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Chapter 10 DNA TRANSCRIPTION and TRANSLATION

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THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN WARM UP What are proteins? Where do they come from?

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THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN DNA in our cells carry the instructions for making proteins in order for our cells to function.

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How an Organisms Genotype Determines Its Phenotype An organisms genotype is its genetic makeup, the sequence of nucleotide bases in DNA. The phenotype is the organisms physical traits, which arise from the actions of a wide variety of proteins.

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DNA specifies the synthesis of proteins in two stages: 1. transcription, the transfer of genetic information from DNA into an RNA molecule 2. translation, the transfer of information from RNA into a protein. How an Organisms Genotype Determines Its Phenotype

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Central Dogma Polypeptide TRANSCRIPTION mRNA DNA Gene TRANSLATION

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Figure 10.8-3 DNA Cytoplasm Nucleus RNA Protein TRANSCRIPTION TRANSLATION

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Back to chapter 3!!!! RNA = ribonucleic acid (ribose sugar) Instead of THYMINE, RNA has URACIL Single strand RNA Overview

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mRNA = messanger RNA tRNA = transfer RNA rRNA = ribosomal RNA 3 Types of RNA

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mRNA = messanger RNA made by transcription of the original DNA molecule a messanger from the DNA to the rest of the cell. 3 Types of RNA

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tRNA = transfer RNA interpreter, converts the language in mRNA into the language of proteins (amino acid monomers) 3 Types of RNA

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rRNA = ribosomal RNA rRNA is combined with proteins to form a ribosome, which is the site of protein synthesis coordinate the functions of mRNA and tRNA 3 Types of RNA

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Figure 10.10a Amino acid RNA DNA strand Polypeptide Codon TRANSCRIPTION TRANSLATION

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DNA to mRNA Problems Given the DNA sequence, construct an mRNA for the following pieces of DNA. TTCAGCGATACCGTAGGA TACCCCGTATTGGAAATT AAACCGGCAAAATTGCTC

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Transcription: From DNA to RNA Transcription makes mRNA from a DNA template, substitutes uracil (U) for thymine (T). uses a process that resembles the synthesis of a DNA strand during DNA replication Lets take a closer look at this process!!!

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Transcription: From DNA to RNA THE BIG PICTURE Transfer of genetic information from DNA to RNA resembles the process of DNA replication! Only 1 strand of DNA is used as a template for mRNA synthesis. RNA nucleotides are linked by the transcription enzyme RNA polymerase. End result is mRNA!!!

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Figure 10.13a Newly made RNA RNA nucleotides Template strand of DNA (a) A close-up view of transcription RNA polymerase

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STEP 1: Initiation of Transcription The start transcribing signal is a nucleotide sequence called a promoter located in the DNA sequence at the beginning of the gene which is being transcribed. a specific place where RNA polymerase attaches. The first phase of transcription is initiation, in which RNA polymerase attaches to the promoter. RNA synthesis begins.

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STEP 2: RNA Elongation Elongation, the second phase of transcription the RNA grows longer the RNA strand peels away from its DNA template.

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STEP 3: Termination of Transcription Termination, third phase of transcription RNA polymerase reaches a special sequence of bases in the DNA template called a terminator, signaling the end of the gene polymerase detaches from the RNA and the gene (DNA) the DNA strands rejoin.

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Figure 10.13b (b) Transcription of a gene RNA polymerase Completed RNA Growing RNA Termination Initiation Terminator DNA Elongation RNA Promoter DNA RNA polymerase DNA of gene 213

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The Processing of Eukaryotic RNA Sowe now have an RNA strand.now what? Prokaryotic cells RNA transcribed from a gene immediately functions as messenger RNA (mRNA), the molecule that is translated into protein. Eukaryotic cells localizes transcription in the nucleus (because they have one!!) modifies, or processes, the RNA transcript in the nucleus before it move to the cytoplasm for translation by a ribosome.

