chapter17

=**Chapter 17: From Gene to Protein**= by Cynthia Ma

Related activities

 * Chapter 17: From Gene to Protein outline (we filled in the blanks)
 * Central Framework of Molecular Biology Powerpoint
 * [[file:Chapter_17_answers.doc]]
 * [[file:DNA overhead notes]]
 * [[file:DNA Question]]

Vocabulary

 * auxotrophs (p. 295)
 * one gene-one-peptide hypothesis (p. 296)
 * Transcription (p. 296)
 * Messenger RNA/mRNA (p. 296)
 * RNA processing (p. 296)
 * Primary transcript (p. 297)
 * RNA polymerase (p. 300)
 * Transcription Unit (p. 301)
 * Promotor (p. 301)
 * Transcription factors (p. 301)
 * Transcription initiation complex (p. 301)
 * TATA box (p. 301)
 * Terminator (p. 302)
 * 5' Cap (p. 302)
 * poly(A) tail (p. 302)
 * RNA splicing (p. 302)
 * Introns (p. 302)
 * Exons (p. 302)
 * Spliceosome (p. 303)
 * Ribozymes (p. 303)
 * Domains (p. 304)
 * Transfer RNA (tRNA) (p. 304)
 * Wobble (p. 305)
 * Aminoacyl-tRNA synthetase (p. 306)
 * Ribosomal RNA (rRNA) (p. 306)
 * P site (p. 306)
 * A site (p. 306)
 * E site (p. 306)
 * Initiation (p. 307)
 * Elongation (p. 308)
 * Termination (p. 309)
 * Polyribosomes (p. 309)

Important Content
Beadle and Tatum's experiment demonstrated the relationship between genes and enzymes. In this experiment, they found that the wild-type mold Neurospora can survive on agar mixed only with inorganic salts, sucrose, adn the vitamin biotin. This is called the minimal medium, and the mold uses its metabolic pethaways to produce all the other molecules it needs. The two scientists found that mutants couldn't survive on minimal medium because they can not synthesize essential molecules from the minimal ingredients. These nutritional mutants are called auxotrophs. Most auxotrophs can survive on a complete growth medium (minimal medium supplemented with all 20 amino acids and a few other nutrients). Beadle and Tatum took samples from the mutant growing on complete medium and distributed them to several different vials, each one containing minimal medium plus a single additional nutrient. They found that there are three steps in the synthesis of arginine--> 1. a precursor nutrient is converted to orthinine 2. which is then converted to citrulline and then 3. converted to arginine. Beadle and Tatum found there 3 classes of mutants, some required arginine, some could grow when citrulline or arginine was present, and some could grow when one of the 3 were present.

This section talks about transcription and translation being the two main precesses linking gene to protein. First we have transcription, being the synthesis of RNA under the directions of DNA. We know that DNA is inside the nucleus, and so we need another way for it to copy itself and leave the nucleus, thus we have RNA. The information is just trancribed from one molecule to the other, DNA is just a template. The result is mRNA (messenger RNA), which takes the product to the protein-synthesizing machinery of the cell. The difference between RNA and DNA is that RNA is one stranded, whereas DNA is two stranded. The three stages are as follows: Remember, there is a difference between Exons and Introns. They are the opposite of what you think they mean, Introns are the noncoding regions that are removed, whereas the Exons are the coding regions that are expressed!
 * 1) Initiation--occurs in the promotor region and is the initial site of RNA polymerase attachment. It includes the start codon. Transcription factor + RNA polymerase=transcription initiation complex. And finally, the TATA box, where the trancription factor binds.
 * 2) Elongation--the RNA polymerase moves down the DNA sequence, unwinding it 10-20 bases at a time at the rate of 60 nucleotides per second.
 * 3) Termination--Transcription produces a precursor to the polished RNA molecule called pre-RNA

Translation is the actual synthesis of a polypeptide; the mRNA is the director of this process. The cell translates the base sequence of an mRNA molecule into the amino acid sequence of a polypeptide, and are translated at ribosomes (faciliates orderly linking of amino acids into polypeptide chains). An anticodon is the sequence of tRNA complementary to the mRNA codon. On the tRNA molecules, the base pairing rules relax (known as a wobble). The U in the 3rd position of a anticodon can pair with either A or G, and the I in the 3rd position can pair with either U, C or A. 1 amino acid may correspond with multiple codons, only differing in the last letter. There are two steps, the transcription of a eukaryotic gene results in pre-RNA, and RNA processing yields the finished RNA. The stages are the same as transcription.... 3. Termination--the release factor binds to the site where the stop codon is "read". Causes the hydrolyzation of pp from ribosome, and everything disassembles, leaving a completed polypeptide behind. The stop codons are UAA, UAG, and UGA. There are some mutations that may occur, some being not so serious, and some being possibly fatal. Transcription:
 * 1) Initiation--requires GTP as the source of energy and mRNA, tRNA, 2 ribosomal subunits come together
 * 2) Elongation--also requires GTP.
 * Codon Recognition--mRNA codon is A site of the ribosome forms H bonds with the anticodon of an incoming molecule of tRNA carrying its appropriate amino acid. Elongation factor ushers tRNA into A site.
 * Peptide bond formation--rRNA molecue catalyzes the formation of a peptide bond and joins the polypeptide form the P site to the amino acid in the A site. Polypeptide separates from tRNA to which it was attached
 * Translocation-the tRNA moves from the A site to the P site, then the E site
 * Point mutations-can change only a tiny piece in the DNA and may or may not have dramatic results
 * Base pair substitutions-replacement of a nucleotide pair with another pair.
 * 1) Silent Mutations-do not change which amino acid is synthesized
 * 2) Missense Mutations-still codes for an amino acid, but the wrong one
 * 3) Nonsense Mutations-codes for the stop codon, causing the production of a non-functional protein
 * Insertions and Deletions (the addition or subtraction of one or more nucleotide pairs). Frameshift mutations occurs of the number of nucleotides added or deleted does not equal 3, thus alters all of the codons located "downstream". This causes all the codons to be different then what they were originally intended to be.
 * [|Amazing hippy video on protein synthesis (think tRNA)]
 * [|DNA Transcription Video]



Translation: