What is the difference between mitosis and meiosis? When will each occur?

The cell cycle Objectives Outcomes 3: Identify stages of the cell cycle. 5: Describe the stages of the cell cycle. 7: Explain the consequences of the cell cycle not being properly controlled. Key terms: cell cycle, interphase, mitosis, cytokinesis.

The Cell Cycle, Mitosis, and Meiosis New cells can only be made when existing cells divide. All cells have the ability to divide – but some cells lose this ability. Intestinal epithelial lining - replaced every five days by cell division Liver cells - divide only to repair damage, and then stop dividing Bone marrow cells - divide repeatedly to produce red and white blood cells Meristem cells (tips of roots and shoots) – divide to produce new growth Cambium cells (plants) – divide to form vascular tissue (xylem and phloem) These are relatively unspecialised cells. Specialised cells often go through the cell cycle only once - the nerve cells, once formed cannot divide again. In eukaryotic cells, there are two types of cell division – mitosis and meiosis. Mitosis is used to produce new cells for growth and repair. Meiosis is used in the formation of gametes only. In prokaryotes (bacteria), cell division does not involve mitosis or meiosis – bacteria reproduce asexually, by a type of cell division termed by binary fission. Yeasts reproduce asexually by budding. The cell cycle is the process that all body cells from multicellular organisms use to grow and divide. The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells.

Key terms: cell cycle, interphase, mitosis, cytokinesis. The cell cycle The cell cycle describes the sequence of cell growth and cell division. It includes: Interphase cell growth synthesis of organelles DNA copying and checking of genetic information Mitosis chromosomes divide Cytokinesis cytoplasm divided between the daughter cells Key terms: cell cycle, interphase, mitosis, cytokinesis.

Key terms: cell cycle, interphase, mitosis, cytokinesis. The cell cycle The cell cycle describes the events during one complete cycle of division, they are represented in the chart: Key terms: cell cycle, interphase, mitosis, cytokinesis.

Key terms: cell cycle, interphase, mitosis, cytokinesis. The cell cycle Key terms: cell cycle, interphase, mitosis, cytokinesis.

G1 S phase G2 Mitosis (M) INTERPHASE Period of cell growth; cell prepares cell for cell division (mitosis); genetic material (DNA) is copied and checked for errors – prevents mutations being passed on No apparent activity New organelles and proteins are made Divided into three phases (G1, S, and G2 phase) G1 S phase CELL CYCLE G2 MITOSIS (M) Process by which a nucleus divides into two – each with an identical set of chromosomes – the nuclei are genetically identical Four phases – prophase, metaphase, anaphase, and telophase Followed by cytokinesis – division of the cell into two genetically identical daughter cells Mitosis (M) Two daughter cells – genetically identical

The Cell Cycle Eukaryotic cells have a well- defined cell cycle of growth and division (mitosis). The length of the cycle varies (from minutes to hours, or , longer) ending with mitosis. Each phase of the cycle involves specific activities, and varies in length from one organism to another. The cell cycle can be divided into stages: G1 (“growth phase” 1) - Cells prepare for DNA replication S (“synthesis”) - DNA replication occurs G2 (“growth phase” 2)- Short gap before mitosis M Mitosis (relatively short) Affected by availability of nutrients Between each stage the cell “checks” to see if it is OK to proceed to the next stage. “Proof-reading” enzymes check the copied chromosomes for mistakes (mutations) – the cell may kill itself (undergo “suicide”) if harmful mutations are – a process known as apoptosis. Bacterial cells complete the cycle every 20 minutes. Muscle cells never complete the cycle – “terminal differentiation” Uncontrolled and repeated cell division by mitosis results in cancer (tumours)

No apparent observable activity The Cell Cycle Cytokinesis – cell divides into two DNA content = normal G2 - Second growth phase - short Short gap before mitosis (cell division) Cytoskeleton of cell breaks down and the protein microtubule components begin to reassemble into spindle fibres – required for cell division DNA content = 40 G1 - First growth phase – longest phase Protein synthesis – cell “grows” Most organelles produced Volume of cytoplasm increases Cell differentiation (switching on or off of genes) Length depends on internal and external factors If cell is not going to divide again it remains in this phase DNA content = 20 (arbitary) S - Replication phase DNA replication – this must occur if mitosis is to take place The cell enters this phase only if cell division is to follow DNA content = double G1 + S + G2 = INTERPHASE No apparent observable activity

The cell cycle Task Outcomes Create a poster outlining the cell cycle. Leave some space for when we fully look at mitosis in the next lesson. Outcomes 3: Identify stages of the cell cycle. 5: Describe the stages of the cell cycle. 7: Explain the consequences of the cell cycle not being properly controlled. Key terms: cell cycle, interphase, mitosis, cytokinesis.

The cell cycle What happens when the cell cycle is not controlled: Cancer Outcomes 3: Identify stages of the cell cycle. 5: Describe the stages of the cell cycle. 7: Explain the consequences of the cell cycle not being properly controlled. Key terms: cell cycle, interphase, mitosis, cytokinesis.

Key terms: cell cycle, interphase, mitosis, cytokinesis. The cell cycle Key terms: cell cycle, interphase, mitosis, cytokinesis.