Download PowerPoint Presentation - 10*1 Cell Growth

10–1 Cell Growth
Limitations on cell sizes
• Unit of measure for most cells = µm
(micrometer)
– Micrometer (10–6m) = 1/1,000,000 meter
• Red blood cells = 8 µm dia.
• Large nerve cells = 1 m in length
• Most cells = 2 – 200 µm dia.
Surface area to volume ratio
Surface area = _____
Volume = _______
Which dimension (area or volume) increases faster as
cubes become larger?
What will be the surface area and volume of the 3rd cube?
If the cell dimensions double, how many times more
cytoplasm requires food/produces waste? Did the surface
area increase this many times too?
Limits to Cell Growth
• What problems does growth cause for cells?
• Problems occur in cells if they get too big; ratio of
surface area : volume
– If ratio gets too small (ex. 1.5:1), cell is in danger of dying.
• Diffusion time tends to limit most cell sizes
– Very slow process; cells would die if they’re too big because
diffused substances could take days/weeks to reach target
organelles.
• DNA control of the cell also limits size -- it relies on
diffusion of regulating molecules it sends out from
nucleus into the cytoplasm
• What must the cell do to overcome . . .
– 1. Surface area : volume ratio problem
– 2. DNA control limit;
– 3. Diffusion time limit ? ? ?
• DIVIDE and stay SMALL
– This will keep surface area LARGE compared to
volume
• Division of the Cell
• Before it becomes too large, a growing cell divides
forming two “daughter” cells.
• The process by which a cell divides into two new
daughter cells is called cell division.
Cells will reproduce in order to .
..
•
•
•
•
•
1. overcome previous limitations
2. replace old, worn out cells
3. replace damaged cells
4. grow an organism
Most humans will divide cells for about 50
generations of cells
• Offspring cells (daughter cells) must each receive
the same DNA information as the original cell
– Chromatin condenses into chromosomes just before cell
division
END OF SECTION
10-2 Cell Division
Chromosomes
• Chromosomes
• Genetic information is passed from one
generation to the next on chromosomes.
• Before cell division, each chromosome is
duplicated, or copied.
Chromosomes
• Each chromosome
consists of two
identical “sister”
DNA: chromatin (colored thread)
chromosome (colored body)
Sister chromatids
chromatids.
• Chromatids: one functions
as a template and the
other is an exact copy
– Each pair of
chromatids is
attached at an area
called the
centromere.
Centromere
[Note: prokaryotic chromosome is a large loop of DNA]
*Binary Fission*
Eukaryotic chromosomes
Human chromosomes –
just before cell division
(950X)
Cell Division
• In eukaryotes, cell division occurs in two major
stages.
• The first stage, division of the cell nucleus, is
called mitosis.
• The second stage, division of the cell
cytoplasm, is called cytokinesis.
Cell Life: Play by play
Cell Life Cycle:
Interphase: most of the life of the cell
G1, S phase, G2
Mitosis: Brief time of cell division: nucleus
division process which produces 2 daughter
nuclei with exactly the same chromosomes as
the parent cell
Prophase, Metaphase, Anaphase,
Telophase (with cytokinesis)
Then the cycle starts over again for the two new
daughter cells.
Events of the Cell Cycle
Cell Cycle
Cell Division
Cell is at maximum size
– Prophase
Mitosis
• Prophase is the first and longest
phase of mitosis.
• Chromatin condenses into
chromosomes.
• The nuclear envelope breaks
down.
• The centrioles separate and
take up positions on opposite
sides of the nucleus. A spindle
begins to form.
Spindle
forming
»The centrioles lie in a region
called the centrosome.
Centromere
»The centrosome helps to
organize the spindle, a fanlike
microtubule structure that
helps separate the
chromosomes.
Chromosomes
(paired
chromatids)
Mitosis
Centriole
–Metaphase
•The second phase of
mitosis is metaphase.
•The chromosomes line up
across the center of the cell.
•Microtubules connect the
centromere of each
chromosome to the poles of
the spindle.
Spindle fibers: made
of microtubules;
attach to centromeres
Spindle
Mitosis
–Anaphase
Individual
chromosomes
•Anaphase is the third phase
of mitosis.
•The sister chromatids
separate into individual
chromosomes.
•The chromosomes continue
to move until they have
separated into two groups.
– Telophase
Mitosis
• Telophase is the fourth
and final phase of
mitosis.
• Chromosomes gather at
opposite ends of the cell
and lose their distinct
shape.
• A new nuclear envelope
forms around each
cluster of chromosomes.
