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Copy of Chapter 12 - The Cell Cycle

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Anna Carlson

on 25 March 2011

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Transcript of Copy of Chapter 12 - The Cell Cycle

Chapter 12 -The Cell Cycle The Key Roles of Cell Division Unicellular Organisms- reproduction

Multicellular Organisms-development, growth, repair
GENETICALLY IDENTICAL DAUGHTER CELLS CONCEPT 1 Key Points: a)Cells duplicate their gentic material before they divide
b) Eukaryotic cells partition their DNA among chromosomes
c) Chromosomes replicate and separate during cell division DNA in eurkaryotic cells is complexed with protein to form . Chromatin is organized into separate structures called chromatin chromosomes Chromosome duplication results in 2 ;
each contains an identical DNA molecule.
The chromatids are attached at the . sister chromatids centromere During cell division the two sister chromatids will separate and move into two new nuclei, thus each new cell receives a group of identical chromosomes. To create two identical somatic daughter cells:

- the division of the nucleus

- the division of the cytoplasm

To create two non-identical gamete (sperm or egg) cells (only in gonads):

- two staged cell division that results in half the chromosome number as the original cell MITOSIS CYTOKINESIS MEIOSIS CONCEPT 2
The mitotic phase alternates
with interphase in the cell cycle. = growth phase and DNA synthesis

3 parts: (DNA synthesis), Interphase G1, S G2 5 Stages of Mitosis:

1) Prophase

2) Prometaphase

3) Metaphase

4) Anaphase

5) Telophase 1)
chromatin condenses
nucleoli disappear
mitotic spindle forms
sister chromatids visible
centrosomes move apart 2)
nuclear envelope fragments
microtubules extend from each centrosome
kinetochore forms at centrosome of sister chromatids
kinetochore microtubules attach to kinetochores to move chromosomes
non-kinetochore microtubules from each pole interact; spindle fully formed 3)
centrosomes at opposite ends of cell; spindle is completely formed
chromosomes line up with their centrosomes on the metaphase plate -an imaginary plane through the center of the cell
the longest stage of mitosis (20 minutes) 4)
sister chromatids separate creating two separate chromosomes which move to opposite ends of the cell
chromosomes move when kinetochore microtubules shorten
non-kinetochore microtubules lengthen and make the cell elongate
shortest stage of mitosis (few minutes)
ends when both ends of the cell have a complete set of equivalent chromosomes 5)
two daughter nuclei begin to form
nuclear envelopes form
chromosomes become less condensed Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis cleavage furrow forms
two daughter cells formed
controls chromosome movement
microtubules: kinetochore-move chromosomes
non-kinetochore-elongate cell
centrosome (organizing center) Mitotic Spindle Cytokinesis Animal cells: cleavage/ cleavage furrow
actin and myosin in contractile ring

Plant cells: cell plate
Prokaryotes divide by Binary Fission CONCEPT 3
The cell cycle is regulated by a molecular control system : control points
in the cell cycle at G1, G2, M

G1 Checkpoint = Restriction Point Checkpoints Cell Cycle Control System : cyclin dependent kinases

cyclin concentrations determine activity Cdks Cell Cycle Checkpoint Signals
Internal- growth factors
External - density and anchorage inhibition Loss of cell cycle control: cancer cells

Uncontrolled cell division due to abnormal signal pathways
or abnormal cell cycle control system
AP Questions/ Chapter 12

1. Why is it more accurate to call mitosis “nuclear replication” rather than “cell division” ?

2. If a cell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of :
a) 23 chromatids b) 23 chromosomes c) 46 chromosomes d) 46 chromatids e) 92 chromosomes

3. All of the following statements are true EXCEPT:
A) Spindle fibers are composed largely of microtubules
B) Centrioles consist of nine triplets of microtubules arranged in a circle
C) All eukaryotic cells have centrioles
D) All eukaryotic cells have a spindle apparatus
E) Many of the microtubules in a spindle apparatus attach to kinetochores of chromosomes

Identify the stage of mitosis characterized by the following events:
4. Cytokinesis begins during this final stage
5. Sister chromatids begin to separate
6. Genetic material of the cell replicates to prepare for cell division
7. Microtubules begin to attach to the centromeres of the sister chromatids

8. After which of the following checkpoints in the cell cycle is the cell most likely fated to divide?
a) G2 phase checkpoint
b) M phase checkpoint
c) Interphase checkpoint
d) G1 phase checkpoint
e) MPF checkpoint

9. What factors might contribute to abnormal cell divisions such as cancer?

10. Describe the stages of mitosis, cytokinesis, and the cell cycle
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