Chapter 8 Cell Cycle 1 In interphase there are 3 steps G1 S and G2 G1 phase is the growth and development phase for the cell GO is the phase where cells go to sleep and take a break it s also where nondividing cells stay There is a restriction point right before S phase and it s the point that if a cell passes it then it s dedicating itself to a complete full cycle It is the point of no return S phase is when the cell synthesizes and duplicates making a copy G2 is another growth phase 2 M phase has prophase metaphase anaphase telophase and cytokinesis M phase or mitosis is when body cells somatic cells divide Prophase is when the nuclear membrane breaks down chromosomes become visible and microtubules begin to make spindle fibers Chromosomes are unwrapped around the protein histone Metaphase is when proteins in the kinetochores pull the chromosomes to the metaphase plate Sister chromatids are pulled to opposite poles by their centromere during anaphase A nuclear membrane forms around the new nucleus at each pole chromatin condenses and centrioles move during telophase Cytokinesis is the separation of the two cells in plant cells a cleavage burrow forms 3 DNA replication is the process of replicating DNA so each daughter cell can have identical DNA A group of enzymes and other proteins bind to the DNA at the replication origin forming a replisome at the replication fork where the leading and lagging strands separate Helicase first unzips the DNA double helix and the DNA polymerase adds in the matching nucleotides while ligase glues the hydrogen bonds back together DNA polymerase only adds nucleotides in the 5 to 3 direction The RNA primer acts as a starter since DNA polymerase needs something to attach to in the beginning but later on another enzyme replace the RNA primer with DNA The leading strand is continuous but on the lagging strand this process is discontinuous Mutations are a change of the sequence in DNA and cells that are mutagenic mean that they have a mutation Excision repair is when the damaged region of the cell is removed DNA polymerase adds in the correct matching nucleotides and ligase seals it Kinase is always in the cell but the amount of cyclin in the cell changes so when cyclin and kinase are bonded together they activate enzymes by adding a phosphate on The purpose of the cyclin kinase bond is to activate enzymes 4 The difference between the leading and lagging strand is that the leading strand is continuous while the laggings strand lags and is discontinuous The lagging strand does this because the two strands are antiparallel so one goes in the correct way and the other strand goes the opposite way But both strands go in the 5 to 3 direction Since the lagging strand is discontinuous it has to stop go back and then have the DNA polymerase fill in the nucleotides in fragments called Okazaki fragments 5 The cell takes many measures to prevent against mutations One is having many checkpoints throughout the cell cycle By having checkpoints the cell cycle is stopped periodically to make sure there are no damaged or mutated cells continuing to divide Cell cycle arrest s when the cell cycle gets stopped because there is a damaged or mutated cell that has to get fixed In excision repair the DNA polymerase proofreads double checks the DNA if it is mutated Proto oncogenes tell the cell to start dividing and tumor suppressors help the cell to stop dividing Tumor suppressors are sometimes found in checkpoints but cancer cells have trouble at these checkpoints because cancer cells continually divide and a rapid pace Chapter 9 Protein Synthesis Creation of a Protein 1 DNA is double stranded has the bases adenine thymine guanine and cytosine has deoxyribose as a sugar and is only found in the nucleus RNA is single stranded has the bases adenine uracil guanine and cytosine has ribose as a sugar and is found in the nucleus and in the cytoplasm DNA holds the instructions for building proteins while ribosomes build the proteins In order to create a protein there are two parts transcription and translation 2 The instructions for making a protein are transferred from a gene to RNA molecules in a process called transcription Helicase first unwinds and separates DNA RNA adds in complementary RNA nucleotides going down Ligase repairs the bonds and seals the backbone RNA then leaves the DNA strand as mRNA and the 2 DNA strands reunite The goal of this process is to make a copy of DNA for mRNA DNA cannot leave the nucleus because it s the original copy so that s why we make a copy of DNA to mRNA messenger RNA Initiation is the stage where it all starts the promoter sequence starts off transcription with the RNA polymerase binding to a strand of DNA by initiation factors attaching it Elongation then happens which is the growing and lengthening stage RNA polymerase adds RNA nucleotides to the growing RNA strand based on pairs Termination is the last stage when the terminator region tells the RNA polymerase to stop adding nucleotides and to dis attach This process creates a primary transcript the first draft or original copy After this RNA processing occurs in the nucleus which is when a guanine cap and a poly A tail is added because it protects enzymes from degrading the RNA In prokaryotes RNA can only last a few minutes before it is destroyed because of its short poly A tail but in eukaryotes RNA can last days even weeks because of its long poly A tail The guanine cap also helps the mRNA attach to a ribosome and the ribosome will eventually make a protein Once the cap and tail are added RNA splicing occurs which is when the introns regions that don t code for a protein are removed and the exons regions that code for a protein are added 3 Translation is when cells use two different types of RNA to read the instructions on the RNA strand and put together the amino acids that make up the protein The purpose of translation is to turn mRNA into a protein mRNA is a sequence of nucleotides and bases every 3 bases are a codon and codes for one amino acid Amino acids make up a protein which is a long polypeptide chain An anticodon is the strand that matched with a codon and has matching bases to it Every start codon codes for the amino acid AUG methionine The ribosome on mRNA first reads the codon and matches it to the tRNA transfer RNA with the opposite nucleotides The order is very important because it the name of the amino acids building the certain protein As the ribosome moves down it