Cytokinesis:
• pinching of cytoplasm
in animal cells;
• formation of a cell
plate in plant cells
Cytokinesis
• During cytokinesis, the
cytoplasm pinches in half.
• Each daughter cell has an
identical set of duplicate
chromosomes
Cytokinesis in Plants
• In plants, a structure known as the cell plate forms
midway between the divided nuclei.
• The cell plate gradually develops into a separating
membrane.
• A cell wall then begins to appear in the cell plate.
Cell plate
Cell wall
Cell Cycle and Mitosis Summary
Prophase
Metaphase
Summary Image
Anaphase
Telophase
A normal human
has 46
chromosomes.
How many sister
chromatids would
be present during
metaphase of a
human cell?
Fill in the missing terms at end of label lines (phase names 1st).
4. Chromosomes
1. Interphase
duplicate
5. Centromere
6. Chromosomes
with sister
chromatids
2. Metaphase
7. Spindle fibers
attach to
centromeres
12. Nuclear
10.Spindle fiber
envelope
reforms
9. Centriole
Disappearing
8. nuclear envelope
11. Two
new cells
13.
3.
Anaphase
Spindle fibers
pull chromatids
towards
centrioles
Results of mitosis
• If organism is unicellular, this is reproduction
(ex. Amoeba, Paramecium) *Binary Fission*
• Development and growth occurs in
multicellular organisms:
–
–
–
–
Cells divide and cluster into tissues
Tissues form into organs
Organs function together as organ systems
Organ systems make the whole organism
10-3 Regulating the
Cell Cycle
Control of the cell cycle
• Normal cells proceed through the cell cycle under the
control of groups of enzymes
– Amounts of different enzymes increase and decrease
• Amounts of enzymes act as triggers for the cell to proceed to
the next step of the cell cycle.
• If enzyme concentrations are incorrect the cell will stop and
degrade
• Normal cells will stop dividing when they contact
other cells (contact inhibition)
• Cancer cells lack contact inhibition
• The type of cancer and its occurrence depend on the
country one lives in.
Controls on Cell Division
• Contact Inhibition
Cell Cycle
Regulators
– Internal Regulators
• Proteins that respond to events inside the cell.
• Allow the cell cycle to proceed only when certain
processes have happened inside the cell.
– External Regulators
• Proteins that respond to events outside the cell.
• Direct cells to speed up or slow down the cell cycle.
Cell Cycle Regulators
Cyclins were discovered during a similar
experiment to this one.
A sample of cytoplasm
is removed from a cell
in mitosis.
The sample is injected
into a second cell in
G2 of interphase.
As result, the second
cell enters mitosis.
–The amount of this protein in the cell rises and falls in time with the cell cycle.
–Scientists called this protein cyclin because it seemed to regulate the cell cycle.
–Cyclins regulate the timing of the cell cycle in eukaryotic cells.
• Cells rely on proper enzymes (a protein
called cyclin) working in sequences
– Structure of enzymes is coded for in the
genes
• A gene is a segment of DNA
• Sometimes a gene is accidentally mutated
(changed) by external factors:
– UV light
– Chemicals from tobacco, water supply, air pollution,
etc.
– X radiation, nuclear radiation
•Incorrect enzymes may lead to loss
of cell cycle control
–Cells divide more rapidly; don’t stop
dividing when they contact other cells -make tumors (benign or malignant) and
invade other parts of the body
(metastasis).
–This is the description of CANCER
Prevention
• Diet
– Low fat, more plant fiber
– More vitamins A, C, E
• These are antioxidants and reduce the amount of free
radicals (charged particles) in the cells
– These chemicals can attach to DNA and cause mutations
which lead to cancer
• More exercise
• Avoid tobacco products
• These all reduce the risk of cancer, but don’t
guarantee escape from getting it -- especially
if it’s in the family gene line.
END OF SECTION
2 cm
1 cm
2 cm
1 cm
1 cm
Cell growth
2 cm
Surface area = __?__
Surface area = __?__
Volume = __?__
Volume = __?__
SA : Vol = __?__
SA : Vol = __?__
4
3
5
2
What does this diagram represent?
What letters belong at numbers?
Where does DNA replicate itself?
Where is interphase?
1
Where are organelles produced?
Where is there a cell plate made?
Where is anaphase?
4
G1
G2
2
1
G0 What kinds of cells in our bodies do this?
Normally
growing cells
Abnormally
rapid growing
small cells
Break-away
cells
A ??
B. Spreading process is
called _____??______
Phase?
1
Phase?
Phase?
3
9
4
2
5
10
6
Phase?
Phase?
7
8
Place terms in ascending order
Cell
Organ
Organ system
Tissue
That’s all . . .
Do well on your test :)