The Cell Cycle PDF

16.1 – The Cell Cycle The Cell Cycle Body cells(somatic cells) go through a life cycle called the cell cycle Depending on the type of cell, each cell’s cycle can be very different Organization of Genetic Material All genetic info is contained in DNA DNA is found in the chromoso...

16.1 – The Cell Cycle The Cell Cycle Body cells(somatic cells) go through a life cycle called the cell cycle Depending on the type of cell, each cell’s cycle can be very different Organization of Genetic Material All genetic info is contained in DNA DNA is found in the chromosomes of a cell Chromosomes are found in the nucleus Organization of Genetic Material One cell has about 3m of DNA that needs to fit into a nucleus that is only 5µm DNA is wrapped around histone proteins The histones form a bead like structure to produce chromatin (long intertwined strands of DNA) Chromatin forms loops and scaffolds which form a condensed chromosome Chromosome Number Each species of organisms have different chromosome numbers E.g. Humans have 46 chromosomes arranged into 22 pairs of homologous chromosomes called autosomes, and 2 sex chromosomes (XX or XY) Chimpanzees have 48 chromosomes Homologous Chromosomes Carry same genes (areas of DNA containing specific genetic info) at the same locus (location) Look similar, similar size, same position of centromere Similar banding They carry different forms of the same gene (alleles) Ploidy If a cell contains pairs of homologous chromosomes, like ours, they are diploid (2n) If a cell contains unpaired chromosomes, they are haploid (n) Some organisms are polyploid and contain sets of more than two chromosomes (3n, 4n, etc) n may be different in different organisms as well In humans n=23, so 2n=46 total chromosomes 2: how many copies of each chromosome 46: total number of chromosomes The Karyotype The particular set of chromosomes that an individual has is represented in a karyotype Done by stopping the cell cycle chemically at a point when the condensed chromosomes are more clearly visible under a light microscope Chromosomes are stained, photographed, then rearranged in order against new The Cell Cycle Composed of 2 main stages: 1. Interphase 2. Cell Division Interphase Made up of 3 stages: 1. G1 Phase (Gap/Growth) 2. S Phase (Synthesis) 3. G2 Phase (Growth) Cells spend most of their life in Interphase, because they need to prepare for division Interphase: G1 Doubling of cellular organelles (mitochondria, ribosomes, etc.) Cell grows in size Cell accumulates structures that will be needed to synthesize more DNA Interphase: S DNA gets replicated (doubled) In humans: 46 single stranded (unduplicated) chromosomes in a somatic cell get replicated to form 46 double stranded (duplicated) chromosomes These double-stranded chromosomes are made up of sister chromatids Interphase: G2 This is a second growth phase for cells DNA replication in S phase has consumed a lot of energy, so G2 lets the cell replenish its energy to prepare for cell division The cell manufactures proteins and structures required for cell division Cell Division (M Phase) 2 main processes in cell division: Mitosis: division of genetic material and contents of the nucleus Cytokinesis: division of the cytoplasm and organelles into 2 separate cells Forms 2 new daughter cells with the same genetic information as the parent cell