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Pitt BIOSC 0815 - Insertion and Deletion of Nucleotides
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Biosci 0815 1st Ediiton Lecture 12Outline of Last Lecture I. Replication and Transcriptiona. How is replication accomplished?II. Types of RNAa. mRNAb. tRNAc. rRNAIII. Transcription.IV. Does DNA only code for proteins?V. Parts of a GeneVI. PolymeraseVII. TranslationVIII. Review of ProteinsIX. Steps of Translation:a. Initiationb. Elongationc. TerminationX. ProteinsOutline of Current Lecture I. Insertion and Deletion of NucleotidesII. Gene Expressiona. Steps: transcription, Splicing, Translationb. Getting Access to DNAc. HistonesIII. Histone Modificationsa. EpigeneticsIV. Protein ModificationsCurrent Lecture- Insertion and deletion of nucleotideso The code is important for understanding genetic diseases. If it is read in the wrong frame, the wrong directions are followed. Where translation begins will determine what amino acids will be linked. If you miss one nucleotide, there is a frame shift. o This could occur if a nucleotide is inserted or deleted during replication. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Tay Sachs: One form of the disease is an insertion of four BP in the gene causing aframe shift. o There is another issue due to mutations in gene and results from an improperly folded protein. Proteins called “chaperones” cannot help and they never make it to the membrane. This is an issue in the disease Cystic Fibrosis.  Recall: - Primary:- Secondary: short chain of hydrogen bonds- Tertiary: folding and covalent hydrogen bonding to hold protein togetherGene Expression- What is Gene Expression? From DNA to the Final Active protein. “The creation of a protein from the DNA all the way to the form of the active final protein.” - Stepso Transcription, splicing, export into cytoplasm, translation into protein.o At each step there are obstacles or helpers necessary to get through the step.These controls make sure that the cell only performs activities such as makingproteins, activating proteins and deactivating proteins when it is necessary.- DNA  transcription  RNA  Translation  protein.- Three types of Gene Expression controlo Making a transcript from DNAo Handling the transcripto Getting the correct protein form.- Getting access to the DNAo To make an mRNA copy, we need to have access to the DNA in the nucleus. This 6 feet of DNA is wrapped around histone proteins (together called a histome). It is then twisted and loops back on itself. The problem with this is that it’s difficult to get access for transcription. Th packing must be loosened to allow transcription. This process of opening up the bound DNA is called chromatin remodeling. o Heterochromatin is tightly wound around DNA. It is inactive and it is inaccessible to transcribing.o Euchromatin (true chromatin) is not tightly wound and can be accessed to make mRNA. o Histones can be modified by adding small chemical groups (Acetylation, Methylation, Phosphorylation). One directly modifies DNA, and it is methylation. This one is usually going from euchromatin to heterochromatin. o Histones have tails: parts of the proteins that project outwarn. When they areunmodivied the tail s hold the nucleosomes together. These tails will interactwith those of histomes nearby. The reason for heterochromatin tightly packing is because of the opposite charges of attraction. This attraction is because phosphates on DNA have a negative charge while the Amino Acids n the histones is positively charge. Adding the acetyl group neutralizes the charge of the histone so there is less attraction. o Some enzymes add to make decondensed chromatin (euchromatin) some condenses it (heterochromatin). o Now the DNA is opened, ad next the transcription factors have to join and bring RNA polymerase. - Parts of a gene:o Regulatory regions: Sequences to attract transcription factors and polymerase.  Promoter contains TATA with gs and c’s around it. The TATA binding protein attaches and then other transcription factors attach and then RNA polymerase attaches.  Acetylase enzyme binds to an area before TATA and puts acetyl groupson histone tails. o Coding Region: Has the codons for amino acids.- Histone modification Epigeneticso When histones are permanently changed, they remain either ecetylted or phosphorylated or methylated. These tags are passed onto daughter cells.o This causes identical twins to begin to differ.o The epigenetics is the collection of tags added to histones over an individual’slifetime. Decides how much or whether the gene is expressed. o The epigenome is the pattern of tagged DNA in an individual. These tags can be influenced by environmental factors such as stress, diet, activity, habits, stress.o Genome does the work, epigenome says to do it. These epigenomes can be passed on to children, though MOST are stripped from the genes. o Epigenetic inheritance: If there is an epigenetic change, it is passed onto daughter cells. Changes in gene expression is not due to sequence of DNA but what iscalled the histone code.o Methyl groups can be placed directly ono DNA. It usually occurs on cytosines.This inactivated DNA. Example: female inherit 2X chromosomes, males inherit one X. There is information unrelated to gender. To be certain that females do not express more of this information, one x chromosome is “turned off.”Whether it is paternal or maternal “X” that is turned off differs. It is called a bar body and it sits on the edge of the cell. - DNA methylation and development:o Methylated DNA remains methylated after cell division. o Some genes have less methylation. They have to be on all the time. These arecalled housekeeping genes. They are responsible for everyday life of the cell, transcription genes, genes that make enzymes to create ATP. o Test of mice: what the mother mouse ate while pregnant affected her offspring. They were fed BPA and without a supplemented diet, the baby mouse had genetic problems. - Handling the transcript:o Once the transcript is made, we add a 5’ cap and a 3’ polyA tail. It is spliced and it is stable. o The 5’ Cap and 3’ polyA tail prevents degrading, splicing.o Splicing: not all mRNA is used. Introns, and Exons. Introns are not used, exonsare what is used to make the protein. Some proteins facilitate removal of introns.  This gives a lot of possibilities from one length of DNA. o The stability of transcript,


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Pitt BIOSC 0815 - Insertion and Deletion of Nucleotides

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