BIOL1020 Week 4 : Cell Division and Cell Cycle Control

Cell Division

Process that results in genetically identical daughter cells

Mitosis

Occurs in somatic cells (2 sets of chromosomes)

Meiosis

Occurs in gametes/sex cells (1 set of chromosomes)_

Binary Fission

Asexual reproduction, occurs in prokaryotes

Eukaryotic Cell Cycle

Consists of 2 main phases

1) Interphase

2) Mitotic Phase

Interphase

3 Parts of Interphase

G1: normal cell metabolism ‘resting state’

S: DNA replication, this occurs prior to the cell dividing

G2: Preparation for cell division

The time a cell spends during interphase is dependant on the cells, interphase cells are metabolically active

Mitotic Phase

2 parts of the Mitotic Phase

M: division of the nucleus, consists of 5 phases, prophase, prometaphase, metaphase, anaphase, telophase

Cytokinesis: the division of the cytoplasm

G0 Phase

Cell hibernation, do not divide

Prophase

First Step of Cell Replication

The chromosomes condense and centrosomes move to the opposite sides of the nucleus, initiating the formation of the mitotic spindle

Prometaphase

Second Step of Cell Replication

The nuclear envelope breaks down and the condensed chromosomes attach onto the mitotic spindle

Both sister chromatids of each chromosome attach to the spindle at a specialized region called the kinetochore

Metaphase

Third Step of Cell Replication

The mitotic spindle moves the condensed chromosomes to the middle of the cell

Anaphase

Fourth Step of Cell Replication

The microtubules pull the sister chromatids apart

As the microtubules contract, the chromatids are pulled into opposite sides of the cell

Telophase

Fifth and Final Step of Cell Replication

The two separate sets of chromosomes each start to form their own new nuclei

Cell splits into 2 via Cytokinesis

Cytokinesis

The split of a cell into two daughter cells

Actin filaments congregate near metaphase plate to form a ring around the inside of a cell

Pinching action separates cytoplasm into two separate cells

Cell Checkpoints

Ensures all requirements are satisfied before the continuation of the cell cycle and does not result in defective cells

Checkpoints are regulated by differing concentrations of cyclin, Cyclin-Dependant Kinase (CPK), and Maturation-Promoting Factors (MPF)

G1 Checkpoint

First Checkpoint

Cell decides whether replication is necessary, dependant on cell size, nutrients, and growth factors

G2 Checkpoint

Second Checkpoint

Ensures that DNA replication occurs properly, prevents the cell from entering mitosis when DNA is damaged

M Checkpoint

Third and last Checkpoint

Occurs during the Metaphase stage and ensures that the sister chromatids are properly attached to the spindle microtubules.

Cancer cause

Caused by the loss of cell cycle control and the uncontrolled proliferation of cells. Mutations thar result in oncogenes and defective tumour suppressor genes can lead to cancer

Oncogenes

When genes that actively promote cell division (proto-oncogenes), are not turned off at the right times, they become oncogenes and lead to cancer

Can occur in several ways, such as translocation or transportation (gene moved to a new locus under new controls), gene amplification (multiple copies of the gene) and point mutation, within the control element or in the gene

Tumour Suppression Genes

Normally inhibit cell division, when it stops working it can also lead to cancer

Common Suppressor gene is p53, when mutated leads to increased cell division