, B) - Cyclin-dependent kinases (CDKs)
-Cyclin-CDK complex allows the cell to progress through each phase of the cell cycle - Locations of proteins Cyclins (D, E, A, B) and CDKs: -(G0-G1) : Cyclin D and CDK
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-Early S: Cyclin E and CDK 1/2
-Late S: Cyclin A and CDK 1/2
-G2: CDK 1/2 and cyclin A
-Before M: CDK 1 and Cyclin B - Inhibitory proteins: -prevent progression of the cycle when DNA damage is
detected
-An example of an inhibitory protein is p53 (AKA TP53) - DNA Damage Checkpoints: -If DNA damage is present, cells are programmed to stop dividing or undergo apoptosis (programmed cell death)
-The retinoblastoma protein (Rb), p53, and p21 are some of the most well-under- stood
inhibitory proteins (IP) - Inhibitory proteins p53: -Levels of this IP regulate several important target genes
-Will increase when DNA damage is present
-Protects against inappropriate signal proliferation
-sometimes called the “suicide gene” - M Phase Checkpoints: When the cells prepare to divide, the chromosomes line up
in the mitotic spindle.
If the chromosomes are not properly aligned, division is not allowed to continue