Cell Cycle and Mitosis Overview

Cell Cycle

• Continuity of life depends on cell reproduction (cell division)
• Unicellular organisms reproduce the entire organism through cell division
• Multicellular organisms depend on cell division for development (from a fertilized cell), growth, and repair
• A video titled "Cell Division & Cell Cycle" is available online
• The video runs for 5:34 minutes

Genetic Identical Daughter Cells

• Most cell division results in genetically identical daughter cells (Mitosis)
• Meiosis is an exception, it produces sperm and egg cells.
• All DNA in a cell comprises the genome
• The genome is made up of a single DNA molecule in prokaryotic cells, or several DNA molecules in eukaryotic cells
• DNA molecules are packaged into chromosomes
• Each eukaryotic species has a specific number of chromosomes per cell nucleus
• Somatic cells (non-reproductive cells) have two sets of chromosomes
• Gametes (reproductive cells, sperm/eggs) have half as many chromosomes as somatic cells – one set

Distribution of Chromosomes

• Before cell division, DNA is replicated and chromosomes condense
• Each duplicated chromosome has two sister chromatids joined together
• The centromere is the narrow region of a duplicated chromosome, where the two chromatids are most closely attached

During Cell Division

• During mitosis, the two sister chromatids of each duplicated chromosome separate and move into two nuclei
• Once separated, the sister chromatids are called chromosomes

The Cell Cycle

• The cell cycle consists of Interphase and Mitotic (M) Phase
• Interphase, which takes up about 90% of the cell cycle, includes three subphases:
  • G1 phase ("first gap")
  • S phase ("synthesis") – DNA replication
  • G2 phase ("second gap")
• The cell grows throughout all phases of Interphase, but DNA is only duplicated during S phase
• The mitotic (M) phase includes Mitosis and Cytokinesis

Eukaryotic Cell Division

• Eukaryotic cell division includes Mitosis (division of the genetic material in the nucleus) and Cytokinesis (division of the cytoplasm).
• Mitosis is divided into five phases.
• The stages of mitosis are; Prophase, Prometaphase, Metaphase, Anaphase, Telophase.

P²MAT

• A mnemonic device for the five stages of mitosis: Prophase, Metaphase, Anaphase, Telophase. Each stage has distinct characteristics. A video demonstrating the five stages of mitosis is available (title and details provided in the provided text)

Mitosis in Animal Cells

• The nuclear envelope breaks down before metaphase and re-forms during telophase
• Centrosomes and the mitotic spindle are stained yellow
• DNA is stained blue/purple

The Mitotic Spindle

• The spindle is a microtubule structure that controls chromosome movement during mitosis
• Mitotic Spindle is composed of centrosomes, spindle microtubules, and asters (radial arrays of short microtubules from the centrosome).
• The centrosome replicates during interphase, forming two centrosomes.
• Two centrosomes migrate to opposite ends of the cell.
• Some spindle microtubules attach to the kinetochores, protein complexes associated with centromeres, of chromosomes.
• During prometaphase, the chromosomes begin to move.
• Each centrosome consists of two centrioles, each being an array of 9 microtubules

Mitosis Continued

• In anaphase, sister chromatids separate and move along the kinetochore microtubules to opposite ends of the cell.
• Nonkinetochore microtubules overlap and push against each other, elongating the cell.
• In telophase, genetically identical daughter nuclei form at opposite ends of the cell
• Cytokinesis begins during anaphase or telophase.
• The spindle disassembles.

Cytokinesis

• In animal cells, cytokinesis occurs by cleavage, forming a cleavage furrow.
• In plant cells, a cell plate forms during cytokinesis.

BIO 1300 Schedule

• This section contains a schedule for a BIO 1300 course. The dates and activities are provided in the image.

Binary Fission in Bacteria

• Prokaryotes (bacteria and archaea) reproduce asexually by binary fission - a cell division.
• Chromosome replicates at the origin of replication
• Two daughter chromosomes migrate apart.
• The plasma membrane pinches inward, dividing the cell into two.

Eukaryotic Cell Cycle Control

• Eukaryotic cell cycle frequency varies by cell type (e.g., frequency is different for neurons vs. skin cells).
• Cell cycle is driven by specific chemical signals present in the cytoplasm.
• The cell cycle is regulated by both internal and external controls
• Signals such as growth factors can trigger these controls
• A cell cycle control system is like a cell's clock, including checkpoints where the cycle pauses until a go-ahead signal is received
• G1 checkpoint is the most important for many cells.

Control of Cell Cycle

• If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues the cycle (S, G2 and M phases) to divide.
• If the cell does not get a go-ahead signal the cell cycle stops and enters G0 phase. A non-dividing state.

Loss of Cell Cycle Controls in Cancer Cells

• Cancer cells escape normal cell cycle controls
• Cancer cells don't need growth factors, sometimes creating their own
• Normal cells can be converted to cancerous cells through a process called transformation.
• Cancer cells that aren't eliminated form tumors (masses of abnormal cells).
• Benign tumors remain at the original site. Malignant tumors invade surrounding tissues and can metastasize (moving to other body parts).

Cancerous Cells

• Often have variations in size and shape.
• Have nuclei larger and darker than normal
• Abnormal chromosome numbers in a disorganized pattern.

p53 Gene

• The p53 gene is a tumor suppressor gene.
• In cancer cells, p53 is nonfunctional.
• Cancer cells undergo repeated cell division without stopping at the G1 checkpoint.
• Normal p53 functions to monitor DNA, destroy cells with irreparable DNA damage
• Abnormal p53 leads to uncontrolled cell division leading to cancerous growth