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Transcription: The whole truth (… I didn’t reveal the whole story……) • The rate of amino acid synthesis is 200 per minute • There are 10 million ribosomes in an average mammalian cell • The LARGEST protein is called “Titin”. It is 34,000 amino acids long (muscle fiber protein) • The smallest human protein is “Sarcolipin”. It is only 31 amino acids long (another muscle protein) • The smallest is “TRP Cage” which is a saliva protein found in Gila Monsters ( 20 amino acids long ) Why Proteins? Proteins are keys to almost everything that living cells do. *They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs. •Genes code for pigments (eye and skin color) •Surface antigens are produced from proteins •Regulate growth rates and patterns •Proteins regulate chemical reactions (enzymes) Titin - youtube (the longest word in english pronounced) Which organelles in a cell are involved in protein production and distribution? * * nucleus rough * mitochondria * Rough Endoplasmic Reticulum 1) The ER is the compartment where newly-synthesized polypeptides fold 2) where many protein complexes are assembled (2 or more proteins = quaternary structure) 3) and where glycoproteins acquire their “glycans” (polysaccharides) ex. Some hormones, anti-freeze protein, components of mucus 4) Exocytosis of ER delivers the “almost complete” proteins to the Golgi Apparatus by means of a vesicle Golgi Apparatus 1) They attach various sugar monomers to proteins as the proteins move through the apparatus (finishes them!). 2) The Golgi apparatus packages proteins into membranebound vesicles inside the cell before the vesicles are sent to their destination. (determines final destination) THE CENTRAL DOGMA “The central dogma of molecular biology is “the flow of genetic information within a biological system”……….. deals with the detailed residue-by-residue transfer of sequential information. It states that information cannot be transferred back from protein to either protein or nucleic acid.” In other words, once information gets into protein, it can’t flow back to nucleic acid. DNA mRNA (Transcription) Protein (Translation) A closer look at Transcription Making mRNA from DNA (not quite as easy as previously shown) (2 new things) Nuclear Membrane A Problem….. DNA is too big to leave the nucleus! Nuclear Pore The Solution!!! Make something that can leave the nucleus Solution = Ribonucleic Acid (RNA) – smaller (thinner) Three types: 1. mRNA (messenger RNA) 2. tRNA (transfer RNA) 3. rRNA (ribosomal RNA) Transcription - RNA production •Message on the DNA molecule is “transcribed” onto RNA To do this: 1. DNA is unzipped by DNA Helicase 2. RNA Polymerase binds free floating RNA nucleotides to one exposed strand of DNA. 3. New strand of RNA breaks away and is free to leave the nucleus. a. Introns removed, Exons stay b. Methyl cap added to 5’ c. Poly-A tail added 3’ 4. DNA reattaches to reform the double helix 5. mRNA is made at the rate of (on avg.) 40 bases/second. Dictionary: •Scribe - somebody who copied manuscripts in medieval times •Transcribe - to rewrite something 1) Gene Expression - One gene can actually code for more than one protein. What? How? …….. the end that leaves the nuclear pore is protected by something called a methyl cap THE FAT COW CAT ATE THE HAY RAT EITHER Green OR Red represent….. Black represents….. (and color not chosen as an intron) Introns Exons Prokaryotes don’t have introns and exons. Why? Over time, introns were lost from prokaryotes as a way to make proteins more efficiently. ... The mixing and matching of exons from the same gene can lead to proteins with different functions. Eukaryotes might need this diversity in proteins because they have many types of cells all with the same set of genes The enzyme that removes the introns is called a “spliceosome” There are about 20,000 genes in your genome (all your DNA) but you can make 100,000+ proteins * The promoter (aka TATA Box) is an area that lets other molecules know where transcription starts – found in eukaryotes & archae Poly A tail is a string of A’s (AAAAAAAAA) - What reason would it have this? Exonucleases – their job is to “cut” the A’s off……. The more it cuts or the longer the tail the more protein that is made. 1. DNA Learning Center RNA Splicing 2) Gene Regulation A gene coding for a protein can regulate when a protein is made and when to stop producing it! How? Example: lac operon system – in prokaryotic cells (p 235) THIS IS DNA In Eukaryotic cells (like ours)… We have about 19,000 to 20,000 genes in the human body….. The rest is what they used to call “Junk DNA” We have about 19,000 to 20,000 Genes in the human body….. The rest is what they used to call “Junk DNA” We have about 19,000 to 20,000 Genes in the human body….. The rest is what they used to call “Junk DNA”..... ...... But now they know its importance!! THIS IS DNA THIS IS DNA THIS IS DNA Gene Regulation in Eukaryotic Cells Basal Factors Binding Protein (DNA Strand) RNA Polymerase 3’AAGTATAACGCCTTACGCCGCTACCCCGCATGCTAGAG 5’ Pre-mRNA Coding region (protein) mRNA 5’ AUGCGGCGAUGGGGCGUACGAUCUC 3’ (no introns taken out in this example) *Where does the Binding Protein go? *Where does the RNA Polymerase attach? *How does the Binding Protein keep the RNA Polymerase from moving until a protein is “signaled” from the activators? *Where is the Coding Region? (protein produced) The DNA “folds over” like a switch to activate (like a current of electricity) the RNA primase to produce the mRNA strand Actual DNA in a eukaryote undergoing transcription Our most chronic diseases, including various cancers, diabetes, heart disease and hypertension, probably result from a complex recipe of dysfunction, not just in the genes, but in a variety of hormones, enzymes and other metabolic factors (including these “switches” that affect them. Rare diseases may be caused by mutations in the genetic code while the more common, complicated diseases may be traced to genetic changes in the switches. 1. HHMI.org – click on “BioInteractive” search box – DNA Transcription (advanced detail) activators Students: This is where we stopped this powerpoint New info: • …. The code of TTATTT (on the DNA) is what the mRNA Polymerase recognizes as a stopping point to finish making the mRNA. • Then more bases ... #? .... And then the poly-A tail is added.... #? (use AP text to find these numbers) • Teacher note: Should this info be added in 2017-18? Translation Using mRNA to make a protein! Ribosomal RNA - rRNA •Where tRNA & mRNA come together Ribosome subunits How a ribosome works….. Start here Protein Synthesis Section 12-3 Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. Phenylalanine tRNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome Go to Section: mRNA Transfer RNA Methionine mRNA Lysine Start codon Translation (Continued) Section 12-3 The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome tRNA tRNA mRNA Completing the Polypeptide mRNA Ribosome Go to Section: Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. Structure of tRNA tRNA Amino Acid (Lysine) This tRNA molecule carries the anticodon UUU. It will be called in by the mRNA codon AAA. Since there are 4 bases, and they work in groups of 3, there are 64 possible combinations possible for codons (4 x 4 x 4 = 64). There are 20 different amino acids, so more than one codon can code for each amino acid. The codon AUG is called the start codon and three separate codons are called stop codons.