Transcript Cell division - HRSBSTAFF Home Page

ASSESSMENT STATEMENTS
2.5.1
Outline the stages in the cell cycle, including interphase (G1, S, G2),
mitosis, and cytokinesis
2.5.2
State that tumors (cancers) are the result of uncontrolled cell division and
that these can occur in any organ or tissue
2.5.3
State that interphase is an active period in the life of a cell when many
metabolic reactions occur, including protein synthesis, DNA replication,
and an increase in the number of mitochondria and/or chloroplasts
2.5.4
Describe the events that occur in the four phases of mitosis (prophase,
metaphase, anaphase, and telophase)
2.5.5
Explain how mitosis produces two genetically identical nuclei
2.5.6
State that growth, embryonic development, tissue repair, and asexual
reproduction involve mitosis
THE CELL CYCLE
The cell cycle consists of three main phases:
1. Interphase (G1, S, G2)
 interphase involves the cells increase in size and doubling of cytoplasmic
components and chromosomes
2. Mitosis
 Produces two cells (daughter cells) with the same genetic material
3. Cytokinesis
 Physical division of the cells
Note: We study the cell cycle in discrete stages but they occur in a continuum.
RATE OF CELL DIVISION
Different types of cells divide at different rates.
Some types of cells like bone marrow reproduce rapidly (1 hour)
Other extreme certain cells like nerve and muscle cells never reproduce once they
mature (stay in interphase)
Other cells divide only when needed for repair (liver cells)
Importance in any cell to maintain balance = homeostasis
If one kind of cell begins to reproduce too rapidly, the normal organization will be
disrupted. This is what causes cancer (multiple cells uncontrollably dividing to
form a tumour)
REGULATION OF CELL CYCLE
Scientists are still trying to figure it out
One known is cell-to-cell contact
Once cells enter DNA replication (S phase) they are committed to complete the cell
cycle meaning division
Scientists are studying this point in interphase to determine what triggers the cell to
undergo DNA replication
Their focus has been on
 chemical controls like proteins
 Genes required for cell division
WHY RESEARCH THE CELL CYCLE?
Mitosis is the process behind growth of organisms, development of embryos, tissue
repair, and asexual reproduction.
This knowledge may be used to replace cells damaged by injury or disease
Help live longer lives
Control the spread of cancers
INTERPHASE
Longest and most variable part of the cell cycle
In G1 phase the major event is growth of the cell. At the beginning of G1 the cell is the
smallest it will ever be.
In S phase the main activity is replication of the DNA of the cell, the chromosomes.
This phase is sometimes referred to as the synthesis phase.
G2 is a second growth phase, where the cell grows and makes preparations for
mitosis. During this phase, organelles may increase in number, DNA begins to
condense from chromatin to chromosomes, and microtubules may begin to form.
DNA PACKAGING
During G2 the chromatin (elongated DNA and histones) begins to condense. This is
accomplished via a process called supercoiling.
First the DNA wraps around histones to produce nucleosomes.
The nucleosomes are further wrapped into a solenoid.
Solenoids group together in looped domains.
Looped domains coil together to produce the chromosome.
http://www.rikenresearch.riken.jp/eng/frontline/6485
DNA NAMING
Before replication, in the S phase, chromosomes are composed of one molecule of
DNA.
After replication, the chromosome includes two molecules of DNA. These two
identical molecules are held together by the centromere, and each molecule is
referred to as a chromatid. Together they are called sister chromatids.
During mitosis the sister chromatids separate, then they do each is called a
chromosome and his its own centromere.
MITOSIS
Mitosis is made up of 4 phases:
 Prophase - condensation of chromosomes, microtubule organization
 Metaphase - microtubule attachment and chromosomal organization
 Anaphase - separation of chromosomes
 Telophase - chromosomal decondensation and cell separation
Using page 41 of the textbook draw a diagram of each stage in your
notes, and provide a short summary of what is going on.
CYTOKINESIS
Happens after nuclear division
In animal cells  inward pinching of fluid plasma membrane to form cleavage furrows
In plant cells  due to the relatively firm cell wall, a cell plate is formed. The cell plate
occurs midway between the two poles of the cell and moves outward toward the
side of the cell from a central region.