The lectures for this week focus on the cell cycle in eukaryotic cells. A cell must carry out an orderly
sequence of events in which it duplicates its contents and then divides in two. We will consider three
major questions:
1. How do cells duplicate their contents – including the chromosomes, which carry the genetic
information?
2. How do they partition the duplicated contents and split in two?
3. How do they coordinate all the steps and machinery required for these two processes?
We have already talked about the first question (DNA replication – Chapters 5 and 6 and lectures 4 and
5). So, for these lectures we will address questions 2 and 3.
Lecture 22 (April 26): Overview, The Cell Cycle Control System and G1 Phase (Chapter 18)
The eukaryotic cell cycle consists of several distinct phases. In interphase, the cell grows and the nuclear
DNA is replicated; in M phase, the nucleus divides (mitosis) followed by the cytoplasm (cytokinesis).
In most cases, a cell duplicates its materials (genome, macromolecules, organelles) prior to division –
otherwise, it would get smaller and smaller with each round of division.
1. Cell growth and chromosome duplication
2. Chromosome segregation
3. Cell Division
,1. The cell cycle occurs in four phases. What are each of these phases? In general, what occurs in
each phase?
M Phase (1 hr in mammalian cell)
- Mitosis – nuclear division
- Cytokinesis – cytoplasmic division, cell splits in 2
Interphase
- G1 phase – gap phase , cell grows, monitors internal/external state and decides whether to go
to next phase
- S phase – DNA replication / synthesis
- G2 phase – cell grows monitors internal/external state and decides whether to go to next phase
- During all of interphase cell continues to transcribe genes, synthesize proteins, grow
, 2. What is the cell-cycle control system? What “questions” does the cell ask itself and when? Why
is this control system so important?
Cell cycle control system – complex network of regulatory proteins – ensures that cell cycle- DNA
replication, mitosis, cell growth, occur in sequence, and that each process completed before next one
begins
- Regulated by feedback from process being performed
- Control System Regulates cell cycle AT 3 TRANSITION POINTS
o G1 to S Phase
§ Is environment favorable for DNA replication ?
• Enough nutrients, favorable extracellular environment
o G2 to M phase
§ Is all DNA replicated, Is all DNA undamaged
o M phase to G1
§ Are chromosomes attached to mitotic spindle ?
- Control system important because interruption or delay could be disastrous – transition from
G1 to S phase important for cell proliferation, signals stimulate cell proliferation when more
cells needed and block when not needed
o Malfunctions – excessive cell division can result in cancer
sequence of events in which it duplicates its contents and then divides in two. We will consider three
major questions:
1. How do cells duplicate their contents – including the chromosomes, which carry the genetic
information?
2. How do they partition the duplicated contents and split in two?
3. How do they coordinate all the steps and machinery required for these two processes?
We have already talked about the first question (DNA replication – Chapters 5 and 6 and lectures 4 and
5). So, for these lectures we will address questions 2 and 3.
Lecture 22 (April 26): Overview, The Cell Cycle Control System and G1 Phase (Chapter 18)
The eukaryotic cell cycle consists of several distinct phases. In interphase, the cell grows and the nuclear
DNA is replicated; in M phase, the nucleus divides (mitosis) followed by the cytoplasm (cytokinesis).
In most cases, a cell duplicates its materials (genome, macromolecules, organelles) prior to division –
otherwise, it would get smaller and smaller with each round of division.
1. Cell growth and chromosome duplication
2. Chromosome segregation
3. Cell Division
,1. The cell cycle occurs in four phases. What are each of these phases? In general, what occurs in
each phase?
M Phase (1 hr in mammalian cell)
- Mitosis – nuclear division
- Cytokinesis – cytoplasmic division, cell splits in 2
Interphase
- G1 phase – gap phase , cell grows, monitors internal/external state and decides whether to go
to next phase
- S phase – DNA replication / synthesis
- G2 phase – cell grows monitors internal/external state and decides whether to go to next phase
- During all of interphase cell continues to transcribe genes, synthesize proteins, grow
, 2. What is the cell-cycle control system? What “questions” does the cell ask itself and when? Why
is this control system so important?
Cell cycle control system – complex network of regulatory proteins – ensures that cell cycle- DNA
replication, mitosis, cell growth, occur in sequence, and that each process completed before next one
begins
- Regulated by feedback from process being performed
- Control System Regulates cell cycle AT 3 TRANSITION POINTS
o G1 to S Phase
§ Is environment favorable for DNA replication ?
• Enough nutrients, favorable extracellular environment
o G2 to M phase
§ Is all DNA replicated, Is all DNA undamaged
o M phase to G1
§ Are chromosomes attached to mitotic spindle ?
- Control system important because interruption or delay could be disastrous – transition from
G1 to S phase important for cell proliferation, signals stimulate cell proliferation when more
cells needed and block when not needed
o Malfunctions – excessive cell division can result in cancer
