L2.pdf

Length of DNA Each human cell has a 2 meter long DNA It contains 3 billion base pairs (each DNA strand has 1.5 billion nucleotides) It contains around 30000 genes  Organization of DNA DNA is organized into chromatin ( the chromosomal material) that c...

Length of DNA Each human cell has a 2 meter long DNA It contains 3 billion base pairs (each DNA strand has 1.5 billion nucleotides) It contains around 30000 genes  Organization of DNA DNA is organized into chromatin ( the chromosomal material) that consists of: - Long double stranded DNA molecules - Histones to condense the DNA in the form of nucleosomes - Non – histone proteins including enzymes of replication and transcription Nucleosomes are connected with filaments of DNA  The first level is: A 4nm DNA filament (which is DNA stripped of its histones). In the normal, unstripped chromosome, the double stranded DNA is wrapped around sets of 8 histones to form a 10 nm filament. These sets of 8 histones are separated by spacer regions of 4 nm DNA filament (double stranded DNA) and Histone 1. The sets of 8 histones wrapped by DNA are called "nucleosomes"  The next level of coiling produces the 30 nm nucleoprotein fibres Further looping of these nucleoprotein fibers around a protein forms the individual chromosomes Levels of coiling in the chromosome Human chromosomes  Chromatin is organized into chromosomes. Each chromosome is formed of identical chromatids. The point where the two chromatids meet is called a centromere. The ends of a chromatid are called telomeres Shortening of telomeres has been associated with malignancy and aging Telomerase, an enzyme for telomeres synthesis has become a target for cancer drug therapy.  Telomeres and Cellular Aging Telomeres are TTAGGG repeats of around 12000 base pairs. It is estimated that human telomeres lose about 100 base pairs (16 TTAGGG repeats) from their telomeric DNA at each mitosis.  Replicative senescence (growing old) phenomenon Cells removed from a newborn infant and placed in culture will go on to divide almost 100 times. Well before the end, however, their rate of mitosis declines. This is called replicative senecenes. Evidence that length of telomeres is important for cell division Some cells do not undergo replicative senescence: 1. Cells of the germline. 2. Unicellular eukaryotes. 3. Some cancer cells.  It turns out that these cells are able to maintain the length of their telomeres. They do so with the aid of an enzyme telomerase Thus telomerase is a reverse transcriptase; synthesizing DNA from an in built RNA template Human chromosomes cont. Human gene structure  The human genome The nuclear genome The mitochondrial genome  Animation link for organization of DNA (copy and paste on google) https://www.google.com/search?q=organization+of+dna+into+ chromosomes+videos+youtube&oq=organization+of+DNA+int o+chromosomes+vd&gs_lcrp=EgZjaHJvbWUqCQgDECEYChigAT IGCAAQRRg5MgkIARAhGAoYoAEyCQgCECEYChigATIJCAMQIRgK GKABMgcIBBAhGI8CMgcIBRAhGI8CMgcIBhAhGI8C0gEMMTgw NzQ1N2owajE1qAIAsAIA&sourceid=chrome&ie=UTF- 8#fpstate=ive&vld=cid:860a128c,vid:gbSIBhFwQ4s,st:0