Genetics Oct 3, 5, and 7
Genetics Oct 3, 5, and 7 BIOL 309
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This 11 page Class Notes was uploaded by Katlyn Burkitt on Friday October 7, 2016. The Class Notes belongs to BIOL 309 at Towson University taught by Dr. Bulmer in Fall 2016. Since its upload, it has received 15 views. For similar materials see Genetics Lecture in Biology at Towson University.
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Date Created: 10/07/16
October 7, 2016 DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM LECTURE PRESENTATION OR TEXTBOOK Polypeptides o tRNA’s and mRNA bring amino acids in close proximity o Enzyme activity in ribosomes links amino acids with a peptide bond forming a polypeptide o Video shown in class http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related o Molecular interactions determine protein structure o Levels of protein structure, review from Biol 202 Macromolecules of translation o Polypeptides and RNA molecules of the ribosme o Amino acid activating Enzymes o tRNA Molecules o Soluble proteins involved in polypeptide chain initiation(Small ribosome subunit and first tRNA come together, then large ribosome subunit joins), elongation (Polypeptide chain is synthesized), and termination (Completed polypeptide released) o rRNA synthesis occurs in the nucleolus of eukaryotes o Further information slides 12- 15 but this video from class summarizes the entire process http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related Codons or groups of 3 nucleotides = an amino acid Beta sheet In a test tube you can have 3 reading frames in life it depends on the location of the start codon October 5 2016 DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM IN CLASS PRESENTATION OR TEXTBOOK Intron: A DNA region within a gene that is not translated into protein Exon: The region of the gene that is translated Introns pre-mRNA Introns are removed through splicing during processing Spliceosomes cut out the intron regions and join the exon regions Video shown in class: http://www.youtube.com/watch?v=FVuAwBGw_pQ Significance of Introns o Crossing over is ore likely to occur within a gene if it spans a greater genetic distance o Alternate splicing of exons where one gene makes several different gene products Ex. DSCAM (Down syndrome cell adhesion molecule) This gene is found in individuals with down syndrome and it plays a role in forming neuron conncetions o Relic of gene evolution o Introns may have old code or sections that were once translated o Introns may have functional significance o Introns may incode miRNAs(microRNAs) that regulate gene expression Self splicing o Intron acts as a ribozyme o No proteins are involved o Evolutionary relic of RNA world RNA stored information like DNA and also acted as enzymes that supported cellular or pre-cellular life Theorized that this world evolved into our world mRNA Protein o Messengerr RNA provides the code for linking amino acids into a protein o Each of the 20 amino acids make up proteins through codons (3 set of nucleotides) o DISCLAIMER: NOTES AND IMAGES MAY OR MAY NOT BE DIRECTLY FROM THE IN CLASS PRESENTATION OR TEXTBOOK. DNA Polymerization DNA synthesis has an absolute requirement for A. 3’ OH A template In Vitro DNA synthesis Kornberg (1957) o DNA polymerase I from E. coli o dNTPs, (dATP), dTTP, dGTP, dCTP o Mg2+ o DNA (template and primer) DNA polymerase I o 5’ 3’ polymerase activity o 5’ 3’ Exonuclease activity o 3’ 5’ exonuclease activity Exonuclease activity is important for repair Slide 4 goes with this image RNA Primase: Initiates new strand synthesis DNA Polymerase: Adds nucleotides too free 3’ OH group in the 5’ 3’ Direction DNA ligase: Covalently closes nick in DNA between free OH and phosphate groups Helicase: Unwinds DNA at the replication fork Single stranded binding proteins: Stabilizes single stranded DNA at the replication fork Topoisomerases: Releases mechanical stress of unwinding DNA polymerase III: Adds deoxyribonucleotides to RNA primer at initiation of replication fork o Elongation of DNA chain 5’ 3’ o 3’ 5’ exonuclease activity proofreading Limitations as DNA polymerase I o Only adds nucleotides to the 3’ – OH end, and is unable to initiate new chain o Leading and lagging synthesis (Okazaki fragments) Video shown in lecture https://www.youtube.com/watch?v=dKubyIRiN84 DNA polymerase III – Holoenzyme is the primary complex involved I prokaryotic DNA replication DNA polymerase II (IV and V) repair enzyme primarily synthesized during stationary phase of bacterial growth DNA polymerase I removes RNA primers with 5’ 3’ exonuclease and replaces DNA with 5’ 3’ polymerase activity Polymerases in mammals Polymerase --starts up polymerization. It has RNA primase