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RNA and Protein Synthesis

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Example 13.1- RNA SC.912.L.16.5 Explain the basic processes of transcription and translation, and how they result in the expression of genes.

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Role of RNA How does RNA differ from DNA? Watson and Crick solved the double helix structure of DNA Ribonucleicacid (RNA) consists of a long chain of nucleotides

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Watson and Crick

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Comparing RNA and DNA Each nucleotide in DNA is made of a 5 carbon sugar The differences between RNA and Dna make it easy for enzymes to tell RNA and DNA apart You can compare the different roles played in RNA and DNA molecules in directing the production of proteins to the Master plan and blueprints Blueprints are the workk the master plan builds off of.

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Differences The sugar in RNA is ribose instead of deoxyribose RNA is generally single stranded and not double stranded RNA contains uracil instead of thymine

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Functions of RNA Visualize an RNA molecule as a disposable copy of a segment of DNA RNA molecules are involved in protein synthesis RNA controls the assembly of amino acids into proteins Each type of RNA molecule specializes in a different aspect of the job mRNA, rRNA, and tRNA

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Messenger RNA (tRNA) Most genes contain instructions for assembling amino acids The molecules that carry copies of the instructions are messenger RNA Carry info from the DNA to other part of the cell

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Ribosomal RNA (rRNA) Proteins are assembled on ribosomes Ribosomes are small organelles composed of two subunits The subunits are made up of several ribosomal RNA Ribosomal RNA carry as much as 80 different proteins

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Transfer RNA Used in building a protein tRNA transfers each amino acid to the ribosome as it is specified by the coded messages in mRNA

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RNA Synthesis How does the cell make RNA? Cells invest large amounts of raw material and energy into making RNA molecules

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Transcription Most of the work of RNA takes place here In transcription, segments of DNA serve as templates to produce complementary RNA molecules Base sequences of the transcribed RNA complement the base sequences of the template DNA

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In prokaryotes RNA synthesis and protein synthesis take place in the cytoplasm In eukaryotes, DNA is is in the nucleus In eukaryotes the DNA moves to the cytoplasm from the nucleus to play a role in the production of protein Transcription requires RNA polymerase

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RNA polymerase binds separates the double helix of the DNA It is possible for a single gene to produce hundreds or thousands of RNA molecules

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Promoters RNA polymerase doesnt bind on DNA anywhere It binds to promoters Promoters are regions of DNA that have specific base sequences Promoters are signals in the DNA molecule that show RNA polymerase exactly where to begin making RNA

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RNA Editing RNA molecules sometimes require a bit of editing before they are ready to be read. Pre-mRNA molecules have bits and pieces cut out of them before they can go into action The portions dicarded are called introns The portions kept are exons

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Introns are taken out of pre-mRNA molecules while they are still in the nucleus Exons are spliced together to form the final mRNA Polypeptide chains are the formation

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Example 13.2- Ribosomes and Protein Synthesis SC.912.L.16.9 Explain how and why the genetic code is universal and is common to almost all organisms

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The Genetic Code What I the genetic code, and how is it read? First step in decoding genetic messages is to transcribe a nucleotide base sequence from DNA to RNA. The info contains a code for making proteins

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As many as 20 different amino acids are found in polypeptides What determines the properties of different proteins is the order in which the specific amino acids in polypeptides are joined. RNA contains Adenine, guanine, cytosine, and uracil G-C and A-U

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The genetic code is read three letters at a time, s that each word is three bases long and corresponds to a single amino acid. Each thee letter word is known as a codon.

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How to Read Codons There are 64 possible three base codons

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Start and Stop Codons The genetic code uses punctuation marks The methionine codon AUG serves as a start codon for protein synthesis After that the sequence continues until it reaches a stop codon

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Translation What role does ribosomes play in assembling proteins? The sequence of nucleotide bases in mRNA molecule is a set of instructions that gives the order in which amino acid should be joined to produce a polypeptide. Once the polypeptide is complete, it folds into it final shape or joins with other polypeptides to become a functional protein.

