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Topic 1: Cells Cell Division Why divide? Chromosomes Growth Each DNA strand is condensed into a chromosome Replacement of infectious cells structure Cell differentiation All sexually reproducing animals have pairs of Replacement of dead cells chromosomes. One set of each pair comes from each parent The Cell Cycle - ordered set of events that cumulates in cell growth and division into two daughter cells Interphase Standard condition of cell, spends most of its time here o Growth 1 Active stage Growing DNA transcribed Proteins Synthesized Organelles Replicates o Synthesis DNA Replicated 2 sister chromatids form from each chromosome o Growth 2 Growth till mitosis Mitochondria divide Chloroplasts divide in plants Mitosis Division of the nucleus into two genetically identical daughter nuclei Division of diploid eukaryotic nucleus o Prophase DNA supercoils Chromosomes become visible Nuclear membrane breaks down Centrosomes migrate to poles o Metaphase Chromosomes line up centromeres on equator cell Centrosomes form spindles o Anaphase Spindles grip centromeres and chromosomes migrate to poles o Telophase Nuclear membranes reform Chromosomes disperse Cytokinesis begins Cytokinesis o Division of the cytoplasm to form two daughter cells Occur during or after Telophase Cell splits to form two new cells each containing a full set of chromosomes identical to parent Capable of doing all parent cell can Animal: Plant Plasma membrane is pulled Vesicles move to equator and form a tubular inwards around equator of cell structure Creates a furrow accomplished Two layers of membrane are formed which by using a contractile ring of develop into membrane Vesicles bring pectin and other materials that are actin and myosin deposited by exocytosis, forming lamella and cell wall. Topic 1: Cells Cell Division Cell Cycle Checkpoints G1-S, G2-M, Exit M Cell asses conditions (favourable for division) If not favourable (eg. DNA damaged) p53 protein stops cycle and cell dies) Absent checkpoint protein can lead to mutant or absent cells which can divide uncontrollably, causing cancer. Cyclins Proteins that bind to enzymes called cyclin dependent kinases. Become active and attach to phosphate groups on other proteins to become active in different stages of the cell cycle. Cyclins have to reach threshold concentration to progress to the next stage. Cancer: Mutagens o Physical or chemical agent that changes genetic material o Causes replication error o Ionizing radiation, UV radiation, deaminating agents, viruses, bacteria Oncogenes o Potential to cause cancer o Prevent apoptosis (programmed cell death) and lead to proliferation o Promote cell cycle in various ways o Tumour suppressor genes inhibit cell cycle in various ways o Normally regulated in coordination with organisms growth plan o Either mutates, can loose control and become oncogene Metastasis o Movement of cells o Primary tumour to set us secondary tumours in other parts of the body