* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 3 - Transcription (student)
Gel electrophoresis of nucleic acids wikipedia , lookup
Gene regulatory network wikipedia , lookup
RNA interference wikipedia , lookup
Community fingerprinting wikipedia , lookup
Molecular cloning wikipedia , lookup
List of types of proteins wikipedia , lookup
Molecular evolution wikipedia , lookup
Real-time polymerase chain reaction wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
RNA silencing wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Point mutation wikipedia , lookup
Polyadenylation wikipedia , lookup
Messenger RNA wikipedia , lookup
Non-coding DNA wikipedia , lookup
Biosynthesis wikipedia , lookup
Promoter (genetics) wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Non-coding RNA wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Epitranscriptome wikipedia , lookup
Gene expression wikipedia , lookup
BUT MOM... I don’t want to be a protein! Too bad. Once upon a time... In 1902... • Archibald Garrod, a UK physician, noticed certain illnesses recurring in families • He came up with a hypothesis – Enzymes are under the control of THE hereditary molecule – A defective enzyme causes an “inborn error of metabolism” Once upon a time... In 1902... • He analyzed blood/urine samples of patients with alkaptonuria – A condition that turns urine black due to the presence of alkapton • He proposed that individuals with alkaptonuria had a defective enzyme – A alkapton-metabolizing enzyme! 33 years later... • George Beadle and Edward Tatum confirmed Garrold’s hypothesis studying red bread mold – Neurospora Crassa (N. Crassa) • Hoped to discover a relationship between genes and enzymes • Used multiple strains of N. Crassa and grew them on different media 33 years later... Procedure: • Grew one strain of N. Crassa on a nutrient medium with simple inorganic salts, sugars, and vitamins – Result: N. Crassa was able to synthesize all complex AAs • Mutant strains were produced via x-rays – Result: Descendents could NOT grow on medium • they could no longer produce all essential compounds to sustain life 33 years later... • To find out which AA they could not produce – They placed mutant strains in vial that had basic nutrients plus ONE EXTRA AA • The only growth occurred with ARGININE – Thus, 1+ enzymes in the arginine pathway were defective • Conclusion: a lack of a specific enzyme corresponded to a mutation in specific gene Final piece of the puzzle... • In 1956, Vernon Ingram confirmed all previous experiments using sickle cell anemia – Condition where red blood cells are deformed • He studied the AA sequence of hemoglobin for individuals that had sickle cell anemia • He found a single AA mutation that completely altered the shape of the red blood cell Final piece of the puzzle... • Ingram found that valine replaces glutamic acid in individuals with sickle cell anemia Conclusion: genes specify the type and location of each amino acid in polypeptide chain Other examples of simple AA mutations: hemophilia and cystic fibrosis What’s the deal with proteins? • Are the REAL building blocks of life. • Technically… they shouldn’t exist at all. – There may be as many as a million types of proteins & each one is a miracle! • You need to assemble AA in a particular order – Similar to assembling letters to spell a word – Except… • Words using the AA alphabet are INCREDIBLY LONG Try this out… • Collagen needs 1,055 AA in its sequence – Get this! You don’t make it, it creates itself… • AUTOMATICALLY Picture a slot machine… *That has 1,055 wheels (not 3) *that’s 90ft long! *20 symbols on each wheel Try this out… • Most proteins have 200 AA – The odds of creating that is 1 in 10260 • That’s A LOT of zeros • Hemoglobin has 146 AAs – Max Perutz took 23 years to unravel the sequence “Assembling a protein is like a whirlwind spinning through a junkyard… … and leaving behind a fully assembled jumbo jet” - Fred Hoyle So how are proteins made? • There is a problem: • DNA makes proteins, but… – DNA can’t leave the nucleus or it will be destroyed – Proteins are constructed outside the nucleus • mRNA acts as the middle man – It can take the DNA message out of the nucleus to synthesis polypeptides RNA – RiboNucleic Acid The world’s greatest translator Different from DNA in 3 ways 1. DNA has deoxyribose sugar RNA has ribose sugar (-OH on 2’ carbon) 2. DNA contains Thymine (A T) RNA contains Uracil (A U) 3. DNA is double stranded RNA – RiboNucleic Acid 3 types of RNA 1. mRNA – messenger RNA *synthesizes proteins using DNA’s info 2. tRNA – transfer RNA *transfer appropriate AAs to build proteins 3. rRNA – ribosomal RNA *structural component of ribosome that is used TRANSCRIPTION • The process of converting DNA’s genetic information into a more usable form (mRNA) • There are 4 phases in transcription 1. Initiation 2. Elongation 3. Termination 4. Post-transcriptional Modifications **VERY SPECIFIC ENZYMES ARE USED** PHASE 1: INITIATION • A promoter is used to signal where RNA polymerase should bind to DNA strand – A promoter is a segment of DNA that is usually high in A&T • They only have 2 H-bonds and will break open easily • If RNA polymerase were to bind randomly, – correct genes & proteins wouldn’t be produced • RNA polymerase will unwind DNA and begin to synthesize the complementary RNA strand PHASE 2: ELONGATION • RNA polymerase starts to build mRNA in the 5’ 3’ direction – Starts as soon as RNA polymerase hits promoter • **The promoter DOES NOT get transcribed** • RNA polymerase uses one strand as a template is the TEMPLATE STRAND • The strand not used for transcription is called the CODING STRAND PHASE 3: TERMINATION • mRNA will continue elongation until RNA polymerase hits the terminator sequence – Causes dissociation of RNA from DNA • RNA polymerase is then free to bind to another promoter region PHASE 4: Post-transcription mod’s mRNA can’t leave nucleus immediately after transcription ◦ Primary transcript The following 3 steps must first occur: 1. 5’ cap of GTP is added to start of mRNA *this protects mRNA from enzyme attack which is inevitable in the cytoplasm PHASE 4: Post-transcription mod’s mRNA can’t leave nucleus immediately after transcription ◦ Primary transcript 2. 3’ end obtains a poly-A tail (string of 200 As) Introns vs. Exons • The very interesting part of DNA is that 97% of it does nothing – Only 3% of our DNA code for genes that make proteins • INTRONS = non-coding DNA • EXONS = coding DNA Introns vs. Exons • If introns are not removed, proper protein folding will not occur – Leads to decreased function or death of proteins • Introns are removed by spliceosomes • Once removed, introns remain in nucleus – Broken down by enzymes to recycle parts Errors with Transcription • DNA replication used DNA polymerase I & III to act as proof readers to fix mistakes – Chances of mistakes are less likely • Transcription has no quality control mechanism – Errors are more likely • However, errors aren’t as detrimental because a gene is transcribed hundreds of times – If one copy of the gene has an error, it won’t have a huge effect