Cell Growth &
Division
Chapter 10
Section 10-1: Cell Reproduction
Why do cells reproduce in a growing organism?
- because when an organism grows its cells don’t get larger, they have to make more.
Why do cells reproduce in an adult organism?
- to replace old, dead or damaged cells.
Why is there a limit on cell size? Give two reasons.
1.
Cell size is limited by the surface area to volume ratio. Smaller cells are
more efficient at taking in nutrients & disposing of wastes.
2.
The larger a cell is the more proteins it needs to maintain it. The more
proteins the quicker the instructions in DNA have to be copied.
Genes & Chromosomes
Tell how genes and chromosomes are related.
- A gene is a segment of DNA that codes for a protein. DNA is made up of
thousands of genes. DNA is organized and packaged into structures called
chromosomes.
How is genetic material organized in a prokaryotic cell?
- A prokaryote has a single circular molecule of DNA.
What makes it challenging to package genetic material in eukaryotic cells?
- Eukaryotes have many thousands of genes arrange on several linear pieces of DNA.
Ex. Humans have 46 separate strings of DNA that are all packaged into
chromosomes.
What is chromatin?
- Chromatin is DNA that has been “wound up”
on many “spools” called histones.
1.
2.
3.
4.
5.
6.
DNA is wrapped around “spools” called histones.
8 of these histone “spools” come together to form a histone core.
These histone cores are wound up into a structure called a nucleosome.
These nucleosomes are wound up to form a nucleosome cord.
These cords are wrapped around a protein scaffold to form a looped domain which are then
wound up to form a chromatid.
Two chromatids connected at the middle by a centromere form a chromosome.
All this means is that DNA is wound around spools which are then coiled into coils, those
coils are then coiled into bigger coils that coil up to form a chromsome. Don’t let
the details bog you down.
Chromosomes
Why do chromosomes become more condensed during cell reproduction?
- So that they don’t become tangled during cell division (think Xmas lights).
What are sister chromatids? What happens to them during cell division?
- Sister chromatids are an identical
pair of long molecules of DNA attached
at the center by a centromere. During
cell division the chromatids are pulled
apart into opposite new daughter cells
to ensure that each new cell has the
exact same genetic information as the
parent cell.
Cell Division in Prokaryotes
1. DNA is copied.
2. A new cell membrane forms between the two DNA copies.
3. The cytoplasm divides and the cell grows, doubling in size.
4. The cell develops a squeezed part in the middle.
5. A new cell wall forms around the new membrane, pushing inward.
6. The cell is pinched into two independent cells.
Section 10-2: Mitosis
The cell cycle is a repeating sequence of growth and ________
division during the life
of a cell.
The first three phases of the cell cycle are collectively called _____________
interphase.
Nucleus divides into two nuclei:
- mitosis
Cytoplasm divides and daughter cells become physically separated:
- cytokinesis
Preparations are made for the cell to divide, such as the organization of
microtubules:
- G2 phase
DNA is copied:
- S phase
Cell carries out its
routine functions:
- G1 phase
Spindles & Centrosomes
What function do spindles perform during mitosis?
- Spindles form a link between the cell’s poles and the centromere of each
chromosome. They shorten and pull the sister chromatids apart and to
opposite sides of the cell.
What function do centrosomes perform during mitosis?
- They help assemble the spindle.
Steps of Mitosis
1. Prophase:
Chromosomes begin to condense, and the nuclear membrane begins to dissolve.
2. Metaphase:
Chromosomes move to the cell center, lining up there. Spindle fibers link the
centromeres to the poles.
3. Anaphase:
Sister chromatids move toward opposite poles as the spindle fibers attached to them shorten.
4. Telophase:
http://www.youtube.com/watch?v=AhgRhXl7w_g
A nuclear envelope forms around the chromatids at each pole. The spindle dissolves.
Cytokinesis
Cytokinesis begins after mitosis.
During cytokinesis in animal cells, the cell is pinched in
half by a belt of proteins.
In plant cells, a new cell wall is formed by cell plates
holding cell wall materials. These fuse to form a
membrane-bound cell wall.
The Cycle Continues
After cytokinesis, the new daughter
cells enter the G1 phase of interphase.
Each daughter cell is about
half the size of the original cell.
Find the daughter cells.
Section 10-3: Regulation
A scientist places a few healthy cells in a dish that contains nutrients for the
cell. What happens?
- They divide rapidly
How is the process you described in question 1 similar to what happens with a
wound?
- The cells reproduce rapidly until they have closed up the wound at which time
they slow down and stop reproducing.
What are three sources of signals related to the regulation of cell growth and
division?
1.
Proteins within the cell
2.
Signals from surrounding
cells or organs
3.
Environmental conditions
like the availability of nutrients.
Many ________
signals within the cell control the phases of the cell cycle.
Feedback signals at key _____________
in the cell cycle can trigger or delay
checkpoints
the continuation of the cycle.
Checkpoints
Describe when and how each of the checkpoints listed below functions to
regulate the cell cycle.
G1 checkpoint
- The cell checks to see that it is large and healthy enough to reproduce. If so
DNA copying proceeds, if not it goes into a resting phase.
G2 checkpoint
- Newly synthesized DNA is checked for mistakes. If the DNA has been fixed
and the cell is large enough to divide mitosis will proceed.
Mitosis checkpoint
- The cell checks that the chromosomes
are lined up properly and that the spindle
fibers are correctly attached.
http://www.cellsalive.com/cell_cycle.htm
Cancer
What is cancer?
- A group of severe diseases that are caused by uncontrolled cell growth.
How do cancer cells affect healthy cells?
- They invade and destroy healthy tissues.
What is the reason that cancer cells do not respond properly to cell signals and
controls? What is the result?
- The cancerous cell’s DNA has been damaged.
Lung Cancer
Breast Cancer
Tumors
What is the difference between a benign tumor and a malignant tumor?
- A benign tumor does not spread to other parts of the body & can usually be
removed by surgery. A malignant tumor invades and destroys nearby
healthy tissues and organs.
Malignant Tumors
Cancer Treatments
What are three treatments for cancer?
- Chemotherapy: using drugs or chemicals to kill cancerous cells
- Surgery: physical removal of tumor or cancerous cells
- Radiation therapy: high energy rays are focused on a specific area to
destroy cancerous cells.
Cancer Prevention
What are two things you can avoid to help prevent getting cancer?
1.
Avoid unnecessary exposure to UV radiation.
2.
Avoid intake of chemicals like those found in cigarette smoke.
http://www.mayoclinic.com/health/cancer-prevention/CA00024