Chapter 10

Cell Growth & Division

Why are cells so small?1. DNA “Overload”

- Large cells can’t get the info from its DNA to ribosomes far away from the nucleus.

2. Difficult to exchange materials- In large cells, many organelles would be too far from the cell membrane, thus they would be unable to get nutrients or get rid of their waste.

10-1: Cell GrowthChapter 10 – Things You Will be Able to Do:• Name 2 reasons why cells divide.• Describe what problem cell growth causes for cell

efficiency and homeostasis.• Name the main events of the cell cycle.• Describe what happens during the 4 phases of mitosis.• Recognize, name and explain the various stages of the

cell cycle including interphase (G1, S, G2 ) and the M phase or cell division(mitosis and cytokinesis).

• Recognize and name the phases of mitosis on prepared slides and in digital imagery.

• Identify a factor that can stop cells from growing.• Describe how the cell cycle is regulated.• Explain how cancer cells are different from normal cells.• List 3 causes (carcinogens?) of cancer. Describe how cells become specialized (differentiate) for different functions.

Why is the surface area (SA) to Volume (V) ratio (SA/V) so important?It is a mathematical way to express the exchanging materials dilemma.

1. Cells require a large SA to Volume ratio.- the surface area must be a lot larger than the volume

2. As a cell grows, its volume increase much more rapidly than it surface area- this makes the SA/V smaller

10-1: Cell Growth

How big can a cell get?About twice its original size.

What does it do when it reaches this size? Divide into two “daughter cells”

- this process is called cell divisionStep 1: DNA Replication & Division (each new cell gets a complete copy of the DNA)Step 2: Fission (the action of dividing or splitting something into two or more parts )

10-1: Cell Growth

What is the difference between asexual & sexual reproduction?Asexual – one parent- offspring is genetically identical to the parent- easier to do, but there is a lack of genetic varietySexual – two parents- offspring is genetically different from the parents - harder to do, but offers much more genetic variety (genetic variety is the raw material for evolution)

10-1: Cell Growth

Prokaryotic Chromosomes:1. Only contain a single, circular molecule of

DNA called a nucleoid2. They also have other small pieces of DNA

called plasmids.

10-2: Cell DivisionChapter 10 – Things You Will be Able to Do:• Name 2 reasons why cells divide.• Describe what problem cell growth causes for cell

efficiency and homeostasis.• Name the main events of the cell cycle.• Describe what happens during the 4 phases of mitosis.• Recognize, name and explain the various stages of the

cell cycle including interphase (G1, S, G2 ) and the M phase or cell division(mitosis and cytokinesis).

• Recognize and name the phases of mitosis on prepared slides and in digital imagery.

• Identify a factor that can stop cells from growing.• Describe how the cell cycle is regulated.• Explain how cancer cells are different from normal cells.• List 3 causes (carcinogens?) of cancer. Describe how cells become specialized (differentiate) for different functions.

Prokaryotic cell division is called binary fission.

Step 1: DNA Replication- Each of the 2 daughter cells will have a complete set of DNA

Step 2: Fission- The mother cell divides in two to produce the two daughter cells.

10-2: Cell Division

Eukaryotic Cell Division:Step 1: Mitosis

- This is the division of the nucleus after DNA Replication. - Each daughter cell will receive a complete nucleus- Has four phases (PMAT)

Step 2: Cytokinesis- This is the division of the cell.

10-2: Cell Division

What is a chromosome?- Condensed chains of DNA- A cell’s DNA is usually divided into several chromosomes- The 3 billion base pairs that make up the DNA in one of your cells is divided into 46 different chromosomes.

10-2: Cell Division

Eukaryotic Chromosome Structure:

10-2: Cell Division

Unduplicated Chromosomes (one from each parent)

Chromosome Structure:1. Has an “X” shape (when

duplicated)2. Each side of the X is

called a sister chromatid.

3. Sister chromatids are held together by a centromere.- centromeres are basically protein velcro.

4. Kinetochores are where the mitotic spindle will attach during mitosis

10-2: Cell Division

Chromosome Structure: the confusing part

1. Chromatin condenses into chromosomes

2. Chromosomes are made of chromatids.

3. When the chromatids separate during mitosis, they are called chromosomes again.

They are all made of the same stuff, just a different name at different times.

10-2: Cell Division

The Eukaryotic Cell Cycle:Has Two Main Phases:1. Interphase

- The time between cell divisions2. M Phase

- Mitosis & Cytokinesis occurs during this phase.

10-2: Cell Division

Interphase: 1. Growth Phase 1 (G1

Phase)- Cell doubles its size

2. Synthesis Phase (S Phase)- DNA Replication occurs

3. Growth Phase 2 (G2 Phase)- Cell produces the materials that will be used during cell division- The Centrioles replicate- “Spell Checks” the DNA to make sure it is ready for cell division.