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RNA processing includes adding a cap and tail consisting of extra nucleotides at the ends of the RNA transcript helps to protect the RNA from enzyme attack! help ribosomes recognize RNA as mRNA. removing introns (noncoding regions of the RNA) RNA splicing, joining exons (the parts of the gene that are expressed) together to form messenger RNA (mRNA). The Processing of Eukaryotic RNA

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Figure 10.14 Transcription Addition of cap and tail Coding sequence mRNA DNA Cytoplasm Nucleus Exons spliced together Introns removed Tail Cap RNA transcript with cap and tail Exon Intron

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RNA splicing is believed to play a significant role in humans in allowing our approximately 21,000 genes to produce many thousands more polypeptides by varying the exons that are included in the final mRNA. The Processing of Eukaryotic RNA

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The flow of information from gene to protein is based on a triplet code. A codon is a triplet of bases, which codes for one amino acid. From Nucleotides to Amino Acids: An Overview

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The Genetic Code The genetic code is the set of rules that convert a nucleotide sequence in RNA to an amino acid sequence. Of the 64 triplet codes, 61 code for amino acids 3 are stop codons, instructing the ribosomes to end the polypeptide.

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Figure 10.11 Second base of RNA codon First base of RNA codon Phenylalanine (Phe) Leucine (Leu) Cysteine (Cys) Leucine (Leu) Isoleucine (Ile) Valine (Val) Met or start Serine (Ser) Proline (Pro) Threonine (Thr) Tyrosine (Tyr) Histidine (His) Glutamine (Gln) Asparagine (Asn) Alanine (Ala) Stop Glutamic acid (Glu) Aspartic acid (Asp) Lysine (Lys) Arginine (Arg) Tryptophan (Trp) Arginine (Arg) Serine (Ser) Glycine (Gly) Third base of RNA codon UUU UUC UUA UUG UAU UAC CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG UGU UGC AGU AGC AGA AGG GGU GGC GGA GGG CGU CGC CGA CGG GCU GCC GCA GCG ACU ACC ACA ACG CCU CCC CCA CCG UCU UCC UCA UCG CUU CUC CUA CUG GUU GUC GUA GUG AUU AUC AUA AUG UAA UAG UGA UGG UCAG U C A G UCAGUCAG UCAGUCAG UCAGUCAG UCAGUCAG

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The genetic code is almost universal Because diverse organisms share a common genetic code, it is possible to program one species to produce a protein from another species by transplanting DNA. The Genetic Code

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Translation Translation is the conversion from nucleic acid to protein. Involves three crucial players mRNA result of transcription, direct message from DNA tRNA molecular interpreter, carries amino acids rRNA makes up a ribosome, which coordinates mRNA and tRNA functions

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Translation: requirements Translation requires mRNA ATP enzymes ribosomes transfer RNA (tRNA)

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Transfer RNA (tRNA) matches amino acids with codons in mRNA using anticodons, a special triplet of bases that is complementary to a codon triplet on mRNA.

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Figure 10.15 tRNA polynucleotide (ribbon model) Anticodon Hydrogen bond Amino acid attachment site tRNA (simplified representation) RNA polynucleotide chain

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Ribosomes Ribosomes are organelles that coordinate the functions of mRNA and tRNA are made of two subunits. Each subunit is made up of proteins ribosomal RNA (rRNA).

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Figure 10.16b Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA (b) The players of translation Codons

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Translation: The Process Translation is divided into three phases: 1.initiation 2.elongation 3.termination

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Initiation Initiation brings together mRNA, tRNA and the two subunits of the ribosome (rRNA) The mRNA molecule has a cap and tail that help the mRNA bind to the ribosome. The pink portion also helps the mRNA bind to the ribosome.

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Initiation occurs in two steps. 1.An mRNA molecule binds to a small ribosomal subunit, then a special initiator tRNA binds to the start codon AUG codon, UAC - anticodon, 2.A large ribosomal subunit binds to the small one, creating a functional ribosome. Initiation

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Elongation Elongation occurs in three steps. Step 1: Codon recognition. The anticodon of an incoming tRNA pairs with the mRNA codon at the A site of the ribosome.

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Figure 10.19 Amino acid Anticodon A site Codons mRNA P site Polypeptide Codon recognition Peptide bond formation Translocation Stop codon New peptide bond mRNA movement 2 1 3 ELONGATION

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Step 2: Peptide bond formation. The polypeptide leaves the tRNA in the P site and attaches to the amino acid on the tRNA in the A site. The ribosome catalyzes the bond formation between the two amino acids. Elongation

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Step 3: Translocation. The P site tRNA leaves the ribosome. The tRNA carrying the polypeptide moves from the A to the P site. Elongation

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Termination Elongation continues until a stop codon reaches the ribosomes A site, the completed polypeptide is freed, and the ribosome splits back into its subunits.

