Chapter 12 The Cell Cycle and Mitosis

The Key Roles of Cell Division Cell division functions in reproduction, growth, and repair Unicellular organisms (ex. Amoeba) will divide to reproduce entire organisms Cell division also will allows a multicellular organism to develop from a single cell

The Key Roles of Cell Division DNA is passed from one generation of cells to the next without dilution. -cell duplicates it DNA - moves the 2 copies to opposite ends of the cell - and then splits into 2 daughter cells

The Key Roles of Cell Division

Concept 12.1 Cell Division distributes identical sets of chromosomes to daughter cells A cell’s genetic material is called its genome - prokaryote = single long DNA strand - eukaryote = number of DNA molecules

Concept 12.1 The replication and distribution of DNA is manageable because it is packaged into chromosomes - the nuclei in human somatic cells contain 46 chromosomes - the nuclei in human gametes contains 23 chromosomes

Concept 12.1

The DNA-protein complex is called the chromatin and is a long thin fiber. After the chromatin is duplicated, it will prepare for division. It will condense and coil up to form chromosomes.

Concept 12.1 Each duplicated chromosome has 2 sister chromatids. - each contains identical copies of the chromosome’s DNA molecule - they are connected together at the centromere

Concept µmChromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

Concept 12.2 The mitotic phase alternates with interphase in the cell cycle The mitotic (M) phase (mitosis and cytokenesis) is the shortest part of the cell cycle. Interphase accounts for about 90% of the cell cycle.

Concept 12.2 Interphase can be divided into subphases - G 1 (first gap), S (synthesis), and G 2 (second gap) - during subphases, cell grows by producing proteins and organelles - chromosomes are only duplicated during the S phase

Concept 12.2 S (DNA synthesis) MITOTIC (M) PHASE Mitosis Cytokinesis G1G1 G2G2

Concept 12.2 Mitosis is broken down into 4 subphases - prophase, metaphase, anaphase, and telophase Prophase - chromatin coil into chromosomes - nucleoli disappears - spindles begin to appear as centrosomes move to the poles of the cell

Concept 12.2 The cell moves into prometaphase - nuclear envelope fragments - kinetochore attaches to forming spindles - cell prepares for metaphase

Concept 12.2

Metaphase - centrosomes area at opposite poles - chromosomes are on equator of cell, the metaphase plate Anaphase - begins when the centromeres of the chromosomes separate

Concept sister chromatids begin moving toward opposite poles - by the end, the poles have equal sets of chromosomes Telophase - daughter nuclei form at the poles - nuclear envelope begins to reform

Concept chromosomes become less tightly coiled -Cytokenesis, the division of the cytoplasm, follows immediately

Concept 12.2

The mitotic spindle distributes chromosomes to the daughter cells -during interphase, the single centrosome replicates to form 2 centrosomes; during the early stage of mitosis, they separate and move toward opposite poles helping the spindle fibers

Concept 12.2

Cytokenesis divides the cytoplasm - in animals, cytokenesis occurs by the formation of a cleavage furrow - in plants the cleavage cannot occur because of the cell wall; vesicles will move to the center of the cell to form the cell plate.

Concept 12.2 Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM)(b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate Daughter cells New cell wall 1 µm

Concept 12.2 The origins of mitosis are believed to be from bacterial organisms of cell reproduction - prokaryotes reproduce by binary fission (“dividing in half”) - prokaryotes do not have mitotic spindles; instead, once the DNA replicates, the copies of the region move apart rapidly

Concept 12.2 Origin of replication Two copies of origin E. coli cell Bacterial chromosome Plasma membrane Cell wall Origin

Concept 12.3 The cell cycle is driven by specific chemical signals present in the cytoplasm Sequential events of the cell cycle are directed by a distinct cell cycle control system - driven by a built in clock - the cell cycle is regulated at certain checkpoints by internal and external controls

Concept 12.3

The checkpoint is a control point where stop and go-ahead signals can regulate the cycle - kinases, a type of regulatory protein that activate or inactivate other proteins, give the signals for G 1 and G 2 checkpoints Concept 12.3

To be active the kinase must be attached to a cyclin (kinases become cyclin- dependent kinases or Cdks) - the activity of Cdks rises and falls with changes in the [cyclin] - first called MPF = “maturation promoting factor” or “M-phase- promoting factor”

Concept when cyclins accumulate during G 2, MPF initiates mitosis Internal and external cues help regulate the cell cycle - for cells to divide a growth factor, a specific protein, is released to stimulate cell division

Concept 12.3

The discovery of growth factors has led us to understand density-dependent inhibition of cell division - when a cell population reaches a certain density, the amount of growth factors and nutrients needed for division becomes insufficient for increased growth

Concept 12.3 Most animal cells also exhibit anchorage dependence - to divide, the cell must be attached to a substratum (ex. inside of a culture jar or extracellular matrix of a tissue)

Concept 12.3 Anchorage dependence Density-dependent inhibition (a) Normal mammalian cells (b) Cancer cells 25 µm

Concept 12.3

Cancer cells have escaped from cell cycle controls - they do not respond to the control mechanisms - they do not stop dividing when growth factors are depleted; don’t respond to density dependant inhibition

Concept if cancer cells stop dividing, it is at random points and not at the checkpoints Caner begins when a single cell tissue undergoes a transformation - if the cell evades destruction by the immune system it may form a tumor

Concept if the abnormal cell remain at the original site, it is called a benign tumor - a malignant tumor becomes invasive enough to impair the functions of organs - the spread of cancer cells from the original site is called metastasis

Concept 12.3