10-2: Cell Division

M Phase: the cell division phase & has two parts

A. Mitosis – division of the nucleusThe 4 Mitotic Phases:

1. Prophase2. Metaphase3. Anaphase4. Telophase

B. Cytokinesis – starts during Telophase

10-2: Cell Division

The Mitotic Phases:

1. Prophase- Chromatin condenses into chromosomes.- The nuclear envelope begins to break down.- Centrioles begin to move towards the poles.- The mitotic spindle begins to form.

10-2: Cell Division

The Mitotic Phases:

2. Metaphase- The chromosomes line up on the cell’s equator.- The nuclear envelope is gone.- Centrioles are at the poles.- The spindle is complete and attached to the kinetochores.

10-2: Cell Division

The Mitotic Phases:3. Anaphase

- The centromeres separate & the chromatids become individual chromosomes.- The kinetochores drives the movement toward the centrioles.- Chromosomes move all the way to the poles.

10-2: Cell Division

The Mitotic Phases:

4. Telophase- Basically the opposite of

the Prophase.- Chromosomes uncoil.- Nuclear

Envelope reforms.

- Spindle breaks down.

10-2: Cell Division

Cytokinesis:1. Occurs during Telophase.2. The actual division of the cytoplasm into

two daughter cells.Animal Cells:3. Starts with the formation of the cleavage

furrow.4. Cleavage furrow pinches in until the cells

are separated.Plant Cells:5. Starts with the formation of the cell plate

along the cell’s equator.6. Cell plate will form a cell wall between the

two cells.

10-2: Cell Division

10-2: Cell Division

How often can cell divide?About 50 times. This is known as the Hayflick limit.

How does this happen?Think of your chromosomes as a shoestring with the plastic end. The ends on the chromosomes are called telomeres and they keep the DNA from unraveling. After about 50 cell ÷, the telomeres are too short to withstand anymore.

10-2: Cell Division

How is the cell cycle controlled in multicellular organisms?

1. Contact Inhibition- Cells will divide until the are

touching another cell on all sides.2. Internal & External Growth Factors

A. Cyclins – control the timing of the cell cycle

B. Internal Regulators – a type of quality control

C. External Regulators – many of these are hormones

10-3: Regulating the Cell CycleChapter 10 – Things You Will be Able to Do:• Name 2 reasons why cells divide.• Describe what problem cell growth causes for cell

efficiency and homeostasis.• Name the main events of the cell cycle.• Describe what happens during the 4 phases of mitosis.• Recognize, name and explain the various stages of the

cell cycle including interphase (G1, S, G2 ) and the M phase or cell division(mitosis and cytokinesis).

• Recognize and name the phases of mitosis on prepared slides and in digital imagery.

• Identify a factor that can stop cells from growing.• Describe how the cell cycle is regulated.• Explain how cancer cells are different from normal cells.• List 3 causes (carcinogens?) of cancer. Describe how cells become specialized (differentiate) for different functions.

How is the cell cycle controlled in multicellular organisms?

3. Apoptosis – a.k.a “programmed cell death.”- The cell basically self-destructs by breaking into small pieces in a process called “blebbing.”- The pieces are then cleaned up by white blood cells- Apoptosis is often used in development: apoptosis makes the tail on a tadpole go away.- Many cells have an “expiration date” & then go through apoptosis. Many cancers are caused when these cells fail to go through apoptosis.

10-3: Regulating the Cell Cycle

Uncontrolled Cell Growth (cancer):1. Cancer cells do not respond to normal

regulatory signals. A mass of tumor cells is called a tumor.

2. Their telomeres often do not get shorter after each ÷. The Hayflick Limit doesn’t apply to them.

3. The p53 gene is often involved. The p53 protein is the spell checker of DNA Replication. A functional p53 recognizes mistakes and if they are severe enough, will cause the cell to go through apoptosis (Programmed Cell Death). When it malfunctions, mistakes (mutations) remain and are passed on to the daughter cells.

- The carcinogens in tobacco smoke have been shown to directly damage the p53 gene.

10-3: Regulating the Cell Cycle

What are stem cells?They are undifferentiated or unspecialized cells.

Types of embryonic stem cells:

1. Totipotent – these stem cells can develop into any type of cell. Only the fertilized egg & the first few cell made by the early cell divisions are totipotent.

2. Pluripotent – these stem cells are found in the inner cells mass (ICM) of the blastocyst. These cells can turn into most of the 200+ different human cell types. The ICM will become the organism.

10.4: Cell Differentiation

What are adult stem cells?These stem cells are found in

many organs.They are called multipotent

because they can only turn into the cell of the various tissues of the organ.

10.4: Cell Differentiation