2. Learning objectives for DNA
replication, cell cycle, and mitosis
• Explain how cells divide to give rise to identical cells
• Describe the steps of replication and the function of enzymes in each step
including:
• helicases
• RNA polymerase
• DNA polymerase
• ligases
• Explain what features of DNA allow semiconservative replication to occur
• Describe the steps that occur as a chromosome folds into chromatin
• Explain what is happening in a cell at each stage of the cell cycle
• Diagram and identify the phases in mitosis
• Explain what is meant by a checkpoint and how these relate to cancer
• Compare and contrast the role of an oncogene and tumor suppressor in cancer
• Compare and contrast the growth of a normal cell and a stem cell
4. 1 day 2–3 days 4 days 7 days 13 days 21 days 26 days
28 days
32 days
33 days
37 days
41 days
44 days
47 days
50 days
52 days
54 days
56 days
LM 50 μm LM 50 μm LM 50 μm 50 μm 50 μm 80 μm 1 mm 2 mm
5 mm
5 mm
5 mm
5 mm
5 mm
5 mm
5 mm 5 mm 5 mm 5 mm 5 mm
9. DNA polymerase adds DNA
nucleotides to the RNA
primer. Proofreading activity
checks and replaces
incorrect bases just added.
Leading (continuous)
strand synthesis continues
in a 5′ to 3′ direction.
Helicase separates strands.
Binding proteins prevent
single strands from rejoining.
Primase makes a short stretch
of RNA on the DNA template.
Overall direction of replication
Discontinuous
synthesis of the lagging
strand produces
Okazaki fragments.
After RNA primer is replaced with DNA,
ligase seals the sugar–phosphate backbone.
Steps in DNA replication
RNA primers
New DNA
strands
Okazaki
fragment
Leading strand
Lagging strand
Figure 8.5 contd.
3’
3’
3’
3’
3’
3’
3’
3’
3’
3’
3’
3’ 3’
3’
3’
3’
3’
3’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’5’
5’
5’
5’5’
10. Figure 8.6
Origins of replication
Original
DNA
molecule
Daughter strands
Parental
strands
Two
identical
DNA
molecules
Parental
strands
Daughter strands
11. Cell membrane
DNA
Cell wall
Parent cell contains
one chromosome.
DNA replicates and
attaches to cell
membrane.
Membrane growth
between the two
attachment points
moves the DNA
molecules apart as
new cell wall material
is deposited.
The result of
binary fission: two
daughter cells,
each identical to
the original.
Prokaryotes - Binary Fission
14. Figure 8.10
G1 phase
(normal cell function
and cell growth)
S phase
(DNA replication)
G2 phase
(additional growth
and preparation
for division)
G0 phase
(nondividing)
The Cell Cycle
21. G2 checkpoint
• Has all DNA replicated?
• Can damaged DNA be repaired?
• Is spindle-making machinery
in place?
Metaphase
checkpoint
• Do kinetochores
attach to spindle?
• Are chromosomes
aligned down
equator?
S phase checkpoint
• Is DNA replicating
correctly?
S phase
(DNA replication)
G2 phase
(additional growth
and preparation
for division)
G1 phase
(normal cell function
and cell growth)
G1 checkpoint
• Is DNA damaged?
G0 phase
(nondividing)
Regulation of
Cell Division
Growth Factors
Checkpoints
22.
23. Malignant cells can "seed" new
tumors throughout the body.
Blood
vessel
Malignant
tumor
Benign
tumor
Capsule of connective tissue
keeps tumor from spreading.
Lymph
vessel
Lymph
vessel
a. Benign tumor b. Malignant tumor
Metastasis
Blood
vesselsNew
tumor
New
tumor
Lymph
vessel
Capsule
29. Figure 8.16
Proto-oncogene Tumor suppressor gene
Mutated or silenced
proteins
block cancer
development.
Proteins absent or
fail to block cancer
Development.
proteins
accelerate cell cycle.
Normal
Normal proteins
stimulate cell
division.
Oncogene
Cancer cells No CancerNormal cells
Mutated or overly activeNormal
Normal cell
30.
31. Figure 8.18
To avoid or reduce the risk of cancer
Eat a healthy diet, low in saturated
fat and rich in fruits and vegetables
Avoid UV radiation
from sunlight and
tanning beds.
Stop using
tobacco,
or better yet,
never start.
Use self tests
and medical exams
for early detection.
Use condoms to
avoid exposure
to viruses known
to cause cancer.
Get regular
vigorous
exercise.
Avoid obesity:
32. Term Definition
Chromatin
Cleavage furrow
Chromosome A single, continuous molecule of DNA wrapped around protein. Eukaryotic cells contain multiple linear
chromosomes, whereas bacterial cells typically have one circular chromosome.
Collective term for all of the DNA and associated proteins in a cell
Chromatid One of two identical attached copies that make up a replicated chromosome
Centromere A small part of a chromosome where sister chromatids attach to each other
Interphase Stage of the cell cycle in which chromosomes replicate and the cell grows
G1 phase
G0 phase
G2 phase
S phase
Gap stage of interphase in which the cell grows and carries out its functions
Gap stage of interphase in which the cell functions but does not divide
Gap stage of interphase in which the cell produces membrane components and spindle proteins
Synthesis stage of interphase when DNA replicates
Mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Cell plate
Centrosome
Spindle
Kinetochore Protein complex to which the spindle fibers attach on a chromosome’s centromere
Array of microtubule proteins that move chromosomes during mitosis
Structure that organizes the microtubules that make up the spindle in animal cells
Material that forms the beginnings of the cell wall in a plant cell undergoing cytokinesis
Indentation in cell membrane of an animal cell undergoing cytokinesis
Distribution of cytoplasm to daughter cells following division of a cell’s chromosomes
Stage of mitosis when chromosomes arrive at opposite poles and nuclear envelopes form (telo- = end)
Stage of mitosis when the spindle pulls sister chromatids toward opposite poles of the cell
Stage of mitosis when chromosomes line up along the center of the cell (meta- = middle)
Stage of mitosis when the nuclear membrane breaks up and spindle fibers attach to kinetochores
Stage of mitosis when chromosomes condense and the spindle begins to form (pro- = before)
Division of a cell’s chromosomes into two identical nuclei
Table 8.1
