G1: The gap between M (mitosis) and S.

S: DNA synthesis occurs in this period

G2: Gap between S and M

The membrane that separates the contents of the nucleus (mostly DNA) from the cytosol

1. Growing cells divide once with each doubling of mass and size.

2. DNA must replicate only once with each cell division.

Once DNA replication has started, it must be completed.

3. If DNA is damaged it must be repaired before replication

4. A differentiated cell must not resume replication or cell division.

Immortal Cell

• Cells that continue to divide forever
• Can be a cell line
• Can be transformed

Cell line

• Can be immortal
• Show most of the growth characteristics of the orginal cells

Transformed Cell

• No longer show normal growth control and have many other alterations
• Transformation can be induced by a cancer-causing tumor virus or a chemical carcinogen

Characteristics of transformed cells

1. Decreased adhesion to other cells
2. Loss of contact inhibition
3. Decreased anchorage dependance
4. Decreased requirement for serum growth factors
5. May cause tumors if injected into appropriate host animal
6. Altered apprearance, altered gene expression, altered metabolism

Which of the following is NOT a characteristic of transformed cells?

A.  Altered appearance

B.  Altered gene expression

C.  Altered metabolism

D.  Increased adhesion to other cells

D.  Increased adhesion to other cells

Transformed cells decrease adhesion to other cells

Which of the following is NOT a transformed cell characteristic?

A.  Will grow without adhering to a surface

B.  Can lead to metastasis

C.  Increase of contact inhibition

D.  Can cause tumors

C. Increase of contact inhibition

Transformed cells lose contact inhibition

True or False:

RNA and protein synthesis occurs at each phase in the cell cycle, while DNA synthesis occurs at S only.

True

True or False:

Variation in cell cycle time is mainly due to variations in length of M phase.

False

Variation in cell cycle time is mainly due to variations in length of G1.

The other phases are fairly constant.

Chromosome

A single large molecule of DNA

Microtubules

• Part of the structural network (the cytoskeleton) within the cell
• They are capable of growing and shrinking in order to generate force including force needed to separate duplicated chromosomes during cell division

Centriole

Chromatid

True or False:

Cells maintain the same average size over many generations.

MPF

M-phase-promoting factor/ maturation promoting factor

• Is needed for entry into the M phase
• Consists of cyclin-dependent protein kinase (Cdk1) and the regulator protein cyclin B.

Which of the following is NOT associated with entry into M phase?

A.  MPF (M-phase-promoting factor/ maturation promoting factor)

B.  cyclin-dependent protein kinase (Cdk1)

C.  Regulator protein cyclin B

D.  All the above are associated with entry into M phase

Which of the following is true about Cdk1?

A.  It is a protein kinase

B.  It is present throughout the cell cycle

C.  It is only active when complexed with cyclin

D. All of the above

Which of the following is true about Cyclin B?

A. It accumulates until the end of interphase.

B.  It does not degrade

C.  It is a protein kinase

D.  It rapidly degrades

D. It rapidly degrades

Cyclin B accumulates until the middle of mitosis. Then it is rapidly degrades, so that mitosis will not occur again until the next cell cycle. It is a regulator protein

Histones

Tumor suppressor gene Rb

• Retinoblastoma protein
• A critical cell cycle regulator

True or False

If DNA is damaged, it must be repaired before replication.

True

p53 is the sensor of DNA damage and prevents entry into S phase until the DNA is repaired.

p53 is:

A. Is absent in tumor causing cancers.

B. A tumor suppressor protein.

C. Will allow cell apoptosis when damage is "too" much to fix.

D. All of the above

Most cancer treatments work by damaging DNA and stimulating apoptosis. If suppressor protein p53 is absent:

A. The tumor cells are very responsive to such treatments.

B. The tumor cells are often unresponsive to such treatments.

C. The tumor cells are sometimes responsive to such treatments.

B. The tumor cells are often unresponsive.