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Human Biology Notes- the cell cycle and cancer

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Human Biology Growth, Development and Disease The Developing Cell DNA Structure DNA is made up of small units called nucleotides, each containing a phosphate, deoxyribose and a nitrogenous base. There are two types of bases, Purine and Pyrimidine. There two bases of each type, Adenine and Guanine are Purine and Cytosine and Thymine are Pyrimidine. Complementary base pairing means Adenine can only pair with Thymine, and Cytosine with Guanine. The phosphates and sugars form a bond through condensation reactions, called a phosphodiester bond, which links all the nucleotides together making the sugar-phosphate backbone. This makes a polynucleotide chain, with H bonds between the bases. Replication DNA replicates through semi-conservative replication. The enzyme DNA helicase breaks the H bonds between the bases, unzipping the molecule. Newly synthesised nucleotides pair with the exposed bases through complementary base pairing. The enzyme DNA polymerase joins the nucleotides together by forming phosphodiester bonds between the phosphates and sugars, rebuilding the sugar-phosphate backbone. The Cell Cycle Interphase This is the stage of the cycle the cell spends most of its time in. ...read more.


Telophase A nuclear envelope forms around the chromosomes at either end of the cell. The chromosomes then uncoil. Cytokinesis This is when the spindle fibres, after Mitosis, form a draw string at the centre of the cell, just inside the plasma membrane, and this pinches inwards and fuses. The cytoplasm is split equally, along with the cell organelles. Apoptosis This is programmed cell suicide. This is important for cells that are infected with a virus and may be a threat to other cells, or cells with damaged DNA, that may become cancerous. It is also in normal development, such as the shedding of the lining of the uterus during menstruation, and the formation of synapses between neurones in the brain. The tumour suppressor gene TP53 codes for the protein p53 to be made. This protein inhibits mitosis and leads the cell into undergoing apoptosis. At first the enzymes in the cell are released from their vesicles, breaking down the cells exoskeleton. The cell then shrinks, and blebs form on the membrane. ...read more.


This means it has had more time to accumulate damage to their DNA. Heredity Some people may inherit genes that make them predisposed to particular gene mutations resulting in cancer. Detecting Cancer X-rays X-rays are shot through the body, and the denser cancerous tissue will show up as white, as they absorb more. Mammography Low dose X-rays are passed through the breast tissue and cancerous tissue will show up as white, as they absorb more. CT Scans X-ray images are taken from all angles and 3D images are built up of the inside of the body. Thermography IR-sensitive cameras produce thermographs of the area of tissue. Tumours will come up as brighter yellow due to it being hotter as its respiring more. Ultrasound Sounds waves are sent from a hand held probe, and build up and image with reflected waves. These are good with tumours in softer tissue. MRI A machine measures the magnetic alignment of hydrogen atoms in the body, showing tumours standing out due to their high amounts of water. PET Gamma ray emitted by radioactive substances injected into the patient, shows which cells are more metabolically active. Breast Cancer ...read more.

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