Ch. 12 Cell Cycle

What are the 3 key roles of cell division?

1. Reproduction

2. Growth and Development

3. Tissue Renewal

Genome

A cell’s DNA or genetic information

What is the difference between a prokaryotes and eukaryotes genome?

Prokaryotes: single long circular DNA molecule (chromosome)

Eukaryotes: number of DNA molecules (chromosomes)

What is a somatic cell?

Any cell in a organism besides the gametes

What are gametes?

Egg and sperm

How many chromosomes are found in a mature human sperm?

23 (n): one set of 23 chromosomes

Does bigger species size = more chromosomes?

No, bigger size doesn’t = more chromosomes

True or False: Every species has a defined number of chromosomes

True

Chromosomes are made of chromatin. What is chromatin?

A complex of DNA and associated protein molecules

Chromatin is a complex of DNA and associated protein molecules. What is the function of the DNA and associated proteins?

In eukaryotes, the DNA is a single linear molecule containing several hundred to a few thousand genes.

The associated proteins function to maintain the structure of chromosomes and to help control gene activity.

Centromere

Region where 2 sister chromatids are tightly attached

Sister chromatids are attached by what?

Cohesions

True or False: Sister chromatids are considered “one” chromosome when attached

True

Mitosis occurs in what and produces what?

Occurs in somatic cells (2n to 2n). Produces two daughter cells that are genetically identical.

Meiosis in occurs in what and produces what?

Occurs in germ cells (2n to 1n). Produces 4 daughter cells that are genetically different.

Cytokinesis

Division of the cytoplasm

What are the phases of the cell cycle?

M phase, G1 Phase, S Phase and G2 Phase

What happens in M Phase?

Mitosis and cytokinesis. The cell divides.

What happens in the G1 phase (a.k.a first gap)?

Cell grows

What happens in the S phase?

DNA synthesis. Cell grows and chromosomes are duplicated.

What happens in the G2 phase (a.k.a. 2nd gap)?

Cell grows

Mitosis is broken down into 5 stages. What are they?

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

What is the difference between mitosis and cytokinesis?

Mitosis is the division of the nucleus, and cytokinesis is the division of the cytoplasm

Centrosome

Microtubule organizing center. Duplicate during interphase (S phase) in animals cells and move apart during mitosis (prophase and prometaphase)

Kinetochores

A protein structure at the centromere region of each sister chromatid

Kinetochore Microtubules

Attach to kinetochores. Moves a chromosome towards the pole from which the microtubule extends

Aster

Radial array of short microtubules that attach to the plasma membrane

Nonkinetochore microtubules

Function in elongating the whole cell during anaphase

Mitotic spindle is composed of what?

1. Centrosomes

2. Spindle microtubules (kinetochore and nonkinetichore microtubules)

3. Asters

Spindle microtubules

Elongate by adding subunits of tubular and shorten by losing subunits of tubulin

Each centrosome contains how many centrioles?

2

What happens in prophase?

• chromatin fibers condense

• Mitotic spindle begins to form

• Centrosomes begin to move away from each other

What happens in prometaphase?

• nuclear envelope fragments

• Microtubules invade the nuclear area

• A kinetchore microtubule attaches to each sister chromatid

• Nonkinetochore microtubules interact with those of the opposite spindle

What is the longest stage in mitosis?

Metaphase. Lasts for 20 minutes.

What happens in metaphase?

• Chromosomes align on the metaphase plate

• Kinetochore microtubules are attached to the kinetochore on each sister chromatid

What is the shortest stage in mitosis?

Anaphase. It lasts just a few minutes.

What happens in anaphase?

• cohesions proteins are cleaved by the enzyme, separase, and the sister chromatids separate as kinetochore microtubules shorten

• Once separated, each chromatid becomes a full-fledged chromsome

• Cells elongate as the Nonkinetochore microtubules lengthen

What happens in telophase?

• nuclear envelope forms

• Mitosis - divisor of one nuclear into 2 nuclei is complete

What happens in cytokinesis?

• division of cytoplasm is usually well underway by late telophase

• Daughter cells appear shortly after the end of mitosis

How does cleavage of an animal cell occur?

Actin microfilaments interact with myosin molecules causing the ring to contract. Cleavage furrow depends until the parent cell is pinched in 2. Generate 2 completely separate cells (daughter cells). Each daughter cell has its own nucleus and a share of cytoskeleton, organelles, and other subcellular structures.

Eukaryotic Cell Cycle

Timing and rate of cell division in plants and animals is crucial to normal growth, development and maintenance

How often do skin cells divide?

Frequently

How often do liver cells divide?

Only when a need arises (ex. To repair a wound)

How often do muscle and nerve cells divide?

Never

How often do cancer cells divide?

Uncontrollably

What controls the cell cycle?

Cell cycle control system

Cell cycle control system

Cyclically operating set of molecules in the cell that triggers and coordinates events in the cell cycle

How does the control system proceed?

On its own. It’s driven by a built-in clock. It’s like an automatic washing machine.

Checkpoint in cell cycle control system

A cell cycle control point where “stop” and “go” signals can regulate the cycle

What question does the G1 checkpoint have?

Is DNA damaged?

What question does the G2 checkpoint have?

Is all DNA replicated?

What question does the M checkpoint have?

Are all chromosomes attached to the spindle?

What is the most important checkpoint?

The G1 checkpoint

If a cell receives the go-ahead signal at the G1 checkpoint, what will happen?

It will enter G1, S, G2, M, and divide

If a cell does not receive the go-ahead signal, what will happen?

It will exit the cell cycle and switch to a non-dividing state called G0 phase

What phase are most cells in the human body in?

G0

Anaphase will not begin until all chromsomes are what?

Are properly attached to the spindle at the metaphase plate

The regulatory protein complex protein is only activated when?

When all the chromsomes are properly attached to the spindle

Separase

An enzyme that cleaves cohesions and allows the sister chromatids to separate

Why is the M checkpoint so important?

T makes sure that cells do not end up with missing or extra chromsomes