IB BIO - U1 L5 - Cell Cycle and Cancer.

Interphase

Interphase

90% of a cells lifetime

3 parts of interphase

• G₁

  • Growth, normal job.

• S

  • DNA replication.

• G₂

  • Growth, prepares to divide.

DNA initially appears as ____________________________

Chromatin

• Thread-like DNA

• Not visible under microscope

Mitosis (M Phase)

Mitosis is the division of the nucleus’ contents.

Phases of Mitosis.

1. Prophase.

2. Metaphase.

3. Anaphase.

4. Telophase.

Chromosomes and Chromatids.

• DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division (via supercoiling).

• Able to be easily segregated however is inaccessible to transcription machinery.

Prophase

• DNA supercoils and chromosomes condense (visible under microscope)

• Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)

• Paired centrosomes move to opposite poles of cell and form microtubule spindle fibres

• Nuclear membrane and nucleus dissolve

Metaphase

• Microtubule spindle fibres from both centromeres connect to centromere of each chromosome

• Microtubule depolymerization causes spindle fibres to shorten in length and contract

• Causes chromosomes to align along centre of cell (equatorial plane or metaphase plate)

Anaphase

• Continued contraction of spindle fibres causes genetically identical sister chromatids to separate

• Once chromatids separate, they are each considered an individual chromosome in their own right

• Genetically identical chromosomes move to opposite poles.

Telophase

• Once two chromosome sets arrive at poles, spindle fibres dissolve

• Chromosomes decondense (not visible under microscope)

• Nuclear membranes reform around each chromosome set

• Cytokinesis occurs concurrently, splitting the cell in two

Cytokinesis.

Cytoplasm division.

Cytoplasm in Plant Cells.

Carbohydrate rich vesicles form at centre- fuse to form cell plate- centrifugal (separation originates in centre and moves laterally).

Cytoplasm in Animal Cells.

Microfilaments constrict to form cleavage furrow- centripetal (separation occurs from outside and moves towards centre).

Mitotic Index.

• Mitotic Index is determined by analysing micrographs and counting relative number of mitotic cells versus non-dividing cells

• Mitotic index is a measure of proliferation status of a cell population (ie. proportion of dividing cells)

• Ratio of number of cells in mitosis and total number of cells

• Important for predicting response of cancer cells to chemo Cells undergoing mitosis will lack a clearly defined nucleus and possess visibly condensed chromosomes

Cyclins

• Cyclins are a family of regulatory proteins that control progression of cell cycle

• Cyclins activate Cyclin Dependent Kinases (CDKs), which control cell cycle processes through phosphorylation (it will stick the phosphate group on itself onto the protein- turns it on)

• Cyclin levels would be lower in interphase because it doesn't need proteins to accomplish cell division, that is needed during the M-phase

Mutasis

Agent that changes genetic material of an organism (either acts on DNA or replicative machinery)

Ex. viruses, radiation, reactive oxygen species (ROS), and metals (arsenic)

Metastasis

Spread of cancer from one location (primary tumour) to another forming a secondary tumour .

If it doesn't affect other cells, the tumour is benign, if it does, it is malignant.

Oncogene

Gene that has potential to cause cancer.

How can an oncogene cause cancer?

When a proto-oncogene is mutated or subjected to increased expression it becomes a cancer-causing oncogene.

What do Tumour suppressor genes do?

Tumour suppressor genes prevent cancer.

Cell Mutation and Cancer.

If a cell is mutated it doesn’t always mean it will cause cancer, it has to hit a region of a genome that is responsible for regulating the cell cycle (oncogene)

Oncogene and Cell Cycle.

Oncogene regulates the cell cycle, mutation in that region can be cancerous, now it will go faster and make potential mistakes, too fast, uncontrolled and unregulated.

The 2nd region is . . .

Tumour suppressor genes

Smoking and Cancer

Cigarette smoke contains over 4,000 chemical compounds, over 60 of which are known to be carcinogenic 90% of lung cancers attributable to tobacco use Not only lung cancer, but any other type of cancer relating to the digestive tract and respiratory tract