Chapter 7 Class Notes
Chapter 7 Class Notes Biol 201
Loyola Marymount University
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This 3 page Class Notes was uploaded by Tiffany Norris on Friday September 30, 2016. The Class Notes belongs to Biol 201 at Loyola Marymount University taught by Yiwen Fang in Fall 2016. Since its upload, it has received 14 views. For similar materials see Cell Function in Biology at Loyola Marymount University.
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Date Created: 09/30/16
CELL FUNCTION: Chapter 7 Friday 9/30/16 Recall: Ch. 6 covered “DNA makes copy to pass to next generation” Gene Expression (two processes) A. Transcription B. Translation Flow of Gene Information Can be... 1. Between generations: mother cells to daughter cells in DNA replication 2. Within the same cell: DNA to RNA to Protein (Central Dogma) [slide 3] DNA is going to be transcribed, to make RNA, then in translation RNA is used as template to make protein. o When gene is active we call it “expressed,” “on,” or “active.” A. TRANSCRIPTION Transcription is the process of forming RNA Questions to understand genes and transcription: o Is all of the genomic DNA being copied into RNA? No. Only portions of it, called genes. o Are all genes transcribed to the same place with the same amount? No every cell has different gene expression. For example, if your skin cells have the same protein as your bone cells, would they look different? No. They are different because they serve different purposes. Differences in DNA & RNA a. RNA has Uracil, DNA has Thiamine b. DNA has deoxyribose sugar, RNA has ribose sugar c. RNA is single stranded, DNA is double RNA has the same direction as DNA (5’ phosphate group to 3’ OH group), connected by phosphodiester bonds RNA molecules can take on all kinds of shapes o [Slide 5] Why? They can also fold. They can bond with own segments on the same molecule creating a hair-pin loop structure o They can also form non-conventional base pairs i.e. U with C, G with A this affects the structure (see slide 5) Mechanism for Transcription [slide 7] Uses RNA polymerase (enzyme) o Copies the template DNA strand via complementary base pairing o Produces the RNA transcript Is identical to the coding strand of DNA except it has uracil Transcription starts at promoter (found in template DNA) Ends at terminator The parts in between is called the gene Types of RNA that transcription makes: mRNA is “destined” to be translated in the ribosome rRNA goes to ribosomes tRNA is an adaptor used during protein synthesis. They also go to ribosomes. micro RNA are tiny RNA used as a regulator non-coding RNA used for splicing, gene regulation and maintenance of telomere. Video Notes on Transcription: The sigma factor, dissociates from RNA polymerase. RNA polymerase synthesizes the complementary bases as it moves down the DNA, melting a new stretch of DNA, allowing the previous stretch to close. The hair-pin loop is made at the end and then the new strand leaves. Comparing DNA Replication & Transcription Similarities Both use DNA as a template o “coding” only used in transcription and translation Both use a polymerase enzyme o dNTP used in DNA replication while NTP used in transcription. Both are synthesized in the same direction (5’ to 3’) o Only adding to 3’ end Differences One makes DNA the other makes RNA (obvi) RNA isn’t bound to the template once it’s made, whereas in DNA it remains bonded Only part of DNA is used for transcription but all of it is used in DNA replication DNA replication makes 1 copy, while transcription can make more than one copy. RNA does not proof read as much as DNA o There are thousands of copies of RNA so it is not as important o DNA replication is much more accurate (happens 1 in 10 million times, while transcription mistakes happen 1 in a thousand) DNA replication requires a primer, transcription does not (“de novo”) Prokaryotic vs. Eukaryotic Transcription In prokaryotes transcriptions occurs in cytosol, in eukaryotes it occurs in DNA (therefore can find RNA polymerase in the nucleus) STEPS OF TRANSCRIPTION Same as DNA replication 1. Initiation Start at promotor region: the region where the RNA polymerase initially binds **Every gene has 1 promoter, and they’re all different. So we have 30,000 promoters o Other proteins (called sigma factors) also help to bind the promoter and initiate transcription 2. Elongation 3. Termination Ends at terminator region where the RNA polymerase releases the DNA “downstream” = more on 3’ end “upstream” = more on 5’ end Will talk about this next class: Bacterial Transcription o Conserved sequences called elements o -35 o -10
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