DNA molecules = Chromatids? Chromosomes only exist during mitosis.

Gamete = sperm and egg cells.

Cell Cycle

G0 Gap Zero
Quiesent Phase An interphase stage

Normal cell functions.

G1 Gap 1 An interphase stage

Cell Growth

S Synthesis An interphase stage

DNA Replication

G2 Gap 2 An interphase stage

Cell Growth

M Mitosis

Cell Division

Gap 1

Normal cellular functions

• Grows larger
• Makes Cytoplasm
• Makes organelles
• Makes proteins

Synthesis

DNA Replication

Gap 2

Continues to grow.

• Makes proteins specifically for mitosis.
  • sa. Condensing proteins and the spindle aparatus.
• Organelles duplicate

Gap Zero

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.

Liver prefers regeneration over stability (more chance for errors to occur during replication). Neurons preserves information over repair capacity.

Decisions Cells Make

• Divide - is a stem cell.
• Differentiate - specialize its function, doesn't divide, becomes a specific cell. A child of a stem cell.
• Die

What tells cells to divide

• Growth factors
  • Ligand (proteins) that signal to "grow and divide".
• Cell-Cell Contact
  • Crowded cells stop dividing.
• Nutrient Availability
  • ?
• Hormones
  • ?

Wound Healing

Platelets that arrive at the wound site and release growth factors.

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.