Rebecca DavenportBIOL 1406-BWI11/6/16Ch 17 blueprint1. Gene expression: information stored in DNA is expressed as protein.a. Central Dogma- DNA to (through transcription) RNA to (through translation) Protein/Polypeptideb. Transcription and Translationi.ii. Transcription- rewrites DNA into RNA form 1. DNA is the template for RNA synthesis2. DNA = (nucleotide—Deoxyribose—A,T,G,C—Double stranded)RNA = (Nucleotide—Ribose—A,U,G,C—Single stranded)3. Where does transcription occur?a. Prokaryotes = cytosolb. Eukaryotes = nucleus 4. The promoter is the start site of Transcription!!5. Three stages of transcription:a. Initiationb. Elongationc. Termination6. RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and joins together the RNA nucleotides. 7. RNA polymerase does not need any primer.8. The stretch of DNA that is transcribed is called a transcription unit.9.a. Initiation: Stage 1i. The DNA sequence where RNA polymerase attaches is called the promoter. 1. In eukaryotes: Transcription factors bind the promoter first then recruit Rpol and the initiation of transcription forming the transcription initiation complex.2. In prokaryotes: Rpol will bind to Promoter. Rpol will separate DNA starnds and use 1 strand as a template. Rpol will lay down a few nucleotides. 3. A promoter called a TATA box is crucial in forming the initiation complex Rpol unwinds DNA and ii. Rpol binds the promoter, unwinds DNA, and starts RNA synthesisiii.b. Elongation: stage 2i. As RNA polymerase moves along the DNA, it untwists the double helix.ii. Nucleotides are added to the 3 end of the′growing RNA molecule.iii. As Rpol moves along the DNA, the helix reforms and then RNA molecule hang off Rpol like a tail.iv. RNA peels away from DNA strand and the DNA helix reformsv. A gene can be transcribed simultaneously by several RNA polymerasesvi.c. Termination: stage 3i. Rpol has copied entire gene and can down dissipate. ii. The mechanisms of termination are different in bacteria and eukaryotes.iii. In bacteria, the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification.iv. In prokaryotes, Rpol hits terminator sequence, causing Rpol to fall off DNA. v. In eukaryotes, polyadenylation signals sequence and it falls off.1. AAUAAA (RNA)2. RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10–35 nucleotides past this polyadenylation sequence.vi. RNA processing- its goal is to modify the RNA that was made after transcription.1. Only happens in eukaryotes.a. Happens in nucleus.2. Edit the pre-mRNA that was made during transcription. a. Enzymes in the nucleus modify pre-mRNA before the genetic messages are dispatched to the cytoplasm3. Modify ends: 5’ cap and 3’ poly-A taila. During RNA processing, both ends of the primary transcript are usually altered.b. Why modify ends?i. Export from the nucleusii. Protection from degradation iii. Attachment to the ribosome4. Modify the middle = Splicinga. EX: Netflix cuts out the annoying commercials(Introns) so you can just watch Exons (greys anatomy).b. Exon: “Expressed” as protein, we NEED this!c. Intron: intervening sequence, noncoding, we NEED to get rid of these!d. Also, usually certain interior sections of the molecule are cut out, and the remaining parts spliced together. ( remove introns and join together the exons)vii. Alteration of mRNA ends-1. Each end of a pre-mRNA molecule is modified ina particular waya. The 5 end receives a modified ′nucleotide 5 cap′b. The 3 end gets a ′ poly-A tail2. These modifications share several functionsa. They seem to facilitate the export of mRNA to the cytoplasmb. They protect mRNA from hydrolytic enzymesc. They help ribosomes attach to the 5 ′end.3.viii. Split genes and RNA Splicing-1. Most eukaryotic genes and their RNA transcriptshave long noncoding stretches of nucleotides that lie between coding regions2. These noncoding regions are called intervening sequences, or introns3. The other regions are called exons because theyare eventually expressed, usually translated intoamino acid sequences4. RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence5. Spliceosomes-a. In some cases, RNA splicing is carried out by spliceosomesb. Spliceosomes consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sitesc. The RNAs of the spliceosome also catalyze the splicing reactiond.d. Example coding:i. Template- 3’ TACGTGTCACTAATT 5’ coding: 5’ TGCACAGTGATTAA 3’(Transcription)mRNA: 5’ AUGCACAGUGAUUAA 3’- 4x4x4 = 64 codons o 61 of the codons = amino acido 3 of codons = stop codonso Codons are on mRNA. (coded message analogy) - Redundancy- multiple codons give the sameamino acids.o Wobble spot- third spot varies but gives same amino acid.o CCC- ProCCG- ProCCA- ProCCU- ProPolypeptide Sequence: Met His Ser Aspiii. Translation: mRNA (nucleotide) to Protein (amino acid)1. Changing the language from nucleotides to amino acids.2. Translator = tRNA (transfer RNA)3. Occurs on a ribosome in the cytosol.4. Genetic information flows from mRNA to protein through the process of translation.5. Accurate Translation Requires Two Steps:a. First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetaseb. Second: a correct match between the tRNA anticodon and an mRNA codonc. Flexible pairing at the third base of a codon is called wobble andallows some tRNAs to bind to more than one codoni. Key player #1: tRNA1. A cell translates on mRNA message into protein with the help of transfer RNA (tRNA)2. tRNAs transfer amino acids to the growing polypeptide in a ribosome.3. Molecules of tRNA are not identicala. Each carries a specific amino acid on one endb. Each has an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA.4.a. Top end of tRNA is Amino acid attachment site.b. Bottom is anticodon.ii. Key player #2: Ribosomes1. Facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis2. The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)3. A ribosome has three binding sites for tRNAa. The P site (peptidyl) holds the tRNA that carries the growing polypeptide chainb. The A site (Aminoacyl) holds the tRNA that carries the next amino acid to be added to the chainc.
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