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Review: DNA RNA Protein In a cell, genetic information flows from DNA to RNA in the nucleus RNA to protein in the cytoplasm. As it is made, a polypeptide coils and folds and assumes a three-dimensional shape. Determines the appearance and capabilities of the cell and organism. Transcription and translation are how genes control the structures and activities of cells.

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Figure 10.20-6 Transcription RNA polymerase mRNA DNA Intron Nucleus mRNA Intron Tail Cap RNA processing tRNA Amino acid Amino acid attachment Enzyme ATP Initiation of translation Ribosomal subunits Termination Anticodon Codon Elongation Polypeptide Stop codon Anticodon A 346521

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HOW AND WHY GENES ARE REGULATED Every somatic cell (body cell, not sex cell) in an organism contains identical genetic instructions. They all share the same genome. So what makes cells different from one another?

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In cellular differentiation, cells become specialized in structure and function. Certain genes are turned on and off in the process of gene regulation. HOW AND WHY GENES ARE REGULATED

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Patterns of Gene Expression in Differentiated Cells In gene expression, a gene is turned on and transcribed into RNA information flows from genes to proteins genotype to phenotype. Information flows from DNA to RNA to proteins. The great differences among cells in an organism must result from the selective expression of genes.

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Gene Regulation in Bacteria Natural selection has favored bacteria that express only certain genes only at specific times when the products are needed by the cell. E. coli living in your intestines survive on what you eat, adjusting production of enzymes as needed for digestion of various food items. So how do bacteria selectively turn their genes on and off?

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An operon includes a cluster of genes with related functions the control sequences that turn the genes on or off. The bacterium E. coli uses the lac operon to coordinate the expression of genes that produce enzymes used to break down lactose in the bacteriums environment. Gene Regulation in Bacteria

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The lac operon uses a promoter, a control sequence where the transcription enzyme attaches and initiates transcription an operator, a DNA segment that acts as a switch that is turned on or off a repressor (protein), which binds to the operator and physically blocks the attachment of RNA polymerase and transcription. Gene Regulation in Bacteria

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Figure 11.2 Operon turned on (lactose inactivates repressor) Lactose Protein mRNA DNA Protein mRNA DNA Operon turned off (lactose absent)

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Figure 11.2a Protein mRNA DNA Operon turned off (lactose absent) Active repressor RNA polymerase cannot attach to promoter Regulatory gene Promoter Operon Genes for lactose enzymes Operator 21

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Figure 11.2b Operon turned on (lactose inactivates repressor) Lactose Protein mRNA Lactose enzymes DNA Translation Inactive repressor RNA polymerase bound to promoter Transcription 21345

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Gene Regulation in Eukaryotic Cells Eukaryotic cells have more complex gene regulating mechanisms with many points where the process can be turned on or off. The multiple mechanisms that control gene expression are like the many control valves along a water supply.

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Mutations A mutation is any change in the nucleotide sequence of DNA.

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Mutations can change the amino acids in a protein. Mutations can involve large regions of a chromosome just a single nucleotide pair, as occurs in sickle-cell disease. Mutations

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Mutations within a gene can be divided into two general categories: 1.nucleotide substitutions (the replacement of one base by another) 2.nucleotide deletions or insertions (the loss or addition of a nucleotide). Types of Mutations

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Nucleotide substitutions can be divided into 3 different type of mutations. Silent mutation = change in the nucleotide may transform one codon into another but due to the redundancy of the genetic code, is translated into the same amino acid. Missense mutation = change in the nucleotide when translated, changes one amino acid into another. May or may not be detrimental to the proteins function. (sickle cell anemia) Nonsense mutation = change in the nucleotide that changes a codon for an amino acid into a stop codon. Types of Mutations

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Nucleotide insertions and deletions can change the reading frame of the genetic message lead to disastrous effects. can alter the reading frame of the genetic message = frameshift mutations. Types of Mutations

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Mutagens Mutations may result from errors in DNA replication physical or chemical agents called mutagens. X-rays UV light Mutations are often harmful but are useful in nature and the laboratory as a source of genetic diversity, which makes evolution by natural selection possible!!!