Cell Cycle and Mitosis

Cell Cycle

•Only a Eukaryotic Process•Unicellular: asexual reproduction•Multicellular: growth and repair•Rate may differ depending upon:• Type of cell•Age of cell• External factors that affect cells

Type of Cell•The function of the cell, type of tissue often determine the rate of it’s cell cycle•Fastest include: intestinal, skin, bone marrow, hair•Slowest: bone, liver, kidney

Age of Cell/Organism• In multicelled organisms the rate of the cell

cycle also depends upon the age of the cells• “Age” is a factor of cell division and cell death• Young: cell division > cell death = growth• Middle: cell division = cell death• Old: cell division< cell death

Why can’t organisms live forever?Cells cannot grow and divide indefinitely. At the end of chromosomes are small ‘caps’ called telomeres that help keep the

DNA from uncoiling. Every time the DNA is replicated a piece of the telemere is lost. When the telomere is gone the DNA can no longer replicate and the cell dies.

Interestingly, telomeres are found in the cells of multicelled organisms, but, not unicellular…what would happen if there were?

External Factors• Factors outside of the cell or organism can affect the cell cycle. • Cells are exposed to many environmental factors

that can directly influence the control and regulation of the cell cycle• Examples include: Drugs, Alcohol, Smoke, Radiation,

Toxins, Viruses• All of these substances disrupt the cell cycle and can

cause cells to divide uncontrollably forming the tumors associated with many cancers and so are referred to as carcinogens

Genetic Factors

• Some mutations to genes can result in changes to the cell cycle.• The BRCA1 gene can cause breast cancer• Progeria is a genetic disorder marked by rapid aging

The Cell Cycle•Occurs in 3 phases• Interphase: preparation for division• Mitosis: nuclear division• Cytokinesis: cell division

INTERPHASE

• Use to be referred to as the cell’s ‘resting phase’, however, actually a lot of activity is occurring during this time.• Approximately 80% of cell’ life is spent in interphase• Marked by 3 distinct stages:• Gap 1 (G1 ) follows cytokinesis, time of cell growth,

replication of organelles (1st Checkpoint)

• Synthesis(S) Replication of DNA in preparation for division• Gap 2: (G2 )growth slows, cell enzymes check DNA (2nd Checkpoint)

MITOSIS

• M Phase: Process that divides the nucleus with replicated DNA• Approximately 15% of cell’s life cycle• 4 Stages• PROPHASE: “before”; replicated DNA uncoils• METAPHASE: “after”; chromosomes align (3rd Checkpoint)

• ANAPHASE: “opposite”; chromosomes separate• TELOPHASE: “across”; chromosomes recoil

G0

• Resting phase where certain cells leave the cell cycle and stop dividing• Some cells, once formed, remain in G0 for the life

of the organism. These cells cannot be replaced once damaged. Examples: Nerve and Muscle

• Some cells enter an extended period of G0 , however, can be replaced overtime.

Examples: Liver and Kidney

CYTOKINESIS• Division of the cell• Means “to move the cell”• Approximately 5% of cell’s life• Process differs in Heterotrophs(Animals)

Autotrophs(Plants) due to presence of cell wallHETEROTROPHS AUTOTROPHS

Cell membrane indents at cleavage furrow and cell is ‘pinched’ in half

The cell divides from the center with the formation of cell plate(cellulose) and cell is ‘cut’ in half

Cell Cycle

Checkpoint 1: Is cell getting to large ?

Checkpoint 2: Has DNA replicated correctly

Checkpoint 3Are chromosomes aligned? cytokinesis

NECK TIE