activity. Polymerase --Implicated in repairing DNA, in base excision repair and gap-filling synthesis. Polymerase --Thought to be the main polymerase involved in lagging strand synthesis. Polymerase --Thought to be the main polymerase involved in leading strand synthesis. Polymerase --mitochondrial DNA replication Telomerase -Replication of Chromosome Termini Telomerase makes telomeres: Which are nucleotide repeats at the end of chromosomes DNA replication results in shortening of chromosomes With each round replication chromosomes get shorter and may cause apoptosis (Cell death) Video shown in class http://www.youtube.com/watch?v=AJNoTmWsE0s Telomerase adds tandem repeats at chromosome termini in germline cells Telomerase activity often lacking in somatic cells and the cells get shorter after each round of replication Progeria disease (Werner Syndrome): The aging disease where telomeres degrade rapidly Hayflick Limit o Normal human fetal cells in cell culture divide between 40 or 60 times o Each mitosis shortens the telomeres on DNA of the Cell. Telomere shorting in humans eventually blocks cell division and correlates with aging o Cancers cells produce telomerase and do not shorten, Book: The immortal life of Henrietta Lacks by Rebecca Skloot o Hayflick limit may prevent normal cells from becoming cancerous ^ PCR or Polymerase chain reaction Taq polymerase: One of the most important enzymes in molecular biology Thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus Video shown in Lecture http://www.youtube.com/watch?v=n0mDBQcquGA&feature=related What do you need to complete a PCR reaction o DNA polymerase 2+ o Mg o NTP (ATP, CTP, GTP, TTP) o Primer o Template Why can inhibiting telomerase combat cancer o The production of telomerase prevents cell death, most cells have a hayflick limit and it prevents them from being eternal Central dogma of Molecular Biology 1 2 o DNA RNA Protein = Gene Expression 1Transcription 2Translation o Collinearity: DNA Base sequence determines protein amino acid sequence o DNA mRNA Protein Information flow goes in one direction, DNA to protein Evolutionary implication Phenotype cannot influence genotype Acquired phenotypic characteristics cannot be inherited (Lamarckian) o Transcription and Translation occurs in all cellular organisms Prokaryotes: Transcription and translation occur simultaneously Eukaryote cells: Transcription in the nucleus (Includes RNA Processing) Translation occurs in the cytoplasm o Uracil Base pairs with adenine and replaces thymine during DNA transcription into RNA Methylation of uracil produces thymine Uracil believed to be the original base when life first evolved. Thymine replaced uracil as one of the bases in the heritable code because it is more stable and allows for more efficient DNA replication RNA stability RNA polymerase 5” 3’ chain elongation does not need a primer for initiation Only one strand of DNA required for template of RNA synthesis could be either strand RNA polymerase starts at a specific sequence that promotes polymerization- Promoter Nontemplate strand = Sense strand = Coding strand o Four stages of Transcription Promoter recognition Specific DNA sequences for RNA polymerase binding which are conserved (Consensus sequence) Chain initiation RNA polymerase unzips double helix Bind/Unwind then first few phosphodiester bonds made 2 E. coli RNA Polymerase has a complex of proteins, α β β’ form complex and then σ factor added for initiation- sigma factor released after 8-9 bases transcribed. Eukaryotic RNA polymerase must have the TATA binding protein and several other transcription factors attached at the promoter region to initiate transcription Chain elongation RNA Polymerase moves down DNA with transient transcription bubble d Chain termination Prokaryotes o Rho independent: G + C rich to form a hairpin structure followed by A+ U rich region Self terminating o Rho dependednt: 50- 90 bases long (Rich in C bases and low in G bases) Rho releases the RNA transcript when polymerase encounters sequence Eukaryotes o 1000 -2000 bases downstream from the last nucleotide that will be part of the protein coding message o Actual signals for termination unknown o mRNA cleaved 11-30 bases down from conserved sequence AAUAAA Video shown in class http://www.youtube.com/watch?v=WsofH466lqk mRNA processing Early in the Transciption process 7-methyl guanosine cap is added to the 5’ End of pre-mRNA Important in translation initiation Potects mRNA from 5’ degradation After transcription termination a poly-A tail (200 adenine nucleotides long) is added to the 3’ end of the mRNA protects against 3’ Degradation of the mRNA Video shown in class http://www.youtube.com/watch?v=YjWuVrzvZYA&feature=related
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