1.6 Cell Division

1.6 Cell Division Nature of Science: serendipity & scientific discoveries: The discovery of cyclins was accidental! Understandings: Mitosis is division of the nucleus into 2 genetically identical daughter nuclei. Chromosomes condense by supercoiling during mitosis. Cytokinesis occurs after mitosis & is different in plant & animal cells. Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus & cytoplasm. Cyclins are involved in the control of the cell cycle. Mutagens, oncogenes & metastasis are involved in the development of primary & secondary tumours. Application: The correlation between smoking & incidence of cancers. Skills: Identification of phases of mitosis in cells viewed with a microscope. Determination of a mitotic index from a micrograph.

Understanding: Mitosis is division of the nucleus into 2 genetically identical daughter nuclei. Mitosis = division of nucleus Cytokinesis = division of cell Mitosis produces 2 identical nuclei DNA replication must happen before mitosis Purposes of mitosis: Embryonic development Growth of tissues Repair of tissues Asexual reproduction

Understanding: Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus & cytoplasm. Cell cycle = series of events in a cell leading to its division and duplication (replication) that produces 2 daughter cells. (In cells without a nucleus (prokaryotic), the cell cycle occurs via a process termed binary fission.) 2 main phases of cell cycle: Interphase Cell division Activities happening during interphase: In the nucleus: DNA replication In the cytoplasm: transcription & translation (protein synthesis), cell respiration, mitochondria & chloroplasts replicate to increase in number, plants make sugar (cellulose) & add to their cell walls Cell growth

Cell Cycle model

Understanding: Chromo’s condense by supercoiling during mitosis Chromosome = linear DNA & associated proteins in eukaryotes Condense = pack chromosome into shorter structure (must fit 50,000 μm DNA into 5μm cell) Supercoil = repeatedly coiling DNA around proteins to make it shorter Histones = proteins that DNA winds around (help supercoil DNA & regulate genes)

Chromosome structure

Eukaryotic Chromosome structure

Prokaryotic chromosome structure

Location of the centromere

Single-stranded vs Double-stranded chromo’s

Skill: Identification of phases of mitosis in cells viewed with a microscope Prophase Metaphase Anaphase Telophase

Skill: Determination of a mitotic index from a micrograph

Understanding: Cytokinesis occurs after mitosis & is different in plant & animal cells Cytokinesis = division of cell Begins during last part of telophase

Understanding: Cyclins are involved in the control of the cell cycle Proteins 4 main types in human cells Control cell cycle so cells only divide when needed

Nature of Science: Serendipity & scientific discoveries: the discovery of cyclins was accidental! Sir Tim Hunt Studying protein synthesis in sea urchins Accidentally discovered cyclins when he noticed a protein increasing & decreasing at regular intervals & times around mitosis Awarded Nobel Prize for Physiology in 2001 Serendipity = a happy & unexpected discovery made by accident; a pleasant surprise! https://www.youtube.com/watch?v=WGFQMUDkISE

Understanding: Mutagens, oncogenes & metastasis are involved in the development of primary & secondary tumours Tumours (tumors) = abnormal groups of cells Benign = non-life threatening; do not spread Malignant = life-threatening; tend to spread Cancer = the disease associated with tumor-growth Carcinogens = agents that cause cancer Carcinoma = malignant tumor Mutagens = agents that cause gene mutations (which can cause cancer) Mutations = random changes to base sequence of genes Oncogenes = genes that control cell cycle, so if they mutate uncontrolled cell division can occur Oncology = study of cancer Metastasis = spreading of a tumor; movement of cells from primary tumor to secondary tumors in other parts of body

Application: Correlation between smoking & incidence of cancers. Correlation = relationship between 2 variable factors Positive = when one factor increases (or decreases), so does the other Negative = when one factor increases, the other decreases There is a positive correlation between cigarette smoking and the death rate due to cancer. Correlation does not necessarily imply causation! Positive correlation does not prove that smoking causes cancer. However, 20 chemicals cause cancer in lab animals or humans, and may be 40 more carcinogens in cigs.