17. 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
• Signaling molecule in
animals, promotes
cell division
• Example: Dog saliva,
wound-licking
Checkpoints
• Protein sensors
determine if cell is
OK to continue
through the cell
cycle
21. 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
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’
…proteins of DNA
Replication.
28. 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.
30. Progression of lung cancer.
Tumor takes up critical
surface area for gas
exchange.
Note invasion of underlying
tissue by cancerous cells.
32. “Cancer Genes” = mutated versions
of normal genes
Oncogenes
• Overactivity of gene
• Non-mutated form
known as proto-
oncogene
• Increase cell division
• Gas pedal
Tumor-suppressor Genes
• Mutations cause loss of
activity
• Normal function,
decrease cell division,
promote apoptosis
• Brake pedal
33. 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
34.
35. Think about the consequences of
mutated ‘cancer genes’
• Gas pedal stuck “ON” but brakes still working
• Brakes not working but can still take foot off the gas
pedal
• Gas pedal stuck ”ON” AND brakes not working!!
38. 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:
Cancer risk factors
Carcinogens AND Genetics
