Summary Chapter 5 The cell cycle

Chapter 5 The cell cycle
Introduction
Genetic information is on chromosomes and chromosomes
are made of DNA
We all have 23 chromosomes form mother and 23
chromosomes from father

4 phases of the cell cycle (1 cell cycle = ± 1 day)
1. G1-phase; Prepare for DNA synthesis (grow phase 1) –
takes 6 hours
 Helicase opens up the double stranded helix
 Accumulate (verzamelen) ingredients
(nucleotides) to make new DNA
 Growing and expanding the cells as well as
making new organelles and components that are
needed in the further daughter cells

2. S- phase; DNA replication – takes 6 hours
 Make identical copies of all the DNA (each chromosome)
 DNA polymerase add new DNA
 Leading and lagging strand are formed
 Duplicated and original chromosomes are kept
together by protein rings  X-shaped

3. G2 phase; Prepare for mitosis (grow phase 2) – takes
more than 6 hours
 Chcked if all the DNA is duplicated in the right way
 Check if there is no DNA damage. In this phase when there is damage
on one arm of the X-shaped form it can be repaired by using the
information on the other arm that can be used as template to repair the
DNA. When cells are divided the template is not available anymore.
The repair process is able to hold the cell cycle and
can keep the cell in G2 for long time.

4. M-phase; mitosis (PMATI) – takes 1 hour (because the
compaction of DNA is dangerous for cells)
 Prophase; the chromosomes condense (they
become visible under microscope) – the
membranes around the nucleus dissolves – the
mitotic spindle starts to form and centrioles starts to
move
 Prometaphase; membranes around the nucleus are fully removed –
chromones are starting to bind to mitotic spindle (microtubules)
 Metaphase; the duplicated and original chromosomes
line up in the center – centrioles are at opposite poles
and all chromones are bind to mitotic spindle fibers
(microtubules)
 Anafase; the duplicated and original chromosomes are
pulled apart by mitotic spindle. They are now called
separate chromosomes or sister chromatids.

,  Telophase and cytokinesis; at each pole a full set of chromosomes
gather together -- membranes are formed around each set of
chromosomes – the single cell then pinches in the middle to form 2
separate daughter cells
 Interfase

Interphase: G1, S and G2 phase
Mitosis: M-phase

The cell division comes with 2 problems:
1. Make identical copies of all the DNA (each chromosome)  S-phase
2. Distribute those equal copies over 2 daughter cells  M-phase

Coordination of passage through different
phases
The coordination of passage through the
different phases is regulated by cyclins and
their associated cyclin-dependent kinases
(CDKs). The pairing of cyclins to CDKs is
very specific.

Cyclin D: production in G1 and activated by
extracellular signals like growth factors
Cyclin E: production in G1 and S
Cyclin A: production in G1 and S
Cyclin B: production in G2

 G1 phase:
Cyclin D together with Cdk 4 and 6 drives progression through G1 phase.

 From G1 to S-phase:
G1 checkpoint (restriction point (R)) – from this point
the cell cannot go back but have to finished the cell
cycle – leads to arrest in response to DNA damage
ensuring that DNA damage is not replicated during S-
phase

Transition governed by Cdk 2. Cyclin E binds to Cdk 2

 S phase:
Cyclin A together with Cdk2 drives progression through
S phase

 S-phase to G2:
Transition governed by Cdk 2. Cyclin A binds to Cdk 2

 G2 phase:
Cyclin A together with Cdk2 drives progression through S phase

 From G2 to mitosis phase: