5.1 THE CELL CYCLE AND MITOSISName:

Date:

Block:

(Refer to pp. 150 – 161 of BC Science 9)

  • The body must replacecells regularly.

Ex. You shed millions of skins cells every hour.

  • In order to produce new cells for replacement or growth, cells divide. Cell division is controlled by specialized proteins in the nucleus.

CELL REPLACEMENT AND DEVELOPMENT

  • From the time life begins as a fertilized egg, cells divide as you continue to grow.
  • Even though growth slows after puberty, cells continue to divide to replace worn out cells, such as:

Stomach liningcells (every 2 days),

Intestinal liningcells (every 3 days),

Red bloodcells (every 120 days) and

livercells (every 200 days).

  • braincells divide every 30 – 50 years!
  • musclecells and nervecells do not usually continue to divide in an adult, but they continue to carry out the functions necessary for survival.

THE CELL CYCLE

  • The life of a cell is divided into three stages known as the cell cycle.
  • Interphase
  • Mitosis
  • Cytokinesis

INTERPHASE

  • Cell carries out normal functions and prepare for division
  • thelongestcell cycle stage (90%)
  • divided into 3phases:
  1. Growth and preparation

cell increases in sizeand makes the proteinsand molecules necessary for the cell to function.

some organelles begin to duplicate

  1. Replication

second phase of interphase

DNAcopies itself:replication

Replication involves several steps:

  1. Enzymes unzips the DNA molecule, separating the sides
  2. New bases pair with the bases on the original DNA
  3. Two new identical DNA molecules are produced.

ensures that newly formed cells will have an identicalcopy of the genetic information contained in the original DNA molecule.

  1. Continued Growth and preparation

At the end of interphase

Cell continues to grow and make proteins in preparation for mitosis and cytokinesis

During this phase, DNA is in the form of loosely coiled chromatinso that it can be copied into RNA.

RNA carries the code for the production of proteinsneeded for cell division.

Organelles, such as mitochondria and chloroplasts are also duplicated

  1. MITOSIS
  • nucleuscontents divided into two equal parts and two daughter nucleiare formed.
  • theshorteststage of the cell cycle.
  • As the nucleus prepares to divide, replicated DNA from interphase joins together to form sisterchromatidswhich are joined by a centromere
  • Mitosis occurs in 4stages:
  • prophase(Early and Late)
  • metaphase
  • anaphase
  • telophase
  1. Early Prophase **PREPARE**

Replicated chromosomes coil up into X-shaped chromosomes

nucleolusdisappears

nuclear membranebreaks down

spindle fibresform

stretch from centrioles in animal cells

in animal cells, the centrioles begin to move.

Late Prophase

spindle fibresfinish forming

spindle fibresattach to the centromereof each chromosome

nuclear membranedisappears

  1. Metaphase **MIDDLE**

Spindle fibrespull X-shaped chromosomes,causing them to line upacross the middle (equator) of the cell.

  1. Anaphase **AWAY**

Spindle fibrespull sister chromatidsto opposite polesof the cell

once separated, each sister chromatid is considered to be a chromosome

  1. Telophase**TA-DA or THE END**

finale stage of mitosis

one complete set of chromosomesis now at each pole ofthe cell

spindle fibresdisappear

anuclearmembrane forms around each separated set of chromosomes.

a nucleolusappears within each nucleus

now there are two nucleiin one cell so it is ready to divide (cytokinesis)

CYTOKINESIS

  • separationof the two nuclei and cell contents into two daughtercells(identical to the original parent cell).
  • the finalstage of the cell cycle
  • In animal cells, the cell membranepinches together to divide the cell’s cytoplasm and organelles.
  • In plant cells, a cell plateforms along the centre of the cell to divide the two daughter cells.

CHECKPOINTS IN THE CELL CYCLE

  • There are checkpoints within the cell cycle in which activities within the cell are monitored and controlled by specific proteins
  • These proteins then send messages to the nucleuswhich then instructs the cell to divide or not.
  • Checkpoints in the cell cycle will prevent division if:

There are not enough nutrients to support cell growth

The DNA has not been replicated

The DNA is damaged