Download Cell Cycle Notes

Cell Cycle Notes
I. Chromosomes: thread-like structures of DNA and histones (protein)
forming a unit called a nucleosome
A. Chromatid: 2 sister chromatids make up a chromosome
B. Centromere: attaches 2 chromatids
C. Chromatin: unraveled DNA
D. Humans have 23 pairs of chromosomes = 46 total (diploid/2n)
II. The Cell Cycle:
A. somatic (body) cell grows, prepares for division, and divides to form
2 identical daughter cells
Consists of 2 phases: Interphase (G1
S G2) + Cell Division (M)
B. Interphase – phase between mitosis, 90% of the time that elapses
“Gap”1 – cell growth & assembly of carbs, lipids, and proteins
“Synthesis” – DNA replication
“G”2 – prep for mitosis
1. Proteins and organelles are made during all 3 stages
2. Nuclear envelope is well-defined
C. Cell Division (M) – division of nucleus (mitosis) & cytoplasm (cytokinesis)
mitosis
Prophase: longest phase of M; chromosomes coil and become
visible while the nuclear membrane breaks down
centrioles: separate and move to opposite poles organizing
the mitotic spindle
spindle fibers: microtubules attach to centromere and move
sister chromatids at a site called the kinetochore
Metaphase: chromatids line up on the cell equator and centrioles are
at opposite poles
Anaphase: chromosomes move to opposite poles as spindles pull on
centromere
Telophase: 2 new nuclei form and nuclear membrane reforms
Cytokinesis: division of the cytoplasm
cleavage furrow – cytoplasm in animal cell pinches inward
cell plate – formation of new cell wall in plant cells during
telophase
III. Regulating the Cell Cycle
A. internal regulators – genes and proteins that respond to the
events inside the cell to make sure phases of division do not
occur too early
1. cyclins – regulate timing of cycle
2. Cdks – causes cell to move through interphase
3. p53 gene - blocks cell cycle if DNA is damaged and
will induce apoptosis (cell suicide)
4. BRCA genes – produce tumor suppressing proteins that
help repair damaged DNA
B. external regulators
1. proteins that respond to the events outside the cell
which speed up or slow down the cell cycle
2. growth factors – most important regulators, especially
during embryonic development and healing
3. molecules found on the surfaces of cells slow/stop cell
cycle of neighboring cells
IV. Uncontrolled Cell Growth
A. Cancer - occurs when cells don’t respond to growth signals
1. Cell membrane becomes more permeable
2. proteins are lost, altered, or become abnormal
3. cytoskeleton shrinks and becomes disorganized
4. cell grow and divide abnormally
5. cells have weakened ability for adhesion
B. Malignant tumors
1. cell mass that can damage the surrounding tissue
2. metastasis - cells break loose from tumor spreading
throughout the body disrupting normal cell activities
C. Causes of cancer
1. internal or external regulators are not working
2. smoking, radiation exposure, viral infection
3. defect in p53 and BRCA genes