Why do cells divide?

One called organisms

1. For asexual reproduction

Multi-celled organisms

1. For growth and development

   • from fertilization to adult

2. For repair and replacement

   • Replace cells or repair an injury

Asexual Cell Division

• cells reproduce to for genetically identical daughter cells

• Exact copy

Prokaryotic Cell Division

• Binary fission

• Steps of binary fission

  1. Cell copies its DNA

  2. Cell grows

  3. Cell splits into two

Eukaryotic Cell Division

• the cell cycle

  1. Interphase (G1, S, and G2 phases)

  2. M phase (mitosis)

  3. Cytokinesis

Interphase (time between mitosis)

• Cell spends 90% of its life in interphase

• G1: growth 1

  • Cell growth

  • Some cells never leave (living normally on its own

• S: synthesis

  • DNA is copied

  • Only cells that know they are going to divide

• G2: growth 2

  • Cell growth

  • Preparation

  • Makes sure there is enough of everything for 2 cells

DNA Terms

• Chromatin- unwound in the nucleus

• Chromosome:

  • Sister chromatids- 2 identical halves of a chromosome

  • Centromere- central region holding together 2 chromatids

Mitotic Phase

• After interphase

• 4 phases

  1. prophase (set up)

  2. Metaphase

  3. Anaphase

  4. Telophase (clean up)

Prophase

• Nucleus breaks down

• Chromatin condenses into chromosomes

• Spindle fibers begin to form in cytoplasm

• Centrosomes (centrioles) move away from each other

Metaphase

• Centrosomes are at opposite poles

• Chromosomes line up on metaphase plate

• Mitotic spindle (made of spindle fibers) is fully formed

Anaphase

• Sister chromatids separate at centromere

• Chromatids move towards opposite poles (pulled by spindle fibers)

Telophase

• Nucleus begins to form in each new cell

• Nuclear envelopes reform

• Chromosomes unwind to become chromatin

Cytokineses

• Division of cytoplasm

• Happens with telophase

• Animal cells:

  • Cleavage furrow forms

  • Pinches the cell into 2

• Plant cells:

  • Cell plate forms

  • Divides the cell in 2

Controlling Cell Division

• Internal factors

  • Regulatory proteins

• External factors

  • Growth factors

  • Density of cells

    • If cells become too dense in the area, they will stop dividing

  • Anchorage dependence

    • Some cells must be anchored to a specific surface

Cancer

• Tumor:

  • A mass of cells within an otherwise normal tissue

• Benign tumor

  • Considered non-cancerous cells

• Malignant tumor

  • Cancerous

  • Can be invasive and impure the function of one or more organs

• Metastasis

  • The spread of cancer cells beyond their original site

  1. A tumor grows from a singular cancer cell

  2. Cancer cells invade neighboring tissue

  3. Cancer cells spread through lymph and blood vessels to other parts of the body

Cell Differentiation

• the process by which cells become specialized

  • Stem cells receive signals

    • unspecialized cells that can give rise to one or more types of specialized cells

    • Cord blood, embryonic cells, adult stem cells, bone marrow

    • Totipotent cells- each cell can develop into a new individual (cells of an embryo 1-3 days)

    • Pluripotent cells- each cell can form any cell type (cells of blastocyst 5-14 days)

    • Multipotent- cells differentiate and can form a number of tissue types (adult stem cells and bone marrow)