cell biology and dna

2 major cell cycle phases:

• interphase: long growth period between cell division.

  • g1 (1st gap): primary growth phase, very active growth.

  • s (synthesis): synthesis of the dna between cell division.

  • g2 (2nd gap): final growth phase before cell division.

• mitotic phase: cell division.

  • mitosis: nuclear division. duplicated dna is distributed between 2 daughter nuclei.

  • cytokinesis: cytoplasm divides. 2 new daughter cells are formed.

• complete cycle takes 18-24 hours.

• mitosis and cytokinesis only take 1 hour of the complete cell cycle.

• many cells enter g0 (non-dividing state) either temporarily or permanently,

  • neurons and osteocytes enter g0 after adolescenec.

dna replication: the process of copying dna during cell division.

• steps:

  • dna zips and ‘uncoils’ pulling apart the two strands.

  • a new complementary strand of dna is built apart each strand, using appropriate base pairings.

• dna polymerase: major dna replicating enzyme

• mutation is an alteration in the dna sometimes results from errors during replication.

  • may be caused by physical or chemical forces.

  • somatic cell mutation: may affect tissue functions or cause cancer but not heritable.

cell reproduction regulation.

• internal surveillance and control mechanism: several key checkpoints where ‘go ahead’ signals must be received in order to progress to the next phase.

  • g1, g2, m checkpoints.

• outside influences can modify cell cycle:

  • hormones

  • growth factors

  • presence of other cells