Transcript B. The Cell Cycle

Ch. 9
Cellular
Reproduction
I. Cellular Growth
- Cells grow until they reach their
size limit, then they either stop
growing or divide.
A. Cell Size Limitations
- Why are cells so small?
1. Ratio of Surface Area to Volume
- As a cell grows, its volume increases
faster than its surface area.
1. Ratio of Surface Area to Volume
- As a cell grows, its volume increases
faster than its surface area.
- Large cells don’t have enough surface
area (cell membrane) to support the
cell with food and oxygen by
diffusion.
2. Transport of Substances
- Most materials (O2, CO2, water,
wastes, etc.) enter and exit the
cell by diffusion.
- Diffusion is efficient only over
very short distances.
3. Cellular Communications
- If the cell is too large, it cannot
make proteins fast enough
to support itself.
B. The Cell Cycle
- Cell reproduction enables an organism
to grow, heal injuries, or to
reproduce.
Sea Urchin
Embryo
B. The Cell Cycle
- Cell reproduction enables an organism
to grow, heal injuries, or to
reproduce.
Fertilized
egg
(zygote)
Mitotic cell
division &
Differentiation
Multicell
stage
(embryo)
Tissues
Asexual Reproduction by Mitosis
Binary Fission
in Paramecium
Asexual Reproduction by Mitosis
Budding
in Yeast
- The cell cycle is a continuous process
consisting of 3 stages:
Interphase, Mitosis, and Cytokinesis.
- Takes place in 12 – 24 hours.
1. Interphase
- Stage of normal cell activity, growth,
and DNA replication.
- Occurs in 3 phases:
1. Interpase
- Stage of normal cell activity, growth,
and DNA replication.
- Occurs in 3 phases:
a) G1: cell growth and normal activity
b) S: DNA replication
- Chromosomes: structure in nucleus
that contain DNA
- Chromatin: active, extended
form of chromosomes
c) G2: preparation for mitosis
Chromosome Structure
DNA
Double Helix
Chromatin
Chromosome
DNA Packaging
1:44
2. Mitosis
- Division of the nucleus
3. Cytokinesis
- Division of the cell into
2 identical daughter cells
4. Prokaryotic Cell Division
- Binary fission: simple cell division
E. coli
Binary Fission in Bacteria
1
attachment
site
2
cell
wall
plasma
membrane circular
DNA
DNA Replicates
3
Cell Elongates
Binary Fission in Bacteria
4
Cell Constricts
5
Fission Occurs
II. Cell Division
- Mitosis and Cytokinesis
A. Mitosis
- 4 stages (P, M, A, T)
Prophase
Metaphase
Anaphase
Telophase
1. Prophase
- first and longest stage
a. Chromatin condenses
to form chromosomes.
- Each replicated
chromosome consists
of 2 identical
sister chromatids
attached at the
centromere.
Chromosome Structure
DNA
Double Helix
Chromatin
Chromosome
Chromatid
Human Chromosomes
b. Nuclear membrane and nucleoli disappear.
c. Spindle fibers form
- microtubule structures that aid in
movement of chromosomes
d. Centrioles move to opposite ends of
the cell (animal cells only).
Prophase
2. Metaphase
- second and shortest stage
- Chromosomes line up along the
middle of the cell.
Metaphase
3. Anaphase
- Centromeres split
and chromosomes
move apart to
opposite sides of
the cell.
Anaphase
4. Telophase
- last stage
- "reverse" of prophase
a. Chromosomes revert
to chromatin.
b. Spindle fibers
disappear.
c. Nuclear membrane and
nucleolus reform.
Telophase
B. Cytokinesis
1. Animal Cells
- Cell membrane
pinches in
forming 2
daughter
cells.
Cytokinesis
2. Plant Cells
- Cell plate forms between
2 daughter cells.
Cell plate
Which stage of the cell cycle?
Anaphase
Which stage of the cell cycle?
Interphase
Which stage of the cell cycle?
Metaphase
Which stage of the cell cycle?
Prophase
Which stage of the cell cycle?
Telophase
Which stages of the cell cycle?
Prophase
Interphase
Which stage of the cell cycle?
Early Anaphase
Which stage of the cell cycle?
Metaphase
Which stage of the cell cycle?
Prophase
Which stage of the cell cycle?
Telophase
Onion Root Tip Cells
Mitosis Video
6:11
III. Cell Cycle Regulation
- The timing and rate of cell division
varies by cell type.
Cell Renewal Rates in Different Tissues of the Human Body
A. Normal Cell Cycle
- Cell division is complex, crucial, and
highly regulated.
1. Cyclins and Cyclin-dependent
Kinases (CDKs)
- Various combinations trigger
different stages of the cell
cycle.
2. Quality Control Checkpoints
- Coordinate important events in
the cell cycle.
B. Abnormal Cell Cycle: Cancer
- disease in which cells have lost the
ability to control their own growth
Cervical Cancer
Cell Dividing
1. Causes of Cancer
- due to changes in a gene (mutations)
that controls cell division
- Carcinogens: cancer causing agents
(asbestos, tobacco smoke, dioxin,
UV radiation, X rays)
2. Cancer Genetics
- More than 1 mutation is required to
produce a cancer cell.
- Some genes that lead to cancer
(oncogenes)
can be
inherited.
3. Characteristics of Cancer Cells
a) Rapid cell division
b) Undifferentiated cells
c) Metastasis:
- cells don't
stick together
and can move
elsewhere
C. Apoptosis
- programmed cell death
C. Apoptosis
- programmed cell death
- occurs in worn out cells and during
embryonic development
C. Apoptosis
- programmed cell death
- occurs in worn out cells and during
embryonic development
D. Stem Cells
- unspecialized cells that can
differentiate into specialized cells
1. Embryonic Stem Cells
- Cells from an early embryo can
differentiate into any cell type.
2. Adult Stem Cells
- Stem cells found in various adult
tissues can give rise to several types
of tissues where they are found.
The End
Time after fertilization (hours)
0
Zygote
First cell division
Nervous
system,
outer
skin, musculature
Outer skin,
nervous system
Musculature,
gonads
Germ line
(future
gametes)
Musculature
10
Fate Map of
Cell Lineage
in C. elegans
Hatching
Intestine
Intestine
Eggs
Vulva
ANTERIOR
1.2 mm
POSTERIOR
Caenorhabditis elegans Adult crawling
C. elegans Embryonic Development