DNA Molecules

aka. Chromatids

Chromosomes

Only exist during mitosis.

Gamete

Sperm and egg cells.

Cell Cycle

G0 Gap Zero
Quiesent Phase An interphase stage

Cell performs its normal functions.

Cell exits the cell cycle.

• Not dividing, not dead.

• Either temporary or permanent.

• If temp, can return to G1, cell cycle. sa. Liver cell.

• If perm, cannot return to cell cycle (sa. neurons).

Stem cells = cells responsible for dividing.

Neurons preserves information over repair capacity.

Liver prefers regeneration over stability (more chance for errors to occur during replication).

G1 Gap 1 An interphase stage

Cell performs its normal functions.

Cell starts to grow.

• Grows larger

• Makes Cytoplasm

• Makes organelles

• Makes proteins

S Synthesis An interphase stage

Cell performs its normal functions.

Cell replicates its DNA.

G2 Gap 2 An interphase stage

Cell performs its normal functions.

Cell continues to grow.

• Organelles duplicate.

• Makes proteins specifically for mitosis.
  • sa. Condensing proteins and the spindle apparatus.

M Mitosis

Cell starts to divide.

Decisions Cells Make

Divide

Is a stem cell.

Cell exists to divide and create new cells.

Differentiate

Doesn't divide.

A child of a stem cell.

Cell specializes its function and becomes a specific cell.

Die

Cell exits life.

What tells cells to divide

Growth Factors

Ligand (proteins) that signal to "grow and divide".

When injured: A protein called “Platelet-Derived Growth Factor (PDGF)” arrives at wound sites to signal cell division for repair.

Cell-Cell Contact

Crowded cells usually stop dividing.

Nutrient Availability

Are there enough resources to make new cells?

Hormones

Like estrogen triggering uterine lining growth.

Internal Signals - is the cell ready?

• Act as checkpoints / self checks.
• Cell is large enough?
• Cell has enough nutrients and energy?
• DNA is replicated correctly?
• Chromosomes attaches to spindle fibers?
• if not, cell may die, pause and repair, or exit the cell cycle.

Gap 1 Checkpoint

• Either proceeds with the division or exits the cycle and performs normal cell functions.
• Is large enough?
• Has growth factors?
• Is DNA damaged?
• Has cell enough nutrients?

Outcomes

• Checks out, moves to S phase.
• problem, cell cycle pauses for repair by proteins.
• severe problem, cell dies.

Protein p53

Is made when damaged dna is detected, repairs damaged dna, stops the cell cycle at G1, activated repair genes.

S-Checkpoint

• Makes sure replication is proceeding correctly.
• That nucleotides (dna building blocks) are available.
• Outcomes: Pauses, slows down cell cycle, repairs damage using proteins or dies.

G2 Checkpoint

• Was dna replication completed and undamaged?
• Is cell large enough?
• Are proteins ready for mitosis?
• Outcomes: same

M-Checkpoint

• Makes sure every chromosome has a spindle fiber attached correctly.

Aneuplody

Mistake! Wrong number of chromosomes in daughter cells.

Proto-ancogenes

Proteins that signal a cell to go through with the cell cycle.

Tumor Suppressors

Proteins made by cells that inhibit progress through the cell cycle.

Cancer

Errors in the cell cycle genes get compounded over many generations. Each generation, additional mutations accumulate rapidly.

How Checkpoints Break

• Create too many ancogenes.
• Lose tumor suppressors.

Cancer is usually both

If cell enters G1, it will replicate. If not, it enters G0 and differentiates.

Chemotherapy targets S phase. Checkpoint Inhibitor drugs.