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Chapter 12 – The Cell Cycle
Interactive Questions
IQ 12.1
a) How many chromosomes do you have in your somatic cells? 46
b) How many chromosomes in your gametes? 23
c) How many chromatids in one of your body ells that has duplicated its chromosomes prior
to mitosis? 92
IQ 12.2
a) How are the three sub phases of interphase alike? Most organelles and cell components
are produced continuously throughout the sub phases
b) What key event happens during the S phase? DNA synthesis
IQ 12.3
a) G2 of interphase
b) Prophase
c) Prometaphase
d) Metaphase
e) Anaphase
f) Telophase and cytokinesis
g) Centrosome w/ centrioles
h) Chromatin
i) Nuclear envelope
j) Nucleolus
k) Early mitotic spindle
l) Aster
m) Non-kinetochore microtubules
n) Kinetochore microtubules
o) Metaphase
p) Spindle
q) Cleavage furrow
r) Nuclear envelope forming
IQ 12.4
a) What is MPF? A combination of cyclin and cdk
b) Describe the relative concentrations of MPF and its constituent molecules throughout the
cell cycle:
MPF - complex of cyclin and cdk that initiates mitosis by phosphorylating protein and
other kinases; highest concentration at metaphase
Cdk - levels are constant throughout the cell cycle
Cyclin – levels vary because it is broken down by MPF after anaphase
Structure Your Knowledge
1. Interphase: 90% of cell cycle; growth and DNA replication
G1 – Chromosome consists of thin chromatin fibers made of DNA and associated
proteins. RNA molecules are being transcribed.
S phase – synthesis of DNA; sister chromatids are produced.
G2 – growth continues
Prophase: Sister chromatids become tightly coiled and folded.
Prometaphase: Kinetochore fibers attach to kinetochores, chromosomes move toward
Metaphase: Chromosomal centromeres are aligned on metaphase plate
Anaphase: Sister chromatids separate.
Telophase: Chromatin fibers uncoil and surrounded by reforming nuclear membrane.
2. Draw and label a mitotic spindle.
3. In this photomicrograph of cells in an onion root tip, identify the cell cycle phases for the
indicated cells.
a) anaphase
b) prophase
c) late telophase
d) metaphase
Test Your Knowledge
1. most cells that will no longer divide are in this stage Go
2. sister chromatids separate and chromosomes move apart anaphase
3. mitotic spindle begins to form prophase
4. cell plate forms or cleavage furrow pinches cells apart cytokinesis
5. chromosomes replicate S phase
6. chromosomes line up at equatorial plane metaphase
7. nuclear membranes form around separated chromosomes telophase
8. chromosomes become visible prophase
9. kinetochore-microtubule interactions move chromosomes to midline prometaphase
10. restriction point occurs in this phase G1 phase
Multiple Choice
1. One of the major differences in the cell division of prokaryotic cells compared to
eukaryotic cells is that
D – the chromosomes do not separate along a mitotic spindle in prokaryotic cells (pg
2. A plant cell has 12 chromosomes at the end of mitosis. How many chromosomes would
it have in the G2 phase of its next cell cycle?
C – 12 (pg 221)
3. How many chromatids would this plant cell have in the G2 phase of its cell cycle?
D – 24 (pg 221)
4. The longest part of the cell cycle is
E – interphase (pg 221)
5. In animal cells, cytokinesis involves
B – the contraction of the contractile ring of microfilaments (pg 225)
6. Humans have 46 chromosomes. That number of chromosomes will be found in
C – the somatic cells (pg 219)
7. Sister chromatids
C – each have their own kinetochore (pg 222)
8. Which of the following would not be exhibited by cancer cells?
C – density dependent inhibition (pg 231)
9. Which of the following is not true of a cell plate?
B – it results from the fusion of microtubules (pg 226)
10. A cell that passes the restriction point in G1 will most likely
A – undergo chromosome duplication (pg 229)
11. The rhythmic changes in cyclin concentration in a cell cycle are due to
C its degradation, which is initiated by active MPF (pg 230)
12. In a plant cell, a centrosome functions in the formation of
E – microtubules of the spindle apparatus (pg 221)
13. A cell in which of the following phases would have the least amount of DNA?
A – Go (pg 229)
14. What initiates the separation of sister chromatids in anaphase?
E – the cessation of delay signals received from unattached kinetochores (pg 224)
15. Cells growing up in cell culture that divide and pile up on top of each other are lacking
A – anchorage dependence (pg 231)
16. Knowledge of the cell cycle control system will be most beneficial to the area of
D – cancer prevention and treatment (pg 232-233)