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The ribosome basically reads and assembles Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains Translation is the decoding of an mRNA message into a proten

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Steps in Translation Messenger RNA iss transcribe in the nucleus and enters the cytoplasm tRNA- Translation begins at AUG (the start codon) As each codon passes through the ribosome, tRNAs bring the proper amino aids into the ribosome. The ribosome then joins two amino acids to a growing chain (polypeptide chain)

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The ribosomes bind methionine and phenylalanine, the anticodon is UAC, which pairs with the methionine codon, AUG. The bond between methionine and tRNA breaks away. The process continues until the ribosome reaches one of the three stop codons.

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The Molecular Basis of Heredity What is the central dogma of molecular biology? Most genes contain nothin more than instructions for assembling proteins Proteins have everything to do with traits such as shape of a leaf, color of a flower, the sex of a newborn baby, etc. Proteins catalyze and regulate chemical reactions

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A gene that codes for an enzyme to produce pigment can control the color of a flower. Also produces proteins that regulate patterns of tissue growth in a leaf Also trigger the male or female development in an embryo Pretty much, proteins are microscopic tools, each specifically designed to build or operate a component in a living cell.

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With the genetic code in hand, a new scientific field called molecular biology was established. The central dogma of molecular biology is that information is transferred from DNA to RNA to protein.

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Example 13.3 Mutations SC.912.L.16.4 Explain how mutations in the DNA sequence may or may not result in phenotypic change. Explain how mutations in gametes may result in phenotypic changes in offspring.

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Types of Mutations What are mutations? Mutations are the change of genetic material in a cell Mutations come in many forms The two categories of mutations are the those that produce changes in single gene which are known as gene mutations. Also those that produce changes in a whole chromosome which are known as chromosomal mutations.

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Gene Mutations Gene mutations that involve mutations in one or a few nucleotides are known as point mutations. Point mutations occur at a single point in the DNA sequence Point mutations include substitutions, insertions, and deletions Occur during replication

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Substitutions One base is changed to a different base Affect only a single amino acid Sometimes have no effect at all Ex: if a mutation changed one codon of mRNA from CCC to CCA, the codon will still specify the amino acid proline

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Insertions and Deletions Point mutations in which one base is inserted pr removed from the DNA sequence Effects can be dramatic Also called frame shift mutations

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Chromosomal Mutations Involve changes in the number or structure of chromosomes Can change the location of genes on chromosomes and can even change the number of copies of some genes.

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Effects of Mutations How do mutations affect genes? Genetic material can be altered by natural events or by artificial means, Resulting mutations that affect individual organisms can also affect a species or even an entire ecosystem Mutations are produced by errors in genetic process

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Mutagens Chemical or physical aents in the environment Lead to some mutations Chemical mutagions: pesticide, few natural plant alkaloids, tobaccoo smoke, and environmental pollutants Physical: forms of electromagnetic radiation, such as x-rays and UV light

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Harmful and Helpful Mutations The effects of mutations on genes vary widely. Some have little to no effect; and some produce beneficial variations. Some negatively disrupt gen function. Many if not most mutations are neutral Whether a mutation is negative or beneficial depends on how its DNA changes relative to the organisms situation. Without mutations, organisms couldn'tt evolve

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Harmful effects Some of the most harmful are those that change protein structures or gene activity. The defective proteins produced by these mutations can disrupt normal biological activities Cancers can produce Sickle cell disease

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Beneficial effects Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environment Insects build immunity to the pesticides. Good for them; bad for us When a complete set of chromosomes fail to separate during meiosis, the gametes that result may produce triploid or tetraploid organisms. Condition where there is an extra set of chromosome is called polyploidy. They are generally larger

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Example 13.4 Gene regulation and Expression SC.912.L.16.5 Explain the basic processes of transcription and translation and how they result in the expression of genes.

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Prokaryotic Gene Regulation How are prokaryotic genes regulated? To conserve energy and resources, prokaryotes regulate their activities, using only those genes necessary for the cell to function. By regulating gene expression, bacteria can respond to changes in the environment DNA-binding proteins in prokaryotes regulate genes by controlling transcription.

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The key to gene transcription in bacteria is the organization of genes into operons The genes in operons usually have related functions