Transcript Cell Division

Ch 8 - Growth & the Means to
sexual reproduction
Why do cells divide?
 Replacement
of skin cells
Dead
cells
Epidermis,
the outer
layer of the
skin
Dividing
cells
Dermis
Figure 8.11B
 Asexual
reproduction of a prokaryotic cell
Plasma
membrane
Cell wall
Division into
two cells
Figure 8.3A
 Mitosis
= asexual reproduction
What do all cells need to
function?
DNA

)
genome
 Sum
of genetic information
 Made of autosomes and sex
chromosomes
 Chromosomes occur in homologous
pairs in sexually reproducing
organisms
 Chromosome number of an organism
can be DIploid or HAPloid
Karyotype – array of
chromosomes an organism has
Cell Cycle
The cell division party!!
Interphase
 G1
S
 G2
 G0
End results of Mitosis
1
cell has become 2
 New cells made
 Genetic information has stayed
the same
 Number of chromosomes has
stayed the same in each new cell
Regulation of Mitosis/growth
 Cell
checkpoints and feedback
mechanisms
 Growth hormones
 Density dependence
 Growth
factors tell the cell to divide
Growth factor
Plasma membrane
Receptor
protein
Signal
transduction
pathway
Figure 8.8B
Relay
proteins
 Cells
continue dividing until they touch one
another

This is called density-dependent inhibition
Cells anchor to dish surface and
divide.
When cells have formed a
complete single layer, they stop
dividing (density-dependent
inhibition).
If some cells are scraped away,
the remaining cells divide to fill
the dish with a single layer and
then stop (density-dependent
inhibition).
Figure 8.8A
Cancer
 Cells
Behaving
Badly

unlimited
division, no
apoptosis
 Feedback
signals
not working



Benign vs.
malignant
Metastasize
tumor
• Malignant tumors can invade other tissues and
may kill the organism
Lymph
vessels
Tumor
Glandular
tissue
Metastasis
1
A tumor grows
from a single
cancer cell.
Figure 8.10
2
Cancer cells invade
neighboring tissue.
3
Cancer cells spread
through lymph and
blood vessels to other
parts of the body.
Formation of Sex Cells
 Must
have haploid number of
chromosomes in gametes
 Reduction/Division
 Must reduce the diploid
number by 1/2
 This is Meiosis
Stages …
 One
Interphase and chromosome
doubling
 Meiosis I and Meiosis II
 2 cytokinesis
 End result – 4 gametes with ½
chromosome number
Diploid to haploid
 At
the end of Meiosis I, 2 cells
with ½ the chromosome # (one of
each homologous pair)
 Those chromosomes are still
made of pairs of chromatids
which still need to be pulled apart
Meiosis II
 Simply,
mitosis again
Genetic Diversity
 Crossing
over
 Random line-up on metaphase plate
 Independent assortment
 Union
of individual gametes to form zygote
Which cells undergo Mitosis?
Meiosis?
 The
human
life cycle
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
Figure 8.13
Meiosis
 Forms
sperm
 Spermatogenesis
 Forms
eggs
 Oogenesis
Chromosome Errors
 Deletion
 Inversion
 Translocation
 Sticky
cromosomes